FIELD OF THE INVENTION
- DESCRIPTION OF THE RELATED ART
The field of the present invention relates generally to implanted devices for tissue stimulation, monitoring, and other therapeutic or diagnostic functions, and specifically to implantable devices for the stimulation of cardiac tissue, for example pacemakers or implantable cardioverter-defibrillators (ICDs). More specifically, it pertains to such devices utilizing wireless energy transfer, for example through ultrasonic means.
Conventional wired cardiac pacemaker and defibrillator systems comprise Implantable Pulse Generators (IPGs) configured to be located subcutaneously and connect via leads to stimulator electrodes implanted in the heart. However, because the IPG is connected to leads, the location and surgical process must consider lead insertion into a vascular access.
An ultrasound based wireless cardiac stimulation system has been disclosed in currently pending applications by the applicant (e.g., U.S. patent application Ser. No. 11/315,023). This system employs ultrasonic energy transfer from a subcutaneously implantable controller-transmitter device (C-T), which is directed towards one or more receiver-stimulator (R-S) devices implanted at desired sites in the heart, for example in the left ventricle. Ultrasonic transducers and circuitry in the R-S convert the transmitted ultrasonic energy into electrical energy capable of stimulating the cardiac tissue. The system, C-T, and R-S are described in co-pending U.S. patent applications Nos. (Publication Number) 20060136004, 20060136005, 20070027508, 20070055184, 20070078490 and 20070060961 and Ser. No. 11/752,775, which are herein incorporated by reference in their entirety.
- SUMMARY OF THE INVENTION
Energy and battery life computations show that the range between the C-T and the R-S has a dramatic impact on the efficiency of energy transfer between them. Therefore, it is desirable to reduce the distance between the C-T and the R-S and thereby improve the efficiency of wireless pacing. An optimal location for cardiac stimulation is believed to be the posterio-lateral LV wall, and an optimal subdermal location for an IPG is the fifth intercostal space. These locations are approximately 10 cm apart. It is desirable to have a cardiac stimulation system that simultaneously optimizes the stimulation location and minimizes the wireless energy delivery range between the C-T and the R-S, thereby providing optimal battery life and optimal stimulation location. The present embodiments provide such a system.
Embodiments of the present invention are directed to wireless cardiac stimulation devices comprising a controller-transmitter (C-T), a receiver, and a stimulating electrode, wherein the stimulating electrode and the receiver are separately implantable at different locations of the heart and are connected by a local lead. Separating the receiver from the stimulating electrode improves the efficiency of ultrasound mediated wireless stimulation by allowing the receiver to be placed optimally for reception efficiency, thereby resulting in longer battery life or reduced battery size. Separation of the receiver and stimulating electrode also allows the stimulating electrode to be placed optimally for stimulus delivery, and provides for improved connective reliability.
In one aspect, the C-T is implanted subcutaneously such that its transmission passes through an intercostal space, and the receiver is implanted at the apex of the left ventricle (LV) of the heart, thereby minimizing the distance between the receiver and the C-T. The stimulating electrode is implanted, separately from the receiver, at an optimal posterio-lateral LV location, and connected to the receiver via a local lead for transfer of electrical energy. One advantage of such a system is the longer battery life due to the reduction in distance between the wireless transmitter and the receiver. Another advantage is a reduced risk of embolization, since the receiver and stimulating electrode are attached at two locations of the heart wall, with the connecting local lead serving as a safety tether should either the receiver or the stimulating electrode become dislodged.
