CA1223643A - Implantable cardiac defibrillator employing bipolar sensing and telemetry means - Google Patents
Implantable cardiac defibrillator employing bipolar sensing and telemetry meansInfo
- Publication number
- CA1223643A CA1223643A CA000426300A CA426300A CA1223643A CA 1223643 A CA1223643 A CA 1223643A CA 000426300 A CA000426300 A CA 000426300A CA 426300 A CA426300 A CA 426300A CA 1223643 A CA1223643 A CA 1223643A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- heart
- output signal
- patient
- inverter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
- A61N1/3925—Monitoring; Protecting
- A61N1/3931—Protecting, e.g. back-up systems
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B7/00—Instruments for auscultation
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/02—Details
- A61N1/04—Electrodes
- A61N1/05—Electrodes for implantation or insertion into the body, e.g. heart electrode
- A61N1/056—Transvascular endocardial electrode systems
- A61N1/0563—Transvascular endocardial electrode systems specially adapted for defibrillation or cardioversion
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/37—Monitoring; Protecting
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
- A61N1/3925—Monitoring; Protecting
Abstract
IMPLANTABLE CARDIAC DEFIBRILLATOR
EMPLOYING BIPOLAR SENSING AND TELEMETRY MEANS
Abstract An implantable cardioversion system employing a bipolar electrode for R-wave sensing, the system utilizing heart rate averaging and probability density function techniques in determining whether or not the heart of a patient is to be automatically cardioverted.
An improved bipolar electrode facilitates acquisition of a highly accurate R-wave. The implantable system is further provided with the capabilities of (1) providing, upon magnet-type interrogation, an audible indication of proper placement of the bipolar electrode in the body of a patient, (2) providing an audible indication to verify the status of the implanted device (activated or deactivated), (3) the capability of providing, upon request, a transmitted signal modulated with stored information corresponding to the number of times cardio-version of the patient has taken place, (4) the cap-ability of preventing external cardioversion shock from being shunted across the electrodes, and (5) the capability of detecting average heart rate.
EMPLOYING BIPOLAR SENSING AND TELEMETRY MEANS
Abstract An implantable cardioversion system employing a bipolar electrode for R-wave sensing, the system utilizing heart rate averaging and probability density function techniques in determining whether or not the heart of a patient is to be automatically cardioverted.
An improved bipolar electrode facilitates acquisition of a highly accurate R-wave. The implantable system is further provided with the capabilities of (1) providing, upon magnet-type interrogation, an audible indication of proper placement of the bipolar electrode in the body of a patient, (2) providing an audible indication to verify the status of the implanted device (activated or deactivated), (3) the capability of providing, upon request, a transmitted signal modulated with stored information corresponding to the number of times cardio-version of the patient has taken place, (4) the cap-ability of preventing external cardioversion shock from being shunted across the electrodes, and (5) the capability of detecting average heart rate.
Description
~ ~3~
Description IMPLANTABLE CARDIAC DEFIBRILLATOR
EMPLOYING BIPOLAR SENS ING ANI) TELI~METRY MEANS
T~chnical Field This invention relates -to an implantable defibrillator device for defibrillating -the heart of a patient, but more specifically, to a defibrillating system employing improved arrythmia de-tection means for more reli~bly detecting abnormal heart func-tions and telemetry means for transmitting information indicative of the status and operation of the implan-ted defibril-lator.
Background_Art In recent years, substantial progress has been made in the development of defibrillating techniques Eor effectively cardioverting various heart disorders and arrhythmias. Past efforts have resulted in the development of implantable electronic stand~y defibril-lators which, in response to the de-tection of an abnormal cardiac rhythm, discharge sufficient energy via electrodes connected to the heart to depolarize and restore it to normal cardiac rhythm.
Research efforts have also been direc-ted toward developing techniques for reliably monitoring heart activity in order to determine whe-ther cardio-version is necessary. Such techniques include monitor-ing ventricular ra-te or determining -the presence of fibrillation on the basis of a probability densi-ty func-tion ~PDE'~. A system using the PDF technique statistically compares the location of poin-ts oE a cardiac waveform with the expected locations of points of the normal waveform. When the waveform becomes irregular, as measured by its probability density function, an abnormal cardiac function is sugyested. The ]atter technique is described in commonly owned U.S. Patents 4,184,493 and 4,202,340, both of Langer et al.
A more recent system as disclosed in commonly owned Canadian Patent Application No. 383,279 issued as Canadian Patent No. 1,171,912 filed on September 2, 1982, utilizes both the PDF technique to determine the presence of an abnormal cardiac rhythm and a heart rate sensing circuit for distinguishing between ventricular fibrillation and high rate tachycardia (the latter being indicated by a heart rate above a pre-determined minimum threshold), on the one hand, and normal sinus rhythm or a low rate tachycardia (indicated by a heart rate falling below a pre-determined minimum threshold), on the other hand.
Still further, research in this area has resulted in the development of a heart rate detector system which accurately measures heart rate for a variety of different electrocardiogram (ECG) signal shapes. One such system is disclosed in commonly owned Canadian Application Serial No. 404,527 filed June 4, 1982.
Despite these past efforts and the level of achievement prevalent among prior art devices, there are potential difficulties and drawbacks that may be experienced with such devices. Such difficulties include the following: (1) R-wave detection is still in need of impro~ement since the ability to detect the R-wave with the utmost accuracy is vital to the proper and efficient operation of the implantable defibrillator device; (23 sometimes the sensiny electrode or electrodes ~3 which monitor heart activity become displaced or dis-lodged thus degrading or attenuating completely the sensed ventricular beating signal which thereby causes unreliable or irregular operating cycles of the defibri.l-lator device; (3) once implanted, there presently is nomeans to determine the status (active or inactive) or other operating condition or function of the implanted defibrillator; (43 since the defibrillator device is intended for automatic operation on an as-needed basis, it would be advantageous to provide means for keeping a running count of the number of defibrillating pulses issued by the defibrillator, and upon i.nterrogation, to transmit the memorized count information and other status information without the need to employ invasive surgery; (S) since a significant problem with defibril-lator devices arises when their external high-voltage electrodes are shunted, it would be considered advan-tageous to provide such implan-table defibrillator with an anti-short circuit (anti-shunt) capability to protect sensitive internal circuits and the electrodes; and (6 since there is a danger, when employing conventional defibrillating devices with R-wave asynchronous counter-shock of acceleratiny arrythmia, it is advantageous to provide R-wave synchronous cardioversion.
~25 An object of the present invention is to obviate or mitigate the above said disadvantages.
--4~
According to one aspect of the present invention there is provided an implan~able defibrillation system for automatically defibrillating the heart of a patient comprising:
S detecting means for detecting fibrillation of the heart;
defibrilla~ing means responsive to said detecting means for generating and applying to said heart at least one high-energy defibrillating pulse;
counting means responsive to said defibrillating means for maintaining pulse count information;
telemetry means connected to said counting means for transmitting information signals indicative of said count information externally of the patient, said telemetry means being responsive to a telemetry control signal to transmit said information signals; and control means for providing a telemetry control si~nal in response to an activation signal generated externally of the patient.
In accordance with a comprehensive embodiment of this invention in the attainment of the above-stated and other objectives, a cardioversion system includes an implantable defibrillator and an external non-invasive controller/monitor for altering the state and/or retrieving status information from the implanted dafibrillator. The implantable defibrillator comprises a high-voltage inverter circuit with shunt-prevention means; the combination of a PDF circuit and a heart-rate analysis circuit that each detect abnormal cardiac 3~
rhythms and that jointly activate the high-voltage inverter circuit; a series of electrodes connected to -the heart including a bipolar sensing electrode coupled with the heart-rate analysis circuit for sensing ventricular beating signals, and high-voltage pulse delivery electrodes coupled wi-th the high-voltage inverter circuit and the PDF circuit for, respec-tively, delivering high-energy defibrillating pulses and pxo-viding PDF information signals; a pulse counter/memory for coun-ting and s~oring the number of defibrillating pulses issued by the inverter circuit; a piezoelectric speaker coupled to ~he wall of a case enclosing the defibrillator circuits for generating audible -tones indicative of the status of the defibrillator; and means responsive to an external magnet for changing the state of the defibrillator (active or inactive), enabling internal testing func~ions of the defibrillator and telemetry means for -transmitting encoded status informa-tion (such as pulse count and capacitor charge-time information) of the defibrillator, and permitking audio tones to be emitted by the piezoelectric speaker, which tones non invasively indicate the sta-tus of the defibril-lator and proper placement of the bipolar sensing electrode.
The external controller/monitor in~ludes a hand-held magnet for ini-tiating the aforemen-tioned functions by proper placement thereof over a reed switch inside the implanted defibrillator, and an R.F.
receiver circuit including a demodulator for decoding and displaying on a display device certain status information electromagneti.cally transmitted from the implanted defibrillator.
The invention, though, is poin-ted out with particularity in the appended claims. The above and ..
~3 further objectives and advantages of -this invention will be better understood by referring to the following description of an illustrative embodiment of the inven-tion taken in connection with the accompanying drawings.
Brie Descriptlon of Drawings Fig. 1 depicts a simplified block diagram of the internal and external components of the invention.
Fig. 2 is a detailed circuit diagram of the rate analysis and averaging circuit of Fig. 1.
Fig. 3 is a schematic circuit diagram of the magnet test logic and inverter control circuit of Fig. 1.
Fig. 4 depicts a partial circuit diagram of the inverter control circuitry of Fig. 1.
Fig. 5 depicts the structural details of the bipolar sensing probe of Fig. 1 for sensing el~ctrical signals of the patient's heart.
Fig. 6 depicts the 4-count hold circuitry of Fig. 1.
Fig. 7 shows -the mounting arrangement of a piezoelectric crystal on the wall of a case enclosing the implantable components of Fig. 1.
Best Mode_for Carryi.ng Ou~ the Invention Fig. 1 depicts, in a functional block-diagram format, -the internal and external components of the invention. The implanted components are enclosed in a me-tallic case (not shown) and constitute the standby defibrillator which detects abnormal cardiac rhythms.
In response to the detection of such abnormal cardiac rhythms, the defibrillator issues a series of defibrll~
lating pulses (25 to 30 joules) -to -the heart 10 of a patient, and thereafter, records in a memory (e.g.
counter) an accumulated number of defibrillating pulses issued. In the pref~rred embodiment, the defibrillator can issue three 25 j oule defibrillating pulses followed by a 30-joule pulse if needed. Af-ter -the initial pulse, re-detection -takes place and if the arrythmia is still present, charging is ini-tiated ~nd a second p~llse is delivered after completion of the charging cycle.
This pattern continues, if necessary, until the fourth high-ener~y shock is delivered~ Thereafter, no further pulses can be delivered until at least 35 seconds of normal sinus rhyt~n is detected. Then, the device is ready for a further seguence of four shocks.
In the present invention, several electrodes are connect~d to the patientls heart and the defibril-lator circuits. These electrodes carry sensinginformation from the heart to the defibrillator and deliver the high-energy defibrillating pulses from the defibrillator to the heart. The electrodes include a bipolar sensing electrode 18 adapted to be located in the right ventricle for sensing electrical activity from the ventricular contractions, and transcardiac sensing and high-voltage delivery electrodes 20 and 22 for sensing electrical activity and for delivering the defibrillating pulses. The electrode 20 is adapted to be located in the superior vena cava and the patch electrode 22 is adapted to be connected to the myocardium near the apex of the heart. Their skructure and circuit connections are subsequently explained in greater detail, particularly the bipolar sensing ele~trode 18 as it partly forms a basis of this invention.
The external components of the invention, on the other hand, include a demodulator and decoder circuit 12 which detects RF sign~ls (radio frequency signals) and decodes telemetry data transmi-tted, in the 3~ L3 preferred embodiment, electromagnetically by current-carrying conductors in the implanted defibrillator circuits. Further, a display device 14 displays both the charge-time re~uired for charging a high-voltage energy storage capacitor in the defibrillator and the accumulated pulse-count information stored in the implanted defibrillator. Charge time is derived from detecting RF signals emanating from the h.v. inverter coils in -the inverter when i-t is running while pulse-count information is der~ved by decoding a modulatedtransmission of -the same RF signals emitted by the h.v.
inverter when it is running, as will be discussed below.
With the defibrillator implanted subcutaneously, placing a ring magnet ~1 on the skin of the patient in close proximi-ty to a reed switch 24 (enclosed in the case of the defibrillator) does one of three things.
