Ventricular defibrillation was acheived in active conscious dogs with a chronically implanted automatic system composed of a defibrillator and an alternating current fibrillator. The hermetically sealed defibrillator is encased in titanium, weighs 250 g and has a volume of 145 ml. The sensor continuously monitors ventricular electircal activity and recognizes fibrillation by the absence of isoelectric potential segments. Fibrillation is induced by placing a magnet over the implanted fibrillator. The resulting syncope closely resembles the clinical entity of sudden death, while the defibrillator automatically restores normal rhythm with a truncated exponential pulse of 30 J, 15 seconds after the onset of the arrhythmia. The operational status of the defibrillator can be tested in vitro and noninvasively in vivo with an external analyzer. This experimental model allows for the first time a long-term study of the automatic implantable defibrillator approach to prevent sudden death from ventricular fibrillation under a variety of physiopathologic conditions.
The automatic implantable defibrillator continuously monitors cardiac rhythm, identifies ventricular fibrillation and then delivers corrective defibrillatory discharges when indicated; it weighs 250 grams and has a volume of 145 cc. When a suitable arrhythmia is detected, a 25 Joule pulse is delivered through a superior vena cava catheter electrode and another electrode placed over the cardiac apex. As of March 1981, sixteen survivors of multiple cardiac arrests refractory to antiarrhythmic therapy had undergone implantation of the automatic defibrillator. There was no operative mortality and the morbidity was minimal. Electrophysiologic studies were performed before and after surgery to confirm failure of drug therapy and to ensure the device's ability to terminate malignant arrhythmias. Eight spontaneous and fourteen of the seventeen induced malignant arrhythmias were properly recognized and corrected by the device. The discharges were well tolerated by awake patients. A number of problems including recycling delays and spurious discharges have been identified and corrected. There were three late deaths with pulmonary edema noted in two patients, and asystole in one. The autopsies revealed no myocardial damage attributable to the automatic defibrillator. Although the ultimate role of this approach to prevention of sudden arrhythmic death has yet to be determined, the results obtained to date are encouraging and indicate that a useful modality for treating malignant ventricular arrhythmias has been added to our armamentarium.
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