Hourly air pollution exposure and the onset of symptomatic arrhythmia: an individual-level case–crossover study in 322 Chinese cities

BACKGROUND: Few studies have explored the relationship between air pollution and arrhythmia onset at the hourly level. We aimed to examine the association of exposure to air pollution with the onset of acute symptomatic arrhythmia at an hourly level. METHODS: We conducted a nationwide, time-stratified, case–crossover study in China between 2015 and 2021. We obtained hourly information on the onset of symptomatic arrhythmia (including atrial fibrillation, atrial flutter, atrial and ventricular premature beats and supraventricular tachycardia) from the Chinese Cardiovascular Association Database — Chest Pain Center (including 2025 certified hospitals in 322 cities). We obtained data on hourly concentrations of 6 air pollutants from the nearest monitors, including fine particles (PM(2.5)), coarse particles (PM(2.5–10)), nitrogen dioxide (NO(2)), sulfur dioxide (SO(2)), carbon monoxide (CO) and ozone. For each patient, we matched the case period to 3 or 4 control periods during the same hour, day of week, month and year. We used conditional logistic regression models to analyze the data. RESULTS: We included a total of 190 115 patients with acute onset of symptomatic arrhythmia. Air pollution was associated with increased risk of onset of symptomatic arrhythmia within the first few hours of exposure; this risk attenuated substantially after 24 hours. An interquartile range increase in PM(2.5), NO(2), SO(2) and CO in the first 24 hours after exposure (i.e., lag period 0–24 h) was associated with significantly higher odds of atrial fibrillation (1.7%–3.4%), atrial flutter (8.1%–11.4%) and supraventricular tachycardia (3.4%–8.9%). Exposure to PM(2.5–10) was associated with significantly higher odds of atrial flutter (8.7%) and supraventricular tachycardia (5.4%), and exposure to ozone was associated with higher odds of supraventricular tachycardia (3.4%). The exposure–response relationships were approximately linear, without discernible concentration thresholds. INTERPRETATION: Exposure to air pollution was associated with the onset of symptomatic arrhythmia shortly after exposure. This finding highlights the importance of further reducing air pollution and taking prompt protective measures for susceptible populations during periods of elevated levels of air pollutants.