CA2107147C

CA2107147C - Atrial defibrillator and method for providing synchronized delayed cardioversion

Info

Publication number: CA2107147C
Application number: CA002107147A
Authority: CA
Inventors: John M. Adams; Clifton A. Alferness; Kenneth Ross Infinger; Yixuan Jin
Original assignee: Incontrol Inc
Current assignee: Cardiac Pacemakers Inc
Priority date: 1992-10-23
Filing date: 1993-09-28
Publication date: 1998-01-27
Anticipated expiration: 2013-09-28
Also published as: US5269298A; CA2107147A1; EP0594271A2; DE69322592T2; EP0594271A3; EP0594271B1; DE69322592D1

Abstract

An implantable atrial defibrillator provides cardioverting electrical energy to the atria of a human heart in need of cardioversion. The atrial defibrillator includes a first detector for detecting ventricular activations of the heart, a second detector for detecting atrial activity of the heart, and an atrial fibrillation detector responsive to the second detector for determining when the atria of the heart are in need of cardioversion. The atrial defibrillator further includes a cardioverter for applying the cardioverting electrical energy to the atria of the heart when the atria of the heart are in need of cardioversion, and a timer delay stage responsive to the first detector for causing the cardioverter to apply the cardioverting electrical energy to the atria of the heart a predetermined delay time after the first detector detects one of the ventricular activations and before the T wave of the heart immediately following the one of the ventricular activations.

Description

2~71 ~7 PATENT
~4407-120 ~p~AT-9~0~ L~ FOR P~uv 8r~Rn D~T-~YRn CA~DIO~8ION
8~ ~v O~ ~8 ~ ON
The present invention generally relates to an atrial defibrillator and method for applying cardioverting electrical energy to the atria of a human heart in need of cardioversion. The present invention is more particularly directed to a fully automatic implantable atrial defibrillator which exhibits i~vv~d safety by reducing the potential risk of in~ e~
ventricular fibrillation which may result fro~ the mistimed deli~ery of cardioverting electrical energy to the atria. More spPcifically, the atrial defibrillator and method of th~ prQsent invention guards ~ga ~ ~ct applying cardioverting electrical energy to the atria under conditions believed to contribute to. 1~ ,o~
ventricle fibrillation.
Atrial fibrillation is~probably the mo~t co~on cardiac arrhythmia. Although it is ~ot usually a li~8 threatening arrhythmia, it i~ a~sociated with ~trokes thought to be caused by blood clots forming in ar~a~ o~ :
stagnant bloo~ flow a3 a result of prolonged atrial fibrillation. In add~tion, pati~nts a~flictQd with atrial fibrillation gonerally exp~rience palpitation~ of ., .

:

:

7 1 ~ 7 the heart and may even experience dizzines~ or even 1088 of consciousnes~.
Atrial fibrillation occurs su~enly and ~an~ -times can only b~ corrected by a discharge of electricial energy to the heart through the skin of the patiQnt by way of an external defibrillator o~ the type ~ell known in the art. This treatmsnt i~ c~ ~nly referred to a~
synchronized cardiovQrsion and, as its na~a impli~s~
involves applying electrical defibrillating ener~y to tha heart in syn~hronism with a d~tected ventricular electrical activia~ion (R wave) of the heart. The tr~atment is very painful and, unfortunately, most o~ten only results i~ temporary relie~ ~or patients, lastlng but a f ew weeks.
Drugs are available for reducing the ~na~
of atrial fibrillation. ~ v~r, these drugs hav~ ~any side effect~ and many patient~ are re~i~te~t to th2m which greatly re~u~s their therapeutic e~fect.
Implantable atrial defibrillators hav~ b~n proposed to provide patientC suffering from o~ l.c~
o~ atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of thes atrial de~ibrillators hav~ becom~ a co~erclal reality.~ .
Implantabl~ atrial defibrillator~ o~ in the past:have exhibited a number of disadvantiage3 which ~.
: probably has precluded these defibrillators from beco~ing ':
.

