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The time of onset of a heart attack determines the extent of myocardial damage
Last reviewed: 01.07.2025
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The size of infarctions and subsequent left ventricular failure vary significantly depending on the time of day the ischemia occurs, according to the first study of its kind in humans. The greatest damage to the heart occurs when heart attacks occur between 1 a.m. and 5 a.m.
In previous studies, infarct size in rodents after ischemia and reperfusion showed a circadian dependence on the timing of coronary occlusion. It was previously unknown whether there is a similar circadian dependence of infarct size in humans.
"We were trying to determine whether the time of day a heart attack starts affects the amount of damage to the heart, or whether this is a phenomenon unique to rodents," said senior study author Jay H. Travers, a cardiologist at the Minneapolis Heart Institute.
In a retrospective analysis of 1,031 patients with acute myocardial infarction, ST-elevation myocardial infarction (STEMI), the researchers identified 165 patients with a first heart attack resulting from a blocked artery without evidence of angina before the infarction.
All 165 patients had clearly defined ischemic periods. The findings were confirmed by cardiac MRI measuring infarct size, or areas of increased risk of myocardial infarction.
The researchers noted that the degree of infarction size was significantly related to the time of infarction onset. The greatest myocardial damage was observed at 1:00 a.m. from the onset of ischemia and at 5:00 a.m. from the onset of reperfusion.
"It is important to understand that the heart's ability to protect itself from more serious injury fluctuates over a 24-hour cycle. Identifying these protective changes may be particularly important for pharmaceutical manufacturers seeking to develop cardioprotective drugs," Travers explained.