First, it permits an audio oscillator 50 to emi-t acoustic sounds synshronous with the heart beat if the defibril-lator is active, and continuous if th~ defibrillator isinactiYe. Second, it changes the status of a status 1ip~flop 26 if the magnet is held in place more than a predetermined time period (e.g., 30 seconds). Third, upon -transient application of the magnet 21, when the defibrillator device is in the active state, it initializes the defibrillator to transmit telemetry data of pulse count information and capacitor charge--time information~ These operations also are subsequently described in greater detail.
As previously stated, another attribute of the implan-table defibrillator is high reliability in detecting cardiac arrhythm.ias and in preventing undue issuances of defibrillating pulses. To attain these objectives, -the implantable defibrilla-tor includes a ~ 2~
probability density functio~ (PDF) analysis circuit 28 such as is described in Canadian Patent Application No. 3~3,279 filed on September 2, 1982, issued as Canadian Patent No. 1,171,912, U.S.
Patent No. ~,184,493 and U.S. Patent No. 4,20~,3~0, mentioned above. Furthermore, the implantable defibrillator includes rate analysis and averaging circuit 30 which senses, analyzes, and averages a rate signal indicative of ventricular contractions of the heart 10. When the circuits 28 and 30 detect abnormal cardiac rhythms, they each assert an enabling signal which together energize an AND gate 32 which asserts an INVST signal, which in turn, initializes a high-voltage inverter and control circuit 34 in preparation for clelivering a defibrillating pulse to the patientls heart. Each such pulse passes to the heart across electrodes 20 and 22.
The delivery of the defibrillating pulse, though, does not occur unless the circuit 34 has been placed in an active state. To place it in an active state, the ring magnet 21 is used to toggle the status flip-flop 26 so that it asserts an EN
signal at the Q output thereof and supplies it to the circuit 34 to enable the inverter and control circuit 34. Further, a signal over conductor 35 from the rate circuit 30, being synchronized with the occurrence of a ventricular contraction signal of the heart 10, provides a ti~iing signal to the circuit 34 so that the issuance of defibrillating pulses are synchronized with a ventricular contraction. When so synchronized, the defibrillating pulse is more effective to defibrillate the heart 10, and to reduce the likelikhood of accelerating the arrythmia.
To keep track of the number of defibrillating pulses issued, the circuit 34 produces a CT pulse signa] each time it issues a defibrillating pulse. The CT pulse signal is used by pulse counting circuitry, subsequently explained.
~223~
Still referring to Fig. 1, a compara-tor 36 associated with the ra~e circuit 30 sets the beat rate threshold, ~ox example at 160 beats per minute, at which rate the circuit 30, in conjuncti.on with the PDF
ou-tput via AND gate 32, asserts an enabling signal to initialize the h~v. inverter circuit 34. The ra-te analysis and averaging circui~ 30 generates on conductor 31 an analog RATE signal having a magnitude representa-tive o~ the ventricular rate and supplies it to one terminal of the comparator 36. A RATE THRESHOLD signal is applied to the o-ther terminal of the comparator 36.
During manufacture of the defibrillator, the voltage level of the RATE THRES~OLD signal is set so tha~ the comparator 36 energizes the AND gate 32 when the ventricular beating rate, as indicated by the RATE
signal, reaches the predetermined triggering magnitude of, say 160 beats per minute.
Should an actual fibrillation of the heart occur and the inverter issue a defibrillating pulse, a digital pulse counter, comprising register 38, responds to the CT pulse ~ignal generated by the inverter circuit 34. The counter 38 thus keeps a running count of the number o defibrillating pulses issued. Upon demand, this count informat.ion can be electromagnetically transmitted during a "magnet test", as will be explained below. When the device is in the active state, the magnet test is initiated by momentarily placing -the ring magnet 21 over the reed switch 24 and then removing the magnet. In response, the inverter starts running and a Telemetry Control signal from the magnet test logic 40 enables converter 3g to serialize the digital count information, and to transform the serial data bits to a pulse-width-modulator circuit 90 which frequency modul~tes the fre~uency of the high~voltage 3~i~3 inver-ter via the frequency modulator 92. When the inverter i~ running, RF is generated by -the inverter coil which is detected outside the body by the demodulator 12. By demodulating and detecting the RF
frequency, the storage capacitor charge time is de-t.ected (corresponding -to the maximum time that the RF is present~ as w~ll as the -total number of defibrillator pulses delivered to the patient. The demodulator circuit 12 is a conventional FM demodulator and detector.
It is located pre~erably within a few inches of the patient~ When demodulated, the circuit 12 displays capacitor charge time, indicating the condition of the implanted battery, and displays the accumulated number of pulses issued by the defibrillator.
Status Indication and Change Certain audio sounds emitted by the audio oscillator 50 and piezoelectric transducer 52 indicate the state of the implantable defibrillator In the active state, the status flip-flop 26 of Fig. 1 holds 2Q enabled one input of an AND gate 44, the other input thereof being periodically enabled by ventricular beating signals from the rate circuit 30. Thus, when the magnet 21 is placed near the reed switch 24, the occurrence of each ventricular beating pulse from the rate circui-t 30 momentarily energizes the AND gate 48 and an audio oscillator 50. (When reed switch 24 is closed by magnet 21, a low or "O" state is provided to inverter 46, and a "1" input is pro~ided to AND ga~e 48.) The oscillator 50 then drives an acoustical speaker (piezoelectric transducer) 52 coupled directly to the case of the implantable defibrillator. So, when residing in the active state, e.g., status flip-.Elop 26 asserting its Q output, sounds synchronous with the 3~3 ~12-heart beat are periodically emitted. In the preferred embodiment, the piezoelectric transducer 52 resonates at about 3,Q00 Hertz and is aurally detected by a person within range of the sound emitted by the transducer. Thus, pulsed tones emitted hy the piezoelec-tric crys-tal 52 synchronous with t~le heart bea-t indicate that the bipolar electrode 18 is properly positioned within the heart of the patient.
On the other hand, if the status flip-flop 26 is in the ina~tive state~ e~g. EN signal deasserted, the AND ga-te 44 is disabled and flip-flop 26 provides, through its Q output, a continuous enabling signal to one input of the AND gate 48. In the inactive state, placement of the magne~ 21 near the reed switch 24 also provides, through inverter 46, a continuous enabling signal to the other input of AND gate 48. The result is that the oscillator 50 is continuously driven to provide a steady-state audible tone from the piezo electric transducer 52, of approximately 3000 Ez.
Thus, a pulsed tone indica-tes that the defibrillator is active, and a continuous tone indicates that it is inactive.
When the device is in the active state, if the bipolar sensing probe 18 is not properly positioned within the right ventricle, no tones at all will be emi-tted as the ventricular signals are not being sensed.
Thus, the presence or absence of an audible tone indicates whether the probe 18 is properly lodged about the right ventricle.
The frequency of operation of the oscillator 50 and piezoelectric transducer 52 is chosen to be substantially egual to the natural resonan-t frequency of vibration of the rigid case which encloses -the defibrillator circuits so that the transducer 52 consumes ~23~
~13-a minimum amount of enexgy for a given level of audio emissions.
The moun-ting of the piezoelectric crystal on an inner wall 51 o~ the implanted case is depicted in Figure 7. To efficiently resonate the wall 51 of -the case, a solid layer 53 of epoxy cement, such as Eccobond 24 adhesive, serves as ~ bonding medium between a surface of the crystal 52 and the surface of the wall 51 via an insulating tape 55. Preferably, no air cavity between the crys~al and the wall exists to generate the audible emissions. ~ather, the wall 51 itself vibrates to generate the sound.
State changes of the defibrillator (by status flip-flop 26) are accomplished by holding the magnet in place over the reed switch more than a predetermined time period, which in the preferred embodiment, is thirty seconds. To change the state, a 30-second timer circui-t 54 produces a CK signal which toggles the status flip-flop 26 when the magnet 21 is held in place (reed switch 24 closed) for more than thirty seconds.
~he timer 54 preferably comprises an R-C charging network in a triggering circui-t to produce the CK
signal. Any suitable timer, such as a digital timer responsive to the reed switch, could be employed as a delay timer. When in the inactive state, status flip-flop 26 also effects opening of the power circuits to all non-essential components of the defibrillator to reduce current drain from the batteries (not shown).
While being in the inactive state, only the status change and audio indicating circuits need power.
Similarly, when in the active state, the EN signal enables an electronic switch (not shown) -to pxovide electrical power to the rate circuit 30 and PDF circuit 28.
~Z3~3 Rate Analysis and Averagin~ Circui-t 30 Fig. 2 is a circuit diagram of the rate analysis and averaging circuit 30 of Fig. 1. As pre-viously stated, the circuit 30 senses depolarizations of the righ~ ventricle and, in response thereto, generates an analoy signal having a voltage level proportional to the average ven~ricular beating rate.
In the circuit 30, a paix of conductors 56 and S7 receive ventricular signals from the bipol~r sensing probe 18. The ventricular beating signal then passes to a high pass filter S8 which attenua-tes signal components ~elow a fre~uerlcy of 30 Hz. Thereafter, pre-amplifier Sg amplifies ~he signal from the high pass filter. A high voltage protection circuit 55 is interposed between the electrode 18 and the high pass filter 58 to protect the circui-t from high voltage resulting from a defibrillating pulse.
The pre-amplifier 59 is connected with amplifier 66 having an automatic gain contxol (AGC) in the feedback circuit. The AG~ tries to maintain a constant amplitude output wi-th varying input signal levels. ECG input signals are known to vary dramatica]ly in amplitude.
A pulse shapin~ circuit comprising a compara-~or 76 receives the gain controlled ventricular beating signal and generates in response thereto a series of square-wave pulses. Advantageously, both -the positive and negative swings of the ventricular beating signal produce triggering pulses, and thus the circuit 30 responds equally well to various charac-teristic ventri-cular signals associated with patients who have eithera strong positive or negative ventricular signal, or -to characteristic signals derived from various locations about the ventricle about which the bipolar sensing probe 18 may be positioned. For this reason and o-thers, the circuit 30 is very reliable.
~L~23~
The square-wave pulses f.rom compara-tor 7&
triyger a one-shot multivibrator 7~ which produces another s~uare-wave pulse of a fixed duration of approximately 150 milliseconds, preferably. This period represents the reractory pe.riod of the device.
During this 150 millisecond refractory period, the multivibrator 78 canno-t be re-triggered by o~her signals, such as T-waves, e-tc., until the period has expired.
The REFRAC signal comprising uniform-width refractory pulses from the mul-tiviblator 78 is then fed to both an averaging circuit 80 and the AND gate 44 (Fig. 1). In addition, the R~wave output signal is provided, via line 35, to the high-voltage inverter control circuit 34 to synchronize defibrillation pulses with the R-wave output ~see Figs. 1 and 3). The rate averaging circuit 80, comprising a resistor 82 and a capacitor 84, integrates the REFRAC signal from the multivibra-tor 78.
The circuit 80 is similar in operation to a frequency-to-voltage converter. At sixty beats per minute, for example, the REFRAC signal has a duty cycle of 15%.
When integrat~d, iOe. averaged, it produces the afore-mentioned RATE signal of a pre-determined magnitude.
As the beating rate increases, the duty cycle of the REFRAC signal also increases as the constant-width pulses occur more often and, when in-tegrated, the circuit 80 p.roduces the RATE signal of a correspondingly highex magnitude. The RATE signal is compared with a RATE THRESHOLD signal by the comparator 36 ~also shown in Fig. 1) which generates the enabling signal for energizing the AND gate 32. The RATE THRESHOLD signal of comparator 36 is selected so that the comparator produces the enabling signal at a prede-termined rate.
Although not shown in Figure 1, a delay 86 interposes a two~second delay and only passes a signal ~2~ L3 to -the AND gate 32 if the i.nput to the delay 82 is maintained for 2 sec. or more. This delay reduces the likelihood of de-tecting short, self--terminating arrythmias.
High-Voltage Inverter And Control Circuits The high-voltage inverter and control circuit 34, along with the magnet test logic circuit 40, i5 shown in greater detail in Figures 3, 4 and 6. Turning firs-t to Figure 4, the high-voltage inverter 200, also known as a DC~to-DC converter, is a conven-tiorlal element well known in the implantable defibrillator art.
