Morton M. Mower

Predictors of first discharge and subsequent survival in patients with automatic implantable cardioverter-defibrillators.

BackgroundTwo hundred eighteen patients were evaluated in a two-phase approach (time to first appropriate discharge, survival after discharge) to identify factors that may be related to maximal benefit derived from use of an automatic implantable cardioverter-defibrillator (AICD). Methods and ResultsOne hundred ninety-seven patients survived implantation of AICD, with or without concomitant cardiac surgery. One hundred five patients had an AICD discharge associated with syncope, presyncope, documented sustained ventricular tachycardia or fibrillation, or sleep at 9.1 ± 11.1 months after implantation. Patients survived 23.8 ± 18.0 months after AICD discharge. Left ventricular dysfunction (p =0.008 for ejection fraction less than 25%) was associated with earlier AICD discharge and shortened survival after AICD discharge (p =0.008 for ejection fraction less than 25%;p=0.01 for New York Heart Association functional class III and IV). B-Blocker administration (p =0.006) and coronary bypass surgery (p =0.06) were associated with later AICD discharge. Coronary bypass surgery (p =0.035) but not P-blockers was associated with more prolonged survival after AICD discharge. ConclusionsThese data suggest that a relatively easy algorithm can be applied to predict which patient will benefit most from AICD implantation.

The automatic implantable defibrillator

The automatic implantable defibrillator is an electronic device programmed to monitor the cardiac rhythm continuously, to recognize ventricular fibrillation and ventricular tachyarrhythmias characterized by sinusoidal waveform, and to deliver corrective difibrillatory discharges when indicated. Three patients suffering from recurrent malignant ventricular arrhythmias refractory to medical therapy underwent permanent implantation of this device. Seven episodes of ventricular tachycardia and flutter-fibrillation were documented during the weeks following the implantations; two were induced at electrophysiologic studies and five occurred spontaneously. All were correctly identified and six were automatically reverted to normal sinus rhythm by the implanted device; one induced episode was cardioverted externally before the unit could recycle. Although many problems remain to be solved and the ultimate value of this therapeutic modality has to be determined, a new approach to prevention of sudden death in patients at high risk of developing lethal ventricular arrhythmias has become available.

Defibrillator Versus β-Blockers for Unexplained Death in Thailand (DEBUT) A Randomized Clinical Trial

Background—Sudden Unexplained Death Syndrome (SUDS) is the leading cause of death in young, healthy, Southeast Asian men. The role of an implantable cardioverter defibrillator (ICD) for mortality reduction in these patients remains unclear. Methods and Results—The Defibrillator Versus &bgr;-Blockers for Unexplained Death in Thailand (DEBUT) study is a randomized, clinical trial conducted in 2 phases (pilot study followed by the main trial) to compare the annual all-cause mortality rates among SUDS patients treated with &bgr;-blockers versus that among those treated with an ICD. A total of 86 patients who were SUDS survivors and probable SUDS survivors were randomized to receive an ICD or propranolol (20 patients were in the pilot study and 66 were in the main trial). The primary end point was death from all causes. The secondary end point was recurrent ventricular tachycardia/ventricular fibrillation (VF) or cardiac arrest. During the 3-year follow-up period of the main trial, there were 4 deaths; all occurred in the &bgr;-blocker group (P =0.02). Seven subjects in the ICD arm had recurrent VF, and all were effectively treated by the ICD. On the basis of the main trial results, the Data Safety Monitoring Board stopped the study. In total (both from the Pilot study and the main trial), there were 7 deaths (18%) in the &bgr;-blocker group and no deaths in the ICD group, but there were a total of 12 ICD patients receiving ICD discharges due to recurrent VF. Conclusions—ICD treatment provides full protection from death related to primary VF in a SUDS population and is superior to &bgr;-blockade treatment.

A chronically implanted system for automatic defibrillation in active conscious dogs. Experimental model for treatment of sudden death from ventricular fibrillation.

SUMMARY Ventricular defibrillation was achieved 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 electrical 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.