~ 071 ~7 a com~ercial reality~ Two such proposed defibrillators, although represented as being implantable, were not *ully automatic, requiring human in~eraction ~or cardioverting or de~ibrillatinq the heart. Both of these proposed de~ibrillators re~uire the patient to recognize the ~ympto~s of atrial ~ibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator re~uiring the patient to activate ths defibrillator from external to the patient's skin with a magnet.

Improved atrial de~ibrillators and lead sys~ems which ~h;~it ~oth automatic operation and ~ , o~ed ~a~e~y are fully described in cop~n~ing U.S. Applications, Serial h~ . 07/685,130, ~iled April 12, 1~1, in ~h~ name~ o$ ~ohn M. Adams and Cli~ton A. ~lfernes8 for IMPROVED ATRIAL DEFT~TT-T~ToR AND ..~n~ and Serial Numb2r 07f856,514 ~iled March 24, l~g2, in ~he nam~ o~ John M~ Adams, Cli~ton A. Alferness, and Paul E. Krey~n~g~n for ~ kv~u ~TRTAT
DEFT~RTT~T~OR, LEAD ~Y~ , A~D HET~OD wh~ch applications are assigned to the assigne~ o~ the pre~ent inven~ion. A~ di~closed in tne aforementioned re~erenced appllcations, ~ynchronizing t~e delivery of the de~ibrlllating or cardioverting electrical energy to the atria with a ventri~ular electrical ~¢tivation ~ wav~) of the heart ~as been con~id~red important to avoi~

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cardioverting the heart during the heart's vulnerabl~
period or T wave to thus prevent induced ventricular fibrillation. Ventricular fibrillation i~ a ~atal arrhythmia which can be cau~ed by electrical energy beln~-deli~ered to the heart at the wrong ti~e in the cardiaccycle, such as during the T wav~ of the cycl~. Th~
atrial defibrillators of the aforementionQd re~5~n~Q~
applications exhibit improved safety from tn~tt~in~
ventricular fibrillation by sansing ventricular lQ activation~ of the heart in a manner which avoids detecting noise as ventricular elactrical activations for generating reliable ~yll~hLo~ization signals. HenGQ~
these implantable atrial defibrillator~, by pro~ldi~g~ -such noise i ~ty in R wavQ detection assur~ r~l~Ahl~
synchronization.
Another mea ure for reducing the ri~k of inducing ventricular fibrillation during the deli~xy of cardioverting electric~1 en~rgy to the atria of the haart employed by the deflbrillator~ of the af~- ~ Lt~d referenced applications i5 the reduc~ion of th~ amount o~
the electrical energy which i~ pa~s~ through thQ
ventricles during cardioversion of the atria. Thi~
achieved by locating the cardioverting electrode~ in or near the heart to provide a cardio~erting energy path :25 which con~in~s substantially all of the cardiov~rting electrical energy to the atria of ths heart.

4 -:~

~ ~7~ f~7 It has also been obser~ed that during epi~e~
of atrial fibrillation, the cardiac rate increases to a high rate and/or becomes extremely variable. At high cardiac rates, the R wave of each cardlac cycl~ b~co~s~
closely spaced from the T wav~ o~ the imm~diat~ly preced1n~ cardiac cycle. This create3 a condition known in the art as an "R on T" con~ition which is beli~v~d to contribute to induced ventricular fibrillation i~ th~
atria are cardioverted in synchronism with thQ R wav~
close to the prece~i n~ T wave. For highly variabl~
cardiac rates, a long cardiac cy~le can be followed by a relatively short cardiac cycle. Thi~ condition i~
believed to cause disper~ion o~ r~ractoriness and al~o can result in a vulnerable R on T condition~ For a more complete understanding of the aforementioned highly variable cardiac rate and the conseql~e~c~R ther20f, rPference may be had to an article entitled El-Sheri~ ~t al., Reentrant Vsntricu1~r Arrhyth~ias in the ~ts Myocardia1 Infarction Period: N~chanism by ~h~ah a Short-Long-Short Cardlac Sequence F~cilitat~s th~
Inductlon o~ Reentry, Circulation, g3(1):26~ 8 (1991).
It ha3 been further ob~er~ed t~at a~
ventricular activation~ propagate through th~ heart~ th~
riqht ventricle apex activates slightly prior to the superior left ventricle. Hence, if the atria ar~
cardioverted in synchronis~ with an activation of th~

; 5 .