In one aspect, the system comprises a plurality of stimulating electrodes, thereby providing multi-site stimulation. In another aspect, the receiver itself comprises a stimulating electrode, thereby providing dual-site stimulation. In another aspect, the receiver and stimulating electrode are implanted in different ventricles, thereby providing biventricular stimulation, with the local lead crossing the ventricular septum to connect the receiver and stimulating electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
Another aspect of the invention is methods of using acoustic energy to stimulate cardiac tissue by (a) subcutaneously implanting a transmitter; (b) implanting a receiver at a first cardiac tissue location, wherein the receiver receives acoustic energy transmitted by the transmitter and produces a biologically stimulating electrical output in response to the received acoustic energy; and (c) implanting a stimulating electrode at a second cardiac tissue location, wherein the stimulating electrode is connected to the receiver by a local lead, and wherein the stimulating electrode receives the biologically stimulating electrical output from the receiver and delivers said output to cardiac tissue. Additionally, the first cardiac tissue location can be chosen to optimize acoustic energy transmission from the transmitter to the receiver. Another embodiment of the above method involves implanting additional stimulating electrodes, wherein the stimulating electrodes are connected to the receiver by the local lead. Alternatively, the additional stimulating electrodes are connected to the receiver by additional local leads.
The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows an example embodiment of a system for electrically stimulating the heart, comprising separately implantable receiver and stimulating electrode implanted at endocardial locations of the heart wall.
FIGS. 2 a and 2 b show other example embodiments of a system for electrically stimulating the heart, comprising a separately implantable receiver and/or stimulating electrode implanted at an epicardial location of the heart wall.
FIG. 3 shows an example embodiment of a receiver.
FIGS. 4 a-4 c show example embodiments of systems configured with a single receiver and a plurality of stimulating electrodes.
FIG. 5 shows an example embodiment of a system configured with a plurality of receivers and a plurality of stimulating electrodes.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 6 shows the reception range of an exemplary fixed-focus transducer.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details.
An ultrasound based wireless cardiac stimulation system is disclosed which improves the efficiency of ultrasound mediated wireless stimulation and results in longer battery life. The system comprises two separately implantable subsystems. The first subsystem is a receiver-stimulator (R-S) configured to be implanted within the heart to provide electrical stimulation. The second subsystem is a controller-transmitter (C-T) configured to be implanted subcutaneously to wirelessly power and control the R-S.
To increase the operational efficiency and battery life of the system, the R-S itself comprises two separately implantable elements that are connected by a local lead. The first is an implantable receiver element (hereinafter also referred to as “receiver”), and the second is an implantable stimulating electrode element (hereinafter also referred to as “stimulating electrode”). The receiver wirelessly receives energy from the C-T, converts the received energy to electrical energy, and electrically powers the stimulating electrode via the local lead. The stimulating electrode receives the electrical energy and provides electrical stimulation to the tissue.
It is an advantageous aspect that the separation of the receiver from the stimulating electrode allows two goals to be simultaneously met. First, it allows the receiver to be implanted closest to the C-T, thereby minimizing the travel range of the wireless energy transmission from the C-T to the receiver. Second, it allows the stimulating electrode to be implanted at an optimal location within the heart for the delivery of electrical stimulation to heart tissue, independent of the location of the implanted receiver.
Reducing the distance between the C-T and the receiver allows more of the transmitted acoustic energy to be harvested by the receiver, since (a) less of the acoustic energy is spread to where the receiver cannot harvest it, providing a quadratic increase in gain as a function of the inverse of the distance between the C-T and the receiver, and (b) there is less intervening tissue between the C-T and the receiver that could lead to undesired energy dissipation. This means that the C-T needs to transmit less energy to achieve the same stimulation output. This provides not only a longer battery life, but also simpler C-T and receiver design, for example by using fewer transducers in the construction of the C-T and/or the receiver (such as only one transducer, in some embodiments).
Optionally, as disclosed in co-pending U.S. Patent Application Ser. No. 61/016,869, the C-T itself may comprise an implantable transmitter as well as a separately implantable battery for powering the transmitter via a subcutaneously routable electrical cable, thereby improving patient comfort and providing a larger usable aperture.
While the present embodiments refer to stimulating the heart, it is understood herein that the disclosed embodiments can be used to stimulate any living tissue in humans or animals. For example, published PCT application WO2007149936 with common inventor and assignee of this application, which is incorporated herein by reference, describes using a wireless stimulation system for stimulating various tissues.
