Sequential shocks are comparable to single shocks employing two current pathways for internal defibrillation in dogs.

Sequential pulse defibrillation using two current pathways was compared with single shocks simultaneously utilizing both pathways in 16 dogs to assess the effects of temporal summation. A cardioverter-defibrillator catheter was positioned via the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the proximal 8 cm2 electrode located in the superior vena cava. Three electrode configurations were tested: (1) single pulse, distal electrode (cathode) to proximal electrode and chest wall patch (common anode), (2) sequential 5 ms pulses with 1 ms interpulse delay, distal electrode (cathode) to proximal electrode (anode) followed by distal electrode (cathode) to chest wall patch (anode), and (3) sequential 10 ms pulses with 1 ms interpulse delay using same current pathways described for configuration 2. The lowest energies resulting in termination of AC induced ventricular fibrillation on four trials were 27.9, 26.6, and 42.3 joules respectively for configurations 1, 2, and 3. The mean energy levels were not significantly different for configurations 1 and 2, both of which were significantly lower than that for configuration 3. The lowest peak voltages terminating ventricular fibrillation on four trials were 595 +/- 176, 521 +/- 134 and 579 +/- 171 volts for configuration 1, 2, and 3. The mean voltage level for configuration 2 was significantly lower than that for configurations 1 and 3, which were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of defibrillation efficacy in humans using a new catheter and superior vena cava spring-left ventricular patch electrodes.

The automatic implantable cardioverter-defibrillator currently utilizes an electrode system that requires a major operation for implantation. Effective defibrillation using an implantable cardioverter-defibrillator catheter positioned transvenously would eliminate the morbidity associated with such surgery. Fifteen patients undergoing defibrillator implantation were studied to compare the efficacy of the catheter with that of the superior vena cava spring (6.7 cm2, anode)-left ventricular patch (13.5 cm2, cathode) electrode system using truncated exponential waveforms with 60% tilt. The catheter is 11F in diameter and tripolar. A distal platinum-iridium tip used for pacing was separated by 4 mm from a middle 4.3 cm2 platinum electrode; these were positioned at the right ventricular apex. The proximal 8.5 cm2 platinum electrode was situated at the superior vena cava-right atrial junction. Defibrillation was performed using the middle (cathode) and proximal (anode) electrodes. Ventricular fibrillation was induced by alternating current six times, and defibrillation shocks of 1, 5, 10, 15, 20 or 25 J were given in random order, first using the catheter and then the spring-patch system. Rescue shocks of higher energy were given if there was failure. Although very low energy levels appeared to be slightly more efficacious when using the spring-patch system, there was no statistically significant difference between the electrode systems for any of the energies tested. Permanent implantation of the catheter would have been suitable in 45% of the patients, as compared with 54% of patients with the spring-patch system (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Nonthoracotomy internal defibrillation in dogs: threshold reduction using a subcutaneous chest wall electrode with a transvenous catheter electrode.

The efficacy of truncated exponential waveform shocks using a cardioverter-defibrillator catheter with and without a 13.9 cm2 subcutaneous thoracic patch electrode was examined in 10 pentobarbital-anesthetized dogs. The cardioverter-defibrillator catheter was positioned through the external jugular vein with the distal 4 cm2 shocking electrode located in the right ventricular apex and the 8 cm2 proximal electrode located in the superior vena cava. Four electrode configurations were tested: 1) distal electrode (cathode) to proximal electrode and chest wall patch (common anodes), 2) distal electrode (cathode) to chest wall patch (anode), 3) distal electrode (cathode) to proximal electrode (anode), and 4) chest wall patch (cathode) to proximal electrode (anode). The lowest randomized energy resulting in termination of alternating current-induced ventricular fibrillation on four trials at that energy was 20.2, 21.3, 27.4 and greater than 40 J, respectively, for configurations 1 through 4. The energy requirements for configurations 1, 2 and 3 were significantly lower than for configuration 4 (p less than 0.001). Additionally, configurations incorporating the distal electrode and the patch electrode (configurations 1 and 2) were significantly better than the catheter alone (configuration 3; p less than 0.05). There was no significant difference between configurations 1 and 2. In conclusion, the addition of a subcutaneous chest wall electrode to the cardioverter-defibrillator catheter significantly lowered energy requirements for defibrillation, suggesting that a nonthoracotomy approach for the automatic implantable cardioverter-defibrillator is feasible.

Automatic implantable cardioverter-defibrillator structural characteristics.

There are a number of equipment options and surgical techniques available for automatic implantable cardioverter-defibrillator implantation. The system can be successfully used even in problem cases where restrictions may be imposed because of physical build or the presence of other implanted devices. The sensing requirements and energy output of the units can be tailored to the exact needs of the particular patient. Battery life and device function are easily monitored periodically following implantation, making possible elective replacement of the pulse generator when the batteries become depleted.

