Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1998-04-17
2001-07-03
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
C607S122000, C607S126000, C607S127000, C607S128000, C607S005000
Reexamination Certificate
active
06256541
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to medical devices and in particular to implantable endocardial catheters for use with medical devices.
BACKGROUND OF THE INVENTION
Ventricular fibrillation of the heart is characterized by fine, rapid, fibrillatory movements of the ventricular muscle that replace the normal cardiac contraction. Since very little pumping action occurs during ventricular fibrillation, the situation is fatal unless quickly corrected by cardiac conversion. During conversion, defibrillation level electrical energy is applied to the heart in an attempt to depolarize the myocardial tissue of the heart and allow a normal sinus rhythm to be reestablished.
One theory that has been proposed to explain the mechanism of conversion by the application of defibrillation electrical current is the critical mass hypothesis. The critical mass hypothesis suggests that it is not necessary to halt all fibrillation activity in order to have defibrillation occur, but that it is sufficient to halt only a “critical mass” (perhaps 75%) of the myocardium in the ventricles. In this theory, the assumption is made that if all fibrillation activity is localized to a region smaller than the critical mass of myocardium, the remaining fibrillation activity is not capable of maintaining fibrillation and will die out after one or two cycles, resulting in normal sinus rhythm.
Implantable cardioverter/defibrillators (ICDs) have been successfully used to treat patients who have experienced one or more documented episodes of hemodynamically significant ventricular tachycardia or ventricular fibrillation. The basic ICD consists of a primary battery, electronic circuitry to control both the sensing of the patient's cardiac signals and the delivery of electrical shocks to the patient's heart, and a high-voltage capacitor bank housed within a hermetically sealed titanium case. One or more catheter leads having defibrillation electrodes are implanted within the heart of the patient or on the epicardial surface of the patient's heart. The catheter leads are then coupled to the implantable housing and the electronic circuitry of the ICD and are used to deliver defibrillation level electrical energy to the heart.
It has been suggested that a minimum and even (i.e., similar in all parts of the ventricles) potential gradient generated by a defibrillation level shock is necessary for effective cardiac defibrillation. This potential gradient is affected, and thus determined, by the voltage of the shock and the electrode configuration employed. It has also been suggested that a maximum potential gradient also exists that, beyond this value, deleterious electrophysiological and mechanical effects may occur, such as new arrhythmias, myocardial necrosis, or contractile dysfunction. Therefore, how and where defibrillation electrodes are placed on and/or within the heart has a major effect on whether or not a critical mass of cardiac tissue is captured during a defibrillation attempt.
Endocardial defibrillation catheters, those not requiring a thoracotomy to be place on the heart, have a major advantage over the epicardial lead systems by reducing the morbidity, mortality, and cost of thoracotomy procedures. However, a major problem with these systems is the potential for high defibrillation thresholds as compared to system employing epicardial defibrillation electrodes. Changes to the waveform of the defibrillation shock and to the combinations of endocardial leads implanted into a patient and the current pathways used can result in efficacious defibrillation therapy being delivered to the patient.
The easiest and most convenient way to perform the implantation of a fully transvenous system is to use only one endocardial lead with both sensing and pacing and defibrillation capabilities. One such endocardial lead is sold under the trademark ENDOTAK C (Cardiac Pacemaker, Inc./ Guidant Corporation, St. Paul, Minn.), which is a tripolar, tined, endocardial lead featuring a porous tip electrode (placed in the apex of the right ventricular) that serves as the cathode for intracardiac right ventricular electrogram rate sensing and pacing, and two defibrillation coil electrodes, with the distal one serving as the anode for rate sensing and as the cathode for morphology sensing and defibrillation which the proximal coil electrode positioned within the superior vena cava functions as the anode for defibrillation.
However, single body endocardial leads used for both defibrillation and rate sensing have been reported to suffer technical inadequacies that may pose significant risks to the patient. Endocardial electrograms obtained from integrated sense/pace-defibrillation leads have been shown to be affected after shock delivery, with their amplitude decreasing to such a significant degree that arrhythmia redetection is dangerously compromised. As already mentioned above, obtaining adequate defibrillation thresholds has been a major problem with the nonthoracotomy endocardial lead systems. Therefore, a need exists to design an endocardial lead system that effectively reduces defibrillation thresholds and allow for reliable post-defibrillation shock sensing and pacing.
SUMMARY OF THE INVENTION
The present invention provides a single body endocardial lead, and an implantable apparatus for its use, that reduces defibrillation thresholds and improves post-defibrillation shock therapy redetection. One aspect of these improvements is the placement of the electrodes on the endocardial lead. The electrode configuration on the endocardial lead improves the potential gradient generated by a defibrillation level shock, which increases the effectiveness of the cardiac defibrillation shock and reduces the defibrillation threshold as compared to conventional endocardial leads. Also, the position of the pacing electrode relative to the defibrillation electrodes provides for a more reliable and accurate post-defibrillation shock electrogram. Furthermore, the reduction in defibrillation thresholds allows for reduced battery consumption of the implantable device, potentially prolonging the life of the device and/or allowing for an overall reduction in the size of the device.
The endocardial lead of the present invention has an elongate body with a peripheral surface, a proximal end, a distal end, and a first defibrillation coil electrode and a first pacing/sensing electrode on the peripheral surface. The first defibrillation coil electrode is positioned on the endocardial lead at or near the distal end of the elongate body. The first pacing/sensing electrode is spaced longitudinally along the peripheral surface from the first defibrillation coil electrode to afford positioning both the first defibrillation coil and the first pacing/sensing electrode in a right ventricle of a heart. In one embodiment, the endocardial lead is positioned within the right ventricle of the heart with the first defibrillation coil electrode positioned longitudinally adjacent the right ventricular septal wall. In an additional embodiment, the endocardial lead is positioned within the right ventricle of the heart with the first defibrillation coil electrode positioned directly within the ventricular apex, where the first defibrillation coil is longitudinally adjacent to the apex of the right ventricle of the heart.
In an additional embodiment of the invention, the endocardial lead further includes a second defibrillation coil electrode on the peripheral surface. The second defibrillation coil electrode is spaced longitudinally along the peripheral surface from the first pacing/sensing electrode to afford positioning the first defibrillation coil and the first pacing/sensing electrode within the right ventricle and the second defibrillation coil within the supraventricular region of the heart. In one embodiment, the second defibrillation coil electrode is positioned within a right atrial chamber or a major vein leading to the right atrial chamber of the heart.
Different types and configurations of first pacing/sensing electrodes can be
Bye Lyle A.
Heil John E.
Heil, Jr. Ronald W.
Lattuca J. John
Lin Yayun
Cardiac Pacemakers Inc.
Schaetzle Kennedy
Schwegman Lundberg Woessner & Kluth P.A.
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