?:~ ~71 /~

right ventricular apex, the activation of th~ ~uperior left ventricle may not be completed. Recent studie3 have shown that cardioverting the atria when the ventricular activation is not fully completed may contr~buts t~
induced ventricular fibrillation.
The atrial defibrillator and method Or th~
present invention greatly re~ he ri~k o~ ~ n~ n~
ventricular fibrillation during atrial cardiov~r3ion or defibrillation by assuring that the card~overting electrical ener~y is not applied to the atria during both an R on T condition and a not yet completed ventri~ular activation. As will be seen hereinafter, this is acc~mplished by d~laying the application o~ ~h~ : .
cardioverting or defibrillating Ql~ckrical en~r~y ~ntil a predeter~ined delay time has elapsed after detecting a ventricular aativation. The delay tim¢ is chosen to b~
o~ suf f icient duration to a~sure thzt the ventricul~r activation has fully complet~d and of insu~icient duration to avoid applying the cardioverting el~ctrlc~l energy to the atria during the T wave i~med~ately following the detected ven~ricular activation. A~ a result, a reduced risk of i.n~ e~ ventricu~ar ~ibrillation is assured be~aus~ the cardiovor~ing electrical energy will not be applied to fhe atria during an R on T condition, during an llnr , leted ve~ $cl~
activa~ion, or during a vulnerabla period of the he~r~.

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~ ~ ~ i7 ~ ~ 7 S~A~ OF ~ NV~ ON
The pr~sent invention therefore provide~ atrial defibrillator for providing cardioverting elsctrical energy to the atria of a human heart. The atrial defibrillator includes detecting means for dQtecting ventricular activations of the heart, cardioverting m~n3 for applying the cardioverting electrical en~rgy to the atria of the heart, and d~lay m~an~ L~o~,~iva to th~
detecting means ~or causing the cardioverting ~e~n~ to apply the cardioverting electrical energy to the atria o~
the h2art a predetermined delay time a~ter the ~irst detecting mean~ detects one ~f the ventricular activations and before khe T wave of thQ heart ; le~iately followlng one of the ventricular act~vation~.
The present invention also provides an implantable atrial defibrillator for providing cardioverting electrical energy to the atria of a hu~a~
heart in need o~ cardiover~ion. The atrial defibrillator include~ first detecting ~ean~ ~or dQtecting ventricular ZO activations of the heart and second detecting mean~ ~or d~ecting atrial activity of the heart. ~he ~tri l de~ibrillator further includes atrial defibrillation detecting mean~ respons ve to the second detecting mean~
~or deteL i~i~g when the atria of the heart are in nee~
of cardioversion and cardiovert1ng mean~ for applying the cardioverting ~lectrical en~xgy to the atria o~ the heart .

.. , . . ~ , ., ~ . . ~ . . . . . .. .

~ ~7~ ~7 when the atria of the heart are in need of cardioversion.
The atrial defibrillator further includes delay me2ns responsive to the fir~t det~cting means for causiD~ th~
cardioverting means to apply the cardioverting electric~L
energy to the atria of the heart a predetermined d~lay tim~ after the first detecting mean~ detects one of th~, ventricular activations and before ths T wava o~ th~
heart ~ tely following the one o~ the ventri~ula~:
activations~ :
The present invPntion further provide~ a m~thod of applying cardioverting electrical energy to th~ atria of a human heart in need of cardiover~ion. Ths ~thod include~ the steps o~ detectin~ ventricular activ~t~Q~
o~ the heart, detecting atrial activity of the heart, and determining, responsive to the detected atrial acti~ity of the heart, when ths atria of the heart are in ne~d 9 cardioversion. The method further include~ the st~p o~
applying the cardioverting electrical energy to thQ atria of the heart when the atria of the heart are in nQ~d 0~
cardioversion and a predQtermined delay tim~ a~t~r detecting one of the ventricular activation~ and b~or~-~
the T wav~ of the heart i ~di~ely following the ona og :~
th~ ventricular activations.
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9~E~ DE~Ca~PT~ON OF ~H~ D~INa8 The features of the present invention which ara believed to be novel are set forth with particularity in the appended claims. The invention, togethQr ~ith further objects and advantages thereof, may b~st b~
understood by maklng reference to the following-description tak~n in con-Junction witb the accompanying~
drawing, in the sole fiqure of which like r~f~a~c~
numerals identify identlcal elements, and wherein the sole Figure is a schematic block diagram of a ~ully implantable atrial dePibrillator e~bodying ths ~
invention for applying defibrillating electrical ~n~ ~y to the atria of a human heart and which i3 shown in association with a human heark in need oP atrial fibrillation monitoring and potential cardiovers~on of the atria.