Reference should be made, for example, to U.S. Pa-tent No. ~,16~,94~ which descri~es the DC-to-DC converter (element 30 in the '946 patent). The high-voltage inverter 200 charges an intern~1 energy storage capacitor 202 which is charged to a predetermined level and is discharged ei^ther across the heart of the patient via the SVC electrode 20 and patch electrode 22, ox is dischaxged through a test load resistor 212 under conditions as will be described below. The high-voltage inver-ter 200 includes an implanted coil (not shown) which emits RF signals during the operation of the inverter, i.e., during the charge time of the capacitor 202. It is this RF emission that is detectable outside the body of -the patient in a manner to be described.
When the high-voltage inverter is enabled, by the EN signal from status flip-flop 26 (described above), the inverter 200 is in condition for operation.
The high-voltage inverter 200 begins operation upon receipt of an INVERTER START signal which, as shown in Figure 3, is initiated by receipt of either an INVST
signal from -the AND gate 32 or an MGTST signal from the ~223~3 magnet test logic circuit 40 (as shown in Figs. l and 3). The high-voltage inverter begins running and provides an INV RUNNING signal to the magnet test logic circuit 40, in a manner to be described bel.ow. The high-voltage inverter keeps running until the energy storage capacitor 202 is charged to its predetermined level. It should be apparent that the period of time that the high-voltage inverter is running, i.e., the period of time it takes to charge the capacitor 202, is an indication of the defibrillator battery strength.
(See, the description in U.S. Patent No. 4,164,946.3 Further, during the charge time of the high~voltage inverter, the RF emissions of the inver-ter coil are fre~uency modulated to represent the number of inverter discharges across the electrodes 20, 22, which informa-tion is detectable outside the body of the patient by the demodulator and decoder 12.
The capacitor 202 is discharged either through the test load 212 or across the patient electrodes 20 and 22 dependent upon receipk of a trigger pulse eithex to the test load SCR 204, via line 206, or a trigger signal across leads 208, which enables the patient SCR 210. Line 206 and leads 208 are actuated by control circuitry as will be described further below in connec-tion with Figure 3. When SCR 204 is triggered via apulse on line 206, the capacitor 202 discharges across the test load resistor 212; when patient SCR 210 is actuated, via signals over leads 208, the capacitor 202 discharges across the patient electro~es 20, 22. When the capacitor discharges across the patient electrodes, a count signal, at CT, is provided which, as shown in Figure l, increments the counter 38 representing -the number of discharges across the patient's heart.
Similarly, a pulse feedback signal, as shown in Figure 4, ~3~
~18-is provlded which is sent to control circuitry as shown in Figure 3 Eor triggering the truncate SCR 214, as will be described.
The patient SCR 210 is triggexed by signals across the leads 208, via an anti-shunt circuit. The anti-shunt circuit includes a small pulse -transformer 216 connected to -the patient SCR 210 for triggering same in response to a trigger input across leads 208.
The trigger input signal is applied to the primary winding of transformer 216 and the secondary winding of the transformer activates the patient SCR 210 permi-tting khe high-voltage defibrillation pulse to pass to the SVC and patch electrodes/ 20 and 22. Such a circuit avoids the drawback that when an exkernal defibril-lation voltage is applied to the heart of the pa-tient having an implanted device connected to the patient's heart~ the external defibrillation voltage will not pass through the implanted device and specifically through the high-voltage inverter. The transformer ~0 coupling eliminates a low impedence path to ground.
The truncate SCR 214 is activated by a signal on line 216, as shown in Figures 3 and 4. The purpose of the truncate SCR is as follows. When the capacitor ~02 discharges across the implanted electrodes, the discharge is an exponentially decaying waveform. When the waveform decays to a certain voltage, the truncate SCR 214 is fired to truncate the decaying pulse.
Preferably the predetermined point of decay is approxi-mately 2/3's of what a fully decayed pulse would other-wise look like.
The triggering signals to the circuit ofFigure 4 are provided by the inverter control circuitry, in conjunction with the magnet tesk logic circui-txy 40, as shown in Figure 3. As shown in Figure 3, receipt of ~23~ 3 an INVST signal from ~ND gate 32 or receipt of a MGTST
signal from magnet test logic circuit 40, is applied to OR gate ~18 which provides an INVERTER START signal -to initiate the high-voltage inverter to charge the charg-ing capacitor 202. Assuming a need for defibrillationoccurs, .resulting in an INVST signal from AND gate 32, such signal starts the inverter running, via OR gate 218, and sets a patient flip-flop 220. The patient flip-:Elop output is applied to AND gate 222. A second input to the AND gate 222 is connec-ted to the R-wave detected output signal tover line 35~ from the rate analysis circuit 30 as shown in Figure 1. The third input to the AND gate 222 is coupled with the high-voltage in~erter to receive the INV RUNNING signal via inverter logic element 224. During ~he time that the inverter is running, the third input to the AND gate 222 is low and the output of the AND gate 222 is low. When the inverter stops running, i.e., at the completion of the charging of the defibrillator capacitor, the inverter logic element 224 output is high. Thus, subsequent R wave inputs to the ~ND gate 222 cause a pulse to be emitted, through a suitable RC pulse shaping network 226 and bu~fer 228 to a transistor 230. The transistor 230 is actuated and a patient trigger pulse is applied over leads 208. As previously described, the receipt of a patient trigger pulse over leads 208 fires the patient SCR 210, as shown in Figure 4, and the capacitor 202 discharges across the electrodes connected to the pa-tient's heart. This discharge also provides a count CT pulse which resets the patient ~lip flop 220 via OR gate 232.
When the patient SCR 210 is triggered, the capacitor 202 discharges to provide a high-vol-tage exponentially decaying pulse across the electrodes 23 ~ ~ 3 connected to the patient's heart. This exponentially decaying pulse is fed back, via pulse feedback terminal to a threshold compara-tor ~34. When the exponentially decaying pulse feedback signal drops to a prede-termined reference level, as provided -to the negative input terminal of compara~or 234, the comparator provides an output which is inverted by inver-ter 236, shaped by pulse shaping network 238, and a pulse is provided at lead 216 ~o fire the -trwncate SCR 214 as shown in Figure 4. When the trunca~e SCR 214 is fired, khe exponentially decaying pulse across the electrodes 20, 22 is truncated. This is done because it is undesirable to require the pulse to exponen-tially decay to a zero level.
The operation of the magnet test logic circuit 40 and the triggering of test load SCR 204 will now be described. The magnet test logic circui-t is initiated when AND gate 240 is asserted. AND ga-te 240 is asserted when the defibrillator is enabled, i.e., receipt of an EN input from status flip-flop 26, and the magnet 21 is removed from the reed switch 24 -to provide a positive, or high, signal to the AMD gate 240. That is, when the magnet 21 is brought into close proximity to the reed switch 24, thus closing the reed switch contacts, a negative or zero input is provided to the AND gate 240.
Upon removal of the magnet, thus opening the reed switch 24, the input to AND gate 240 from the reed switch becomes high -thus asserting the AMD gate 240.
It should be noted -that the magnet 21 must be removed from proximity ko the reed switch 24 in less -than 30 seconds to cause a magnet test to be initiated. If the magnet 21 is in proximity to the reed switch 24 ~or greater than 30 seconds, then the status flip-flop 26 is disabled and the input -to AND ga-te 240 from -the ~2~3~;~3 -21~
status flip-flop 26 is low, -thus preventing asser-tion of the ANn gate 240.
Assertion of the ~ND gate 2~0 sets delay flip-flop 242 which provides a MGTST signal to the inverter and control circui~ 34 via OR gate 218, thus starting the inverter. Further, the Elip-:Elop 242 output se-ts a magnet test flip-flop 244. Setting of magnet test flip-flop 244 results in an input signal, after a brief delay by delay element 246, ~o AND gate 248. A second input to AND gate 248 is connected -to the INV RUNNING line via inverter logic element 224.
When the inverter has completed running, thus reflecting that the internal capacitor 202 is completely charged, the second input to AND gate 248 goes high and the AND
gate 248 is asserted. Output pulse from AND gate 248 is provided to the test load SCR trigger line 206, via pulse shaping and huffer circuits, and the test load SCR 204 is fired. The capacitor then discharges across the test load resistor 212.
It should also be noted that when the magnet test flip-flop 244 is set and its Q-output is high, the Q-output is also provided to OR gate 232 to keep the patient flip-flop 220 in a reset condition. Thus, during a magnet test condition, the patient ~lip-flop is prevented from operation and no defibrillating pulses across -the patient's heart can be emitted.
During a magnet test, when the magnet test flip-flop 244 is set, telernetry control AND gate 250 is enabled during the time that the invert~r is running.
This provides a telemetry control signal from the magnet test logic 40 which signal is provided to -the 8-bit parallel-to-serial converter 39, as shown in Figure l.
~3~
As previously discussed, t.he number of defibril-la~ing shoc~s administered to the patien~ resul-ts in CT
signals which are applied to counter 38, as shown in Figure 1. When the -telemetry control signal from the magnet test logic 40 i5 issued, the conten-ts of th~
counter 33 are provided to the 8-bit parallel-to-serial converter 39. The serial data bits from -the converter 39 are provided to pulse width modulation circuit 90 which in turn provides a pulse width modulated signal to the inverter frequency modulator 92. The inverter frequency modulator 92 frequency modulates the RF
signal emitted by the inverter coil during -the time the inverter is running. This frequency modulated informa-tion is detectable outside the body of the patient by the external demodulator and decoder 12 which demodulates -the frequency modulated signals to display the number of defibrillation pulses that have been counted.
Further, by detecting -the pexiod of time that the inverter coil is emitting radio freguency, the charge time of the defibrillator capacitor is determined. It should be noted that, whereas it takes approximately seconds for telemetry information to be read from the counter 38, converted, pulse width modulated, and inverter frequency modulated, in contras-t, it takes 5-6 seconds for the high vol-tage capacitor con-tained within high voltage inverter and control circuit -to charge up.
The demodulator and decoder 1~ and display 14 may be any suitable external device suitable for demodu-lating, decoding and displaying the transmitted informa-tion.
Turning now to Figu.re 6, the 4-count hold circuit is disclosed. As previously discussed, the 4-count hold circuit inhibits the inverter after four defibrillating pulses are applied to the patient until ~3~L3 after 35 seconds of normal sinus rhy-thm is detected.
The 4-count hold circuit includes a four-stage shift register with an inverte.r inhibi-t line provided to the fourth Q3 stage. As defi~rillating pulses are detected over the CT input, each CT pulse representative of a de~ibrillating shock is counted. Upon receipt of four coun~s, ~he inverter inhi~it ou~pu-t is asserted to inhibit the high-voltage inverter~ Receipt of each CT
pulse is also provided, via OR gate 302 to a 35-second delay timer 304. Recei~t of eac~ CT input starts the 35-second delay timer running. If, after four CT
pulses, the INVST input to OR gate 302 is s-till receiving inputs, reflecting the fact that the patient is still in need o~ defibrillation, the 35-second delay timer keeps runningO Only when normal sinus rhythm is detected, i.e., by absence of the INVST signal, does the 35-second delay timer reset the shift register 300 thus enabling the high-voltage inverter to operate.
Bipolar Sense Electrode 19 Fig. 5 depicts the details of -the bipolar sense electrode 18 shown in Fig. 1. The elec-trode 18 is implanted in -the right ventricle and, as previously mentioned, senses .relatively weak electrical signals produced by ventricular contractions. This signal, ~5 known as the R-wave, is then supplied to the rate analysis and averaging circuit 30 of Fig. 1.
The electrode 18 consists of a firs-t wi.re lead 301 and a second wire lead 302 spaced apart from the lead 301. The lead 301 electrically communicates with a conductive distal tip 303 which is crimped around the lead 301, while the lead 302 electrically communicates with a conductive ring electrode 304 in contact therewith and encircling a flexible insulating ~ . . .
3~L3
Description IMPLANTABLE CARDIAC DEFIBRILLATOR
EMPLOYING BIPOLAR SENS ING ANI) TELI~METRY MEANS
T~chnical Field This invention relates -to an implantable defibrillator device for defibrillating -the heart of a patient, but more specifically, to a defibrillating system employing improved arrythmia de-tection means for more reli~bly detecting abnormal heart func-tions and telemetry means for transmitting information indicative of the status and operation of the implan-ted defibril-lator.
