Poor air quality puts a short-term strain on the heart | Breaking news for doctors, nurses and pharmacists


Exposure to elevated concentrations of small particles appears to immediately increase the risk of out-of-hospital cardiac arrest (OHCA), which decreases a few days after exposure, according to data from the Pan-Asian Resuscitation Outcomes Study (PAROS) conducted in Singapore.

For every 10 μg/m3 increase in PM2.5increased the OHCA risk by about 2 percent (relative risk [RR]1.022, 95 percent confidence interval [CI], 1.002–1.043), a trend that continued through the first 2 days. However, this risk subsequently decreased over the next 3 days (days 3-5; RR, 0.976, 95 percent CI, 0.955-0.998). [Lancet Public Health 2022;7:e932-e941]

In particular, the connection between increasing PM2.5 Concentration and OHCA 0-2 days after exposure was determined by cardiac arrest rhythm (non-shockable: RR, 1.027, 95 percent CI, 1.004-1.050 vs. shockable: RR, 1.002, 95 percent CI, 0.956-1.051) and location the OHCA (at home: RR, 1.033, 95 percent CI, 1.008-1.057 vs. away: RR, 0.955, 95 percent CI, 0.957-1.035).

“One possible explanation for the short-term increase in risk is a harvesting effect, i.e. an increase in particulate matter2.5 The concentration used to trigger OHCA in those who were compromised and likely later would have suffered cardiac arrest,” said PAROS researchers from Duke-NUS Medical School, Singapore.

“After this initial harvesting effect within the first few days of exposure, the number of cases of OHCA may decrease as the susceptible population has decreased,” they added.

In hypothetical scenarios, investigators found that the number of OHCA events related to PM2.5 could be reduced by 8 percent and 30 percent for 1 and 3 μg/m, respectively3 PM reduction2.5 concentrations or

“Public health strategies to reduce PM2 5 Concentrations could reduce the population’s exposure to out-of-hospital cardiac arrest and reduce demand for PM2.5-Relatable emergency medical services,” they said.


The analysis included 18,131 people who had experienced OHCA over a period of 8 years (2010-2018). The median age of the cohort was 65 years, and 11,647 (64.2 percent) were males. In terms of ethnicity, 12,270 (67.7 percent) were Chinese, 2,873 (15.8 percent) were Malay, and 2,010 (11.1 percent) were Indian.

exposure to pm10Ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2) had no zero effect on OHCA risk at any time point. Meanwhile, carbon monoxide (CO) was associated with a cumulative reduced risk of OHCA over days 0–5 after exposure (RR, 0.876, 95 percent CI, 0.770–0.997) and on days 3–5 after exposure (RR, 0.810 , 95) associated percent CI, 0.690–0.949).

The results are consistent with another study conducted in Nanjing, China, which examined the association between PM2.5 Concentration and all-cause or cardiovascular mortality were initially positive 0-1 day post-challenge but became negative 2 days post-challenge. In addition, a separate study examining seven major cities in South Korea found the incidence of PM-related cardiovascular deaths10 increased 0-1 day after exposure, decreased within 28 days after exposure, and increased again over 0-45 days after exposure. [Chemosphere 2021;265:129035;
Int J Epidemiol

“Taken together, PM can lead to an acute increase in OHCA in the first days of exposure due to a harvesting effect, but in the medium and longer term to a real increase in OHCA incidence. Further research with longer delay times is needed to confirm this hypothesis,” the researchers said.

Underlying Mechanisms

Investigators cited multiple mechanisms for the association between PM and OHCA. First, PM could promote systemic inflammation, which subsequently leads to increased coagulation, platelet aggregation, and thrombus formation in the coronary arteries. In addition, PM can cause autonomic imbalance, which has been associated with cardiac events, sustained ventricular tachycardia, and mortality. [Transl Res 2007;149:324-332;
Circulation 2000;101:1267-1273]

“Particularly PM2.5 is more strongly associated with ST elevation myocardial infarction (STEMI) than non-STEMI… PM2.5 could trigger STEMI through increased oxidative stress and inflammatory responses, elevation of blood pressure due to endothelial dysfunction and autonomic dysfunction, and thrombosis caused by the hypercoagulable state,” they said. [Int J Environ Res Public Health 2016;13:748]

“Singapore has variability in air quality contributed by both local and non-local sources of emissions, including regional landfires. The resulting variation in air quality, in addition to Singapore’s robust monitoring, provides optimal real-world data to assess its impact on population health,” the investigators said. [Int J Cardiol 2018;271:352-358]

Environmental Monitoring Data

In an accompanying editorial, an expert not involved in the study pointed out that PAROS had made several important contributions to the understanding of air pollution and cardiovascular disease incidence. First, increases in PM concentrations, even at low levels of air pollution, could increase the risk of OHCA. [Lancet Public Health 2022;7:e890-e891]

“Second, this research provided real-world evidence for the different types and locations of cardiac arrest events. pm2.5 Concentrations affected non-shockable OHCA events and had a lesser effect on shockable OHCA events, the cause of which remains to be determined. Eventually, investigators found the effects of increasing particulate matter pollution2 5 Concentrations were highest in the immediate 2 days after exposure, indicating an acute manifestation of OHCA due to air pollution,” wrote Prof. John Ji of Tsinghua University in Beijing, China.

Nonetheless, Ji acknowledged the existence of some issues not addressed by PAROS, as follows: “Is peak exposure or cumulative average exposure most predictive of health outcomes? In particular, for cardiovascular events, is the greatest risk within the first hour of exposure, during the day, or within a few days? Second: How do individual pollutants or pollutant mixtures affect the results?”

Ji pointed to an opportunity to use new health monitoring and sensor technologies to advance understanding of the link between air pollution and OHCA. He explained that these technologies could help provide environmental monitoring data on exposure duration, exposure severity, exposure timing, co-exposure and exposure location, which could be useful in predicting the onset of cardiac arrest at short time-lapse intervals.

“Future clinical guidelines should include air pollution assessments and ways to alert patients and providers to a pollution event to prevent medical emergencies,” he said.


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