Air pollution and ozone levels may also play a role in precipitating heart attacks, warns fresh research from the US.
Rice University (Houston) statisticians Katherine Ensor and Loren Raun analysed eight years worth of data drawn from Houston's extensive network of air-quality monitors and more than 11,000 concurrent out-of-hospital cardiac arrests (OHCA) logged by Houston Emergency Medical Services (EMS).
"The bottom-line goal is to save lives," Ensor said. "We'd like to contribute to a refined warning system for at-risk individuals. Blanket warnings about air quality may not be good enough. At the same time, we want to enhance our understanding of the health cost of pollution - and celebrate its continuing reduction."
The researchers found a positive correlation between OHCAs and exposure to both fine particulate matter (airborne particles smaller than 2.5 micrograms) and ozone, the American Heart Association journal Circulation, reports.
They found that a daily average increase in particulate matter of six micrograms per day over two days raised the risk of OHCA by 4.6%, with particular impact on those with pre-existing (and not necessarily cardiac-related) health conditions, according to a Houston statement.
For the study, OHCA events were defined as cases where EMS personnel performed chest compressions. Ensor and Raun noted that the patients died in more than 90% of the cases, which occurred more during the hot summer months (55% of total cases).
The researchers also looked at the effects of nitrogen dioxide, sulphur dioxide and carbon monoxide levels, none of which were found to impact the occurrence of OHCA.
These findings were presented at the American Association for the Advancement of Science (AAAS) conference in Boston.