DETAI~D DB8CRIP~ION O~ ~B PR~E~R~D ~M~ODI~E~.
Prior to re~erring to the sole Figur~, a ~eneral description of a typical or normal cardiac cycla m~y be helpful in underst~n~ing th~ operation and varlou~
aspQcts of the present invention. The beginni n~ 0~ a Gardiac cycle is ini~iated by a P wave which is nor~ally a snall positive wave. The P wave in~ucps depolarization of the a~ria of the heart. Following the P wav~ th-r~ i~
a cardiac cycle portio~ which is substantially con~tant : ~ g ~ n7~ 7 have a time duration on the order of, for exampl~, 120 milliseconds.
The QRS complex of the cardiac cycla then normally occurs after the substantially c~nstant portion.
The ~ ting feature of th~ QRS complex i~ tha R wav~
which is a rapid positive or negative de~lection. Thc R wave ge~erally ha~ an amplitude gr~ater than any other wave of the cardiac cycle and will have a spik~d qh~pe o~
relatively short duration with a ~harp rise, a peak amplitude, and a sharp decline. The R wave i3 the : :
depolarization o~ the ventricle~ and hence, as us~d herein, the term "ventricl~ activation~l' denote~ R Wa~B
o~ the heart cardiac cycle. As previously m~ntion~d, a~
ventricular activations propagate through the he~rt, th~
right ventricle ap~x is generally depolartzed 81ig~1y prior to the depolarization of the supsrior le~t ve~tricle. :
Following the QRS complex, the cardiac cyaln i~
completed with the T wave whic~ eparated from th~ QR~
complex by about 250 milli~econ~. The T ~av~ is relatively long in duration o~, for example, on the order oP 150 ~ conA~0 It i~ during thQ T wav~ that the heart i5 most vulnerable to in~c~ ventricular fibrillation should the heart be cardiovert~d during th~s ~eriod. The next ~ardiac cycle begins with th~ n~xt ' "- 2.~ 7 P wave. The duration of a cardiac cycle may be on thei order of 800 milliseconds.
As will be appreciated hy those skilled in the art, thei characteristics of a cardiac cyclG of a h~a~t experiencing atrial fibrillation will be di~tinctly differ~nt than described above for a normal cardiac cycle~ During atrial fibrillation, there gsnerally are no discernable P waves because the atria are in a~
unstable or fibrillating condition. Also, the cardiac rate may be extremely high and highly variable which result~ in the previously referred to R on T condition where the ventricular acti~ation (R wave) of one cardiac cycle i5 closiely adjacent in time to the T wave o~ th~
i -~iately preceding cardia~ cycle.
Referring now to the sole Figure, it illustrates a fully implantable atrial deflbrillator 30 embod~ing the present invention shown in association wit~
a schematically illustrated human heart 10 in neQd o~
atrial fibrillation monitoring and potential cardioversion of the atria. The portion~ of the heart 10 illustrated in Figure 1 are the right ventricle 12, the le~t ~entricle 14, the right atrium 16, the left atrium 18, the superior vena cava 20, the ccronary sinus ~h~n~l 21 which, as used herein, deno es the coronary sinu$ 22 and the great cardiac vein 23, th~ coronary sinus ost~um 11 - ' ~ .

