Triggering of Myocardial Infarction by Increased Ambient Fine Particle Concentration: Effect Modification by Source Direction

Abstract : Background Previously, we reported a 18% increased odds of ST-elevation myocardial infarction (STEMI) associated with each 7.1 µg/m3 increase in PM2.5 concentration in the hour prior to MI onset. We found no association with non-ST elevation myocardial infarction (NSTEMI). We examined if this association was modified by PM2.5 source direction. Methods We used the NOAA HYbrid Single-Particle Lagrangian Trajectory (HYSPLIT) model to calculate each hourly air mass location for the 24 hours before each case or control time period in our previous PM2.5/STEMI case-crossover analysis. Using these data on patients with STEMI (n=338), hourly PM2.5 concentrations, and case-crossover methods, we evaluated whether our PM2.5/STEMI association was modified by whether the air mass passed through each of the 8 cardinal wind direction sectors in the previous 24 h. Results When the air mass passed through the West-Southwest direction (WSW) any time in the past 24 h, the odds of STEMI associated with each 7.1 µg/m3 increase in PM2.5 concentration in the previous hour (OR=1.27; 95% CI=1.08, 1.22) was statistically significantly (p=0.01) greater than the relative odds of STEMI associated with increased PM2.5 concentration when the wind arrived from any other direction (OR=0.99; 95% CI=0.80, 1.22). We found no other effect modification by any other source direction. Further, relative odds estimates were largest when the time spent in the WSW was 8–16 h, compared to ≤7 h or 17–24 h, suggesting that particles arising from sources in this direction were more potent in triggering STEMIs. Conclusions Since relative odds estimates were higher when the air mass passed through the WSW octant in the past 24 h, there may be specific components of the ambient aerosol that are more potent in triggering STEMIs. This direction is associated with substantial emissions from coal-fired power plants and other industrial sources of the Ohio River Valley, many of which are undergoing modifications to reduce their emissions.