Severe heat stress exposure as a hidden driver of future cardiovascular disease: a narrative review of animal and human studies.

Abstract

The cardiovascular system is particularly vulnerable to damage from severe environmental heat stress in both man and animals, particularly during exertion. However, the mechanisms underlying this vulnerability are not well understood, and the potential long-term impacts in surviving patients with sub-clinical symptoms are not well recognized in medical practice. Human case series have described cardiovascular damage in some heat injury victims but linking these to more general risks in adult healthy populations is difficult. However, in recent years, preclinical animal models in a variety of species have provided new insights into cause-and-effect outcomes, broadening our understanding of pathophysiological mechanisms, but many questions remain. This review looks at what is known about short- and long-term cardiovascular consequences of two contrasting types of heat exposures in animals. The first is passive heat lasting 24 hours or more, mimicking conditions of environmental heat waves. The second is acute, exertional heat injury, designed to mimic conditions of intense exercise in the heat as experienced by athletes, military personnel or outdoor laborers. Evidence is provided that both can induce substantial acute damage to the myocardium that could contribute to long-term cardiovascular complications. The potential mechanisms for long-term effects on the heart include direct impacts on Ca2+ regulation, metabolic control and inflammation, indirect effects from gut, kidney or endothelial damage and dyssynchronous adrenergic myocardial activation, i.e. typical of stress-induced heart disease (takotsubo syndrome). The study highlights the need for future clinical and basic research in the long-term cardiovascular risks of all forms of severe environmental heat exposures.