Ventricular fibrillation detection by a regression test on the autocorrelation function

The paper investigates quantitative differences in the signal characteristics of ventricular fibrillation (VF) and other cardiac arrhythmias. The analysis procedure comprises two steps: calculation of a short-term autocorrelation function (ACF) followed by a regression test on a plot of peak magnitudes of the ACF against lag values (the ACF/lag plot). We detect VF by testing the hypothesis that the ACF/lag plot of VF does not pass a linear regression test. Analysis of 31 separate episodes (of VF and other ventricular arrhythmias), each comprising three successive segments of 1·5s each produced the following results: (1) 100 per cent sensitivity (Se), 62 per cent specificity (Sp) and 74 per cent test efficiency (TE) after analysis of the first segment; (2) 100 per cent Se, 86 per cent Sp and 90 per cent TE after the second segment; and (3) 100 per cent Se, 100 per cent Sp and 100 per cent TE after the third segment. This method quantifies the notion that VF signals are nonperiodic with a random amplitude distribution, whereas ventricular tachycardia (VT) signals are usually periodic with more uniform amplitude distributions. Accurate discrimination and identification of VF can be very important in intensive-care settings, as well as in the design of automatic cardioverters and defibrillators.

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.

The Automatic Implantable Cardioverter-Defibrillator

The automatic implantable cardioverter‐defibrillator is an electronic device designed to monitor the heart continuously, to identify malignant ventricular tachyarrhythmias, and then to deliver effective countershock to restore normal rhythm. There are two defibrillating electrodes which are also used for waveform analysis; one is located in the superior vena cava, the other is placed over the cardiac apex. A third bipolar right ventricular electrode serves for rate counting and R‐wave synchronization. When ventricular fibrillation occurs, a 25 joule pulse is delivered; when ventricular tachycardia faster than a preset rate is detected, the discharge is R‐wave synchronized. The device can recycle three times if required. Special batteries can deliver over 100 shocks or provide a 3‐year monitoring life. Implantation of the device is made either through a thoracotomy or by a subxiphoid approach. Thus far, the device has been implanted in 160 patients with a follow‐up of 42 months. Acceleration of ventricular tachycardia to a faster rhythm or to ventricular fibrillation occurred only rarely and is dealt with most successfully through recycling. Actuarial analysis of the initial 52 patients has indicated 22.9% one‐year total mortality, a 52% decrease from the 48% mortality that would be expected in the same group of patients without the device: the mortality attributed to arrhythmias was only 8.5%. In conclusion, the automatic cardioverter‐defibrillator can reliably identify and correct potentially lethal ventricular tachyarrhythmias, leading to a substantial increase in survival in properly selected high‐risk patients.

Implantation of the Automatic Defibrillator: The Subxiphoid Approach

The automatic implantable defibrillator is an electronic device capable of diagnosing and correcting malignant venticular arrhythmias. While major thoracic surgery was required in the original 24 implants, a new technique for implanting the device has been developed. The first subxiphoid implantations have been accomplished with the defibrillatory function successfully tested intraoperatively. The advantages and indications of the subxiphoid technique are reviewed.

The Automatic Implantable Defibrillator.: New Modality for Treatment of Life-Threatening Ventricular Arrhythmias

New Modality for treatment of life‐threatening ventricular arrhythmias. The automatic implantable defibrillator continuously monitors cardiac rhythm, identifies ventricuiar 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 oj March 1981, sixteen survivors of multiple cardiac arrests refractory io 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 devices 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. (PACE, Vol. 5, May‐June, 1982)

Unusual patterns of conduction produced by pacemaker stimuli

Abstract Four cases showing unusual patterns of conduction produced by pacemaker stimuli are presented. Some of the possible explanations for these phenomena are considered. It is suggested that the pacemaker stimuli in these cases were conducted through specialized conductive tissue rather than preferentially through the myocardial fibers. Thus, the pattern of right bundle branch block occasionally produced by transvenous catheter pacemakers in the right ventricle does not necessarily imply that the catheter has perforated the septum.