Night-time Infarction Increases the Risk of Left Ventricular Systolic Dysfunction

Diurnal variation in the onset of acute myocardial infarction has been demonstrated with a peak in the morning. Few data are available about the occurrence of left ventricular systolic dysfunction according to the time of infarct.
We performed a prospective cohort study that included 100 patients with acute myocardial infarction (AMI). Left ventricular systolic dysfunction (LVSD) was defined by echocardiography when ejection fraction (EF) was less than 55%. Of these patients, 72 (72%) had EF < 55%, and 37 of them experienced myocardial
infarction between 6 AM and 5:59 PM (group 1) and 63 (63%) experienced their AMI between 6PM and 5:59 AM (Group 2). Left ventricular EF less than 55% occurred in 22 (30.6%) patients of group 1 compared with 50 (69.4%) patients in group 2 (p=0.04). Mild, moderate and severe LVSD were also more frequent in group 2 patients (p=0.01). The risk of mild, moderate and severe left ventricular systolic dysfunction after AMI is higher among infarctions that occur at night