Introduction: Particulate matter (PM) air pollution has been linked to cardiovascular morbidity and mortality with large public health burdens. Although associations between PM and subclinical autonomic and vascular changes have been shown to occur within minutes to hours, studies have been limited in their ability to investigate such short time scales for clinical cardiac events. Accurate onset time is essential for risk estimation of such short exposures, but publically available data lack this information. This study utilized unique telemedicine data to more accurately estimate the short-term effects of PM exposure in triggering acute cardiac events.
Hypothesis: We assessed the hypothesis that elevated short-term (1-24 hours) concentrations of coarse PM(2.5 to 10 μm in aerodynamic diameter, PM10-2.5) and fine PM (<2.5 μm, PM2.5) in two metropolitan areas in Israel are associated with an increased risk of clinical cardiac events.
Methods: We conducted a time-stratified case-crossover study in which cardiac events were identified using time-resolved telemedicine data from the Tel Aviv and Haifa areas, Israel, between 2002 and 2013. Calls to the telemedicine service for cardiac-related symptoms that resulted in an in-home examination by a mobile intensive care and transfer to a hospital were classified into ischemic, arrhythmia, or non-specific events. Onset time was determined by the time of a medical phone call. Ambient pollutant concentrations measured at central monitoring stations were compared between case and control periods using multivariate conditional logistic regression after adjusting for meteorology and other risk factors. We further explored sensitivity for certainty of diagnosis and effect modification by personal characteristics.
Results: A total of 7,617 telemedicine subscribers reported 12,661 (20% ischemic, 31% arrhythmic and 49% non-specific) cardiac events that resulted in an evacuation to a hospital over our 12 year period. After adjustment for confounders, a 10 μg/m3 higher PM10-2.5 concentration was associated with a greater odds of a clinical cardiac event, with the strongest associations for events due to arrhythmia (OR 1.006, 95% CI: 1.001-1.011) within 12 hours. Similar associations were found at other time points, for ischemic and non-specific cardiac events, as well as for PM2.5 but these associations often had wider confidence intervals. Risks tended to be higher for subjects who had diabetes, previous ischemic heart disease or were obese, although these differences did not achieve statistical significance.
Conclusions: Exposure to PM air pollution over the course of hours may increase the risk of acute clinical cardiac events. Telemedicine allows for more accurate information on event onset and thus can be a powerful tool for epidemiologic studies focusing on short-term exposures to environmental or other stressors.