Spikes in air pollution could cause more people to need surgery to clear blocked arteries, research suggests.
Researchers in Poland found rates of angioplasty procedures are more common when levels of tiny pollutants increase.
The life-changing procedures also occur more in winter – the most polluted time of the year, according to the study.
Doctors at the University Hospital in Krakow used data from nearly 16,000 patients who had undergone the operation.
Angioplasties, which involve placing a stent in narrow or blocked arteries, are often emergency procedures after a heart attack.

Researchers in Poland found rates of angioplasty procedures are more common in areas plagued by toxic air
Almost two thirds of the volunteers lived in polluted cities, which were plagued by high levels of a tiny pollutant called PM10.
PM10, particles ten micrometers or less in diameter, can be inhaled deep into the lungs where they irritate the lining and enter the bloodstream.
Sources include industrial processes like iron making and quarrying, lawn mowing, wood and coal stoves, bushfires, dust storms, and vehicle exhaust emissions.
Average concentrations were 50.95 μg/m3 – well above the guideline limit by the World Health Organization of 20μg/m3.
In contrast, the other third of participants came from unpolluted cities, which had PM10 levels of 26.62 μg/m3, on average.
The researchers compared the air quality on the date of the procedures – which are often dished out in an emergency – with the average over the course of a year.
In both polluted and unpolluted cities, a rise in PM10 concentration was significantly associated with a greater frequency of the procedure.
Every 1μg/m3 increase in PM10 concentration was linked to an additional 0.22 stent procedures per week in the cleaner cities.
This was the equivalent of 2.2 extra procedures every 10 weeks. For polluted cities, the rate was 0.18 per week – 1.8 extra every 10 weeks.
The researchers also analysed how rates of angioplasties varied between the winter and other seasons.
They found the procedure was much more common in the colder months, in both the polluted and clean cities.
‘The higher incidence in winter is related to greater air pollution during this period,’ said study author Dr Rafal Januszek.
He added: ‘This is due to several factors such as artificial heating and the resulting smog.
‘The study shows that the incidence of acute coronary syndromes treated with PCI was higher in winter and rose along with increasing pollution.
‘This is further evidence that more needs to be done to lower pollution levels and protect the public’s health.’
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, said: ‘Air pollution is a public health emergency and is responsible for up to 11,000 heart and circulatory deaths every year in the UK alone.
‘This latest research shows that a rise in urban air pollution increases the number of people admitted to hospital for heart attack.
‘This extends the findings from recent studies that show a significant increase in exposure to airborne pollution in cities is linked with a small, but detectable, increase in deaths – the majority of which are caused by heart and circulatory diseases.
‘This was noticeable in cities with both good and poor air quality, when pollution was highest, emphasising the importance of introducing stricter standards to reduce deaths caused by urban air pollution.
‘Currently, the UK subscribes to EU guidelines on air pollution, which are far more lenient than those set out by the World Health Organisation.
‘We desperately need to see the Government protect the nation’s health by setting out a clear and robust plan to adopt these stricter guidelines by 2030.’
The findings will be presented at the European Society of Cardiology’s Congress 2019 in Paris.