Circadian and Seasonal Variation of Malignant Arrhythmias in a Pediatric and Congenital Heart Disease Population

Circadian Rhythms in Pediatric De. brillator Discharges. Introduction: Recent studies in adult populations have revealed seasonal variation in the frequency of acute cardiovascular events, including life‐threatening arrhythmias, demonstrating increased events during winter and early spring. Trends in the time of day that arrhythmias occur also were noted. We sought to establish whether pediatric and young adult congenital heart disease implantable cardioverter defibrillator (ICD) recipients have circadian or seasonal variability in shock frequency, similar to adult populations. Methods and Results: Data from ICD patients at six pediatric centers in North America were analyzed to assess the timing of life‐threatening arrhythmias. The populations consisted of children and adults with congenital heart disease and ICDs placed for malignant arrhythmias. Data were considered in 46 patients who received appropriate therapy (total 139 episodes) for ventricular tachycardia or ventricular fibrillation. Multiple variables were analyzed, including time of day, day of week, and month of year. In contrast to previously studied adult patients, fewer events occurred in the early morning (7.5%), with the most therapies occurring between 6 P.M. and midnight (35%). An increased frequency of therapies was observed in the fall and winter (September‐January), representing 60% of all appropriate shocks. Unlike adult populations, Mondays did not have an increased frequency of malignant arrhythmias. Conclusion: Pediatric and adult congenital heart disease populations have moderate seasonal and 24‐hour variation in ICD event rate, with some distinctly different peaks than those seen in typical adult ICD populations. These findings suggest circadian variation in arrhythmia vulnerability that may differ from conventional occupational, physical, or emotional stressors.