WEEKLY VARIATION OF ACUTE MYOCARDIAL-INFARCTION - INCREASED MONDAY RISK IN THE WORKING POPULATION

Background Seasonal and circadian variations in the occurrence of myoc ardial infarction and sudden cardiac death have been documented, sugge sting that triggering factors may play a role in the causation of card iac events. However, there are only sparse and conflicting data on the weekly distribution of the disorders. Methods and Results To determin e the weekly variation of acute myocardial infarction and sudden cardi ac death, 5596 consecutive patients (71% men; age, 63+/-1 years) were analyzed in a regionally defined population (n=330 (300; age, 25 to 74 years) monitored from 1985 to 1990. The exact time of onset of sympto ms was used to determine the day of the event. Patients with myocardia l infarction (n=2636) demonstrated a significant weekly variation (P<. 01) with a peak on Monday, whereas patients with sudden cardiac death (n=2960) were evenly distributed throughout the week. A similar weekly pattern was observed in subgroups of patients with myocardial infarct ion defined with respect to age, sex, cardiac risk factors, prior card iac medication, and infarct characteristics. The working population de monstrated a weekly variation of myocardial infarction as opposed to t he nonworking population, with a 33% increase in relative risk of dise ase onset on Monday (P<.05) and a trough on Sunday compared with the e xpected number of cases, if homogeneity was assumed. Conclusions The o nset of acute myocardial infarction demonstrates a peak on Monday prim arily in the working population. If this finding is confirmed in other communities, it may aid in identifying acute triggering events of myo cardial infarction and perhaps in improving prevention of the disease.