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Background. Two 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 Results. One 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.Conclusions. These data suggest that a relatively easy algorithm can be applied to predict which patient will benefit most from AICD implantation. (Circulation 1991;84:558-566) Automatic implantable cardioverter-defibrillators (AICD) have become an important alternative to conventional treatment of patients with recurrent hypotensive ventricular tachyarrhythmias. Several groups, including our own, have demonstrated effective termination of sustained ventricular tachycardia or fibrillation by this device.1-9 AICD implantation thus far has been largely reserved for cardiac arrest survivors when antiarrhythmic medication is not efficacious. Prolongation of life by this device has not been proven by a prospective, randomized trial because withholding AICD therapy has not been possible because of ethical considerations. Whether survival has been improved by the AICD, therefore, has been the subject of discussion.10 Similarly, factors associated with improved survival or enhanced benefit in patients with the AICD remain unknown.

The role of ventricular dysrhythmias as determinants of sudden coronary death (SCD) was studied prospectively in 160 male survivors of myocardial infarction, all under 65 years of age and in New York Heart Association (NYHA) functional class I or II. Twelve-hour electrocardiographic recordings were taken in all patients at serial intervals and analyzed for frequency and type of ventricular ectopic beat (VEB). Eighty percent showed VEB's on at least one tape recording. There have been 14 SCD's in a follow-up period ranging between 30 and 54 months, 12 in 87 patients (13.8%) with significant VEB's (frequent, unifocal, multifocal, paired or coupled, and ventricular tachycardia), and only two in 66 patients (3%) with absent or infrequent VEB's ( P < 0.02). Although the number of patients in this study is small, the results show that all complex VEB forms together were associated with an excess risk of SCD, notwithstanding the absence of SCD in 27 patients with ventricular parasystole. It is suggested that the differential association with SCD between ventricular extrasystoles and parasystole in the late postinfarction period may have bearing on the mechanism of ventricular fibrillation and SCD.

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 ␤-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 ␤-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 ␤-blocker group (Pϭ0.02). 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 ␤-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 ␤-blockade treatment.

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Fifty-two patients who survived several arrhythmic cardiac arrests had implantation of an automatic defibrillator along with additional cardiovascular surgery as indicated. The mean follow-up was 14.4 months and the longest was 3 years. In the hospital, the implanted devices identified and reverted 82 episodes of spontaneous and 81 of 99 episodes of induced malignant tachyarrhythmias. There were 62 automatic resuscitations in 17 patients outside the hospital. Twelve patients died; four of the deaths were not witnessed. These deaths represent a 22.9% total and 8.5% sudden-death 1-year mortality rate. Because the expected 1-year mortality in patients without the automatic defibrillator was calculated to be 48%, there was an estimated 52% decrease in anticipated total deaths. The automatic implantable defibrillator can identify and correct potentially lethal ventricular tachyarrhythmias, leading to a substantial increase in 1-year survival in properly selected high-risk patients.

BACKGROUND In the canine model, an upper limit of shock strength exists that can induce ventricular fibrillation during the vulnerable period of the cardiac cycle. This shock strength (the upper limit of vulnerability) closely correlates with the defibrillation threshold and supports the "upper limit of vulnerability" hypothesis of defibrillation. It is not known whether an upper limit of vulnerability exists in humans or whether this limit correlates with the defibrillation threshold. METHODS AND RESULTS In 13 patients undergoing implantable cardioverter-defibrillator implantation, the shock strengths associated with a 50% probability of reaching the upper limit of vulnerability (ULV50) and a 50% probability of reaching the defibrillation threshold (DFT50) were determined by the up-down algorithm. The ULV50 was determined only for the mid-upslope of the positive T waves and for the mid-downslope of the negative T waves. No major complications occurred during surgery. An upper limit of vulnerability was demonstrated in each patient. The ULV50 was 300 +/- 138 V or 6.8 +/- 5.8 J, which was significantly lower than the DFT50 of 347 +/- 167 V (p = 0.038) or 9.1 +/- 7.3 J (p = 0.013). The correlation between the ULV50 and the DFT50 was significant (r = 0.90, p < 0.001 for voltage; r = 0.93, p < 0.001 for energy). CONCLUSIONS An upper limit of vulnerability is present in humans. There is a significant correlation between the ULV50 and the DFT50, and the ULV50 is significantly lower than the DFT50.