. J1 7 or opening 24, the left ventricular free wall 26 and th~
inferior vena cava 27.
The atrial defibrillator 30 gensrally incl~des an enclosure 32 for hermetically sealing the inter~al circuit elaments of the atrial defibrillator to bo described her~inaft~r, an endocardial first lead 34, and an intravascular seco~ lead 36. The enclosur~ 32 and.
first and second leads 34 and 3C are arranged to be implanted beneath the skin of a pati~nt so as to L~n'~
the atrial defibrillator 30 fully i~plantable.
The en~oc~rdial first lead 34 pre~rably comprise~ a endocardial bi-polar lead having ele~trod~
38 and 40 arranged for establj~h~n~ electrical cont~t with the right ventricle 12 o~ th~ heart 10. Th~
electrodes 38 and 40 permit bi-polar sen~ing o~
ventricular activation in the right ventricl~. A~
illustrated, th~ lead 34 is fed ~hrough the ~uperior vQna cava 20, into the right atrium 16, and then in~o th~ : :
right ventricle 12.
The second lead 36 generally include~ a ~ir~t or tip electrode 44 and a second or proximal ele~ 0~2 46. As illustrated, the s~cond lead 36 is ~ ;hl~ and arranged to be passed down the superior vena ca~a 20, into the right atrium 15, into the coronary sinus ostium 24, and advanced into th~ coronary sinu~ ~h~nn~l 21 of the heart near the le~ side thereof ~o that the ~lr~t or .

tip electrode 44 i~ within the coronary sinus ch~el 21 either within the coronary sinus 22 adjacent the left ventricle 14 and beneath the l~t atrium 18 or mo~t preferably within the yreat cardiac vein 23 adjacent t~
left ~entricle 14 and beneath the left atrium 18. Th~
electrodes 44 and 46 are paced apart such that when thQ
first electrode 44 is positioned a~ described abovQ~ the second electrode 46 is in the right atriu~ 16. Tha fir~t electrode 44 together with the second electxod~ 4Ç
provide bi-polar sensing o~ heart activity in tha a~ria 16 and 18. The first electrode 44 and the RecQ~
electrode 46 further provide ~or khe deliv~y of defibrillating electrical energy to the atria. B~a~l~~~
the first el2ctrode 44 i~ locat~d beneath the l~t ~trium 18 near the left ventricle 14 and the ~econd ~le~L~o~e 46 is within the right atrium 16, the electrical ~ y applied between these electrodes will be substantially con~ined to the atr~a 16 and 18 o~ the heart 10. A~ a re~ult, the electrical energy applied to the rig~t ventricle 12 and left ventricle 14 when the atria are cardioverted or de~ibrillated will be minimized. This greatly re~uce~ the potential for ventricular fibrillation of the he~rt to be in~uce~ as a reeu~ o~ -the application o~ defibrillating ~lectrical en~r~y o~
the atria of the heart~