Background_Art In recent years, substantial progress has been made in the development of defibrillating techniques Eor effectively cardioverting various heart disorders and arrhythmias. Past efforts have resulted in the development of implantable electronic stand~y defibril-lators which, in response to the de-tection of an abnormal cardiac rhythm, discharge sufficient energy via electrodes connected to the heart to depolarize and restore it to normal cardiac rhythm.
Research efforts have also been direc-ted toward developing techniques for reliably monitoring heart activity in order to determine whe-ther cardio-version is necessary. Such techniques include monitor-ing ventricular ra-te or determining -the presence of fibrillation on the basis of a probability densi-ty func-tion ~PDE'~. A system using the PDF technique statistically compares the location of poin-ts oE a cardiac waveform with the expected locations of points of the normal waveform. When the waveform becomes irregular, as measured by its probability density function, an abnormal cardiac function is sugyested. The ]atter technique is described in commonly owned U.S. Patents 4,184,493 and 4,202,340, both of Langer et al.
A more recent system as disclosed in commonly owned Canadian Patent Application No. 383,279 issued as Canadian Patent No. 1,171,912 filed on September 2, 1982, utilizes both the PDF technique to determine the presence of an abnormal cardiac rhythm and a heart rate sensing circuit for distinguishing between ventricular fibrillation and high rate tachycardia (the latter being indicated by a heart rate above a pre-determined minimum threshold), on the one hand, and normal sinus rhythm or a low rate tachycardia (indicated by a heart rate falling below a pre-determined minimum threshold), on the other hand.
Still further, research in this area has resulted in the development of a heart rate detector system which accurately measures heart rate for a variety of different electrocardiogram (ECG) signal shapes. One such system is disclosed in commonly owned Canadian Application Serial No. 404,527 filed June 4, 1982.
Despite these past efforts and the level of achievement prevalent among prior art devices, there are potential difficulties and drawbacks that may be experienced with such devices. Such difficulties include the following: (1) R-wave detection is still in need of impro~ement since the ability to detect the R-wave with the utmost accuracy is vital to the proper and efficient operation of the implantable defibrillator device; (23 sometimes the sensiny electrode or electrodes ~3 which monitor heart activity become displaced or dis-lodged thus degrading or attenuating completely the sensed ventricular beating signal which thereby causes unreliable or irregular operating cycles of the defibri.l-lator device; (3) once implanted, there presently is nomeans to determine the status (active or inactive) or other operating condition or function of the implanted defibrillator; (43 since the defibrillator device is intended for automatic operation on an as-needed basis, it would be advantageous to provide means for keeping a running count of the number of defibrillating pulses issued by the defibrillator, and upon i.nterrogation, to transmit the memorized count information and other status information without the need to employ invasive surgery; (S) since a significant problem with defibril-lator devices arises when their external high-voltage electrodes are shunted, it would be considered advan-tageous to provide such implan-table defibrillator with an anti-short circuit (anti-shunt) capability to protect sensitive internal circuits and the electrodes; and (6 since there is a danger, when employing conventional defibrillating devices with R-wave asynchronous counter-shock of acceleratiny arrythmia, it is advantageous to provide R-wave synchronous cardioversion.
~25 An object of the present invention is to obviate or mitigate the above said disadvantages.
--4~
According to one aspect of the present invention there is provided an implan~able defibrillation system for automatically defibrillating the heart of a patient comprising:
S detecting means for detecting fibrillation of the heart;
defibrilla~ing means responsive to said detecting means for generating and applying to said heart at least one high-energy defibrillating pulse;
counting means responsive to said defibrillating means for maintaining pulse count information;
telemetry means connected to said counting means for transmitting information signals indicative of said count information externally of the patient, said telemetry means being responsive to a telemetry control signal to transmit said information signals; and control means for providing a telemetry control si~nal in response to an activation signal generated externally of the patient.
In accordance with a comprehensive embodiment of this invention in the attainment of the above-stated and other objectives, a cardioversion system includes an implantable defibrillator and an external non-invasive controller/monitor for altering the state and/or retrieving status information from the implanted dafibrillator. The implantable defibrillator comprises a high-voltage inverter circuit with shunt-prevention means; the combination of a PDF circuit and a heart-rate analysis circuit that each detect abnormal cardiac 3~
rhythms and that jointly activate the high-voltage inverter circuit; a series of electrodes connected to -the heart including a bipolar sensing electrode coupled with the heart-rate analysis circuit for sensing ventricular beating signals, and high-voltage pulse delivery electrodes coupled wi-th the high-voltage inverter circuit and the PDF circuit for, respec-tively, delivering high-energy defibrillating pulses and pxo-viding PDF information signals; a pulse counter/memory for coun-ting and s~oring the number of defibrillating pulses issued by the inverter circuit; a piezoelectric speaker coupled to ~he wall of a case enclosing the defibrillator circuits for generating audible -tones indicative of the status of the defibrillator; and means responsive to an external magnet for changing the state of the defibrillator (active or inactive), enabling internal testing func~ions of the defibrillator and telemetry means for -transmitting encoded status informa-tion (such as pulse count and capacitor charge-time information) of the defibrillator, and permitking audio tones to be emitted by the piezoelectric speaker, which tones non invasively indicate the sta-tus of the defibril-lator and proper placement of the bipolar sensing electrode.
The external controller/monitor in~ludes a hand-held magnet for ini-tiating the aforemen-tioned functions by proper placement thereof over a reed switch inside the implanted defibrillator, and an R.F.
receiver circuit including a demodulator for decoding and displaying on a display device certain status information electromagneti.cally transmitted from the implanted defibrillator.
The invention, though, is poin-ted out with particularity in the appended claims. The above and ..
~3 further objectives and advantages of -this invention will be better understood by referring to the following description of an illustrative embodiment of the inven-tion taken in connection with the accompanying drawings.
Brie Descriptlon of Drawings Fig. 1 depicts a simplified block diagram of the internal and external components of the invention.
Fig. 2 is a detailed circuit diagram of the rate analysis and averaging circuit of Fig. 1.
Fig. 3 is a schematic circuit diagram of the magnet test logic and inverter control circuit of Fig. 1.
Fig. 4 depicts a partial circuit diagram of the inverter control circuitry of Fig. 1.
Fig. 5 depicts the structural details of the bipolar sensing probe of Fig. 1 for sensing el~ctrical signals of the patient's heart.
Fig. 6 depicts the 4-count hold circuitry of Fig. 1.
Fig. 7 shows -the mounting arrangement of a piezoelectric crystal on the wall of a case enclosing the implantable components of Fig. 1.
Best Mode_for Carryi.ng Ou~ the Invention Fig. 1 depicts, in a functional block-diagram format, -the internal and external components of the invention. The implanted components are enclosed in a me-tallic case (not shown) and constitute the standby defibrillator which detects abnormal cardiac rhythms.
In response to the detection of such abnormal cardiac rhythms, the defibrillator issues a series of defibrll~
lating pulses (25 to 30 joules) -to -the heart 10 of a patient, and thereafter, records in a memory (e.g.
counter) an accumulated number of defibrillating pulses issued. In the pref~rred embodiment, the defibrillator can issue three 25 j oule defibrillating pulses followed by a 30-joule pulse if needed. Af-ter -the initial pulse, re-detection -takes place and if the arrythmia is still present, charging is ini-tiated ~nd a second p~llse is delivered after completion of the charging cycle.
This pattern continues, if necessary, until the fourth high-ener~y shock is delivered~ Thereafter, no further pulses can be delivered until at least 35 seconds of normal sinus rhyt~n is detected. Then, the device is ready for a further seguence of four shocks.
In the present invention, several electrodes are connect~d to the patientls heart and the defibril-lator circuits. These electrodes carry sensinginformation from the heart to the defibrillator and deliver the high-energy defibrillating pulses from the defibrillator to the heart. The electrodes include a bipolar sensing electrode 18 adapted to be located in the right ventricle for sensing electrical activity from the ventricular contractions, and transcardiac sensing and high-voltage delivery electrodes 20 and 22 for sensing electrical activity and for delivering the defibrillating pulses. The electrode 20 is adapted to be located in the superior vena cava and the patch electrode 22 is adapted to be connected to the myocardium near the apex of the heart. Their skructure and circuit connections are subsequently explained in greater detail, particularly the bipolar sensing ele~trode 18 as it partly forms a basis of this invention.
The external components of the invention, on the other hand, include a demodulator and decoder circuit 12 which detects RF sign~ls (radio frequency signals) and decodes telemetry data transmi-tted, in the 3~ L3 preferred embodiment, electromagnetically by current-carrying conductors in the implanted defibrillator circuits. Further, a display device 14 displays both the charge-time re~uired for charging a high-voltage energy storage capacitor in the defibrillator and the accumulated pulse-count information stored in the implanted defibrillator. Charge time is derived from detecting RF signals emanating from the h.v. inverter coils in -the inverter when i-t is running while pulse-count information is der~ved by decoding a modulatedtransmission of -the same RF signals emitted by the h.v.
inverter when it is running, as will be discussed below.
With the defibrillator implanted subcutaneously, placing a ring magnet ~1 on the skin of the patient in close proximi-ty to a reed switch 24 (enclosed in the case of the defibrillator) does one of three things.
First, it permits an audio oscillator 50 to emi-t acoustic sounds synshronous with the heart beat if the defibril-lator is active, and continuous if th~ defibrillator isinactiYe. Second, it changes the status of a status 1ip~flop 26 if the magnet is held in place more than a predetermined time period (e.g., 30 seconds). Third, upon -transient application of the magnet 21, when the defibrillator device is in the active state, it initializes the defibrillator to transmit telemetry data of pulse count information and capacitor charge--time information~ These operations also are subsequently described in greater detail.
As previously stated, another attribute of the implan-table defibrillator is high reliability in detecting cardiac arrhythm.ias and in preventing undue issuances of defibrillating pulses. To attain these objectives, -the implantable defibrilla-tor includes a ~ 2~
probability density functio~ (PDF) analysis circuit 28 such as is described in Canadian Patent Application No. 3~3,279 filed on September 2, 1982, issued as Canadian Patent No. 1,171,912, U.S.
Patent No. ~,184,493 and U.S. Patent No. 4,20~,3~0, mentioned above. Furthermore, the implantable defibrillator includes rate analysis and averaging circuit 30 which senses, analyzes, and averages a rate signal indicative of ventricular contractions of the heart 10. When the circuits 28 and 30 detect abnormal cardiac rhythms, they each assert an enabling signal which together energize an AND gate 32 which asserts an INVST signal, which in turn, initializes a high-voltage inverter and control circuit 34 in preparation for clelivering a defibrillating pulse to the patientls heart. Each such pulse passes to the heart across electrodes 20 and 22.
The delivery of the defibrillating pulse, though, does not occur unless the circuit 34 has been placed in an active state. To place it in an active state, the ring magnet 21 is used to toggle the status flip-flop 26 so that it asserts an EN
signal at the Q output thereof and supplies it to the circuit 34 to enable the inverter and control circuit 34. Further, a signal over conductor 35 from the rate circuit 30, being synchronized with the occurrence of a ventricular contraction signal of the heart 10, provides a ti~iing signal to the circuit 34 so that the issuance of defibrillating pulses are synchronized with a ventricular contraction. When so synchronized, the defibrillating pulse is more effective to defibrillate the heart 10, and to reduce the likelikhood of accelerating the arrythmia.
To keep track of the number of defibrillating pulses issued, the circuit 34 produces a CT pulse signa] each time it issues a defibrillating pulse. The CT pulse signal is used by pulse counting circuitry, subsequently explained.
~223~
Still referring to Fig. 1, a compara-tor 36 associated with the ra~e circuit 30 sets the beat rate threshold, ~ox example at 160 beats per minute, at which rate the circuit 30, in conjuncti.on with the PDF
ou-tput via AND gate 32, asserts an enabling signal to initialize the h~v. inverter circuit 34. The ra-te analysis and averaging circui~ 30 generates on conductor 31 an analog RATE signal having a magnitude representa-tive o~ the ventricular rate and supplies it to one terminal of the comparator 36. A RATE THRESHOLD signal is applied to the o-ther terminal of the comparator 36.
During manufacture of the defibrillator, the voltage level of the RATE THRES~OLD signal is set so tha~ the comparator 36 energizes the AND gate 32 when the ventricular beating rate, as indicated by the RATE
signal, reaches the predetermined triggering magnitude of, say 160 beats per minute.
