The relationships between ambient PM2.5 and PM10 and arrhythmia and the effect modification by cigarette smoking were investigated. Data from EPA air quality monitors and an established national-scale, log-normal kriging method were used to spatially estimate daily mean concentrations of PM at addresses of 57,422 individuals from 59 examination sites in 24 US states in 1999-2004. The acute and subacute exposures were estimated as mean, geocoded address-specific PM concentrations on the day of, 0-2 days before, and averaged over 30 days before the ECG (Lag0; Lag1; Lag2; Lag1-30). At the time of standard 12-lead resting ECG, the mean age (SD) of participants was 67.5 (6.9) years (84% non-Hispanic White; 6% current smoker; 15% with coronary heart disease; 5% with ectopy). After the identification of significant effect modifiers, two-stage random-effects models were used to calculate center-pooled odds ratios and 95% confidence intervals (OR, 95% CI) of arrhythmia per 10 μg/m3 increase in PM concentrations. Among current smokers, Lag0 and Lag1 PM concentrations were significantly associated ventricular ectopy (VE) - the OR (95% CI) for VE among current smokers was 2 (1.32-3.3) and 1.32 (1.07-1.65) at Lag1 PM2.5 and PM10, respectively. The interactions between current smoking and acute exposures (Lag0; Lag1; Lag2) were significant in relationship to VE. Acute exposures were not significantly associated with supraventricular ectopy (SVE), or with VE among non-smokers. Subacute (Lag1-30) exposures were not significantly associated with arrhythmia. Acute PM2.5 and PM10 exposure is directly associated with the odds of VE among smokers, suggesting that they are more vulnerable to the arrhythmogenic effects of PM
