Particulate air pollution and risk of ST-segment depression during repeated submaximal exercise tests among subjects with coronary heart disease - The exposure and risk assessment for fine and ultrafine particles in ambient air (ULTRA) study

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 occur-red during 342 exercise tests among 45 subjects. Simultaneously, particle mass <2.5 mum (PM2.5) and the number concentrations of ultrafine particles (particle diameter 10 to 100 nm [NC0.01-0.1]) and accumulation mode particles (100 to 1000 nm [NC0.1-1]) 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 NC0.1-1 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 NO2 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 beta-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.