Particulate Air Pollution and Risk of ST-Segment Depression During Repeated Submaximal Exercise Tests Among Subjects With Coronary Heart Disease

Abstract

Background— Daily variations in ambient particulate air pollution have been associated with cardiovascular mortality and morbidity. We therefore assessed the associations between levels of the 3 main modes of urban aerosol distribution and the occurrence of ST-segment depressions during repeated exercise tests. Methods and Results— Repeated biweekly submaximal exercise tests were performed during 6 months among adult subjects with stable coronary heart disease in Helsinki, Finland. Seventy-two exercise-induced ST-segment depressions >0.1 mV occurred during 342 exercise tests among 45 subjects. Simultaneously, particle mass <2.5 μm (PM2.5) and the number concentrations of ultrafine particles (particle diameter 10 to 100 nm [NC 0.01–0.1 ]) and accumulation mode particles (100 to 1000 nm [NC 0.1–1 ]) were monitored at a central site. Levels of particulate air pollution 2 days before the clinic visit were significantly associated with increased risk of ST-segment depression during exercise test. The association was most consistent for measures of particles reflecting accumulation mode particles (odds ratio 3.29; 95% CI, 1.57 to 6.92 for NC 0.1–1 and 2.84; 95% CI, 1.42 to 5.66 for PM2.5), but ultrafine particles also had an effect (odds ratio 3.14; 95% CI, 1.56 to 6.32), which was independent of PM2.5. Also, gaseous pollutants NO 2 and CO were associated with an increased risk for ST-segment depressions. No consistent association was observed for coarse particles. The associations tended to be stronger among subjects who did not use β-blockers. Conclusions— The present results suggest that the effect of particulate air pollution on cardiovascular morbidity is at least partly mediated through increased susceptibility to myocardial ischemia.