Environmental exposures and cardiac arrhythmias

Abstract: Cardiac arrhythmias lead to substantial mortality and morbidity world-wide. The most severe form of cardiac arrhythmia, cardiac arrest, is one of the leading causes of death in Europe and North America. Further, the prevalence of atrial fibrillation, the most common arrhythmias among adults, is expected to increase substantially during the coming decades with increased mortality and morbidity as a consequence. At present atrial fibrillation affects more than 30 million people world-wide. Ambient environmental exposures, i.e. temperature and air pollution, have a well-established association to cardiovascular disease with significant health impact. The association to cardiac arrhythmias is less well understood. The aim of this thesis was to investigate the associations between short-term exposure to ambient temperature, and air pollution with out-of-hospital cardiac arrest, hereafter referred to as cardiac arrest, and atrial fibrillation. In Study I we investigated the association between ambient temperature and cardiac arrest. The study included 5,961 cases of cardiac arrest in Stockholm. We observed a V-shaped relationship between preceding mean 24-hour and 1-hour ambient temperature and the occurrence of cardiac arrest with statistically significant associations for temperatures below the optimum temperature. In Study II we investigated the association between short-term air pollution exposures and cardiac arrest. We estimated daily air pollution levels in 1x1 km grids using a satellite-based machine learning model. Among 29,604 cases of cardiac arrests from all of Sweden we observed a higher risk associated with short-term particulate matter <2.5 μm (PM2.5) and particulate matter <10 μm (PM10) exposure. In Study III we investigated short-term air pollution exposure and risk of atrial fibrillation episodes in 75-year-olds living in Stockholm, Sweden that underwent atrial fibrillation screening. We estimated air pollution exposure by use of single fixed monitors representing urban background levels. Among 218 participants with 469 episodes of atrial fibrillation we observed increased risks associated with PM10 exposure. The associations were more pronounced for participants with overweight and diabetes. In Study IV we investigated the association between air pollution and atrial fibrillation in patients with intracardiac devices, i.e. pacemakers, able to store atrial fibrillation episodes. Air pollution exposure was assessed in a similar way as in Study III. 91 participants contributed data to the final analysis of 584 episodes of atrial fibrillation. We observed increased risk of atrial fibrillation episodes with short-term exposure to PM2.5. In conclusion, our findings indicate an increased risk of cardiac arrhythmias with exposure to ambient temperature and air pollution. We observed associations for air pollution exposure even at very low levels, below current regulatory guidelines.

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