Clusters of life-threatening ventricular arrhythmias in patients with implanted cardioverter-defibrillators: prevalence, characteristics, and risk stratification

BACKGROUND: Series of discharges from an implanted defibrillator (ICD) to terminate life-threatening ventricular tachyarrhythmias are one particular aspect of energy use and success of ICD therapy. Little is known about prevalence. characteristics, and risk stratification of so-called "cluster arrhythmias." HYPOTHESIS: The objective of this study was to examine the frequency of cluster arrhythmias, to characterize the temporal relationship precisely, and to assess the accompanying circumstances of their occurrence, whereby risk stratification was to be made if appropriate. METHODS: In all, 63 consecutive patients were followed prospectively over 727 +/- 684 days to determine the presence and characteristics of cluster arrhythmias (45,801 patient days). In 30 patients, 374 ICD episodes of ventricular tachyarrhythmias were analyzed for their temporal relationship. After a first successfully terminated ventricular tachyarrhythmia, further ICD discharges within 3 h were observed during 145 of 374 (39%) episodes; mean time interval between these arrhythmias was 25 +/- 32 min. RESULTS: Arrhythmia clusters occurred in 19 of 30 (63%) patients. In multivariate analysis, only underlying heart disease was predictive for accumulation of ventricular tachyarrhythmias. Cluster arrhythmias were more frequent among patients with ischemic heart disease than among those with nonischemic heart disease (40.0 vs. 29.2%, p < 0.05). Ejection fraction, age, gender, and other parameters were not predictive for occurrence of arrhythmia clusters. In 4 of 19 patients, accumulation of ICD discharges was predictive for new onset of myocardial ischemia elicited by exercise test. CONCLUSIONS: Cluster arrhythmias are most common in patients with ICDs with coronary heart disease and may indicate disease progression and increasing instability, for example, due to new onset of myocardial ischemia.