MORNING PEAK IN VENTRICULAR TACHYARRHYTHMIAS DETECTED BY TIME OF IMPLANTABLE CARDIOVERTER DEFIBRILLATOR THERAPY/

Background A morning peak in occurrence of sudden cardiac death has be en identified in epidemiological studies, but the studies are subject to selection bias, with the exclusion of unwitnessed deaths, which are more likely to occur at night. The recent availability of implantable cardioverter/defibrillators that record the time of ventricular tachy arrhythmias requiring either pacing or shock therapy provides an oppor tunity to clarify the timing of ventricular tachyarrhythmias predispos ing to sudden cardiac death. Analysis of the timing of arrhythmias in different patient subgroups, such as patients with poor left ventricul ar function, may provide further insight into the mechanism of onset o f sudden cardiac death. Methods and Results We studied patients in who m a cardioverter/defibrillator (Ventak PRx) was implanted between Sept ember 1990 and September 1993 in US centers. Events that could be time d occurred in 483 patients. With an RR cycle length of 240 ms as a cut off, corresponding to a heart rate of 250 beats per minute, episodes w ere categorized as rapid (n=1217) or less rapid (n=9266) ventricular t achyarrhythmias. A higher proportion of both rapid and less rapid vent ricular tachyarrhythmias began in the late morning compared with other times of the day. The subgroup of patients with ejection fraction <20 % at the time of implantation demonstrated a more uniform 24-hour dist ribution of tachycardias less than or equal to 250 beats per minute th an patients with higher left ventricular ejection fraction. Conclusion s Further investigation of the late morning peak and of precipitants o f ventricular tachyarrhythmias by use of data from the implantable car dioverter/defibrillator may provide insight into the pathophysiologica l mechanisms causing sudden cardiac death.