Impact of Sporting Disciplines and Body Size on the Athlete’s Heart

Abstract

Regular intensive exercise leads to a series of electrical, structural, and functional changes in the heart, collectively named as the “athlete’s heart”. Sporting discipline has an impact on cardiac adaptation to exercise. Endurance athletes tend to exhibit a significant biventricular enlargement and highly trained cyclists can be characterized by a low normal or even reduced left ventricular ejection fraction at echocardiography. Normal left ventricular geometry prevails in most highly trained athletes; however, while female athletes engaged in dynamic exercise show a greater prevalence of eccentric hypertrophy, male athletes may exhibit concentric hypertrophy/remodeling more frequently than female athletes although the absolute numbers are low. Body size is also strongly associated with cardiac dimensions. The interpretation of cardiac dimensions in any athlete should be based on body-size independent cardiac indices as this facilitates the differential diagnosis of physiological versus pathological cardiac adaptation in athlete screening. Historically, scaling of cardiac data in athletes for individual differences in body size has been either entirely ignored or has used simple “ratiometric” scaling such as normalization of LV mass for individual differences in BSA (LV mass/BSA). We argue that this scaling process may not always be theoretically or practically accurate, resulting in cardiac indices that are still body size-dependent. This only confuses clinical decision-making. An “allometric” approach to scaling is theoretically sound in most cases and practically tends to lead to body size-independent cardiac indices. This evidence-based approach should be encouraged wherever possible and specifically within the sphere of sports cardiology and pre-participation screening. A correct understanding of determinants, type and extent of physiological cardiac adaptation is pivotal to correctly differentiate normal findings from potentially fatal cardiac diseases such as cardiomyopathies.

Review

1.1 Questions

• 1. What are the common forms of left ventricular geometry observed in highly trained athletes from different sporting disciplines?

• 2. Can you describe the impact of endurance sport on right ventricular adaptation to exercise?

• 3. Can you describe the nature of the relationship between a one-dimensional cardiac measure (e.g. septal wall thickness) with a three-dimensional body size variable (e.g. body mass)?

• 4. In the example above, can you describe possible different approaches to scaling, and how you would determine if the scaled index was, indeed, size-independent?

1.2 Answers

• 1. Most athletes would exhibit a normal left ventricular geometry. Athletes may exhibit eccentric hypertrophy, concentric hypertrophy or concentric remodeling. A recent study [11] showed that in the specific subgroup of athletes engaged in dynamic exercise, females showed eccentric hypertrophy more frequently than males, while more men than women had concentric remodeling/hypertrophy, although these geometric presentations were less common than normal geometry.

• 2. A large proportion of young athletes exhibit increased RV dimensions exceeding the reference values commonly used in clinical practice and the values proposed by the revised Task Force Criteria (TFC) for the diagnosis of ARVC. Most available data are on endurance athletes, with less available data on athletes engaging in static sports.

• 3. Whilst the overall relationship will be positive (as body size increases so will septal wall thickness), careful analysis will likely reveal that over the range of data provided the relationship between septal wall thickness and body mass will be curvi-linear (i.e. non-linear) as it involves a one-dimensional cardiac measure and a three-dimensional body size parameter. The curvi-linear relationship is because of the lack of geometric similarity between the two variables.

• 4. Initially you would want to define your body size parameter to scale and in most cases this would likely be BSA or HT (in a clinical setting). Ratiometric approaches with BSA are likely to be problematic due to lack of geometric similarity in septal wall thickness and BSA. An allometric approach with the “b” exponent derived directly from the population to be studied would be optimal but an approach using 0.5 (1-D divided by 2-D) as the “b” exponent could be adopted. If HT was used, a ratiometric approach would likely be very similar to any allometric approach as both septal wall thickness and HT are one-dimensional parameters. To test for size independence all you would need to do is correlate the scaled index (wall thickness/BSA^0.5 or wall thickness/HT) to the body size measure (BSA or HT). Any significant residual correlation would suggest that size-independence of your index had NOT been achieved.