Circadian pattern of ventricular tachyarrhythmias in patients with implantable cardioverter-defibrillators

Objectives. This study examined the temporal patterns of ventricular tachycardi detections by implantable cardioverter-defibrillators for circadian variability. Background. Previous studies of circadian arrhythmi patterns have been methodologically limited by very brief observational periods. Late-generation implantable cardioverter-defibrillators accurately record the times of arrhythmi detections during unlimited follow-up. Methods. Forty-three patients with late-generation implantable cardioverter-defibrillators were followed up for 226 ± 179 days (mean ± SD). The times of all recorded episodes of ventricular tachyarrhythmias were retrieved from the dat log of each device during follow-up. Results. The weighted distribution of 830 ventricular tachyarrhythmi episodes from the 43 patients fit single harmonic sine curve model with peak between 2 and 3 p.m. (95% confidence interval 1:13 to 4:13 p.m., R = 0.75, p < 0.05). The distributions of spontaneously terminating episodes, episodes receiving device therapy, episodes receiving shocks and episodes in the absence of antiarrhythmic therapy also fit the sine curve model (all R = 0.53 and 0.73, all p < 0.05), all with peak frequencies between 2:08 and 3:09 p.m. and 95% confidence intervals for peak frequencies between 11:38 a.m. and 5:07 p.m. Episodes recorded during continuous antiarrhythmic drug therapy did not fit the model (p > 0.05). Conclusions. The distribution of ventricular tachyarrhythmias detected by late-generation implantable cardioverter-defibrillators follows circadian pattern, with peak tachycardi frequency between noon and 5 p.m. This pattern was not observed in patients receiving antiarrhythmic drug therapy. Knowledge of circadian periodicity for these events has implications for patient management.