Background:The relationship between time of onset of acute myocardial infarction (MI) and long-term clinical outcome has not been completely understood. We hypothesized that morning onset acute MI may be associated with adverse cardiac events.

Methods and Results:This study involved 663 patients who underwent primary percutaneous coronary intervention (PCI). The main outcome measures were cardiac death, recurrent acute coronary syndrome (ACS), and re-hospitalization for heart failure. Major adverse cardiac events (MACE) were defined as a composite of individual adverse outcomes. Morning onset acute MI occurred in 212 patients (32.0%); they had higher rates of recurrent ACS (13% vs. 8%, P=0.03) and MACE (21% vs. 14%, P=0.012) than the patients with other times of onset. The PCI rate for progressive lesions was also higher than for patients with other times of onset (23% vs. 14%, P=0.013). On multivariate Cox regression analysis, morning onset was an independent predictor of recurrent ACS, MACE, and PCI for progressive lesions, with adjusted hazard ratios of 1.34 (95% CI: 1.06–2.92, P=0.030), 1.51 (95% CI: 1.02–2.23, P=0.038), and 1.58 (95% CI: 1.03–2.42, P=0.037), respectively.

Conclusions:Morning onset may be associated with increased risk of recurrent ACS and coronary atherosclerosis progression.