Acute heart failure: here’s how extreme heat and cold increase the risk

‘No study had previously analysed, in a Nordic population, the short-term associations between events characterised by extreme temperatures – such as periods of intense cold and heatwaves – or persistently sub-optimal ambient temperatures, and the risk of hospitalisation for heart failure – says Wenli Ni, first author of the study and a postdoctoral researcher at the Centre for Climate, Health, and the Global Environment at the Harvard T.H. Chan School of Public Health –. ‘This is a significant knowledge gap, given that high-latitude areas, such as Sweden, are characterised by frequent exposure to cold but, at the same time, are developing an emerging vulnerability to high temperatures—to which they have not yet adapted—as the global climate continues to warm.’

American researchers analysed 482,000 hospital admissions for heart failure recorded in the Swedish National Patient Register (Sweden is renowned for its health ‘registers’, which, in the age of data mining and artificial intelligence, represent a real treasure trove), between 2006 and 2021.

Periods of intense cold were defined as at least two consecutive days with daily temperatures at or below the 5th percentile, between October and March, whilst ‘heatwaves’ were defined as periods with temperatures at or above the 95th percentile between April and September, relative to the specific temperatures for each municipality.

Periods of extreme cold have been found to be associated with an increased risk of hospital admission for heart failure within 2–6 days of exposure (with peaks between the third and fifth day).

In the case of exposure to high temperatures, however, the increased risk of heart failure is evident within 0–3 days.

According to the authors, the risk of ‘delayed-onset’ hospitalisation following exposure to low temperatures – as opposed to the more immediate risk associated with high temperatures – highlights the need for timely intervention. These should include monitoring patients following cold weather alerts and even faster response strategies during heatwaves.

“We can no longer practise cardiovascular medicine in a meteorological vacuum,” comments Tiantian Li, deputy director of the National Institute of Environmental Health at the Chinese Centre for Disease Control and Prevention in Beijing, in an accompanying editorial.

“There is now substantial evidence linking sub-optimal temperatures to cardiovascular damage. The mission of scientific research can no longer be limited to simply accumulating further epidemiological associations: the time has come to transform this data into an operational early-warning system,” urges Li.

This invitation was accepted by the European Society of Cardiology, which organised a session dedicated to ‘Environmental cardiology: from exposure to action’ as part of its annual congress.