: ~ ~3 Within ~he enclosure 32, the atrial defibrillator 30 includes a first sense amplifier 50, an R wave detector 52, and a second ~ense amplifier 54~ The first sen~e amplifier 50 and the R wave de~ector 52 ~or~
a first detecting ~eans which toge her with ele~L~.7~F 38 and 40 of the ~irst lead 34 to which sense ampli~i~r 50-is coupled, sense~ ventricular activations o~ the right ventricle 12. The second sense ampliSier 5~ ~orms ~
~econd detecting means which, together with th~ ~irst electrode 44 and second electrode 46 of th~ secn~ lead ~ -36 to which it is coupled detects atrial activity o~ th~
heart.
The output of the ~irst sense amplifier 50 18 coupled to the R wave detector 52. ~he R wave dets~tor 52 is ~f the type well known in the art which provide3 an output pulse upon the oc~ ence of an R wav~ bQing sensed during a cardiac cycle of the heart. Th~ ~u~y~
of the second ~ense amplifier 54 i~ coupled to an ~log ~ -to digital convQrter 60 which converts the analog ~i~n~
representative of the atrial activi~y of th~ heart being detected to digita1 samples ~or ~urther proce~3ing in a manner to be dascribed hereinafter. .:.
ThQ enclosure 32 of the atrial de:fibrillator 39 further include~ ~ mioLe~oc2ssor 62. The mi~Lo~ o~e~o~
62 is preferably imple~ented in a manner a~ disclos~d ln : the aforementioned copending U.S~ Applications, S~Eial :.
~: , : ~ 14 Numbers 07/685,130 and U7/856,514 and ~urther a~
dascribed hereinafter. The implementation of th~
microprocessor 62 in accordance with this ~ ho~;r~t o~
the present invention results in a plurality o~
functional stages. The stage~ include a synchronization detector 64, a delay timer stage 66, a comparator ~tage 68, a time delay set stage 70, an atrial arrhythmia detector in the form of an atrial fibrillation dQtQctor 72, and a charge delivery and energy control stage 74.
The microproc~or 62 is arranged to operats in conjunction with a memory (not shown) which may bQ
coupled to the microprocessor 62 by a ml~ltiple-bit addres bu~ (not shown) and a bi-directional mult~p~e bit databus (not shown). This permits the mi~ opioces~r 62 to address desired memory locations within the me~ory ~or executing write or read operations. During a write operation, the mi~ o~,oce~or ~tores data, such a~ tim~
intervals or operating parameter~ in the memory at th~
addresse~ defined by multiple-bit addresse~ co.lYeye~ over the addres~ bu~ and co~eya the data to the - ~ 92 ov~r the multiple-bit data bus. During a read operation, the microprocessor 62 obtains data ~ro~ the memory a~ th~
storage locations identified by the multipl~-~it addresses provided over the addres~ bus and receive~ th~
~5 data from the ~ over the b~-directional data bu~.

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~ ~97~ ~

For entering operating parameters into the miGroproCesSOr 62, as for example the time delay re~erred to hereinafter into time delay set stage 70, th~
microprocessor 62 receive~ programmable ~ ing parameters f rom an external controller 100 wh~ch ~
external to the skin of the patient. The ext~rnal cor.L,oller 100 i5 arranqed to communicat~ w1th a receiver/transmitter 102 within enclosura 32 which ~
coupled to the microproc~ssor 62 ov~r a bi-directional bus 104. The receiver/transmitter 102 may b~ o~ th~ typ~
well known in the art for conveying various inform~tion which it obtains from the micropro~essor 62 to the external controller 100 or for receiving progra~lng parameters from the external col,~Loller 100 whioh the receiver/transmitter 102 then conveys to thQ
mi~u~ocsssor 62 for ~torage in internal memory, ~uch a~
in time delay set stage 70, or in the a~oreman~i~ne~
external me~ory within enclosure 32.
The receiver/transmitter 102 include~ a transmitting coil 106 so that the receiver/tr~itt~r 102 and coil 106 form a communication means. Such communication means are well known in the art and may be utilized a3 noted above for receivin~ ro~
external to the implantable enclosuxe 32 and ~or transmi~ing data to the external con~oller ~00 ~ro~ the 1~

