Clinical significance of consecutive shocks in patients with left ventricular dysfunction treated with implantable cardioverter defibrillators

The purpose of the present study was to determine the clinical significance of consecutive automatic shocks delivered by implantable cardioverter defibrillators (ICDs). Sixty-four patients who received ICDs at our institution between January 1990 and July 1997 were included in this study. There were 53 men and 11 women with a mean age of 50 +/- 14 years. During a follow-up period ranging between 0.2 and 73 months (mean 23 +/- 21 months), 17 patients received consecutive shocks (group A), 29 patients received single shocks (group B), and 18 patients received no ICD therapy (group C). Clinical characteristics, episodes of ICD therapy, and prognosis were compared among the three groups. There were no significant differences among the three groups with regard to clinical characteristics, time to first ICD therapy, number of antitachycardia pacing episodes, or frequency of inappropriate discharges. The mortality rate was higher in group A than in groups B and C (P = 0.0021). The sensitivity of consecutive shocks in predicting death was 70%, the specificity was 88%, and the predictive accuracy was 81% in patients with left ventricular ejection fractions < 35%. In summary, consecutive shocks are a clinically important event in patients with ICDs. Specifically, patients who receive consecutive shocks and have a depressed left ventricular function should be considered particularly high risk.