Prospective Evidence of a Circadian Rhythm for Out-of-Hospital Cardiac Arrests

Objectives. —Published studies have indicated a circadian rhythm in the occurrence of sudden cardiac death. However, these studies have involved either retrospective analyses of death certificates or analyses of data collected during studies of pharmacologic agents in selected populations. Purpose. —To determine whether a circadian pattern could be clearly demonstrated in a prospective study of out-of-hospital sudden cardiac death in a large, unselected population. Design. —All adult cases of sudden death of presumed primary cardiac cause from a large urban population were prospectively evaluated over a 12-month period. The incidence of sudden cardiac death was analyzed using harmonic regression of the data tabulated by hour of the day. Results. —During the year of study, 1019 consecutive primary cardiac arrests were analyzed. A significant circadian pattern was found (P<.0001) with the frequency of cardiac arrests increasing dramatically from 6 AM until noon. Conclusions. —This prospective study of out-of-hospital cardiac arrest confirms the existence of a circadian rhythm. These data have important implications for future investigations concerning the pathophysiology of sudden cardiac deaths.