Circadian periodicity affects the type of ventricular arrhythmias and efficacy of implantable defibrillator therapies.

Introduction: Factors influencing malignant arrhythmia onset are not fully understood. We explored the circadian periodicity of ventricular arrhythmias (VAs) in patients with implantable cardioverter and cardiac resynchronization defibrillators (ICD/CRT‐D). Methods: Time, morphology (monomorphic/polymorphic), and mode of termination (anti‐tachycardia pacing [ATP] or shock) of VAs stored in a database of remote monitoring data were adjudicated. Episodes were grouped in six 4‐h timeslots from 00:00 to 24:00. Circadian distributions and adjusted marginal odds ratios (ORs), with 95% confidence interval (CI), were analyzed using mixed‐effect models and logit generalized estimating equations, respectively, to account for within‐subject correlation of multiple episodes. Results: Among 1303 VA episodes from 446 patients (63% ICD and 37% CRT‐D), 120 (9%) self‐extinguished, and 842 (65%) were terminated by ATP, 343 (26%) by shock. VAs clustered from 08:00 to 16:00 with 44% of episodes, as compared with 22% from 00:00 to 08:00 (p <.001) and 34% from 16:00 to 24:00 (p =.005). Episodes were more likely to be polymorphic at night with an adjusted marginal OR of 1.66 (CI, 1.15–2.40; p =.007) at 00:00–04:00 versus other timeslots. Episodes were less likely to be terminated by ATP in the 00:00–04:00 (success‐to‐failure ratio, 0.67; CI, 0.46–0.98; p =.039) and 08:00–12:00 (0.70; CI, 0.51–0.96; p =.02) timeslots, and most likely to be terminated by ATP between 12:00 and 16:00 (success‐to‐failure ratio 1.42; CI, 1.06–1.91; p =.02). Conclusion: VAs did not distribute uniformly over the 24 h, with a majority of episodes occurring from 08:00 to 16:00. Nocturnal episodes were more likely to be polymorphic. The efficacy of ATP depended on the time of delivery. [ABSTRACT FROM AUTHOR]