Circadian pattern of ventricular fibrillation-terminating shocks among patients with diagnosed and treated congenital...

Episodes of ventricular fibrillation (VF) from coronary artery disease cluster in the early morning hours. The circadian pattern of VF in congenital long QT syndrome (LQTS) is less defined.

To assess the circadian pattern of VF episodes in LQTS, focusing on activity-specific timing.

A retrospective study of LQTS patients with an implantable cardioverter-defibrillator (ICD) evaluated from 1999 to 2025 in the Mayo Clinic Windland Smith Rice Genetic Heart Rhythm Clinic. Events were VF-terminating shocks with the exact time recorded; for ICD electrical storm, the time of first shock was recorded. Statistical analysis used Rayleigh- and 2-harmonic regression tests.

Among 321 LQTS patients with an ICD (224 were female, mean implant age was 21 ± 15 years, 96 had LQT1, 161 had LQT2, and 64 had LQT3), 85 patients (26%) experienced 199 VF-terminating shocks. Per-event and per-patient analysis (correcting for patients with many events) demonstrated clustering in the midafternoon. 2-harmonic regression showed a predominance of events at 15:01 (LRT = 30.6; P < .001), strengthened by the bin-free Rayleigh test with a clustering at 14:58 (Z = 14.1; P < .001). This was driven mainly by LQT1 (Z = 10.9; P < .001) rather than LQT2 (Z = 1.2; P = .3) or LQT3 (Z = 7; P < .001 not maintained by per-patient analysis). Activity analysis showed similar clustering for times of events for daily and exercise/stress-related activities.

VF in LQTS, mainly driven by LQT1, is not uniformly distributed throughout the day but concentrates in a mid-afternoon "torsadogenic window." These results align with a previously published "QT clock" and circadian activity of ion channel expression and may influence future management.