When time of day does myocardial infarction (MI, heart attack) most often occur, and what mechanisms are involved?

Updated: May 07, 2019
  • Author: A Maziar Zafari, MD, PhD, FACC, FAHA; Chief Editor: Eric H Yang, MD  more...
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Answer

MI occurs most often in the early morning hours. Mechanisms that may explain this circadian variation include the morning increase in sympathetic tone leading to increases in blood pressure, heart rate, coronary vascular tone, and myocardial contractility; the morning increase in blood viscosity, coagulability, and platelet aggregability; and the increased morning levels of serum cortisol and plasma catecholamines leading to sympathetic overactivity, thereby resulting in increased myocardial demand. [44, 45]


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