Fine and Coarse Particulate Matter Exposures and Associations with Acute Cardiac Events among Participants in a Telemedicine Service: A Case-Crossover Study

BACKGROUND: Subclinical cardiovascular changes have been associated with ambient particulate matter (PM) exposures within hours. Although the U.S. Environmental Protection Agency continues to look for additional evidence of effects associated with sub-daily PM exposure, this information is still limited because most studies of clinical events have lacked data on the onset time of symptoms to assess rapid increased risk. OBJECTIVE: Our objective was to investigate associations between sub-daily exposures to PM and acute cardiac events using telemedicine data. METHODS: We conducted a case-crossover study among telemedicine participants >= 50 y of age who called a service center for cardiac-related symptoms and were transferred to a hospital in Tel Aviv and Haifa, Israel (2002-2013). Ambient PM2.5 and PM10-2.5 measured by monitors located in each city during the hours before the patient called with symptoms were compared with matched control periods. We investigated the sensitivity of these associations to more accurate symptom onset time and greater certainty of diagnosis. RESULTS: We captured 12,661 calls from 7,617 subscribers experiencing ischemic (19%), arrhythmic (31%), or nonspecific (49%) cardiac events. PM concentrations were associated with small increases in the odds of cardiac events, For example, odds ratios for any cardiac event in association with a 10-mu g/m(3) increase in 6-h and 24-h average PM2.5 were 1.008 [95% confidence interval (CI): 0.998, 1.018] and 1.006 (95% CI: 0.995, 1.018), respectively, and for PM10-2.5 were 1.003 (95% CI: 1.001, 1.006) and 1.003 (95% CI: 1.000, 1.007), respectively. Associations were stronger when using exposures matched to the call time rather than calendar date and for events with higher certainty of the diagnosis. CONCLUSIONS: Our analysis of telemedicine data suggests that risks of cardiac events in telemedicine participants >= 50 y of age may increase within hours of PM exposures.