7 1 ~ 7 implanted enclosure 32. One such c lication sy~t~m i~
disclosed, for example, in U.S. Patent No. 4,586,508.
To complete the identification of the variou~
structural elements within the enclosure 32, the atr~l de~ibrillator 30 further includQ~ a charger and ~tosag2-capacitor circuit 76 o~ the type well known in th~ art which charge~ a storage capacitor to a predet~x~in~d voltage lev~l and a dischargQ circu.~t 78 for ~t~eh~r~ing.
the storage capacitor wi hin circuit 76 by a predetermined amount to provide a c~ .olled ~ q~
out~u~ of electrical energy when required to the atri~ o~
the heart. To that end, the ~ h~rge circuit 7~ i~
coupled to the first electrodQ ~4 and th~ ~o~S-~A"
el~ctrode 46 of the ~acond lead 36 for applying the cardioverting or defibril~ating electrical energy to th~
atria. Lastly, the defibrillator 30 include~ a depletable power source 80, such a lithium batte~y, ~or providing power to the electrical components o~ th~
atrial def~brillator 30.
The sense ampli~ier 50 and the R wave d~t~ctor 52 continuously detect ~he oc~ ence o~ ventr~c~
activations of the right ventricle 12. As ~isa~o~ed in the a~ore~entioned cop~n~ing U.S. Applicatlon~ S~r~al Numbers 07/685,1~0 and 07/856,514, her~in incorporat~d ~y.
25 : ref~rence, when the tim~ intervals between i~media~ely ~ sucoessive R waves indicate the probability o~ an epi~ode :: 17 7 1 ~ 7 of atrial fibrillation, the microprocessor 62 enable3 the atrial fibrillation detector 72, sense ampli~ier 54, and the analog to digital converter 60. If the atrial ~ibrill~tion detector 72 determines that the atria 16 and ~8 are in fibrillation and thus in need of cardiover~lon, the charge delivery control 74 cause the charg~r and storage capacitor circuit 76 to charge the ~tor~g~
capacitor within c~rcuit 76. The atrial de~lbrillator 30 is then ready to apply cardioverting electrical el~e~y~ to the atria 16 and 18 at the a~r~ iate time in a manner described hereinafter.
The synchronization detector 64, tha del~y timer 66, the comparator 68, and t~e time d~lay ~et ~tago ::
70 ~orm a delay mean~ 82 for delaying th~ application o~
the cardioverting electrical enerqy to t~e atria 16 and 18 of the heart 10 until after a predetermined delay ti~e ~ollowing ~he de~ection of a ventricular activation by the sensa amplifier 50 and the R wave detectox 52. The predetermined delay time is prevlously entered into th~
time delay set stage 70 ~rom the external contrcll~r 100 and through the transmitter/receiver 102 a~ pr~iou31y described. Also, he delay timer is reset wh~n the storage capacitor in circuit 76 reA~h~C full char~
The synchronization detector 64 pro~idQ a 25: pulse to the delay ti~er in re~po~ to ths pulse fro~
the R wave detector upon the detection of a ventricul~r :
~ 18 ' 7 1 ~ 7 activation. Prior to starting the delay timer h~
and in accordance with the a~or~mentioned cro~s referenced cop~in~ application~, Serial NumDers 07/68s,~30 and 07/856,514, ~ynchronization pulse counting may be employed wherein the synchronization dete~tor 64 first counts a predetermined numb~r, such as ~iVQ, consecutive R wave datect pulses from R wa~e det~ctor 52 to assure that therQ is still reliable detection o~ th~
ventricular activations.
lo Upon the gixth pulse from R wave det~ctor 52 (if such pulse counting is employed) or upon th~ ~irst pulse from R wave detector 52 (if such pulse counting i~
not employed), th~ ~ynchronization counter 64 provide~
its pulse to delay timer 66 to start the delay ti~r~
The comparator 68 then contlnuously compares th~ tl~e kept by the delay timer 66 to tha predeteL 1 n~ d~lay time stored in the timQ delay set ~tag~ 70. When the time kept by the delay timer 66 equals the stored delay time, the comparator 68 causes the charge delivery control 74 to provide a control signal t~ the di~charge circuit 78 for ~s~h~rging the cardiovertinq electrical energy stored in circuit 76 ~etween ele~o~es 46 and 44.
This applies the ~ardioverting electrical energy to tha ~ atria 16 and 18 of the heart.
: 25 As a result o~ the foregoing, ~he ~ardiovertin~ . .

electrical energy is applied to the atria when the atria . .
.:

are in need of cardiovers.ion and a predetermined~d~lay time after one of the ventricular activation~
detected. The delay time i~ selected to be long t-,~ Jh to assure that the ventricular activation, whic~
ultimately ~tarts delay timer 66, is completed and ~hort enough so as to avoid cardioverting the atria during-th~
T wave which i ~l1~tely follows the v~lL~
activation in abo~t 250 millisecon~. A3 an exampl~, an~-without li~itations, the delay time m~y be in th~ rang~
of five to eighty mill1~eaQn~. Th~ rang~ of suit~blQ
delay times, o~ course, will dep~nd upon the par~qn heart physiology of a particular patient.
In co~trolling tha applica~ion or d~liv0xy o~
the cardio~erting electrical enerqy in the ~L~e~n~
r-nn~r~ it will be assured that th~ atria ~ not cardioverted during a partially completed ventricular activation, an R on T condition, or the vulnerabls p~r~od T wave of the heart. The present invention h~n~e-provide~ an improved atrial defibrillator and ~t~od wh$ch exhibits increased saPety in reducing the ri~k o~
inducing ventricular fibrillation wh~n cardioverting:th~
atria o~ the heart.
While a particular embodiment of th~ p~ t invention has been shown and described, modificatlon~ ~y be made. For examplb~ th~ delayed cardiov~rsion o~ th~
presen~ invention may be utilized to advanta~e in an 2~