Should an actual fibrillation of the heart occur and the inverter issue a defibrillating pulse, a digital pulse counter, comprising register 38, responds to the CT pulse ~ignal generated by the inverter circuit 34. The counter 38 thus keeps a running count of the number o defibrillating pulses issued. Upon demand, this count informat.ion can be electromagnetically transmitted during a "magnet test", as will be explained below. When the device is in the active state, the magnet test is initiated by momentarily placing -the ring magnet 21 over the reed switch 24 and then removing the magnet. In response, the inverter starts running and a Telemetry Control signal from the magnet test logic 40 enables converter 3g to serialize the digital count information, and to transform the serial data bits to a pulse-width-modulator circuit 90 which frequency modul~tes the fre~uency of the high~voltage 3~i~3 inver-ter via the frequency modulator 92. When the inverter i~ running, RF is generated by -the inverter coil which is detected outside the body by the demodulator 12. By demodulating and detecting the RF
frequency, the storage capacitor charge time is de-t.ected (corresponding -to the maximum time that the RF is present~ as w~ll as the -total number of defibrillator pulses delivered to the patient. The demodulator circuit 12 is a conventional FM demodulator and detector.
It is located pre~erably within a few inches of the patient~ When demodulated, the circuit 12 displays capacitor charge time, indicating the condition of the implanted battery, and displays the accumulated number of pulses issued by the defibrillator.
Status Indication and Change Certain audio sounds emitted by the audio oscillator 50 and piezoelectric transducer 52 indicate the state of the implantable defibrillator In the active state, the status flip-flop 26 of Fig. 1 holds 2Q enabled one input of an AND gate 44, the other input thereof being periodically enabled by ventricular beating signals from the rate circuit 30. Thus, when the magnet 21 is placed near the reed switch 24, the occurrence of each ventricular beating pulse from the rate circui-t 30 momentarily energizes the AND gate 48 and an audio oscillator 50. (When reed switch 24 is closed by magnet 21, a low or "O" state is provided to inverter 46, and a "1" input is pro~ided to AND ga~e 48.) The oscillator 50 then drives an acoustical speaker (piezoelectric transducer) 52 coupled directly to the case of the implantable defibrillator. So, when residing in the active state, e.g., status flip-.Elop 26 asserting its Q output, sounds synchronous with the 3~3 ~12-heart beat are periodically emitted. In the preferred embodiment, the piezoelectric transducer 52 resonates at about 3,Q00 Hertz and is aurally detected by a person within range of the sound emitted by the transducer. Thus, pulsed tones emitted hy the piezoelec-tric crys-tal 52 synchronous with t~le heart bea-t indicate that the bipolar electrode 18 is properly positioned within the heart of the patient.
On the other hand, if the status flip-flop 26 is in the ina~tive state~ e~g. EN signal deasserted, the AND ga-te 44 is disabled and flip-flop 26 provides, through its Q output, a continuous enabling signal to one input of the AND gate 48. In the inactive state, placement of the magne~ 21 near the reed switch 24 also provides, through inverter 46, a continuous enabling signal to the other input of AND gate 48. The result is that the oscillator 50 is continuously driven to provide a steady-state audible tone from the piezo electric transducer 52, of approximately 3000 Ez.
Thus, a pulsed tone indica-tes that the defibrillator is active, and a continuous tone indicates that it is inactive.
When the device is in the active state, if the bipolar sensing probe 18 is not properly positioned within the right ventricle, no tones at all will be emi-tted as the ventricular signals are not being sensed.
Thus, the presence or absence of an audible tone indicates whether the probe 18 is properly lodged about the right ventricle.
The frequency of operation of the oscillator 50 and piezoelectric transducer 52 is chosen to be substantially egual to the natural resonan-t frequency of vibration of the rigid case which encloses -the defibrillator circuits so that the transducer 52 consumes ~23~
~13-a minimum amount of enexgy for a given level of audio emissions.
The moun-ting of the piezoelectric crystal on an inner wall 51 o~ the implanted case is depicted in Figure 7. To efficiently resonate the wall 51 of -the case, a solid layer 53 of epoxy cement, such as Eccobond 24 adhesive, serves as ~ bonding medium between a surface of the crystal 52 and the surface of the wall 51 via an insulating tape 55. Preferably, no air cavity between the crys~al and the wall exists to generate the audible emissions. ~ather, the wall 51 itself vibrates to generate the sound.
State changes of the defibrillator (by status flip-flop 26) are accomplished by holding the magnet in place over the reed switch more than a predetermined time period, which in the preferred embodiment, is thirty seconds. To change the state, a 30-second timer circui-t 54 produces a CK signal which toggles the status flip-flop 26 when the magnet 21 is held in place (reed switch 24 closed) for more than thirty seconds.
~he timer 54 preferably comprises an R-C charging network in a triggering circui-t to produce the CK
signal. Any suitable timer, such as a digital timer responsive to the reed switch, could be employed as a delay timer. When in the inactive state, status flip-flop 26 also effects opening of the power circuits to all non-essential components of the defibrillator to reduce current drain from the batteries (not shown).
While being in the inactive state, only the status change and audio indicating circuits need power.
Similarly, when in the active state, the EN signal enables an electronic switch (not shown) -to pxovide electrical power to the rate circuit 30 and PDF circuit 28.
~Z3~3 Rate Analysis and Averagin~ Circui-t 30 Fig. 2 is a circuit diagram of the rate analysis and averaging circuit 30 of Fig. 1. As pre-viously stated, the circuit 30 senses depolarizations of the righ~ ventricle and, in response thereto, generates an analoy signal having a voltage level proportional to the average ven~ricular beating rate.
In the circuit 30, a paix of conductors 56 and S7 receive ventricular signals from the bipol~r sensing probe 18. The ventricular beating signal then passes to a high pass filter S8 which attenua-tes signal components ~elow a fre~uerlcy of 30 Hz. Thereafter, pre-amplifier Sg amplifies ~he signal from the high pass filter. A high voltage protection circuit 55 is interposed between the electrode 18 and the high pass filter 58 to protect the circui-t from high voltage resulting from a defibrillating pulse.
The pre-amplifier 59 is connected with amplifier 66 having an automatic gain contxol (AGC) in the feedback circuit. The AG~ tries to maintain a constant amplitude output wi-th varying input signal levels. ECG input signals are known to vary dramatica]ly in amplitude.
A pulse shapin~ circuit comprising a compara-~or 76 receives the gain controlled ventricular beating signal and generates in response thereto a series of square-wave pulses. Advantageously, both -the positive and negative swings of the ventricular beating signal produce triggering pulses, and thus the circuit 30 responds equally well to various charac-teristic ventri-cular signals associated with patients who have eithera strong positive or negative ventricular signal, or -to characteristic signals derived from various locations about the ventricle about which the bipolar sensing probe 18 may be positioned. For this reason and o-thers, the circuit 30 is very reliable.
~L~23~
The square-wave pulses f.rom compara-tor 7&
triyger a one-shot multivibrator 7~ which produces another s~uare-wave pulse of a fixed duration of approximately 150 milliseconds, preferably. This period represents the reractory pe.riod of the device.
During this 150 millisecond refractory period, the multivibrator 78 canno-t be re-triggered by o~her signals, such as T-waves, e-tc., until the period has expired.
The REFRAC signal comprising uniform-width refractory pulses from the mul-tiviblator 78 is then fed to both an averaging circuit 80 and the AND gate 44 (Fig. 1). In addition, the R~wave output signal is provided, via line 35, to the high-voltage inverter control circuit 34 to synchronize defibrillation pulses with the R-wave output ~see Figs. 1 and 3). The rate averaging circuit 80, comprising a resistor 82 and a capacitor 84, integrates the REFRAC signal from the multivibra-tor 78.
The circuit 80 is similar in operation to a frequency-to-voltage converter. At sixty beats per minute, for example, the REFRAC signal has a duty cycle of 15%.
When integrat~d, iOe. averaged, it produces the afore-mentioned RATE signal of a pre-determined magnitude.
As the beating rate increases, the duty cycle of the REFRAC signal also increases as the constant-width pulses occur more often and, when in-tegrated, the circuit 80 p.roduces the RATE signal of a correspondingly highex magnitude. The RATE signal is compared with a RATE THRESHOLD signal by the comparator 36 ~also shown in Fig. 1) which generates the enabling signal for energizing the AND gate 32. The RATE THRESHOLD signal of comparator 36 is selected so that the comparator produces the enabling signal at a prede-termined rate.
Although not shown in Figure 1, a delay 86 interposes a two~second delay and only passes a signal ~2~ L3 to -the AND gate 32 if the i.nput to the delay 82 is maintained for 2 sec. or more. This delay reduces the likelihood of de-tecting short, self--terminating arrythmias.
High-Voltage Inverter And Control Circuits The high-voltage inverter and control circuit 34, along with the magnet test logic circuit 40, i5 shown in greater detail in Figures 3, 4 and 6. Turning firs-t to Figure 4, the high-voltage inverter 200, also known as a DC~to-DC converter, is a conven-tiorlal element well known in the implantable defibrillator art.
Reference should be made, for example, to U.S. Pa-tent No. ~,16~,94~ which descri~es the DC-to-DC converter (element 30 in the '946 patent). The high-voltage inverter 200 charges an intern~1 energy storage capacitor 202 which is charged to a predetermined level and is discharged ei^ther across the heart of the patient via the SVC electrode 20 and patch electrode 22, ox is dischaxged through a test load resistor 212 under conditions as will be described below. The high-voltage inver-ter 200 includes an implanted coil (not shown) which emits RF signals during the operation of the inverter, i.e., during the charge time of the capacitor 202. It is this RF emission that is detectable outside the body of -the patient in a manner to be described.
When the high-voltage inverter is enabled, by the EN signal from status flip-flop 26 (described above), the inverter 200 is in condition for operation.
The high-voltage inverter 200 begins operation upon receipt of an INVERTER START signal which, as shown in Figure 3, is initiated by receipt of either an INVST
signal from -the AND gate 32 or an MGTST signal from the ~223~3 magnet test logic circuit 40 (as shown in Figs. l and 3). The high-voltage inverter begins running and provides an INV RUNNING signal to the magnet test logic circuit 40, in a manner to be described bel.ow. The high-voltage inverter keeps running until the energy storage capacitor 202 is charged to its predetermined level. It should be apparent that the period of time that the high-voltage inverter is running, i.e., the period of time it takes to charge the capacitor 202, is an indication of the defibrillator battery strength.
(See, the description in U.S. Patent No. 4,164,946.3 Further, during the charge time of the high~voltage inverter, the RF emissions of the inver-ter coil are fre~uency modulated to represent the number of inverter discharges across the electrodes 20, 22, which informa-tion is detectable outside the body of the patient by the demodulator and decoder 12.
The capacitor 202 is discharged either through the test load 212 or across the patient electrodes 20 and 22 dependent upon receipk of a trigger pulse eithex to the test load SCR 204, via line 206, or a trigger signal across leads 208, which enables the patient SCR 210. Line 206 and leads 208 are actuated by control circuitry as will be described further below in connec-tion with Figure 3. When SCR 204 is triggered via apulse on line 206, the capacitor 202 discharges across the test load resistor 212; when patient SCR 210 is actuated, via signals over leads 208, the capacitor 202 discharges across the patient electro~es 20, 22. When the capacitor discharges across the patient electrodes, a count signal, at CT, is provided which, as shown in Figure l, increments the counter 38 representing -the number of discharges across the patient's heart.
Similarly, a pulse feedback signal, as shown in Figure 4, ~3~
~18-is provlded which is sent to control circuitry as shown in Figure 3 Eor triggering the truncate SCR 214, as will be described.
The patient SCR 210 is triggexed by signals across the leads 208, via an anti-shunt circuit. The anti-shunt circuit includes a small pulse -transformer 216 connected to -the patient SCR 210 for triggering same in response to a trigger input across leads 208.
The trigger input signal is applied to the primary winding of transformer 216 and the secondary winding of the transformer activates the patient SCR 210 permi-tting khe high-voltage defibrillation pulse to pass to the SVC and patch electrodes/ 20 and 22. Such a circuit avoids the drawback that when an exkernal defibril-lation voltage is applied to the heart of the pa-tient having an implanted device connected to the patient's heart~ the external defibrillation voltage will not pass through the implanted device and specifically through the high-voltage inverter. The transformer ~0 coupling eliminates a low impedence path to ground.
