Modifiers of timing and possible triggers of acute myocardial infarction in the thrombolysis in myocardial infarction phase II (TIMI II) study group

AbstractObjectives. The aim of this study was to provide insight into the mechanism of acute myocardial infarction by determining the modifiers of timing and possible triggers of onset of infarction.Background. A higher frequency of onset of acute myocardial infarction has been reported in the morning with a peak in the 1st 3 h after awakening. This observation suggests that the onset of infarction may be triggered by activity in the morning and at other times ot the day.Methods. The clinical history of the 3,339 patients entered into the Thrombolysis in Myocardial Infarction phase II study was analyzed to determine characteristics predicting a higher frequency of infarction between 6 amand noon, and onset of infarction during exertion.Results. A higher proportion (34.4%) of infarctions began in the morning (6 amto noon) compared with other limes of the day. Characteristics independently predicting a higher frequency between 6 amto noon were no beta-adrensrgic blocking agent use in the 24 h before infarction, no discomfort other than the index pain in the preceding 48 h, occurrence of the infarction on a weekday and no history of current smoking.In 18.7% of patients, infarction occurred during moderate or marked physical activity. Independent predictors cf exertion-related infarction included male gender, bo history of current smoking, while race, no use of calcium channel blocking agents or nitrates in the preceding 24 h, the absence of either chest pain at rest in the 3 weeks before infarction or any pain in the preceding 48 h, the absence of new onset angina and the presence of exertional pain in the preceding 3 weeks. Compared with patients whose infarction occurred at rest or during mild activity, those with exertion-related infarction had fewer coronary vessels with ≥60% stenosis (p = 0.002) and were more likely to have an occluded infarct-related vessel after thrombolytic therapy (p = 0.01).Conclusions. Further study of the timing and activity at onset of infarction may provide insight into the pathophysiologic mechanisms causing acute myocardial infarction and provide clues to preventive measures