Abstract
BACKGROUND: Ambient temperature is a key environmental factor influencing cardiovascular health. In patients with atrial fibrillation (AF), seasonal variations may affect the risk of clinical events and mortality. We aimed to assess the impact of summer heat on adverse cardiovascular events in anticoagulated AF patients. METHODS: In this prospective study, we included anticoagulated AF patients from two Spanish cohorts located in cities with differing climates: Murcia and Vigo. We followed patients for two years, recording ischaemic stroke/transient ischaemic attack (TIA), major bleeding, major adverse cardiovascular events (MACE), cardiovascular death, and all-cause death. RESULTS: We included 13 629 AF patients, with a median age of 78 years (interquartile range = 71-83), of which 53.4% were female. In both cities, summer was associated with significantly lower incidence rate ratios for MACE, cardiovascular death, and all-cause death compared with other seasons (all P < 0.05). In Murcia, summer was linked to a lower risk of ischaemic stroke/TIA (adjusted hazard ratio (aHR) = 0.58; 95% confidence interval (CI) = 0.35-0.96), MACE (aHR = 0.63; 95% CI = 0.45-0.89), cardiovascular death (aHR = 0.32; 95% CI = 0.19-0.56), and all-cause death (aHR = 0.41; 95% CI = 0.30-0.56) compared with winter. In Vigo, summer was associated only with a reduced risk of all-cause death (aHR = 0.65; 95% CI = 0.56-0.76) compared to winter. When comparing summers, Murcia showed an increased risk of ischaemic stroke/TIA (aHR = 3.58; 95% CI = 1.98-6.45) and MACE (aHR = 1.86; 95% CI = 1.33-2.61) compared with Vigo. CONCLUSIONS: Summer was associated with a lower risk of adverse cardiovascular events compared with winter in patients with AF living in heat-adapted cities. However, extreme heat was associated with a significantly increased cardiovascular risk.