Temporal analysis of acute myocardial infarction in Ontario, Canada

Acute myocardial infarction (AMI) is a substantial cause of morbidity and mortality in Canada. Evidence suggests that the incidence and mortality of AMI increase in the winter. Determining the strength and nature of seasonality patterns in relation to age and sex may be helpful in health care planning.

To examine the seasonal patterns of AMI hospital admissions by age and sex, to assess the strength of the seasonal patterns and to examine the overall trends in admissions.

A retrospective population-based study was conducted to assess temporal patterns in 14 years of hospital admissions for AMI (from April 1, 1988, to March 31, 2002) in Ontario. Seasonality was assessed using the autoregression coefficient (R2Autoreg), and Fisher's Kappa and Bartlett's Kolmogorov-Smirnov tests.

There were 271,321 people in the cohort, of whom 63% (n = 171,546) were male and 37% (n = 99,775) were female. There was an increase in AMI admissions since 1988 that reached a plateau in 1992, which was attributable mostly to the increased rate in the oldest age groups (70 years and older), where admission rates more than doubled. An association between seasonality and AMI admissions was found in most age and sex groups, with men consistently exhibiting a stronger seasonality pattern. The greatest difference in the cohort, 2.5 per 100,000 per month (134 admissions), occurred between December and September (13.64 per 100,000 in September versus 16.14 per 100,000 in December).

AMI admissions show seasonality patterns, which are more pronounced in men. Although statistically significant, the seasonal differences are small in terms of absolute numbers, and are likely irrelevant in health care planning.