FIG. 1 shows one embodiment of a system 100 for electrically stimulating the heart 101, comprising separately implantable receiver and stimulating electrode elements. The system 100 comprises a C-T 102, as well as an R-S comprising a receiver 103, a stimulating electrode 104, and a local lead 105 connecting the receiver 103 and stimulating electrode 104.
C-T 102 is configured to be implanted subcutaneously so as to be close to a location in the heart where the receiver 103 is to be implanted. In one embodiment, the C-T 102 is implanted subcutaneously such that its transmission passes through an intercostal space, such as the 5th intercostal space. FIG. 1 shows C-T 102 implanted thusly, with the transmission passing through an intercostal space between ribs 106.
The receiver 103 is configured to be implanted at a location within the heart where it can be closest to the C-T 102. In one embodiment, the receiver 103 is implanted at the septal apex of the LV, as shown in FIG. 1. This could be done using traditional interventional techniques, wherein a delivery catheter is advanced percutaneously into the left ventricle and the receiver is delivered and fixed at a preferred site. The fixation could be accomplished using various tissue fixing mechanisms such as barbs, tines, etc.
In such an embodiment where the C-T 102 is implanted at an intercostal space and the receiver 103 is implanted at the septal apex of the LV, the distance between the C-T 102 and the receiver 103 is minimized to approximately 2-4 cm, allowing efficient energy transfer from the C-T 102 to the receiver 103, and therefore providing for longer battery life for C-T 102.
While FIG. 1 shows the receiver 103 and stimulation electrode 104 implanted at an endocardial location of the heart wall, in other embodiments one or both may be implanted at an epicardial location. Such an embodiment is shown in FIG. 2 a, with the receiver 103 and stimulation electrode 104 implanted at epicardial locations.
In one such embodiment, the receiver 103 can be placed on the anterior of the heart by using a minimally invasive surgical approach, as shown in FIG. 2 a. Once the receiver 103 is fixed to the anterior surface of the heart and within the desired range of the C-T 102, a stimulating electrode 104 could be localized at an endocardial location by penetrating the stimulating electrode 104 through the heart wall 101 from the epicardial surface. A small diameter trocar or such implement could enable the implantation of the receiver 103 and the stimulating electrode 104 from the external surface (as opposed to interventional means). Alternatively, the stimulating electrode 104 may be placed at an epicardial location to provide stimulation (as shown in FIG. 2 b).
As shown in FIG. 3, the receiver 103 comprises internal circuitry 107 for converting acoustic energy to electrical energy that is transmitted to the stimulating electrode 104. In one embodiment, the circuitry 107 comprises one or more transducers which produce electrical energy in response to the acoustic energy received from the C-T 102. The transducers may comprise piezoelectric material, such as a polycrystalline ceramic piezoelectric material or a single crystal piezoelectric material.
Circuitry 107 further comprises one or more conversion circuits, wherein each conversion circuit is electrically connected to a corresponding transducer such that the electrical energy output from the transducers is converted to a biologically stimulating electrical output. For example, the conversion circuitry may comprise one or more rectifiers, as well as optional protection circuitry (such as comprising one or more Zener diodes) to protect the rectifiers from damage due to high voltages.
The stimulating electrode 104 is configured to be implanted at a cardiac tissue location, separately from the receiver 103, at a location that is optimal for delivering the stimulating electrical output to the heart. The stimulating electrode 104 comprises one or more electrodes (cathode) for delivering the electrical output to tissue, and is powered by the receiver 103 via a local lead 105. In one embodiment, as shown in FIG. 1, the stimulating electrode 104 is implanted at a posterio-lateral location in the LV. As shown in FIG. 3, the receiver 103 comprises an anode 108 electrically connected to circuitry 107 via an electrical connection 109. The anode 108 may comprise part or all of the exterior of the receiver 103 or alternatively may be placed anywhere along the length of the local lead (not shown). Typically, the anode is a large surface area electrode relative to the cathode having a low current density to preferentially stimulate the tissue at the cathode, in this embodiment at the stimulating electrode 104. Alternatively, the anode can be designed to have a small surface area to intentionally stimulate the tissue at the receiver location, thereby providing dual site stimulation from both the anode and cathode.
