With South Africa’s summer being expected to be both wetter and hotter this year, there is a greater risk of adverse cardiovascular incidents, especially for adults with pre-existing cardiovascular diseases. Experts writing in the Canadian Journal of Cardiology discuss how extreme heat affects cardiovascular health, why health professionals should care and what recommendations they can make to minimise consequences.
Extreme heat events are predicted to become longer, more common and more severe. Some 70 000 heat-related deaths occurred during the 2003 European heatwave. Risk factors for heat-related hospitalisation include age, chronic illnesses, social isolation, some medications, and lack of access to air conditioning. Among chronic illnesses, cardiovascular diseases are often identified as a risk factor for heat-related hospitalisation and death.
The Intergovernmental Panel on Climate Change (IPCC) recently reported that global temperatures are rising at a greater rate than previously projected, and that the number of extreme heat days will significantly increase across most land regions,” said senior author Daniel Gagnon, PhD, University of Montreal. “Although we don’t yet fully understand the reasons, people with cardiovascular disease are at greater risk of hospitalisations and death during extreme heat events.”
The researchers reviewed studies and noted a consistent association between extreme heat and increased risk of adverse cardiovascular outcomes. An examination of reviews and meta-analyses on the effect of extreme heat on adverse cardiovascular outcomes showed that heatwaves significantly increase mortality risk from ischaemic heart disease, stroke, and heart failure.
“Although the effects of extreme heat on adverse cardiovascular events have been explained in the context of heatstroke, many events occur without heatstroke, and the mechanisms of these events in the absence of heatstroke remain unclear,” observed Dr Gagnon. “It is likely that heat exposure increases myocardial oxygen needs.”
One possibility is that heat exposure puts excessive strain on the heart for individuals with heart disease and that heat exposure increases the risk of blood clots forming within cardiac blood vessels.
The authors propose that preventive strategies should aim to reduce the extent of hyperthermia and dehydration. In Canada, heat-health warnings systems act as a first line of defence by raising awareness of upcoming heat events and recommending strategies to minimise possible heat complications. For example, heat warnings are issued 18-24 hours before a heat event in Ontario and Québec, when ambient temperature will remain above 30°C for a minimum of two days. Public advisories include identifying the signs of heat stress, ensuring people drink adequate amounts of cold fluid or seeking an air-conditioned environment – though for many people, this is not an option.
Recent research supports electric fan use, skin wetting and immersing the feet in tap water as simple methods to stay cool during extreme heat events. “Air conditioning is the most effective strategy that can be recommended since it effectively removes the heat stimulus and minimises the risk of adverse cardiovascular outcomes,” commented Dr Gagnon. “However, less than one third of global households own air conditioning.”
More studies are needed to explain why extreme heat is linked to increased risk of adverse cardiovascular outcomes; the effect of cardiovascular medication on the human body’s physiological responses during heat exposure; the best cooling strategies in heat waves for individuals with CVD; and safe environmental limits for outdoor exercise in individuals with heart disease.
“Cardiovascular health professionals need to be aware of the negative consequences of extreme heat on cardiovascular health. A better awareness and understanding of the cardiovascular consequences of extreme heat, and of the measures to take to prevent and mitigate adverse events, will help us all assess the risk and optimize the care of patients exposed to an increasingly warm climate,” concluded Dr Gagnon.