Measurement of cardioversion/defibrillation thresholds in man by a truncated exponential waveform and an apical patch-superior vena caval spring electrode configuration.

Defibrillation/cardioversion thresholds were measured in 33 patients undergoing defibrillator implants. Each patient had a 12 cm2 patch placed near the left ventricular apex via a thoracotomy and a 10 cm2 spring lead placed pervenously at the right atrial-superior vena caval junction. Ventricular tachycardia of stable morphology, polymorphic ventricular tachycardia, or ventricular fibrillation was induced four times in each patient and 1, 5, 10, and 25 J truncated exponential shocks with 60% tilt were given in a random sequence. The conversion rate was constant (77%, 86%, 87%, 85%) with increasing energy for ventricular tachycardia but progressively increased for polymorphic ventricular tachycardia and ventricular fibrillation (8%, 33%, 58%, 92%). The ventricular tachycardia acceleration rates for 1, 5, 10, and 25 J were 23%, 14%, 10%, and 15%. Patients not reliably converted with 25 J may require repositioning of leads or two patches. We conclude that for the spring-patch electrodes, increasing energy from 1 to 25 J improves the conversion rate for polymorphic ventricular tachycardia and ventricular fibrillation; the ventricular tachycardia conversion rate is constant. Acceleration of ventricular tachycardia occurs at all energies. Defibrillator implantation requires extensive intraoperative electrophysiologic testing to ensure safe and reliable termination of ventricular tachycardia and fibrillation.

The automatic implantable defibrillator: local ventricular bipolar sensing to detect ventricular tachycardia and fibrillation.

The first-generation automatic implantable defibrillator implanted in man sensed arrhythmias by monitoring a transcardiac electrocardiographic signal. This sensing system reliably detected ventricular fibrillation and sinusoidal ventricular tachycardia but failed to sense all nonsinusoidal ventricular tachycardias. To solve this problem, a new ventricular tachycardia detection scheme was developed using a local ventricular bipolar electrogram and electronic circuits using rate averaging and automatic gain control to permit sensing of electrograms down to 0.1 mV. This detection scheme was tested during electrophysiologic studies in 11 patients with ventricular tachycardia and fibrillation. All 22 episodes of induced ventricular tachycardia with a rate above the selected cutoff were detected after an average of 5.1 +/- 1.8 seconds. No episodes below the rate cutoff were detected. The bipolar circuits also reliably detected ventricular fibrillation. Arrhythmia detection and signal quality in 9 patients receiving automatic defibrillators using the new bipolar rate detection circuit were compared with the findings in 5 patients previously receiving units that sensed arrhythmias using the transcardiac electrocardiographic signal. Compared with the transcardiac monitoring units the newer bipolar units had shorter and more uniform sense times (5.5 +/- 1.4 versus 12.2 +/- 7.1 seconds). It is concluded that malignant ventricular tachyarrhythmias can be sensed accurately using bipolar rate detection and that this system has numerous advantages over the previously used transcardiac electrocardiographic signal.

Clinical evaluation of the internal automatic cardioverter-defibrillator in survivors of sudden cardiac death.

An R-wave synchronous implantable automatic cardioverter-defibrillator (IACD) was evaluated in 12 patients with repeated episodes of cardiac arrest who remained refractory to medical and surgical therapy. Seven men and 5 women, average age 61 years, surgically received a complete IACD system. Coronary artery disease was found in 11 and the prolonged Q-T syndrome in 1. The average ejection fraction was 34%, and 6 patients had severe congestive heart failure (New York Heart Association class III or IV). The IACD is a completely implantable unit consisting of 2 bipolar lead systems. One system uses a lead in the superior vena cava and on the left ventricular apex through which the cardioverting pulse is delivered. The second system employs a close bipolar lead implanted in the ventricle for sensing rate. After the onset of ventricular tachycardia or fibrillation, the IACD automatically delivers approximately 25 J. Postoperative electrophysiologic study in 10 and spontaneous ventricular tachycardia in 1 patient demonstrated appropriate IACD function and successful conversion in all with an average of 18 +/- 4 seconds. The induced arrhythmias were ventricular tachycardia (160 to 300 beats/min) in 9 and ventricular fibrillation in 1. These data demonstrate that ventricular tachycardia, not ventricular fibrillation, was the predominant rhythm induced during programmed ventricular stimulation in these survivors of cardiac arrest and that the IACD effectively responded to a wide range of ventricular tachycardia rates as well as ventricular fibrillation. Use of the IACD offers an effective means of therapy for some patients who otherwise may not have survived.