Circadian and Seasonal Variation of Malignant Arrhythmias in a Pediatric and Congenital Heart Disease Population ELIZABETH A. STEPHENSON, M.D., 1 KATHRYN K. COLLINS, M.D., 2 ANNE M. DUBIN, M.D., 3 MICHAEL R. EPSTEIN, M.D., 4 ROBERT M. HAMILTON, M.D., 5 NAOMI J. KERTESZ, M.D., 6 MARK E. ALEXANDER, M.D., 1 FRANK CECCHIN, M.D., 1 JOHN K. TRIEDMAN, M.D., 1 EDWARD P. WALSH, M.D., 1 and CHARLES I. BERUL, M.D. 1 From the 1 Department of Cardiology, Children’s Hospital, Harvard Medical School, Boston, Massachusetts; 2 Division of Pediatric Cardiology, University of California, San Francisco, California; 3 Division of Pediatric Cardiology, Stanford University, Palo Alto, California; 4 Division of Cardiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio; 5 Division of Cardiology, Hospital for Sick Children, Toronto, Ontario, Canada; and 6 Division of Cardiology, Texas Children’s Hospital, Baylor College of Medicine, Houston, Texas 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 debrillator (ICD) recipients have circa- dian 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 bril- lation. 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 ndings suggest circadian variation in arrhythmia vulnerability that may differ from conventional occupational, physical, or emotional stressors. (J Cardiovasc Electrophysiol, Vol. 13, pp. 1009-1014, October 2002) circadian, debrillator, ventricular tachycardia, congenital heart defects, children Introduction Recent work revealed several trends involving the timing of arrhythmic events or sudden death both in adult and animal populations. 1,2 These events tend to occur more frequently in the winter months, regardless of climate 2 or hemisphere. 3 Although some of the differences noted throughout the year may be explained by changes in psy- chological stressors (i.e., the holidays), similar patterns were observed in animals, 4 which are not considered to be susceptible to such stressors. It is postulated that these changes may reect periods of increased vulnerability sec- ondary to changes in circadian rhythm. 1 Implantable cardioverter debrillators (ICDs) may be used as a monitoring modality to assist in the identication of arrhythmias and their timing. Although some selection bias is inherent, as one can only monitor those patients who were considered at risk and thus had a device implanted, ICDs allow determination of the exact timing and nature of an arrhythmic event in these patients. Pediatric and congen- ital heart disease patients represent ,1% of all ICD recip- ients and constitute a very different population from a pathophysiologic perspective. Recognizing the timing pat- terns of such events may aid in understanding the underly- ing mechanisms and perhaps eventually preventing these arrhythmias. In this study we investigated the timing of life-threatening arrhythmias in this unique population. Methods The medical records of patients with ICDs at six pediat- ric centers in North America were systematically reviewed. Institutional review board approval for a retrospective re- view and database search was obtained at each participating center. Children and adult congenital heart disease patients who received device therapy between October 1991 and September 2001 were selected. Rhythm strips of all device discharges (either shock or Presented in part at the 21st Annual Scientic Sessions of the North American Society of Pacing and Electrophysiology, May 2001, Boston, Massachusetts. Address for correspondence: Charles I. Berul, M.D., Department of Car- diology, Children’s Hospital Boston, 300 Longwood Avenue, Boston, MA 02115. Fax: 617-739-9058; E-mail: charles.berul@cardio.chboston.org Manuscript received 30 April 2002; Accepted for publication 3 September 2002. 1009 Reprinted with permission from JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Volume 13, No. 10, October 2002 Copyright ©2002 by Blackwell Futura Publishing, Inc.