Extreme Temperature Events, Fine Particulate Matter, and Myocardial Infarction Mortality

Abstract

BACKGROUND: Extreme temperature events (ETEs), including heat wave and cold spell, have been linked to myocardial infarction (MI) morbidity; however, their effects on MI mortality are less clear. Although ambient fine particulate matter (PM 2.5 ) is suggested to act synergistically with extreme temperatures on cardiovascular mortality, it remains unknown if and how ETEs and PM 2.5 interact to trigger MI deaths. METHODS: A time-stratified case-crossover study of 202 678 MI deaths in Jiangsu province, China, from 2015 to 2020, was conducted to investigate the association of exposure to ETEs and PM 2.5 with MI mortality and evaluate their interactive effects. On the basis of ambient apparent temperature, multiple temperature thresholds and durations were used to build 12 ETE definitions. Daily ETEs and PM 2.5 exposures were assessed by extracting values from validated grid datasets at each subject’s geocoded residential address. Conditional logistic regression models were applied to perform exposure-response analyses and estimate relative excess odds due to interaction, proportion attributable to interaction, and synergy index. RESULTS: Under different ETE definitions, the odds ratio of MI mortality associated with heat wave and cold spell ranged from 1.18 (95% CI, 1.14–1.21) to 1.74 (1.66–1.83), and 1.04 (1.02–1.06) to 1.12 (1.07–1.18), respectively. Lag 01-day exposure to PM 2.5 was significantly associated with an increased odds of MI mortality, which attenuated at higher exposures. We observed a significant synergistic interaction of heat wave and PM 2.5 on MI mortality (relative excess odds due to interaction >0, proportion attributable to interaction >0, and synergy index >1), which was higher, in general, for heat wave with greater intensities and longer durations. We estimated that up to 2.8% of the MI deaths were attributable to exposure to ETEs and PM 2.5 at levels exceeding the interim target 3 value (37.5 μg/m 3 ) of World Health Organization air quality guidelines. Women and older adults were more vulnerable to ETEs and PM 2.5 . The interactive effects of ETEs or PM 2.5 on MI mortality did not vary across sex, age, or socioeconomic status. CONCLUSIONS: This study provides consistent evidence that exposure to both ETEs and PM 2.5 is significantly associated with an increased odds of MI mortality, especially for women and older adults, and that heat wave interacts synergistically with PM 2.5 to trigger MI deaths but cold spell does not. Our findings suggest that mitigating both ETE and PM 2.5 exposures may bring health cobenefits in preventing premature deaths from MI.

Response by Xu et al to Letter Regarding Article, “Extreme Temperature Events, Fine Particulate Matter, and Myocardial Infarction Mortality”

“…The application of apparent temperature can to some extent avoid the collinearity introduced by adjusting for multiple meteorological conditions in the same statistical model. 1 As noted by Dr Čulić, our stratified analyses revealed that women were more susceptible to heat wave exposure, which was generally in line with previous studies for high temperature exposure and MI mortality. 3 However, the underlying pathophysiological mechanisms remain less clear.…”

“…We thank Dr Čulić for the interest in our study. 1 As Dr Čulić commented, there is an inevitable issue in environmental science research that meteorological conditions often correlate with each other and with air pollutants. The potential multicollinearity among different atmospheric factors often hinders researchers in distinguishing their separate effects on cardiovascular diseases.…”

Ozone, Heat Wave, and Cardiovascular Disease Mortality: A Population-Based Case-Crossover Study

“…15 As proposed in previous studies, mean exposure of the same day of death and 1 day prior, denoted as lag 0−1 day, was used as the main exposure metric in this study. 9,16,17 From the China Meteorological Administration Land Data Assimilation System (CLDAS version 2.0), we extracted grid data (spatial resolution of 0.0625°× 0.0625°) on daily 24 h mean air temperature (°C), specific humidity (kg/kg), surface pressure (mb), and wind speed (m/s), and retrieved daily 24 h mean relative humidity (%) in Jiangsu province, China during 2015−2021. 18 For each day in 2015−2021, we used daily 24 h mean air temperature (T), specific humidity (q), wind speed (w), and surface pressure (p) to calculate daily 24 h mean apparent temperature (°C; AT) by the following formula, 19,20 and built a corresponding grid data set.…”

Extreme Heat and Poor Air Quality: Dual Threats to Cardiovascular Health

“…Interventions such as increasing urban tree cover may have a synergistic benefit of mitigating the urban heat island effect (ie, greater temperature increases in urban areas compared with surrounding, less-developed areas) while reducing the concentration of particulate matter in the air. 13,14 Whether the results of the analysis by Xu et al 1 are generalizable to other geographic settings is uncertain. Both acute and chronic exposure to high levels of PM2.5 may produce adverse cardiovascular effects, and the mean exposure to ambient PM2.5 in Jiangsu province during the study period was 35.6 μg/m 3 , which is higher than typical mean levels in North America and Western Europe, but lower than mean levels in South Asia.…”