Patent Application
20060116729
This invention pertains to apparatus and methods for treating cardiac arrhythmias. In particular, the invention relates to an apparatus and method for electrically terminating tachyarrhythmias.
Tachyarrhythmias are abnormal heart rhythms characterized by a rapid heart rate. Examples of tachyarrhythmias include supraventricular tachycardias such as sinus tachycardia, atrial tachycardia, and atrial fibrillation (AF), and ventricular tachyarrhythmias such as ventricular tachycardia (VT) and ventricular fibrillation (VF). Both ventricular tachycardia and ventricular fibrillation are hemodynamically compromising, and both can be life-threatening. Ventricular fibrillation, however, causes circulatory arrest within seconds and is the most common cause of sudden cardiac death. Atrial fibrillation is not immediately life threatening, but since atrial contraction is lost, the ventricles are not filled to capacity before systole which reduces cardiac output. This may cause lightheadedness or fainting in some individuals, as well as fatigue and shortness of breath, hindering the individual from carrying out normal daily activities. If atrial fibrillation remains untreated for long periods of time, it can also cause blood to clot in the left atrium, possibly forming an emboli and placing patients at risk for stroke.
Cardioversion (an electrical shock delivered to the heart synchronously with an intrinsic depolarization) and defibrillation (an electrical shock delivered without such synchronization) can be used to terminate most tachycardias, including AF, VT, and VF. As used herein, the term defibrillation should be taken to mean an electrical shock delivered either synchronously or not in order to terminate a fibrillation. In electrical defibrillation, a current depolarizes a critical mass of myocardial cells so that the remaining myocardial cells are not sufficient to sustain the fibrillation. The electric shock may thus terminate the tachyarrhythmia by depolarizing excitable myocardium, which prolongs refractoriness, interrupts reentrant circuits, and discharges excitatory foci.
Implantable cardioverter/defibrillators (ICDs) provide electro-therapy by delivering a shock pulse to the heart when fibrillation is detected by the device. The ICD is a computerized device containing a pulse generator that is usually implanted into the chest or abdominal wall. Electrodes connected by leads to the ICD are placed on the heart, or passed transvenously into the heart, to sense cardiac activity and to conduct the impulses from the pulse generator. Typically, the leads have electrically conductive coils along their length that act as electrodes. ICDs can be designed to treat either atrial or ventricular tachyarrhythmias, or both, by delivering a shock pulse that impresses an electric field between the electrodes to which the pulse generator terminals are connected. The electric field vector applied to the heart is determined by the magnitude of the voltage pulse and the physical arrangement of the shocking electrodes, which may serve to concentrate the field in a particular region of the heart. Thus, the particular electrode arrangement used will dictate how much depolarizing current is necessary in order to terminate a given tachyarrhythmia.
Ventricular and atrial fibrillation are probabilistic phenomena that observe a dose-response relationship with respect to shock strength. The ventricular defibrillation threshold (VDFT) is the smallest amount of energy that can be delivered to the heart to reliably revert ventricular fibrillation to normal sinus rhythm. Similarly, the atrial defibrillation threshold (ADFT) is the threshold amount of energy that will terminate an atrial fibrillation. Electrical energy delivered to the heart has the potential to both cause myocardial injury and subject the patient to pain. Whether or not a particular patient is a suitable candidate for ICD implantation is determined in part by that patient's defibrillation threshold, since too a high a threshold would necessitate electrical shock therapy at levels that are dangerous for the patient. Furthermore, the larger the magnitude of the shocks delivered by an ICD, the more the battery is drained, thus decreasing the longevity of the device. It is desirable, therefore, for the defibrillation threshold to be as small as possible in order to minimize the amount of shocking current that the ICD must deliver in order to terminate a given tachyarrhythmia.
Electrode arrangements have been devised in an attempt to minimize the defibrillation threshold for particular types of tachyarrhythmias. For example, the traditional configuration for ventricular defibrillation is to place a cathodic electrode in the right ventricle, with the anode formed jointly by an electrode placed in the superior vena cava and the conductive housing of the ICD acting as an additional electrode. For treating atrial fibrillation, a conventional electrode configuration is to use electrodes disposed within the coronary sinus and in the right atrium. A further modification to the configuration that has been suggested by some investigators is to electrically connect an electrode placed in the right ventricle in common with the coronary sinus electrode.
In order to further improve safety and avoid unnecessary discomfort for ICD patients, there is a continuing need for methods and apparatus that reduce the defibrillation threshold. Such reductions in defibrillation thresholds may also expand the population of patients for whom ICDs are an appropriate therapeutic option. It is toward this general objective that the present invention is directed.
The present invention is a method and apparatus for terminating tachyarrhythmias such as fibrillation by the efficient delivery of electrical energy through an electrode configuration to the heart in response to sensed electrical events from a sensing channel that indicate the occurrence of a tachyarrhythmia. In one embodiment of the invention, the defibrillation energy is imparted to the heart by a pulse generator having one terminal connected to a first electrode disposed within the coronary sinus and another terminal connected to a second electrode disposed within the superior vena cava or right atrium and to an extravascular electrode located in proximity to the heart. In another embodiment, the pulse generator has one terminal connected to a first electrode disposed within the right ventricle and another terminal connected a second electrode disposed within the superior vena cava or right atrium, a third electrode disposed within the coronary sinus, and an extravascular electrode. The extravascular electrode may be a cutaneous patch or may be the conductive housing of the apparatus. The voltage pulse of the pulse generator may be monophasic in which the electrode connected to one of the terminals is a cathode and the electrode connected to the other terminal forms an anode, or may be biphasic in which the polarity of the pulse generator terminals alternates during the pulse.
