SEASONAL DISTRIBUTION OF ACUTE MYOCARDIAL-INFARCTION IN THE 2ND NATIONAL REGISTRY OF MYOCARDIAL-INFARCTION

Objectives. This observational study sought to determine whether cases of acute myocardial infarction (AMI) reported to the second National Registry of Myocardial Infarction (NRMI-2) varied by season. Backgroun d, The existence of circadian variation in the onset of AMT is well es tablished. Examination of this periodicity has led to new insights int o pathophysiologic triggers of atherosclerotic plaque rupture. Althoug h a seasonal pattern for mortality from AMI has been previously noted, it remains unclear whether the occurrence of AMI also displays a seas onal rhythmicity, Documentation of such a pattern may foster investiga tion of new pathophysiologic determinants of plaque rupture and intrac oronary thrombosis. Methods. We analyzed the number of cases of AMI re ported to NRMI-2 by season during the period July 1, 1994 to July 31, 1996, Data were normalized so that seasonal occurrence of AMI was repo rted according to a standard 90-day length. Results. A total of 259,89 1 cases of AMI were analyzed during the study period. Approximately 53 % more cases were reported in winter than during the summer. The same seasonal pattern (decreasing occurrence of reported cases from winter to fall to spring to summer) was seen in men and women, in different a ge groups and in 9 of 10 geographic areas. In-hospital case fatality r ates for AMI also followed a seasonal pattern, with a peak of 9% in wi nter, Conclusions. The present results suggest that there is a seasona l pattern in the occurrence of AMIs reported to NRMI-2 that is charact erized by a marked peak of cases in the winter months and a nadir in t he summer months. This pattern was seen in all subgroups analyzed as w ell as in different geographic areas. These findings suggest that the chronobiology of seasonal variation in AMI may be affected by variable s independent of climate.