Variation in the time and day of onset of myocardial infarction and sudden death

AIM: To examine circadian and weekly variation in the onset of acute myocardial infarction and sudden cardiac death.

METHOD: A large population based coronary heart disease register, the ARCOS Study, which is collaborating in the WHO MONICA Project carried out in Auckland, New Zealand, 1983-90. There were 4983 patients aged 25-64 with definite myocardial infarction or coronary death. Main outcome measures--circadian and weekly variation in onset of symptoms of definite myocardial infarction and sudden cardiac death.

RESULTS: Surviving patients showed a circadian pattern with a single morning peak in symptom onset (30.0%) while sudden death patients exhibited an afternoon peak (32.5%) and a secondary morning peak (27.6%). Within these two subgroups the circadian pattern was analysed by various risk factors and medications. A weekly variation was found with an increased incidence of onset of symptoms during the weekend and on Monday for surviving patients and a Saturday high (18.6%) for sudden death patients.

CONCLUSIONS: Further investigation of physiological changes within subgroups during the key periods may provide insight into triggering mechanisms and lead to better means for prevention.