In the description of particular embodiments that follows, a microprocessor-based ICD will be referred to as incorporating the system and method that is the present invention where programmed instructions in memory are executed by a microprocessor. It should be appreciated, however, that certain functions of an ICD can be controlled by custom logic circuitry either in addition to or instead of a programmed microprocessor. The term “circuitry” as used herein should therefore be taken to mean either custom circuitry (i.e., dedicated hardware) or a microprocessor executing programmed instructions contained in a processor-readable storage medium along with associated circuit elements.
In one primary embodiment of the invention, an electrode configuration is used which is particularly suited for terminating atrial arrhythmias. In this configuration, a lead with a first distal shocking electrode is situated in the coronary sinus (CS) such that the electrode resides in the left lateral heart, just beneath the atrial appendage. The first electrode is connected to one terminal of the pulse generator so as to act as a cathode during a monophasic voltage pulse. A second shocking electrode is connected through its lead to another terminal of the pulse generator so as to form an anode during the voltage pulse and is disposed within the superior vena cava (SVC). Also connected to the pulse generator terminal in common with the second electrode so as to also form an anode is the conductive housing of the device (also referred to as the cannister or CAN). The polarity of the arrangement during a monophasic pulse is thus designated as:
CS−→SVC++CAN+
with the CS electrode acting as the sole cathode and the SVC and CAN electrodes acting as joint anodes for the monophasic defibrillation stimulus.
In another primary embodiment, an electrode configuration is used that is particularly suited for ventricular defibrillation. In this arrangement, a lead with a first distal shocking electrode is situated in the right ventricle, with the first electrode connected to one terminal of the pulse generator so as to act as a cathode during a monophasic voltage pulse. Second and third shocking electrodes are connected through their respective leads to the other terminal of the pulse generator so as to form a joint anode during the voltage pulse and are disposed within the superior vena cava (SVC) and coronary sinus (CS), respectively. Also connected to the pulse generator terminal in common with the second and third electrodes so as to also form a joint anode is the conductive housing of the device. The polarity of the arrangement during a monophasic pulse is thus designated as:
RV−→CS++SCV++CAN+
with the RV electrode as the sole cathode and the CS, SVC, and CAN electrodes acting as joint anodes for a monophasic defibrillation pulse.
The embodiments described above may be modified to form further exemplary embodiments as follows. First, the polarity of the monophasic defibrillation pulse may be reversed so that the first-described embodiment becomes:
CS+→SVC−+CAN−
and the second-described embodiment becomes:
RV+CS−+SCV−+CAN−
In a preferred embodiment, however, a biphasic defibrillation pulse is employed in which the polarity of the pulse generator alternates during the pulse.
In the primary embodiments described above, the conductive housing was used as an extravascular electrode placed in proximity to the heart and connected to one of the pulse generator terminals. In a modified embodiment, an additional subcutaneous array electrode (SQA) may be employed which is located, for example, in the left maxillary space and which is connected so as to be electrically common with the housing. Thus, the polarity would be designated in the case of the atrial defibrillation embodiment as:
CS−→SVC++CAN++SQA+
and for the ventricular defibrillation embodiment as:
RV−→CS++SCV++CAN++SQA+
In another embodiment, the housing electrode is replaced by the subcutaneous array electrode which is then the sole extravascular electrode. In an implementation of either of the primary embodiments as described in which the device is to be used externally rather than being implanted, the housing electrode is replaced by a cutaneous patch electrode.
In another modification to the described embodiments, the SVC electrode is replaced by an electrode in the right atrium (RA) or situated in the right atrial appendage (RAA), which electrodes may be formed along the length of the catheter or not. In further modifications, the SVC or RA electrode may be situated such that it lies partly within the SVC and partly within the RA, or the SVC electrode may extend to the innominate vein. A combination of an RA and SVC electrodes connected electrically in common may also be used, with the RA and SVC electrodes on the same or different lead bodies.
Although the invention has been described in conjunction with the foregoing specific embodiment, many alternatives, variations, and modifications will be apparent to those of ordinary skill in the art. Such alternatives, variations, and modifications are intended to fall within the scope of the following appended claims.
This application is a continuation of U.S. patent Ser. No. 10/629,343, filed on Jul. 28, 2003, which is a continuation of U.S. patent Ser. No. 10/118,603, filed on Apr. 8, 2002, which is a division of U.S. patent application Ser. No. 09/448,648, filed on Nov. 24, 1999, the specifications of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09448648 | Nov 1999 | US |
| Child | 10118603 | Apr 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10629343 | Jul 2003 | US |
| Child | 11275943 | Feb 2006 | US |
| Parent | 10118603 | Apr 2002 | US |
| Child | 10629343 | Jul 2003 | US |
