Bidirectional effect modifications of temperature and PM on myocardial infarction morbidity and mortality in Beijing, China from 2007 to 2021.

Background: Ambient temperatures and PM can trigger myocardial infarction (MI), while little is known about the complex interplay between these two factors on MI, especially morbidity.

Objectives: To investigate bidirectional effect modifications of temperature and PM on MI morbidity and mortality.

Methods: A time-stratified case-crossover study was conducted utilizing high-resolution data of temperature and PM, along with 498,077 MI cases from the citywide registry in Beijing, China from 2007 to 2021. A conditional logistic regression model combined with a distributed lag non-linear model was used to examine linear and categorical effect modifications of temperature and PM on MI morbidity and mortality.

Results: The PM effect on MI morbidity, modified by temperature, showed a progressive increase of odds ratio from 1.013 (95 % CI: 1.001, 1.025) to 1.027 (95 % CI: 1.012, 1.042) with rising temperatures. Stratified analysis revealed a greater PM effect in high temperature strata (1.049, 95 % CI: 1.029, 1.069) compared with low strata (1.007, 95 % CI: 0.993, 1.021) on MI morbidity (P<0.001). The temperature effect on MI morbidity was also modified by PM, with a gradual upward risk trend observed with increasing PM concentration. Specifically, the heat wave effect was greater at high PM concentration strata (1.097, 95 % CI: 1.042, 1.155) than at low strata (0.954, 95 % CI: 0.890, 1.023) (P=0.002). The cold spell effect was greater at high PM concentration strata (1.181, 95 % CI: 1.117, 1.249) than at low strata (0.883, 95 % CI: 0.740, 1.053) (P=0.002). A similar bidirectional effect modification of temperature and PM was also found in MI mortality.

Conclusions: Temperature and PM bidirectionally modify their effect on MI morbidity and mortality. Elevated temperatures exacerbate PM effect, while increased concentrations of PM amplify temperature effect. The combined effect of temperatures and PM should be stressed, encompassing not only extreme conditions but also the entire range of exposures.