The truncate SCR 214 is activated by a signal on line 216, as shown in Figures 3 and 4. The purpose of the truncate SCR is as follows. When the capacitor ~02 discharges across the implanted electrodes, the discharge is an exponentially decaying waveform. When the waveform decays to a certain voltage, the truncate SCR 214 is fired to truncate the decaying pulse.
Preferably the predetermined point of decay is approxi-mately 2/3's of what a fully decayed pulse would other-wise look like.
The triggering signals to the circuit ofFigure 4 are provided by the inverter control circuitry, in conjunction with the magnet tesk logic circui-txy 40, as shown in Figure 3. As shown in Figure 3, receipt of ~23~ 3 an INVST signal from ~ND gate 32 or receipt of a MGTST
signal from magnet test logic circuit 40, is applied to OR gate ~18 which provides an INVERTER START signal -to initiate the high-voltage inverter to charge the charg-ing capacitor 202. Assuming a need for defibrillationoccurs, .resulting in an INVST signal from AND gate 32, such signal starts the inverter running, via OR gate 218, and sets a patient flip-flop 220. The patient flip-:Elop output is applied to AND gate 222. A second input to the AND gate 222 is connec-ted to the R-wave detected output signal tover line 35~ from the rate analysis circuit 30 as shown in Figure 1. The third input to the AND gate 222 is coupled with the high-voltage in~erter to receive the INV RUNNING signal via inverter logic element 224. During ~he time that the inverter is running, the third input to the AND gate 222 is low and the output of the AND gate 222 is low. When the inverter stops running, i.e., at the completion of the charging of the defibrillator capacitor, the inverter logic element 224 output is high. Thus, subsequent R wave inputs to the ~ND gate 222 cause a pulse to be emitted, through a suitable RC pulse shaping network 226 and bu~fer 228 to a transistor 230. The transistor 230 is actuated and a patient trigger pulse is applied over leads 208. As previously described, the receipt of a patient trigger pulse over leads 208 fires the patient SCR 210, as shown in Figure 4, and the capacitor 202 discharges across the electrodes connected to the pa-tient's heart. This discharge also provides a count CT pulse which resets the patient ~lip flop 220 via OR gate 232.
When the patient SCR 210 is triggered, the capacitor 202 discharges to provide a high-vol-tage exponentially decaying pulse across the electrodes 23 ~ ~ 3 connected to the patient's heart. This exponentially decaying pulse is fed back, via pulse feedback terminal to a threshold compara-tor ~34. When the exponentially decaying pulse feedback signal drops to a prede-termined reference level, as provided -to the negative input terminal of compara~or 234, the comparator provides an output which is inverted by inver-ter 236, shaped by pulse shaping network 238, and a pulse is provided at lead 216 ~o fire the -trwncate SCR 214 as shown in Figure 4. When the trunca~e SCR 214 is fired, khe exponentially decaying pulse across the electrodes 20, 22 is truncated. This is done because it is undesirable to require the pulse to exponen-tially decay to a zero level.
The operation of the magnet test logic circuit 40 and the triggering of test load SCR 204 will now be described. The magnet test logic circui-t is initiated when AND gate 240 is asserted. AND ga-te 240 is asserted when the defibrillator is enabled, i.e., receipt of an EN input from status flip-flop 26, and the magnet 21 is removed from the reed switch 24 -to provide a positive, or high, signal to the AMD gate 240. That is, when the magnet 21 is brought into close proximity to the reed switch 24, thus closing the reed switch contacts, a negative or zero input is provided to the AND gate 240.
Upon removal of the magnet, thus opening the reed switch 24, the input to AND gate 240 from the reed switch becomes high -thus asserting the AMD gate 240.
It should be noted -that the magnet 21 must be removed from proximity ko the reed switch 24 in less -than 30 seconds to cause a magnet test to be initiated. If the magnet 21 is in proximity to the reed switch 24 ~or greater than 30 seconds, then the status flip-flop 26 is disabled and the input -to AND ga-te 240 from -the ~2~3~;~3 -21~
status flip-flop 26 is low, -thus preventing asser-tion of the ANn gate 240.
Assertion of the ~ND gate 2~0 sets delay flip-flop 242 which provides a MGTST signal to the inverter and control circui~ 34 via OR gate 218, thus starting the inverter. Further, the Elip-:Elop 242 output se-ts a magnet test flip-flop 244. Setting of magnet test flip-flop 244 results in an input signal, after a brief delay by delay element 246, ~o AND gate 248. A second input to AND gate 248 is connected -to the INV RUNNING line via inverter logic element 224.
When the inverter has completed running, thus reflecting that the internal capacitor 202 is completely charged, the second input to AND gate 248 goes high and the AND
gate 248 is asserted. Output pulse from AND gate 248 is provided to the test load SCR trigger line 206, via pulse shaping and huffer circuits, and the test load SCR 204 is fired. The capacitor then discharges across the test load resistor 212.
It should also be noted that when the magnet test flip-flop 244 is set and its Q-output is high, the Q-output is also provided to OR gate 232 to keep the patient flip-flop 220 in a reset condition. Thus, during a magnet test condition, the patient ~lip-flop is prevented from operation and no defibrillating pulses across -the patient's heart can be emitted.
During a magnet test, when the magnet test flip-flop 244 is set, telernetry control AND gate 250 is enabled during the time that the invert~r is running.
This provides a telemetry control signal from the magnet test logic 40 which signal is provided to -the 8-bit parallel-to-serial converter 39, as shown in Figure l.
~3~
As previously discussed, t.he number of defibril-la~ing shoc~s administered to the patien~ resul-ts in CT
signals which are applied to counter 38, as shown in Figure 1. When the -telemetry control signal from the magnet test logic 40 i5 issued, the conten-ts of th~
counter 33 are provided to the 8-bit parallel-to-serial converter 39. The serial data bits from -the converter 39 are provided to pulse width modulation circuit 90 which in turn provides a pulse width modulated signal to the inverter frequency modulator 92. The inverter frequency modulator 92 frequency modulates the RF
signal emitted by the inverter coil during -the time the inverter is running. This frequency modulated informa-tion is detectable outside the body of the patient by the external demodulator and decoder 12 which demodulates -the frequency modulated signals to display the number of defibrillation pulses that have been counted.
Further, by detecting -the pexiod of time that the inverter coil is emitting radio freguency, the charge time of the defibrillator capacitor is determined. It should be noted that, whereas it takes approximately seconds for telemetry information to be read from the counter 38, converted, pulse width modulated, and inverter frequency modulated, in contras-t, it takes 5-6 seconds for the high vol-tage capacitor con-tained within high voltage inverter and control circuit -to charge up.
The demodulator and decoder 1~ and display 14 may be any suitable external device suitable for demodu-lating, decoding and displaying the transmitted informa-tion.
Turning now to Figu.re 6, the 4-count hold circuit is disclosed. As previously discussed, the 4-count hold circuit inhibits the inverter after four defibrillating pulses are applied to the patient until ~3~L3 after 35 seconds of normal sinus rhy-thm is detected.
The 4-count hold circuit includes a four-stage shift register with an inverte.r inhibi-t line provided to the fourth Q3 stage. As defi~rillating pulses are detected over the CT input, each CT pulse representative of a de~ibrillating shock is counted. Upon receipt of four coun~s, ~he inverter inhi~it ou~pu-t is asserted to inhibit the high-voltage inverter~ Receipt of each CT
pulse is also provided, via OR gate 302 to a 35-second delay timer 304. Recei~t of eac~ CT input starts the 35-second delay timer running. If, after four CT
pulses, the INVST input to OR gate 302 is s-till receiving inputs, reflecting the fact that the patient is still in need o~ defibrillation, the 35-second delay timer keeps runningO Only when normal sinus rhythm is detected, i.e., by absence of the INVST signal, does the 35-second delay timer reset the shift register 300 thus enabling the high-voltage inverter to operate.
Bipolar Sense Electrode 19 Fig. 5 depicts the details of -the bipolar sense electrode 18 shown in Fig. 1. The elec-trode 18 is implanted in -the right ventricle and, as previously mentioned, senses .relatively weak electrical signals produced by ventricular contractions. This signal, ~5 known as the R-wave, is then supplied to the rate analysis and averaging circuit 30 of Fig. 1.
The electrode 18 consists of a firs-t wi.re lead 301 and a second wire lead 302 spaced apart from the lead 301. The lead 301 electrically communicates with a conductive distal tip 303 which is crimped around the lead 301, while the lead 302 electrically communicates with a conductive ring electrode 304 in contact therewith and encircling a flexible insulating ~ . . .
3~L3
-2~ -elastomex 306. In the preferred embodim~nt, the spacing between conductlve elemen~s 303 and 304 is abou-t one centimeter.
Lead coils 307 and 308 are wrapped around and encircle the wire leads 301 and 302. The lead coils 307, 308 are separately enclosed in bilumen tubing 305 and extend into a plug element 310 for plugging into the implantahle device. Lead coil 308 further includes an encircling medical grade silicone tubing 312 near the distal end.
It should be apparent that the exact construc-tion of the bipolar electrode 18 may vary from that described above, ~he impor~ant feature being -~he spaced distance between the distal tip 303 and the ring 304 electrod~s. Moreover, the two electrodes may be separate electrodes, such as corkscrew type or needle -type electrodes that are not part of a unitary structure.
It has been de-termined that by limiting the distance between the tip 303 and ring 304 to between .5 and 1.5 centimeters, and preferably 1.0 centimeter, ra-ther than a distance exceeding 2.5 centimeters, as normally provided by electrodes in prior art pacing devices, a signal characterized by faster rise times more useful or rate countiny, particularly during chaotic cardiac 2$ arrhythmias such as polymorphic ventricular tachycardia and ventricular fibrillation can be obtained.
It should be noted that as used herein, the terms "fibrillation", "cardioversion", "defibrillation", "defibrillator" and "cardioverter" are intended to refer to all arrhythmias of a life-threatening nature that can be reverted to normal sinus rhythm by the application of high-voltage countershock, and the reversion of such arrhythmias to normal sinus rhy-thm;
life-threa-tening high rate tachycardia, for example, should be construed as equivalen-t to "fibrillation" as used herein.
We have set forth an illustra-tive embodiment of our invention wherein we at-tain the above mentioned objectives. It is apparen-t that certain features and aspects of the inven-tion may be constructed and/o practiced in a manner that is not specifically shown or described; however, we intend by the appended claims that all such modifications and variations which can be made by those skilled in the art may come wi-thin the scope of our invention as defined.
Lead coils 307 and 308 are wrapped around and encircle the wire leads 301 and 302. The lead coils 307, 308 are separately enclosed in bilumen tubing 305 and extend into a plug element 310 for plugging into the implantahle device. Lead coil 308 further includes an encircling medical grade silicone tubing 312 near the distal end.
It should be apparent that the exact construc-tion of the bipolar electrode 18 may vary from that described above, ~he impor~ant feature being -~he spaced distance between the distal tip 303 and the ring 304 electrod~s. Moreover, the two electrodes may be separate electrodes, such as corkscrew type or needle -type electrodes that are not part of a unitary structure.
It has been de-termined that by limiting the distance between the tip 303 and ring 304 to between .5 and 1.5 centimeters, and preferably 1.0 centimeter, ra-ther than a distance exceeding 2.5 centimeters, as normally provided by electrodes in prior art pacing devices, a signal characterized by faster rise times more useful or rate countiny, particularly during chaotic cardiac 2$ arrhythmias such as polymorphic ventricular tachycardia and ventricular fibrillation can be obtained.
It should be noted that as used herein, the terms "fibrillation", "cardioversion", "defibrillation", "defibrillator" and "cardioverter" are intended to refer to all arrhythmias of a life-threatening nature that can be reverted to normal sinus rhythm by the application of high-voltage countershock, and the reversion of such arrhythmias to normal sinus rhy-thm;
life-threa-tening high rate tachycardia, for example, should be construed as equivalen-t to "fibrillation" as used herein.
