Heat Waves and Cardiovascular Events in Milan, Italy: A Geospatial Case-Crossover Approach Using Data from Emergency Medical Services

Heat waves (HWs) are becoming more frequent due to climate change. Their impact on cardiovascular (CV) health has been widely studied, and results vary depending on the disease and the geographic area. Our aim was to study this phenomenon using emergency medical service (EMS) data relevant to CV events that occurred out-of-hospital during May–Sept in 2020 and 2021 in Milan, Italy. Mean daily temperature (MDT) was computed in the city, and normal (NL), HW, or extreme HW were defined as days with MDT <90th, ≥90th, and ≥98th percentiles, respectively, resulting in 232 NL and 74 HW days, of which 16 were extreme. In total, 20,266 CV events were reported by EMS (53% in women, 55% in ≥65 yo). A case-crossover design was applied to calculate the odds ratio of the events in HW and extreme HW compared to NL days, accounting for diagnosis and geolocation. Increased odds were found for acute myocardial infarction (1.53 and 1.56), congestive heart failure (2.47 and 2.81), and intermediate coronary syndrome (2.08 and 6.11). Our study showed the potential of using EMS for analyzing the effects of HW on CV health, thus the confirming negative impact of rising temperature.