Lower Framingham risk score and the absence of hypertension are associated with the morning peak in the circadian variation of ST-elevation myocardial infarction onset.

There are few studies analyzing the influences of coronary risk factors on the circadian variation of ST-elevation myocardial infarction (STEMI). Between 2008 and 2011, 293 patients were admitted to Miyazaki Prefectural Nobeoka Hospital with STEMI. The onset time of STEMI was identified in 280 patients (age, 70.5±11.7 years; male subjects, 68%; hypertension (HT), 80%; diabetes mellitus, 28%; current smoking (cSM), 33%; Framingham risk score (FRS), 8.77±3.28). The day was divided into six 4-h periods, with the morning peak between 0800 and 1200 hours. The frequency of HT was significantly lower in the morning incidence group than in the nighttime incidence group. Multivariate logistic regression analysis revealed that the prevalence of HT was the only independent variable associated with the morning peak of STEMI (odds ratio (OR), 0.43; 95% confidence interval (95% CI), 0.23-0.83; P=0.01) and that cSM was significantly associated with the nighttime peak of STEMI (OR, 1.96; 95% CI, 1.01-3.80; P=0.04). A comprehensive evaluation using the FRS showed that the FRS was significantly lower in the morning incidence group than in the nighttime incidence group and the other time incidence group (7.95±3.47 vs. 9.14±2.89 vs. 9.06±3.25, P<0.01), and that having a lower FRS was associated with the morning peak of STEMI (OR, 1.12; 95% CI, 1.02-1.21; P=0.01). A lower FRS and non-HT status are associated with the morning peak in the circadian variation of STEMI onset. The morning incidence of STEMI might be affected by pathogenic factors other than the classic coronary risk factors.