THE CLINICAL OUTCOME OF ACUTE MYOCARDIAL-INFARCTION IS RELATED TO THECIRCADIAN-RHYTHM OF MYOCARDIAL-INFARCTION ONSET

In order to study whether the circadian rhythm of acute myocardial inf arction (AMI) onset has any impact on the clinical outcome, in terms o f enzymatically estimated infarct size, circulatory arrest from ventri cular tachyarrhythmias, and in-hospital mortality, the authors studied a representative population of 10,791 AMIs treated in the same center between 1973 and 1987. In 6,763 cases (63%) the time of symptom onset was known. In these cases a major peak in AMI incidence was observed between 7:01 AM and 10:00 AM, and minor peaks at 12:01 noon, 3:01 PM-4 :00 PM, and 8:01 PM-9:00 PM. In a set of multivariate analyses includi ng several clinical characteristics, symptom onset between 6:00 AM and 12:00 noon significantly predicted a greater infarct size, and sympto m onset between 12:00 AM and 6:00 AM was associated with a significant ly lower risk of circulatory arrests from ventricular tachyarrhythmias . The time of symptom onset was not significantly associated with in-h ospital mortality after adjustment for other clinical characteristics, including infarct size. The authors suggest that the time of day has an impact, not only on the incidence, but also on the severity of AMI and that the ability of beta blockers to blunt the morning increase in AMI incidence may possibly contribute to the beneficial secondary pre ventive effects of such drugs after AMI.