Seasonal variation of unexpected sudden cardiac death in northern Finland.

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Data on the occurrence of unexpected sudden cardiac death (SCD) in different seasons are limited. All unexpected sudden death victims have to undergo medico-legal autopsy obligated by the Finnish law. Consecutive series of all unexpected autopsied SCD victims (n=5,869) were prospectively collected from the geographically defined area in the Northern Finland during a twenty years period from 1998 to 2017. We evaluated the seasonal variation of SCD and its possible causes. Unexpected SCD occurred more frequently during the first quarter of a year (from January to March) than during the other quarters. The occurrence of SCD during the twenty years follow-up was 4.5±0.24 during the first quarter of the year per month and 3.9±0.12 during the other quarters of the year per month on average (SCDs during the quarter of a year per month on average per 100,000 inhabitants per year, p<0.001). The weather was colder during the first quarter of the year (average temperature -9.1 degrees centigrade) than during the other quarters (average temperature +5.7 degrees centigrade). The subjects who experienced SCD during the first quarter of the year had more commonly severe (75%-90%) coronary artery stenosis, (p<0.001). Unexpected SCD occurred more commonly during the first quarter of a year (from January to March) than during the other quarters (from April to December). Cold weather with its physiological consequences and more severe coronary artery disease predisposing to ischemia may have contributed to the increased occurrence of SCD during the first quarter of the year.