METHODS: Six databases were searched to identify studies analyzing the association between OHCA and the main air pollutants. We summarized the pooled estimates using random-effect models. Heterogeneity within studies was assessed using Cochran\'s Q and I2 statistics. Funnel plots, Egger\'s regression test and Begg\'s rank correlation method were constructed to evaluate publication bias. Subgroup analyses and sensitivity analyses were also conducted to evaluate the potential sources of heterogeneity.
RESULTS: A total of 15 studies met the inclusion criteria. PM10, PM2.5, NO2 and O3 were found to be significantly associated with increase in OHCA risk (PM10 1.021, 95%CI: 1.006-1.037; PM2.5 1.041, 95%CI: 1.012-1.071; NO2 1.015, 95%CI: 1.001-1.030 and O3 1.016, 95%CI: 1.008-1.024). The acute exposure to SO2 and CO was not associated with the incidence of OHCA. Additional analyses verified the findings in the overall analyses except SO2 and NO2. Population attributable fractions for PM10, PM2.5, and O3 were 2.1%, 3.9% and 1.6%, respectively.
CONCLUSIONS: The current evidence confirmed the associations between short-term exposure to PM2.5, PM10 and O3 and a high risk of OHCA, with the strongest association being observed for PM2.5.