[Wake up time, thrombocyte aggregation and the risk of acute coronary heart disease. The TRIMM (Trigger and Mechanisms of Myocardial Infarct) Study Group].

A circadian variation in the incidence of acute coronary artery disease (CAD) was observed, but the correlation to possible triggering external factors and pathophysiologic mechanisms is unclear. In the "Trigger and Mechanisms of Myocardial Infarction" (TRIMM) Study, 573 patients (61 +/- 10 years; 74% male) underwent a systematic interview within 2 weeks after myocardial infarction. From 8.00 to 11.00 a.m. (peak) the relative risk of myocardial infarction was 1.9 (1.6-2.3). After statistical adjustment for individual wake-time the relative risk during the initial 3 hours after awakening was 2.7 (2.2-3.3). In 24 hour studies at platelet aggregability in 10 patients with CAD the threshold concentration of ADP (from 4.8 +/- 0.8 to 2.6 +/- 0.4 mumol, p less than 0.02) and epinephrine (from 7.3 +/- 2.3 to 1.8 +/- 0.9 mumol, p less than 0.02) decreased significantly between 6.00 and 9.00 a.m. indicating an increase of aggregability. The temporal coincidence of clinical events and physiological changes suggests a causal relationship. Further possible important factors in increasing the risk of CAD during the morning include the increase of blood pressure enhancing the risk of plaque rupture and of coronary tone at the same time of day. These results are important in determining the acute mechanisms of CAD and in improving its prevention.