Long-term temporal patterns of ventricular tachyarrhythmias

Technological limitations have precluded investigation of long-term temporal patterns of ventricular tachyarrhythmia recurrences. Newer implantable cardioverter-defibrillators permit such analyses by accurately recording the time and date of tachycardia detections during long-term follow-up. This study tests the hypothesis that ventricular tachycardia occurrences are randomly distributed over time in individual patients.

The time and date of 727 episodes of ventricular tachyarrhythmias were recorded from the data logs of 31 patients with implantable cardioverter-defibrillators followed for a median of 177 days (range, 7 to 782 days). All patients had three or more ventricular tachycardia detections and no detections from causes other than ventricular arrhythmias. In 28 of 31 patients, the distribution of the interdetection time intervals during follow-up differed significantly (all P < .01) from an exponential model distribution of interdetection intervals that assumed that detections were equally likely to occur at any time during follow-up (random). The Kolmogorov-Smirnov goodness-of-fit test was used to compare sample and model distributions. In each patient, the nonrandom distributions resulted from a preponderance of interdetection time intervals that were shorter than predicted by the random model, resulting in a temporal clustering of arrhythmic events. The interdetection interval was < or = 1 hour and < or = 91 hours for 55% and 78% of all intervals, respectively. When only those episodes receiving shock or antitachycardia pacing therapy were analyzed, 25 of 29 patients still manifested nonrandom distributions (all P < .01). When only episodes with tachycardia rates > 240 beats per minute were analyzed, 11 of 13 patients manifested non-random distributions (all P < .01).

Ventricular tachycardia detections and delivered antitachycardia therapies by implantable cardioverter-defibrillators are nonrandomly distributed throughout long-term follow-up in the majority of patients. The temporal clustering of these arrhythmic events may allow preemptive antiarrhythmic therapy and should be considered in the design of therapy based on suppression of spontaneous ventricular arrhythmias to statistically derived end points.