As described above, separating the implant locations of the receiver 103 and stimulating electrode 104 allows the system 100 to simultaneously optimize wireless energy transfer efficiency as well as stimulation location. Furthermore, separating the receiver 103 from the stimulating electrode 104 also reduces the risk of embolization, since the R-S ensemble is now attached at two locations in the heart wall, with the local lead 105 serving as a safety tether should either the receiver 103 or the stimulating electrode 104 become dislodged.
Optionally, the system 100 may be extended to provide multi-site stimulation. For example, the system 100 may comprise a plurality of stimulation electrodes to provide multi-site stimulation. In one such embodiment, the receiver 103 itself comprises a stimulation electrode, so that the heart is stimulated at the receiver 103 site in addition to stimulation provided at the stimulating electrode 104 site.
In another embodiment for multi-site stimulation, the system 100 comprises more than one stimulating electrode, each connected to the receiver 103 via a single or multiple local leads. FIG. 4 a shows one such embodiment, wherein multiple stimulating electrodes 104 a, 104 b, and 104 c (at endocardial locations of the heart) are connected via multiple local leads 105 a, 105 b, and 105 c to a receiver 103 (also at an endocardial location), thereby providing multi-site stimulation. FIG. 4 b shows another such embodiment, wherein multiple stimulating electrodes 104 a and 104 b (at epidardial locations) are connected via multiple local leads 105 a and 105 b to a receiver 103 (also at an epicardial location), thereby providing multi-site stimulation. Alternatively or in combination, two or more of the stimulating electrodes may be contained on a single local lead, such as shown in FIG. 4 c with receiver 103 connected in series to stimulating electrodes 104 a and 104 b via local lead 105.
In another embodiment for multi-site stimulation, the system 100 may be configured with a plurality of receivers. FIG. 5 shows one such embodiment, wherein a first receiver 103 a is implanted at a cardiac tissue location of the LV and connected to a first stimulating electrode 104 a via a first local lead 105 a, and a second receiver 103 b is implanted at a cardiac tissue location of the RV and connected to a second stimulating electrode 104 b via a second local lead 105 b. Analogously, system 100 may comprise more than two receivers, each of which may electrically power one or more stimulating electrodes via one or more local leads.
Optionally, the system 100 may be configured to provide biventricular stimulation. In one such embodiment, the receiver 103 comprises a stimulation electrode for providing electrical stimulation, and is implanted at a cardiac tissue location of the septal apex of the right ventricle (RV), allowing the receiver 103 to function as an RV lead for biventricular stimulation. In another embodiment, the receiver 103 may be implanted at a cardiac tissue location of the RV, with the local lead 105 having a very small profile (i.e. a small surface area lead) and puncturing through the ventricular septum to the LV and connecting the receiver 103 with one or more stimulating electrodes 104. Crossing the ventricular septum with such a small profile local lead would cause minimal to no trauma.
It is an advantageous aspect that the present systems 100 can be manufactured to minimize energy loss and thereby maximize battery life. In one particular example implementation, the C-T 102 comprises a fixed-focus transducer 110 with no steering capabilities, as shown in FIG. 6.
Another example implementation comprises a high frequency receiver 103 with a small receiver surface area and a small number of transducers. For example, receiver 103 may be an 800 kHz high frequency receiver with three transducer elements and a receiver surface area of approximately 3 mm2. In such an embodiment, the C-T 102 produces a homing signal using an array of transducers to track the location of receiver 103. It can be estimated that to produce a steering range of approximately 2 radians for a distance of approximately 3 cm, a 6×6 array of about 36 transducer elements could be used, with each transducer element having an element size of about 1 mm2.
While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.