CIRCADIAN VARIATION OF SUDDEN CARDIAC DEATH REFLECTS AGE-RELATED VARIABILITY IN VENTRICULAR-FIBRILLATION

Background. Previous studies report a morning peak in the occurrence o f out-of-hospital sudden cardiac death but lack detailed information o n underlying arrhythmias. We used the documentation system of the semi automated defibrillators used by emergency medical technicians to inve stigate the circadian pattern of defined arrhythmias and the influence of demographic patient characteristics on this pattern. Methods and R esults. From December 1988 to December 1990, 703 consecutive patients (63% men; age, 67+/-17 years) with sudden cardiac death were registere d in the Klinikum Steglitz area of the Berlin emergency care system. D etermination of time of day of the event was based on the arrival time of the rescue squad. A marked circadian variation (P<.0001) in the oc currence of sudden cardiac death was observed with a primary morning p eak (6 AM to noon) and a secondary afternoon peak (3 to 7 PM). The sub group of 294 patients with ventricular fibrillation as initially docum ented arrhythmia showed a similar circadian variation (P<.0001). In si gnificant contrast (P<.01), patients with asystole (n = 260) or pulsel ess bradyarrhythmias (n = 149) were more evenly distributed,during the daytime with a primary night trough. Multivariate logistic regression analysis revealed that the circadian pattern of ventricular fibrillat ion was similar in both gender groups but tended to differ with regard to age: patients older than 65 years demonstrated a monophasic distri bution, whereas patients aged 65 years or less had a biphasic distribu tion with peaks in the morning and in the afternoon. Conclusions. The circadian pattern of sudden cardiac death reflects primarily a circadi an variation in onset of ventricular fibrillation. The different circa dian patterns of ventricular fibrillation, pulseless bradyarrhythmias, and asystole suggest different pathophysiological mechanisms of causa tion of death. The age dependence of the pattern of ventricular fibril lation may indicate different underlying external or endogenous trigge rs.