We have set forth an illustra-tive embodiment of our invention wherein we at-tain the above mentioned objectives. It is apparen-t that certain features and aspects of the inven-tion may be constructed and/o practiced in a manner that is not specifically shown or described; however, we intend by the appended claims that all such modifications and variations which can be made by those skilled in the art may come wi-thin the scope of our invention as defined.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An implantable defibrillation system for automatically defibrillating the heart of a patient comprising:
bipolar electrode means implantable in a heart ventricle for sensing ventricular contractions, comprising a pair of electrodes spaced apart between 0.5 cm and 1.5 cm;
detecting means connected with said bipolar electrode means for detecting the sensed ventricular contractions and for providing a heart beat pulse signal proportional to each detected ventricular contraction, and for providing an arrhythmia signal when the detected ventricular contractions exceed a predetermined rate; and defibrillating means connected with said detecting means for providing a defibrillating pulse to the heart of a patient, said defibrillating means including means for charging an internal storage capacitor to a predetermined voltage level upon receipt of said arrhythmia signal, and means for discharging the voltage stored in said storage capacitor across the heart of a patient synchronous with said heart beat pulse signal.
bipolar electrode means implantable in a heart ventricle for sensing ventricular contractions, comprising a pair of electrodes spaced apart between 0.5 cm and 1.5 cm;
detecting means connected with said bipolar electrode means for detecting the sensed ventricular contractions and for providing a heart beat pulse signal proportional to each detected ventricular contraction, and for providing an arrhythmia signal when the detected ventricular contractions exceed a predetermined rate; and defibrillating means connected with said detecting means for providing a defibrillating pulse to the heart of a patient, said defibrillating means including means for charging an internal storage capacitor to a predetermined voltage level upon receipt of said arrhythmia signal, and means for discharging the voltage stored in said storage capacitor across the heart of a patient synchronous with said heart beat pulse signal.
2. An implantable defibrillation system for automatically defibrillating the heart of a patient comprising:
bipolar electrode means implantable in the ventricle of a heart for sensing ventricular contractions;
rate analysis circuit means connected with said bipolar electrode means for detecting the sensed ventricular contractions and for providing, (1) an analog rate output signal having a magnitude proportional to the average number of ventricular contractions per unit of time, and (2) a heart beat pulse signal proportional to each detected ventricular contraction;
threshold means connected with said rate analysis circuit means for receiving said analog rate output signal and for providing a threshold output signal when said analog rate output signal exceeds a predetermined reference level;
high voltage inverter means for receiving said threshold output signal for charging a storage capacitor to a predetermined voltage level upon receipt of said threshold output signal, and for providing an inverter output signal when the storage capacitor is fully charged;
a storage capacitor connected with said high voltage inverter means for receiving a voltage charge, said storage capacitor coupled with implantable defibrillating electrodes;
logic means connected with said rate analysis circuit means and said high voltage inverter means for receiving said heart beat pulse signal and said inverter output signal and for providing a discharge signal in response to receipt of said heart beat pulse signal and inverter output signal; and discharge means connected with said storage capacitor and said logic means for discharging said storage capacitor across the implantable defibrillating electrodes in response to receipt of said discharge signal.
bipolar electrode means implantable in the ventricle of a heart for sensing ventricular contractions;
rate analysis circuit means connected with said bipolar electrode means for detecting the sensed ventricular contractions and for providing, (1) an analog rate output signal having a magnitude proportional to the average number of ventricular contractions per unit of time, and (2) a heart beat pulse signal proportional to each detected ventricular contraction;
threshold means connected with said rate analysis circuit means for receiving said analog rate output signal and for providing a threshold output signal when said analog rate output signal exceeds a predetermined reference level;
high voltage inverter means for receiving said threshold output signal for charging a storage capacitor to a predetermined voltage level upon receipt of said threshold output signal, and for providing an inverter output signal when the storage capacitor is fully charged;
a storage capacitor connected with said high voltage inverter means for receiving a voltage charge, said storage capacitor coupled with implantable defibrillating electrodes;
logic means connected with said rate analysis circuit means and said high voltage inverter means for receiving said heart beat pulse signal and said inverter output signal and for providing a discharge signal in response to receipt of said heart beat pulse signal and inverter output signal; and discharge means connected with said storage capacitor and said logic means for discharging said storage capacitor across the implantable defibrillating electrodes in response to receipt of said discharge signal.
3. An implantable defibrillation system as claimed in claim 2 further comprising PDF processing means connectable to the heart for receiving ECG waveforms and for processing said ECG waveforms in accordance with a probability density function to provide a probability density function output signal, and wherein said high voltage inverter means includes means for receiving said probability density function output signal and for providing said inverter output signal upon receipt of said probability density function output signal and said threshold output signal.
4. An implantable defibrillation system as claimed in claim 2 wherein said bipolar electrode means comprises a pair of electrodes spaced apart between 0.5 cm and 1.5 cm.
5. The rate detector of claim 1 wherein said pair of electrodes are separated by a distance of one(1) cm.
6. The rate detector of claim 5 wherein said pair of electrodes are mounted at the distal tip of said probe, the other electrode comprising a ring electrode circumferentially surrounding the probe and spaced from said distal tip.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US37019182A | 1982-04-21 | 1982-04-21 | |
US370,191 | 1982-04-21 | ||
US478,038 | 1983-03-23 | ||
US06/478,038 US4614192A (en) | 1982-04-21 | 1983-03-23 | Implantable cardiac defibrillator employing bipolar sensing and telemetry means |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1223643A true CA1223643A (en) | 1987-06-30 |
Family
ID=27004853
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000426300A Expired CA1223643A (en) | 1982-04-21 | 1983-04-20 | Implantable cardiac defibrillator employing bipolar sensing and telemetry means |
Country Status (6)
Country | Link |
---|---|
US (1) | US4614192A (en) |
CA (1) | CA1223643A (en) |
DE (1) | DE3314488A1 (en) |
FR (1) | FR2530475B1 (en) |
GB (2) | GB2121288B (en) |
NL (1) | NL189950C (en) |
Families Citing this family (60)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4488555A (en) * | 1982-12-13 | 1984-12-18 | Mieczyslaw Mirowski | Battery condition warning system for medical implant |
FR2559068B1 (en) * | 1984-02-06 | 1990-01-26 | Medtronic Inc | PROTECTIVE CIRCUIT FOR AN IMPLANTABLE HEART RESTORATION DEVICE |
US4603705A (en) * | 1984-05-04 | 1986-08-05 | Mieczyslaw Mirowski | Intravascular multiple electrode unitary catheter |
CA1290813C (en) * | 1985-08-12 | 1991-10-15 | Michael B. Sweeney | Pacemaker for detecting and terminating a tachycardia |
US4796620A (en) * | 1986-05-13 | 1989-01-10 | Mieczyslaw Mirowski | System for sensing abnormal heart activity by means of heart rate acceleration and deceleration detection |
US4730618A (en) * | 1986-06-16 | 1988-03-15 | Siemens Aktiengesellschaft | Cardiac pacer for pacing a human heart and pacing method |
US4716903A (en) * | 1986-10-06 | 1988-01-05 | Telectronics N.V. | Storage in a pacemaker memory |
US4823796A (en) * | 1987-04-03 | 1989-04-25 | Laerdal Manufacturing Corp. | Defibrillator circuit for producing a trapezoidal defibrillation pulse |
US4847617A (en) * | 1987-08-14 | 1989-07-11 | Siemens-Pacesetter, Inc. | High speed digital telemetry system for implantable devices |
US4774950A (en) * | 1987-10-06 | 1988-10-04 | Leonard Bloom | Hemodynamically responsive system for and method of treating a malfunctioning heart |
US4984572A (en) * | 1988-08-18 | 1991-01-15 | Leonard Bloom | Hemodynamically responsive system for and method of treating a malfunctioning heart |
US4945477A (en) * | 1987-10-22 | 1990-07-31 | First Medic | Medical information system |
US4896671A (en) * | 1988-08-01 | 1990-01-30 | C. R. Bard, Inc. | Catheter with contoured ablation electrode |
US4949719A (en) * | 1989-04-26 | 1990-08-21 | Ventritex, Inc. | Method for cardiac defibrillation |
US5318595A (en) * | 1989-09-25 | 1994-06-07 | Ferek Petric Bozidar | Pacing method and system for blood flow velocity measurement and regulation of heart stimulating signals based on blood flow velocity |
US5044375A (en) * | 1989-12-08 | 1991-09-03 | Cardiac Pacemakers, Inc. | Unitary intravascular defibrillating catheter with separate bipolar sensing |
US5269319A (en) * | 1989-12-08 | 1993-12-14 | Cardiac Pacemakers, Inc. | Unitary intravascular defibrillating catheter with bipolar sensing |
US5321618A (en) * | 1990-05-29 | 1994-06-14 | Lawrence Gessman | Apparatus and method for remotely monitoring implanted cardioverter defibrillators |
US5085213A (en) * | 1990-06-01 | 1992-02-04 | Leonard Bloom | Hemodynamically responsive system for and method of treating a malfunctioning heart |
US5054485A (en) * | 1990-06-01 | 1991-10-08 | Leonard Bloom | Hemodynamically responsive system for and method of treating a malfunctioning heart |
US5086772A (en) * | 1990-07-30 | 1992-02-11 | Telectronics Pacing Systems, Inc. | Arrhythmia control system employing arrhythmia recognition algorithm |
US5271392A (en) * | 1990-08-24 | 1993-12-21 | Siemens-Elema Ab | Method and apparatus for administering cardiac electrotherapy dependent on mechanical and electrical cardiac activity |
EP0473070B1 (en) * | 1990-08-24 | 1995-11-29 | Bozidar Ferek-Petric | Cardiac pacing systems with tensiometry |
EP0474957A3 (en) * | 1990-09-11 | 1992-06-24 | Bozidar Ferek-Petric | Ultrasonic doppler synchronized cardiac electrotherapy device |
US5179945A (en) * | 1991-01-17 | 1993-01-19 | Cardiac Pacemakers, Inc. | Defibrillation/cardioversion system with multiple evaluation of heart condition prior to shock delivery |
SE9300281D0 (en) * | 1993-01-29 | 1993-01-29 | Siemens Elema Ab | IMPLANTABLE MEDICAL DEVICE AND EXTRACORPORAL PROGRAMMING AND MONITORING DEVICE |
US5336253A (en) * | 1993-02-23 | 1994-08-09 | Medtronic, Inc. | Pacing and cardioversion lead systems with shared lead conductors |
US5342403A (en) * | 1993-04-09 | 1994-08-30 | Hewlett-Packard Corporation | Integrated defibrillator/monitor architecture with defibrillator-only fail-safe mode of operation |
FR2709026B1 (en) * | 1993-08-10 | 1995-10-13 | Ela Medical Sa | DC-DC converter for variable voltage load. |
FR2710848B1 (en) * | 1993-10-08 | 1995-12-01 | Ela Medical Sa | Implantable defibrillator with optically isolated shock generator. |
