Take-Home Messages

• Evidence suggests that ultra-endurance exercise causes myocardial injury.
• Structural adaptations to exercise, particularly of the right ventricle, may predispose to tachyarrhythmias and SCD.

Moderate exercise is a powerful therapy in the treatment and prevention of cardiac disease. It helps address many of the most pressing global health concerns—obesity, diabetes, atherosclerotic heart disease, and some cancers. However, intense habitual exercise leads to cardiac adaptations for which the benefits are less clear.

The debate goes back more than 2 decades when Blair et al. first reported a reduction in CV and all-cause mortality in a large cohort of healthy middle-aged subjects but simultaneously suggested a limit beyond which further improvements in health outcomes were no longer significant.1 This outer boundary of benefit was estimated to be around 9 METS for women or 10 METS for men, an intensity that is approximately half that at which competitive endurance athletes regularly train.

Today, there is growing evidence suggesting that intense habitual exercise may not lend itself to the “more is better” dictum in regard to cardiac adaptations. André La Gerche, MBBS, PhD, a marathon runner himself, has been uncovering evidence that the heart can be damaged by endurance activities.

Endurance Activities and the Heart

Assessments soon after completion of endurance races have reported biochemical and functional cardiac abnormalities. Increases in cardiac troponin I (cTnI) and B-type natriuretic peptide (BNP) as well as LV wall motion abnormalities on echocardiography have been described.

The reports have been inconsistent, however, with some studies reporting only very mild or no evidence of cardiac dysfunction. One problem: few early studies combined both biochemical and functional assessments.

Dr. La Gerche and colleagues tested 27 athletes (20 male, 7 female) 1 week before, immediately after, and 1 week after an ultra-endurance triathlon.2 Their findings included:

• Post-race, cTnI was raised in 15 athletes (58%) and the mean value for the entire cohort increased (0.17 vs. 0.49 mg/l; p < 0.01).
• BNP rose in every athlete and the mean increased significantly (12.2 vs. 42.5 ng/l; p < 0.001).
• LVEF was unchanged but integrated systolic strain decreased (16.9% vs. 15.1%; p < 0.01).
• New regional wall motion abnormalities developed in seven athletes (27%); LVEF was reduced in this subgroup (57.8% vs. 45.9%; p < 0.001).
• RV function was reduced in the entire cohort with decreases in fractional area change (0.47 vs. 0.39; p < 0.01) and tricuspid annular plane systolic excursion (21.8 vs. 19.1 mm; p < 0.01).

At follow-up, all variables returned to baseline except in one athlete where RV dysfunction persisted. Their work uncovered three new pieces of information:

1. myocardial dysfunction is transient;
2. strain and strain rate are reliable and sensitive measures in this clinical setting; and
3. endurance exercise can induce significant RV dysfunction.

Whether these findings represent damage or part of the normal physiological process of stress, repair, and recovery is still unclear. However, La Gerche et al. recently published a paper comparing ventricular changes during exercise and whether changes influenced chronic ventricular remodeling in athletes.3 They found greater RV enlargement and greater wall thickening in athletes, which appear to be a product of disproportionate load excess.

Arrhythmias and Endurance Activities

A number of cohort studies have demonstrated an increase in atrial arrhythmias among endurance athletes, particularly when follow-up includes former athletes now middle-aged and older. In light of these studies, some argue that long-term endurance exercise may, at least in some athletes, create a substrate for arrhythmias. For example, highly trained athletes—although at much lower risk of heart disease overall—are much more prone to atrial fibrillation and atrial flutter.

Dr. La Gerche and his team reported that long-term endurance sport is a risk factor for lone atrial flutter.4 They used a database with 638 consecutive patients who underwent ablation for atrial flutter and the proportion of regular sportsmen (≥3 hours of sports practice per week) among patients with lone atrial flutter was higher than that observed in the general population (50% vs. 17%; p < 0.0001).

The proportion of sportsmen engaged in long-term endurance sports (participation in cycling, running, or swimming for ≥3 h/week) was also significantly higher in lone flutter patients than in controls (31% vs. 8%; p = 0.0003). Those flutter patients performing endurance sports had a larger left atrium than non-sportsmen (p = 0.04, by one-way analysis of variance).

The evidence supports earlier work suggesting that athletes presenting with serious arrhythmias had serious RV abnormalities. The study looked at 46 athletes with abnormal heart rhythms in all but one athlete the arrhythmia arose from the right ventricle. Within 5 years, nine of the athletes had died suddenly.

Dr. La Gerche has recently demonstrated similar findings in an extended local cohort of athletes in whom a lack of evidence of inherited disease would imply that extreme exercise may be the cause of RV dysfunction and arrhythmias. Up until that point, he said, it was thought that these arrhythmias, even though they looked serious, could never be life threatening. They also have found a number of athletes who in the year prior to the onset of arrhythmias reported a substantial decline in performance and Dr. La Gerche and his team think the two are linked.

In brief, myocardial dysfunction related to endurance activities most commonly affects RV function. While recovery appears to occur within 1 month following participation, there remains the possibility that the process of repair may result in chronic subclinical myocardial fibrosis with a risk of resultant complications.

References

1. Blair SN, et al. JAMA. 1989;262:2395-401.
2. La Gerche A, et al. Heart. 2008;94:860-6.
3. Claessen G, et al. Heart. 2011;97:918-22.
4. La Gerche A, et al. Med Sci Sports Exerc. 2011;43:974-81.

To listen to an interview with André La Gerche, MBBS, PhD, about ultra-endurance exercise and cardiac adaptations, visit youtube.cswnews.org. The interview was conducted by Robert A. Vogel, MD.

Keywords: Athletes, Neoplasms, Follow-Up Studies, Sports, Risk Factors, Biological Processes, Troponin I, Middle Aged, Ventricular Remodeling, Obesity, Heart Ventricles, Diabetes Mellitus, Natriuretic Peptide, Brain, Swimming, Echocardiography, Atrial Flutter

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