Heat: The Unseen Heart Threat

Singapore braces for hotter days ahead, with annual mean temperatures projected to rise, according to the National Environment Agency, by an additional 0.6 to five degree Celsius by the end of the century.

Heat-related illnesses (HRI) could develop if the body is unable to regulate its temperature in response to heat and humidity, and these illnesses could be mild or severe. Heatstroke is the most serious HRI. It could cause permanent disability or death if emergency treatment is not available^{1, 2}.

Symptoms of HRIs
The symptoms of an HRI could vary. In mild cases, the symptoms could include sweating, weakness, fainting, dizziness, nausea, and elevated body temperature^1,2. Severe cases (i.e., heatstroke) could cause confusion, loss of consciousness, very high body temperature (more than 40℃) and organ damage.

HRI Prevention
HRI could be prevented if and when the person keeps hydrated, takes precautions while exercising in hot and humid environments, and gets sufficient rest. When exposed to hot and humid environments, it is essential that you keep hydrated and cool, seek shade and dress for the weather. Breathable, light-coloured fabrics and relaxed clothing styles help repel heat. Cooling solutions such as cooling vests, or immersing the foot or arm in cool water or ice slurry could also be helpful³.

Take immediate action if you notice HRI symptoms in yourself or others. Move the person to a cooler place, and call for medical help. Try to bring the person’s body temperature down by fanning him/her, or by using cooling devices or cool water. If the person loses consciousness, he/she might be suffering a heatstroke. Immediately call 995 for an ambulance1.

Vulnerable Population
There are mainly two groups that are at higher risk for HRI and heatstroke. The first is the relatively younger population who are engaged in sports, outdoor activity or those who work in a hot and humid environments. Data from the Singapore General Hospital showed that 63% of patients with HRI were between 18 and 64 years old. These incidents of HRI happened on weekends and in daytime⁴; some of these incidents were related to sports events. The other vulnerable people are older adults. In Japan, more than half of the patients with HRI were aged 65 and over⁵. Similar trends were also observed in South Korea, North America and EU countries^6-8. As Singapore is facing a rapidly aging population, we need to pay special attention to our elderly people. Moreover, research shows that people with comorbidity, people living with poverty, and people isolated in low-cost housing have higher risk of mortality because of HRI⁹.

Exposure to heat poses a significant risk to heart patients. Individuals with cardiovascular conditions, such as heart failure, are particularly vulnerable as their heart might struggle to manage heat stress in a hot and humid environment². Furthermore, a known unintended effect of commonly prescribed drugs for cardiovascular disease (CVD) such as antihypertensive, antiarrhythmic drugs, or diuretics², reduce sweating – an essential method for the body to reduce heat. Therefore, heart patients should pay attention to their condition when they are under prolonged exposure to heat.

Exposure to heat may also trigger a cardiovascular event. Studies have shown a significant association between every 1°C increase in temperature and a 2.1% increase in CVD-related mortality¹⁰. This 1°C rise in temperature has also been associated with a marked increase in morbidity due to arrhythmias, cardiac arrest and coronary heart disease. Heatwaves have also been associated with a 11.7% increase in risk of CVD-related mortality. In addition, studies have indicated that people living in tropical climate zones are more vulnerable to CVD-related mortality because of high temperatures¹⁰. It is thus essential for people with cardiovascular risk factors to avoid prolonged exposure to hot and humid environments.

As Singapore faces rising temperatures because of climate change, and the challenge of an increasingly older population, we could expect a higher number of people suffering from HRIs. Fortunately, taking appropriate preventive measures could help reduce the occurrence of heatstroke and other heat-related issues. Prevention is especially important for vulnerable groups like athletes, outdoor workers, and those with pre-existing heart conditions; these groups certainly require additional precautions in hot weather.

Article is contributed by Dr Yohei Okada, Visiting Research Fellow, Office of Research, Duke-NUS Medical School; and Prof Marcus Ong , Senior Consultant, Director of Research and Clinician Scientist at the Department of Emergency Medicine in Singapore General Hospital. Prof Marcus is also the Director for the Unit for Pre-hospital Emergency Care in Ministry of Health, Singapore, and a Committee Member of the Heart Safe Committee at the Singapore Heart Foundation.

References:

1. Sorensen, C., & Hess, J. (2022). Treatment and Prevention of Heat-Related Illness. The New England Journal of Medicine, 387(15). https://doi.org/10.1056/NEJMcp2210623
2. (2022, May 13). Heat Stress – Heat Related Illness. Centres for Disease Control and Prevention. Retrieved April 2, 2024, from https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
3. (2021, September 19). Staying cool sustainably. The Lancet. Retrieved April 2, 2024, from https://www.thelancet.com/infographics-do/cooling-strategies
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8. Gossack-Keenan K, Yeom DS, Kanu J, Hau JP, Rosychuk RJ, Clark D, et al. Heatstroke presentations to urban hospitals during BC’s extreme heat event: lessons for the future. Cjem. 2024;26(2):111-8.
9. Romanello M, Napoli Cd, Green C, Kennard H, Lampard P, Scamman D, et al. The 2023 report of the Lancet Countdown on health and climate change: the imperative for a health-centred response in a world facing irreversible harms. The Lancet. 2023;402(10419):2346-94.
10. Liu J, Varghese BM, Hansen A, Zhang Y, Driscoll T, Morgan G, et al. Heat exposure and cardiovascular health outcomes: a systematic review and meta-analysis. The Lancet Planetary Health. 2022;6(6):e484-e95.