Diurnal, Seasonal, and Monthly Variations in Ventricular Arrhythmias in Patients With Implantable Cardioverter-Defibrillators

Objectives: The aim of this study was to assess the variations in ventricular arrhythmia (VA) occurrence according to seasons, months of the year, days of the week, and the time of day in a large implantable cardioverter-defibrillator patient population. Background: Limited data exist on how VA occurrence varies as a function of time. Methods: Data from 6 prospective studies were pooled to assess VA frequency over time. All adjudicated episodes of VAs ≤500 ms were included. VA distribution as a function of hour, day, month, and season were assessed through the construction of 4 negative binomial models. The models included a random patient effect and offset for days spent in each time period. Results: Among 3,969 patients, 7,126.8 cumulative device-years with an average follow-up duration of 1.8 ± 1.4 years/patient were analyzed. VA occurrence was higher in the spring than the summer (0.86% vs. 0.70%; p = 0.009) but not significantly different from the fall (0.74%; p = 0.069) or winter (0.84%; p = 0.732). The estimated probability of occurrence of at least 1 VA episode in each 1-h block during the hours of 8 AM to 10 PM over 365 days (0.10% to 0.12%) was higher (estimated 35% to 63% higher) than the referent period of midnight to 1 AM (0.07%). No significant variations in VA occurrence were observed according to weekday and individual months of the year. Conclusions: Significantly higher VA occurrence in the spring and during the hours of 8 AM to 10 PM were observed. Additional studies are needed to further understand the reasons for these observations, which may involve variations in temperature or differences in catecholamine triggers.