Objective: To determine whether in a larger data base call for sudden cardiac death exhibits a specific circadian rhythm similar to that recently demonstrated by Levine et al.
Design and setting: The time of the day of calls received for out-of-hospital cardiac arrests (OOHCA) prospectively registered between 1983 and '90 by 7 major Belgian pre-hospital EMS-MICU services. Chrono-biologic assessment was made by two-harmonic linear regression analysis of the data tabulated by hour of the day. The hourly distribution of calls for OOHCAs was subjected to Fourier transformation resulting in a periodogram.
Patients: 3471 OOHCAs with presumed cardiac etiology and age of more than 18 years versus 2007 inpatients registered in the same period.
Measurements and results: Significant and remarkably similar circadian patterns were found (R-square = 0.84) for the cardiac origin OOHCAs and the ventricular fibrillation OOHCAs. There is a low incidence during the night and an increased incidence from 6 a.m. until noon with an additional early afternoon-peak. The data were always better fitted when applying sinusoids with periods of 8 and 24 h instead of 12 and 24 h. Our observed circadian distribution resembles the reported circadian variation of ischaemic episodes, ventricular tachycardia and acute myocardial infarction in the awake hours. The time distribution of OOHCA (cardiac origin) differs significantly from OOHCA (non-cardiac origin) and from in-hospital cardiac arrests. The in-hospital CA pattern shows less deviation. The age dependent variation in the incidence of cardiac origin OOHCAs, was not obvious for the ventricular fibrillation subgroup.
Conclusion: Knowledge about the cyclical nature of incidence of cardiac arrests is useful to improve intersystem comparisons and make sound decisions about prophylaxis, treatment and allocation of resources.