Risk of sudden cardiac death in relation to season-specific cold spells: a case–crossover study in Finland

OBJECTIVE To test a priori hypothesis of an association between season-specific cold spells and sudden cardiac death (SCD). METHODS We conducted a case-crossover study of 3614 autopsy-verified cases of SCD in the Province of Oulu, Finland (1998-2011). Cold spell was statistically defined by applying an individual frequency distribution of daily temperatures at the home address during the hazard period (7 days preceding death) and 50 reference periods (same calendar days of other years) for each case using the home coordinates. Conditional logistic regression was applied to estimate ORs for the association between the occurrence of cold spells and the risk of SCD after controlling for temporal trends. RESULTS The risk of SCD was associated with a preceding cold spell (OR 1.33; 95% CI 1.00, 1.78). A greater number of cold days preceding death increased the risk of SCD approximately 19% per day (OR 1.19; 95% CI 1.07 to 1.32). The association was strongest during autumn (OR 2.51; 95% CI 1.27 to 4.96) and winter (OR 1.70; 95% CI 1.13 to 2.55) and lowest during summer (OR 0.42; 95% CI 0.15 to 1.18) and spring (OR 0.89; 95% CI 0.45 to 1.79). The association was stronger for ischaemic (OR 1.55; 95% CI 1.12 to 2.13) than for non-ischaemic SCD (OR 0.68; 95% CI 0.32 to 1.45) verified by medicolegal autopsy. CONCLUSIONS Our results indicate that there is an association between cold spells and SCD, that this association is strongest during autumn, when the weather event is prolonged, and with cases suffering ischaemic SCD. These findings are subsumed with potential prevention via weather forecasting, medical advice and protective behaviour.