FR2711064B1 (en) * | 1993-10-15 | 1995-12-01 | Ela Medical Sa | Implantable defibrillator / pacemaker with multiphase shock generator. |
HRP931478A2 (en) * | 1993-12-06 | 1995-12-31 | Ferek Petri Bo Idar | An apparatus for cardial electrotherapy containing transmission line uring cardial contractions |
US5749909A (en) * | 1996-11-07 | 1998-05-12 | Sulzer Intermedics Inc. | Transcutaneous energy coupling using piezoelectric device |
SE9704521D0 (en) | 1997-12-04 | 1997-12-04 | Pacesetter Ab | Medical implant |
US5968086A (en) * | 1998-02-23 | 1999-10-19 | Medtronic, Inc. | Pacing and cardioversion lead systems with shared lead conductors |
US6041255A (en) * | 1998-04-16 | 2000-03-21 | Kroll; Mark W. | Disposable external defibrillator |
US6980656B1 (en) * | 1998-07-17 | 2005-12-27 | Science Applications International Corporation | Chaotic communication system and method using modulation of nonreactive circuit elements |
US6066166A (en) * | 1998-08-28 | 2000-05-23 | Medtronic, Inc. | Medical electrical lead |
US6764446B2 (en) | 2000-10-16 | 2004-07-20 | Remon Medical Technologies Ltd | Implantable pressure sensors and methods for making and using them |
US7198603B2 (en) * | 2003-04-14 | 2007-04-03 | Remon Medical Technologies, Inc. | Apparatus and methods using acoustic telemetry for intrabody communications |
US7024248B2 (en) | 2000-10-16 | 2006-04-04 | Remon Medical Technologies Ltd | Systems and methods for communicating with implantable devices |
US7283874B2 (en) * | 2000-10-16 | 2007-10-16 | Remon Medical Technologies Ltd. | Acoustically powered implantable stimulating device |
US8116868B2 (en) * | 2003-04-11 | 2012-02-14 | Cardiac Pacemakers, Inc. | Implantable device with cardiac event audio playback |
US7239915B2 (en) * | 2003-12-16 | 2007-07-03 | Medtronic, Inc. | Hemodynamic optimization system for biventricular implants |
US7136702B2 (en) * | 2004-03-19 | 2006-11-14 | Medtronic, Inc. | Method and apparatus for delivering multi-directional defibrillation waveforms |
US8078278B2 (en) | 2006-01-10 | 2011-12-13 | Remon Medical Technologies Ltd. | Body attachable unit in wireless communication with implantable devices |
US7650185B2 (en) | 2006-04-25 | 2010-01-19 | Cardiac Pacemakers, Inc. | System and method for walking an implantable medical device from a sleep state |
US7908334B2 (en) * | 2006-07-21 | 2011-03-15 | Cardiac Pacemakers, Inc. | System and method for addressing implantable devices |
WO2008118908A1 (en) | 2007-03-26 | 2008-10-02 | Remon Medical Technologies, Ltd. | Biased acoustic switch for implantable medical device |
EP2151009B1 (en) * | 2007-04-27 | 2016-07-13 | Koninklijke Philips N.V. | Implantable device comprising an antenna system with safety mode |
US8041431B2 (en) * | 2008-01-07 | 2011-10-18 | Cardiac Pacemakers, Inc. | System and method for in situ trimming of oscillators in a pair of implantable medical devices |
US8301262B2 (en) * | 2008-02-06 | 2012-10-30 | Cardiac Pacemakers, Inc. | Direct inductive/acoustic converter for implantable medical device |
DE102008024857A1 (en) * | 2008-05-23 | 2009-11-26 | Biotronik Crm Patent Ag | Wireless feedthrough for medical implants |
US8798761B2 (en) | 2008-06-27 | 2014-08-05 | Cardiac Pacemakers, Inc. | Systems and methods of monitoring the acoustic coupling of medical devices |
JP2011529722A (en) | 2008-08-14 | 2011-12-15 | カーディアック ペースメイカーズ, インコーポレイテッド | Performance evaluation and adaptation of acoustic communication links |
US8593107B2 (en) | 2008-10-27 | 2013-11-26 | Cardiac Pacemakers, Inc. | Methods and systems for recharging an implanted device by delivering a section of a charging device adjacent the implanted device within a body |
EP4039322B1 (en) | 2014-02-24 | 2023-09-06 | Element Science, Inc. | External defibrillator |
CA2994436A1 (en) | 2015-08-26 | 2017-03-02 | Element Science, Inc. | Wearable devices |
RU2703640C1 (en) | 2016-01-11 | 2019-10-21 | Конинклейке Филипс Н.В. | Method and device for non-audio reading of defibrillator status indicator |
JP2022504629A (en) | 2018-10-10 | 2022-01-13 | エレメント サイエンス,インク | Wearable medical device with disposable and reusable parts |
Family Cites Families (42)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US27757A (en) * | 1860-04-03 | Geo Fetter | Improvement in cutting apparatus for harvesters | |
US2202340A (en) * | 1938-10-18 | 1940-05-28 | Faist Jacob | Screw cutting nipper |
US3442269A (en) * | 1965-12-20 | 1969-05-06 | Zenith Radio Corp | Defibrillator and control circuit |
DE1282802B (en) | 1966-02-09 | 1968-11-14 | Fritz Hellige & Co G M B H Fab | Device for electrical stimulation of the heart |
US3608545A (en) * | 1968-11-25 | 1971-09-28 | Medical Engineering Research C | Heart rate monitor |
US3554188A (en) * | 1969-02-27 | 1971-01-12 | Zenith Radio Corp | Heartbeat frequency monitor |
US3572324A (en) * | 1969-04-01 | 1971-03-23 | Gen Electric | Automatic gain control for a cardiac monitor |
NL174701C (en) | 1970-02-09 | 1989-12-18 | Mirowski Mieczyslaw | DEFIBRILLATOR. |
US3717140A (en) * | 1970-11-13 | 1973-02-20 | E Greenwood | Heart rate counter with digital storage and numerical readout |
DE2158132C2 (en) * | 1971-11-24 | 1974-01-03 | Robert Bosch Elektronik Gmbh, 1000 Berlin Und 7000 Stuttgart | Stimulation current diagnostic device |
US3857398A (en) * | 1971-12-13 | 1974-12-31 | L Rubin | Electrical cardiac defibrillator |
US3805795A (en) * | 1972-03-17 | 1974-04-23 | Medtronic Inc | Automatic cardioverting circuit |
DE2216043A1 (en) * | 1972-04-01 | 1973-10-04 | Hellige & Co Gmbh F | DEVICE FOR CHECKING THE FUNCTIONAL CONDITION OF IMPLANTED ELECTRIC STIMULAR PULSE GENERATORS, IN PARTICULAR OF PACEMAKERS |
US3804098A (en) | 1972-04-17 | 1974-04-16 | Medronic Inc | Body implantable lead |
US3882277A (en) * | 1972-04-20 | 1975-05-06 | American Optical Corp | Electrocardiographic telemetry and telephone transmission link system |
US3825015A (en) * | 1972-12-14 | 1974-07-23 | American Optical Corp | Single catheter for atrial and ventricular stimulation |
US3939824A (en) * | 1973-10-09 | 1976-02-24 | General Electric Company | Physiological waveform detector |
GB1505130A (en) * | 1974-05-07 | 1978-03-22 | Seiko Instr & Electronics | Systems for detecting information in an artificial cardiac pacemaker |
US3983476A (en) * | 1974-06-28 | 1976-09-28 | Francis Konopasek | Defibrillator testing device |
FR2298909A1 (en) | 1975-01-24 | 1976-08-20 | Medtronic Inc | PROTECTION CIRCUIT FOR A HEART STIMULATOR |
US3974834A (en) | 1975-04-23 | 1976-08-17 | Medtronic, Inc. | Body-implantable lead |
US4184493A (en) * | 1975-09-30 | 1980-01-22 | Mieczyslaw Mirowski | Circuit for monitoring a heart and for effecting cardioversion of a needy heart |
DE7606824U1 (en) | 1976-03-06 | 1977-08-25 | Csapo, Georg, Dr.Med., 7800 Freiburg | Catheters for pacemakers |
US4164946A (en) * | 1977-05-27 | 1979-08-21 | Mieczyslaw Mirowski | Fault detection circuit for permanently implanted cardioverter |
US4102346A (en) * | 1977-09-01 | 1978-07-25 | The Raymond Lee Organization, Inc. | Heart pacemaker monitor, alarm and auxiliary power supply |
US4181134A (en) * | 1977-09-21 | 1980-01-01 | Mason Richard C | Cardiotachometer |
US4210149A (en) * | 1978-04-17 | 1980-07-01 | Mieczyslaw Mirowski | Implantable cardioverter with patient communication |
US4223678A (en) * | 1978-05-03 | 1980-09-23 | Mieczyslaw Mirowski | Arrhythmia recorder for use with an implantable defibrillator |
US4457315A (en) * | 1978-09-18 | 1984-07-03 | Arvin Bennish | Cardiac arrhythmia detection and recording |
US4245641A (en) * | 1979-02-28 | 1981-01-20 | Pacesetter Systems, Inc. | Display and control system and method for programmable living tissue stimulator |
US4312356A (en) * | 1979-03-07 | 1982-01-26 | George Edgar Sowton | Pacemakers for tachycardia control |
DE3064258D1 (en) * | 1979-07-19 | 1983-08-25 | Medtronic Inc | Implantable cardioverter |
US4280502A (en) * | 1979-08-08 | 1981-07-28 | Intermedics, Inc. | Tachycardia arrester |
US4259966A (en) * | 1979-08-22 | 1981-04-07 | American Optical Corporation | Heart rate analyzer |
US4295474A (en) * | 1979-10-02 | 1981-10-20 | The Johns Hopkins University | Recorder with patient alarm and service request systems suitable for use with automatic implantable defibrillator |
US4340063A (en) * | 1980-01-02 | 1982-07-20 | Empi, Inc. | Stimulation device |
US4349030A (en) * | 1980-07-10 | 1982-09-14 | Ross H. Zoll | External noninvasive electric cardiac stimulation |
NL190185C (en) | 1980-08-05 | 1993-12-01 | Mirowski Mieczyslaw | SYSTEM FOR DEFIBRATING THE HEART OF A PATIENT. |
US4475551A (en) * | 1980-08-05 | 1984-10-09 | Mieczyslaw Mirowski | Arrhythmia detection and defibrillation system and method |
GB2083916B (en) | 1980-09-18 | 1984-09-26 | Mirowski Miecyslaw | Implantable automatic defibrillator |
US4407288B1 (en) * | 1981-02-18 | 2000-09-19 | Mieczyslaw Mirowski | Implantable heart stimulator and stimulation method |
US4393877A (en) * | 1981-05-15 | 1983-07-19 | Mieczyslaw Mirowski | Heart rate detector |
-
1983
- 1983-03-23 US US06/478,038 patent/US4614192A/en not_active Expired - Lifetime
- 1983-04-20 GB GB08310661A patent/GB2121288B/en not_active Expired
- 1983-04-20 FR FR8306459A patent/FR2530475B1/en not_active Expired
- 1983-04-20 NL NLAANVRAGE8301391,A patent/NL189950C/en not_active IP Right Cessation
- 1983-04-20 CA CA000426300A patent/CA1223643A/en not_active Expired
- 1983-04-21 DE DE19833314488 patent/DE3314488A1/en active Granted
-
1985
- 1985-05-31 GB GB08513802A patent/GB2159718B/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
NL189950C (en) | 1993-09-16 |
NL8301391A (en) | 1983-11-16 |
GB2159718B (en) | 1986-10-08 |
GB8310661D0 (en) | 1983-05-25 |
GB8513802D0 (en) | 1985-07-03 |
NL189950B (en) | 1993-04-16 |
GB2159718A (en) | 1985-12-11 |
DE3314488A1 (en) | 1983-12-01 |
FR2530475A1 (en) | 1984-01-27 |
GB2121288A (en) | 1983-12-21 |
GB2121288B (en) | 1986-10-08 |
US4614192A (en) | 1986-09-30 |
FR2530475B1 (en) | 1988-05-27 |
DE3314488C2 (en) | 1987-02-05 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
CA1223643A (en) | Implantable cardiac defibrillator employing bipolar sensing and telemetry means | |
US4610254A (en) | Interactive portable defibrillator | |
US4619265A (en) | Interactive portable defibrillator including ECG detection circuit | |
US4210149A (en) | Implantable cardioverter with patient communication | |
US5105809A (en) | System and method for evaluating lead defibrillation requirements of an implanted device without repeated fibrillation induction | |
EP0870519B1 (en) | Atrial flutter cardioverter | |
US6529777B1 (en) | Electrode for tissue stimulation | |
CA2202739C (en) | Atrial defibrillation system having a portable communication device | |
US5423883A (en) | Implantable myocardial stimulation lead with sensors thereon | |
US5321618A (en) | Apparatus and method for remotely monitoring implanted cardioverter defibrillators | |
JP3481940B2 (en) | Atrial defibrillator | |
AU656420B2 (en) | Method and apparatus for wide area antitachycardia pacing | |
US6052617A (en) | System and method for reliably detecting atrial events of a heart using only atrial sensing | |
US5431687A (en) | Impedance timed defibrillation system | |
EP0824935A2 (en) | Electrode for tissue stimulation | |
US6115633A (en) | Implantable stimulator | |
US20030069608A1 (en) | Cardiac rhythm management system with ultrasound for autocapture or other applications | |
WO2003039663A1 (en) | Method and apparatus for inducing cardiac fibrillation | |
JP2001520557A (en) | Heart stimulator with lead wire failure detector and alarm device | |
EP0038080B1 (en) | Patient interactive stimulator | |
US20120303085A1 (en) | Methods and apapratus for manually suspending intrathoracic impedance fluid status measurements | |
Wolpert et al. | Electrical proarrhythmia: Induction of inappropriate atrial therapies due to far‐field R wave oversensing in a new dual chamber defibrillator | |
JPH0336546B2 (en) | ||
WO1999027992A1 (en) | Medical implant |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
MKEX | Expiry |