Review
The Potential Cardiotoxic Effects of Exercise

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Abstract

The emerging controversy related to the potential cardiotoxic effects of high doses of intense exercise need to be considered among the much stronger evidence that supports the pleomorphic benefits of exercise as a whole. However, there is fairly compelling evidence to support the association between long-term sport practice and an increased prevalence of atrial fibrillation and the fact that this relates to a chronic altered atrial substrate. This article was designed to challenge the reader with speculative science that suggests that exercise might promote permanent structural changes in the myocardium which can, in some individuals, predispose to arrhythmias. In terms of long-term health outcomes, it would seem that these small risks are outweighed by the many other benefits of exercise, including a likely decrease in atherosclerotic vascular events, although some recent results have brought into question whether the protective benefits of exercise on vascular events also extends to high-intensity exercise training. Above all else, in this article we sought to highlight current controversies to stimulate research on the many unanswered questions. In particular, there is a lack of adequately powered prospective studies from which we can measure health outcomes and their relationship to exercise-induced cardiac remodelling.

Résumé

La nouvelle controverse relative aux possibles effets cardiotoxiques de l’exercice intensif pendant de longues périodes doit être revue à la lumière des preuves beaucoup plus probantes appuyant les nombreux bienfaits offerts par l’exercice physique en général. Il existe des preuves assez concluantes à l’effet que les sports intenses pratiqués à long terme augmentent la prévalence de la fibrillation auriculaire liée à une modification du substrat auriculaire et cet article a pour but de mettre le lecteur au défi en lui présentant l’hypothèse selon laquelle l’exercice serait susceptible d’entraîner des modifications structurelles permanentes du myocarde qui pourraient prédisposer certaines personnes à l’arythmie. Ces risques, somme toute limités, seraient toutefois amplement compensés par les bienfaits généraux de l’exercice physique, notamment la réduction des accidents vasculaires liés à l’athérosclérose, et ce, même si les résultats de certaines études récentes semblent remettre en question les bienfaits vasculaires de l’exercice intensif. Dans cet article, nous avons avant tout cherché à faire ressortir la controverse actuelle afin de stimuler l’amorce de travaux de recherche visant à fournir des réponses aux nombreuses questions qui demeurent toujours en suspens. Il y a notamment une pénurie d’études prospectives suffisamment importantes pour pouvoir mesurer les effets de l’exercice sur la santé et son association avec le remodelage cardiaque induit par l’exercice.

Section snippets

Nonlinear Dose-Response Relationship With Exercise

The benefits of exercise are most clearly established for low- and moderate-intensities. As described by Blair et al.,6 all-cause mortality decreases progressively with fitness but there appears to be an “asymptote of benefit” at an intensity that represents only approximately 50% of a well trained athlete's capacity.7 This is reinforced by recent large studies in male and female cohorts that have reported little or no additional benefit from performing daily strenuous exercise as opposed to

Improved Mortality in Athletes, but What About Morbidity? Is Endurance Exercise Associated With Arrhythmias?

There is increasingly convincing evidence that long-standing endurance training might promote some cardiac arrhythmias. The range and risk of arrhythmias are discussed in an accompanying review in this issue of the Canadian Journal of Cardiology14 and is also summarized in Figure 2. Almost all studies have observed an association between atrial fibrillation (AF) in middle-aged men and previous endurance sport participation.18, 20, 21, 22, 23, 24, 25, 26 This has not been observed in female

What Predisposes Athletes to Arrhythmias? Potential Mechanisms

If we accept the fairly consistent evidence that reports an increase in AF among athletes then we are left to consider the potential mechanisms. The concept of lone AF (AF in the absence of associated cardiopulmonary or other comorbid disease) is considered a historical concept by many investigators who note that there is an expanding list of pathological associations with AF such as obesity, sleep apnea, and subclinical cardiomyopathies, which are each associated with subtle abnormalities in

Chronic Cardiac Remodelling as a Consequence of Repeated Bouts of Injury

Transient increases in high-sensitivity troponin and B-type natriuretic peptide have been observed in almost all recent studies of athletes who perform intense endurance exercise.42 These biomarkers are relatively specific markers of myocyte damage and hemodynamic stretch, respectively, but their identification does not necessarily equate to permanent myocardial damage. Many of the body's adaptive mechanisms are a result of transient tissue damage, which is subsequently repaired in a manner

Exercise-Induced or Gene-Elusive Arrhythmogenic RV Cardiomyopathy

Two questions arise from the observation of disproportionate RV injury after an acute bout of intense exercise: (1) why the right ventricle?; and (2) are there any long-term consequences? The potential mechanisms that might explain the susceptibility of the right ventricle to exercise-induced strain and injury have been reviewed extensively elsewhere.50 In brief, studies that have compared LV and RV hemodynamics during exercise have measured greater proportional increases in work and wall

Is the Risk of Ischemic Heart Disease Increased With Intense Exercise?

There is no topic in which the paradox between the benefits of low- and moderate-intensity exercise and the potential risk of high-intensity exercise would seem more diametrically opposed. Exercise represents a powerful therapy in coronary artery disease prevention, SCD, and is a positive modulator of coronary risk factors including hypertension, hyperglycemia, and dyslipidemia.61 Against this wealth of evidence there is a small body of literature that asserts that long-term endurance training

Conclusions

Against a backdrop of overwhelming and pleomorphic benefits of exercise, in this report we aimed to challenge the reader with some emerging controversies regarding potential cardiotoxic effects of exercise. In Figure 3, we attempt to provide some context for the controversies discussed to this point and the relative strength of evidence to support them. Many of these emerging controversies are on the basis of small cross-sectional cohort studies and small mechanistic studies, which are dwarfed

What Is Needed?

Much of the discussion regarding the relative risks and benefits of long-term endurance sports training is hijacked by definitive media-grabbing statements, which have fueled an environment in which one might be criticized for even questioning the benefits of exercise. The answers regarding the healthfulness of ‘extreme’ exercise is not complete and there are valid questions being raised. Because this is a question that affects such a large proportion of society it is something that deserves

Funding Sources

Dr La Gerche is supported by a Career Development Fellowship from the National Health and Medical Research Council of Australia and a Future Leader Fellowship from the National Heart Foundation of Australia.

Disclosures

The author has no conflicts of interest to disclose.

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