Time to first shock and clinical outcome in patients receiving an automatic implantable cardioverter-defibrillator
Authors: Robert J. Myerburg, Richard M. Luceri, Richard Thurer, Deborah K. Cooper, Liaqat Zaman, Alberto Interian, Pedro Fernandez, Marilyn Cox, Frances Glicksman, Agustin Castellanos
Journal: Journal of the American College of Cardiology (1989)

The relation between time to first shock and clinical outcome was studied in 60 patients who received an automatic implantable cardioverter-defibrillator (AICD) from August 1983 through May 1988. The mean (±SD) patient age was 64 ± 10 years, 82% were men and the mean ejection fraction was 33± 13%. During follow-up, 38 patients (63%) had one or more shocks; there were no differences in age, gender distribution or ejection fraction at entry between the shock and no shock groups. Among 51 patients with coronary artery disease, 31 (61%) had one or more shocks, whereas all seven patients with cardiomyopathy had one or more shocks (p < 0.05). Neither of the two patients with idiopathic ventricular fibrillation had shocks. Of the 13 deaths, 12 occurred during post-hospital follow-up and 1 during the index hospitalization. Of the four sudden post-hospital deaths, only one was due to tachyarrhythmia in the absence of acute myocardial infarction. All four sudden deaths and five of eight post-hospital nonsudden deaths occurred in patients who had had one or more appropriate shocks during follow-up. Eight of the nine first appropriate shocks among patients who subsequently died occurred within the first 3 months of follow-up but, the actual deaths were delayed to a mean of 14.1 ± 13.9 months (p < 0.05). The mean time to all deaths was 14.8 ± 13.1 months. The ejection fraction was significantly lower among patients who died than among patients who survived (25 ± 7% versus 35 ± 14%, p < 0.02), but it did not distinguish risk of first shocks. Among the 38 patients who had one or more shocks during follow-up, 20 (53%) had their first shock within the first 2 months of follow-up and 29 (76%) by the 6th month. By 1 year, 34 (89%) of the 38 had had one or more shocks; no patient had a first appropriate shock >16 months after AICD implantation. Those patients who died of any cause during follow-up had a shorter time to first shock (2.3 ± 2.0 months) than did those who continued as survivors (5.5 ± 6.1 months) (p < 0.05). After the occurrence of a first shock, the mean total number of shocks was 11.0 ± 17.9, but the distribution was bimodal with 50% of the patients having no additional shocks after the first one. The use of antiarrhythmic drugs at discharge did not influence time to first shock. It is concluded that the majority of patients who have any shocks after AICD implantation tend to have their first shock within the first few months after implantation, and the risk for a first shock is low if it has not occurred within the first 1.5 years. Ejection fraction does not discriminate risk of having shocks, but does discriminate risk of death during follow-up. The AICD appears to prolong duration of survival among those patients who will die during followup, although the magnitude of prolonged survival and impact on total death rate is less clear than is reduction of arrhythmic sudden death.