Background: Analysis of the chronology of acute cardiovascular events may provide important pathophysiologic information. There is a circadian pattern in the onset of acute myocardial infarction (AMI) with a mid-morning peak, ascribed to the catecholamine surge that accompanies awakening and assuming the upright posture. However, in up to 27% of patients the onset of AMI occurs during sleep (without apparent precipitating factors). The reasons for this finding are unknown.
Hypothesis: The aim of the study was to determine why the onset of symptoms of AMI occurs during sleep in some individuals rather than being precipitated by known trigger factors such as physical exertion.
Methods: Using the database from a large multicenter clinical trial, patients were grouped according to whether or not they were awakened from sleep by the symptoms of AMI.
Results: In all, 870 of 3,309 patients (26%) were awakened by AMI. In general, these patients were older and sicker, with poorer left ventricular function, lower quality of life indices, more frequent heart failure, lower ejection fractions, higher incidence of angina, and a greater frequency of atrial arrhythmias. On multivariate analysis, only low ejection fraction and older age were independently associated with awakening by the symptoms of AMI.
Conclusions: Patients who are older and sicker are more likely to be awakened from sleep by the onset of symptoms of AMI. Although the reasons are unknown, we speculate that these individuals are less active and therefore less vulnerable to established trigger factors such as vigorous physical exertion.