7 ~ ~ 7 external atrial defibrillator wherein an ele~L.od~ or electrodes adhered to the sur~ace of th~ ski~ o~ a patient are e~ployed along with an R wav~ detector for detecting ventricular activations and sur~ac~ ~a~:
electrodes are utilized for applying th~ cardlovorting-i electrical energy to the atria of the heart. Such~
surface detecting and pad electrod~s are well known in~
the art. Hence, it i.~ therefore int~n~ed in the ~e-r~
claim~ to cover all su~h change~ and modification~ whi~h fall within the true spirit and ~cope o~ thQ inv~ntlon.

.

Claims

1. An implantable atrial defibrillator for providing cardioverting electrical energy to the atria of a human heart in need of cardioversion, said atrial defibrillator comprising:
first detecting means for detecting ventricular activations of the heart;
second detecting means for detecting atrial activity of the heart;
atrial fibrillation detecting means responsive to said second detecting means for determining when the atria of the heart are in need of cardioversion;
cardioverting means for applying said cardioverting electrical energy to the atria of the heart when the atria of the heart are in need of cardioversion; and delay means responsive to said first detecting means for causing said cardioverting means to apply said cardioverting electrical energy to the atria of the heart a predetermined delay time after said first detecting means detects one of said ventricular activations and before the T wave of the heart immediately following said one of said ventricular activations.

2. An atrial defibrillator as defined in claim 1 wherein said predetermined delay time is of sufficient duration for the completion of said one of said ventricular activations.

3. An atrial defibrillator as defined in claim 1 wherein said predetermined delay time is between five and eighty milliseconds.

4. An atrial defibrillator as defined in claim 1 wherein said delay means includes timing means responsive to said first detecting means for timing said predetermined delay time.

5. An atrial defibrillator as defined in claim 4 wherein said delay means further includes a synchronizing detector for starting said timing means responsive to said first detecting means detecting said one of said ventricular activations.

6. An atrial defibrillator as defined in claim 5 wherein said delay means further includes comparing means for comparing the time of said timing means to said predetermined delay time and for causing said cardioverting means to apply said cardioverting electrical energy to the atria of the heart when the time of said timing means equals said predetermined delay time.

7. A method of applying cardioverting electrical energy to the atria of a human heart in need of cardioversion, said method including the steps of:
detecting ventricular activations of the heart;
detecting atrial activity of the heart;
determining, responsive to said detected atrial activity of the heart, when the atria of the heart are in need of cardioversion; and applying said cardioverting electrical energy to the atria of the heart when the atria of the heart are in need of cardioversion and a predetermined delay time after detecting one of said ventricular activations and before the T ware of the heart immediately following said one of said ventricle activations.

8. A method as defined in claim 7 wherein said predetermined delay time is of sufficient duration for the completion of said one of said ventricular activations.

9. A method as defined in claim 7 wherein said predetermined delay time is between five and eighty millisecond.

10. A method a defined in claim 1 including the further step of timing said predetermined delay time upon detecting said one of said ventricular activations.

11. An atrial defibrillator for providing cardioverting electrical energy to the atria of a human heart, said atrial defibrillator comprising:
detecting means for detecting ventricular activations of the heart;
cardioverting means for applying said cardioverting electrical energy to the atria of the heart; and delay means responsive to said detecting means for causing: said cardioverting means to apply said cardioverting electrical energy to the atria of the heart a predetermined delay time after said detecting means detects one of said ventricular activations and before the T wave of the heart immediately following said one of said ventricular activations.