On the characterization of athlete’s heart using 3D echocardiography 

This editorial refers to ‘Biventricular mechanical pattern of the athlete’s heart: comprehensive characterization using three-dimensional echocardiography’, by A. Fábián et al., https://doi.org/10.1093/eurjpc/zwac026.

The structural and functional adaptations of the athlete’s heart facilitate the performance related increased blood flow.^1,2 These heart changes comprise increases in cardiac chambers size as well as the requisite improvements in inotropic and lusitropic function enabling larger stroke volumes to be ejected from the ventricles during exercise.^1,2 The physiological mechanisms of this process are remarkable and, despite decades of research, remain incompletely understood.

It should be said the majority of investigations about the athlete’s heart cardiac adaptations have focused on the left ventricle (LV). In this regard, the principal established changes can be ascribed (at a basic level) as an increase in LV volumes (both at end-diastole and end-systole, especially in endurance athletes) and myocardial mass. This physiological LV dilatation is naturally associated with a reduction in ejection fraction (EF) at resting conditions, ensuring a higher reserve with exercise. However, it should be highlighted that the EF is the result of longitudinal and circumferential contractions, measured by global longitudinal and circumferential strain (GLS and GCS), respectively.^3,4 Thus, the reduction of overall contraction—indicated by the EF—must necessarily reflect in a corresponding reduction of GLS and/or GCS. However, results about changes of global strain components in athletes are heterogeneous and apparently dependent on the specific sport category.⁵

Fábián et al.⁶ present an interesting evaluation of the mechanical function of both LV and right ventricle (RV) in an extended population of athletes (n = 425) as assesses by three-dimensional (3D) echocardiography (Figure 1A and B).

Figure 1

Progresses in echocardiography allow improved characterization of right-ventricular mechanical function in athletes: (A) two-dimensional speckle-tracking echocardiography from apical four-chamber visualization allows measuring right ventricle area and longitudinal strain limited to that cross section; (B) right ventricle geometry extracted from three-dimensional echocardiography; (C) the contraction can be separated in wall-specific contributions (credit: Kovács et al.⁸, under a Creative Commons Attribution 4.0 International License); (D) principal strain analysis allows to identify direction and entity of contraction.

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They confirm the increase in LV size and mass along with the decrease in EF is accompanied by a significant reduction in GCS and, to a smaller extent, in GLS reflecting the relationship between EF and strain⁴ [EF = 100 − 100 × (GLS/100 + 1) × (GCS/100 + 1)].²

On the other hand, peculiar geometry and anatomical structure of the RV correspond to a specific ventricular contraction mechanical behaviour that likely reflects different adaptation mechanisms. Global measurements give preliminary indications, and a more careful characterization requires to separate the contribution coming from different regions of the RV boundary as recently suggested^7–9 (Figure 1C and D).

The study of Fábián et al.⁶ is rich in data. To the authors’ credit and the benefit of the readers, the study includes a large cohort of highly trained female athletes.^10,11 In this regard, the reported 3D echocardiographic data support the premise that the adaptations in men and women are similar in nature but differ in extent. Right ventricle and LV volumes are increased in both sexes, whilst deformation and EF tended to be lower.⁶ It has been previously well described that overall cardiopulmonary fitness (VO₂max) is lower in women and this has been again observed by Fábián et al.⁶ Furthermore Fabian et al.⁶ demonstrate that the lower VO₂max values are associated with, and largely proportional to, smaller cardiac volumes and lesser changes in functional parameters. In short, sports cardiology clinicians may be reassured that male and female athletes can be considered part of the same spectrum of cardiac adaptations relative to physical conditioning. This would imply that outliers (e.g. very large cardiac volumes and reductions in deformation in an athlete of modest fitness) should be evaluated further for the possibility of underlying pathology regardless of gender.

Within the findings of Fábián et al.⁶ potentially important and novel observations are about the cardiac remodeling in adolescent athletes. In the total cohort there is a strong relationship between cardiopulmonary fitness (VO₂max), and chambers enlargement. However, adolescent athletes were found to have the highest VO₂max and yet cardiac volumes were slightly less than those of adult athletes. This raises some very interesting questions regarding the interaction between healthy athletic cardiac remodeling and aging. According to the Fick equation, VO₂max equates to the product of cardiac output and peripheral oxygen utilization in the working peripheral muscles. Therefore, there are two main possibilities to explain the observation of greater VO₂max with a slightly smaller heart. The first is that the young athlete has better peripheral oxygen utilization. The other possibility is that the young athlete heart can generate greater outputs with lesser resting volumes. This is an intriguing proposition, which evokes the suggestion that the heart in the adult- and middle-aged athletes may compensate by enlarging (and relying on greater elastic recoil) because it has a lesser capacity to rely on enhanced lusitropy and contractility. Referring back to Morganroth’s original simile between athlete’s heart and regurgitant valvular heart disease, it could be that there is a point in which the athlete’s heart relies more on structural enlargement than on functional adaptation. Is there a point at which extreme cardiac enlargement could be considered a failure of functional adaptation? Are there any clinical consequences? These are all questions that cannot be addressed in the cross-sectional design of the Fábián et al.⁶ and again speak to the need for longitudinal data in highly trained athletes.

The rapid advancement of imaging technology will see an ever-increasing number of studies about ventricular function based on 3D techniques.¹² This technological advancement produces a multitude of information and requires the parallel development of feasible and reproducible methods capable of providing a realistic picture of the actual cardiac function and able to synthesize it with a few representative parameters. This is a scientific challenge requiring interdisciplinary and synergistic collaborations in order to progress toward a ground-based understanding of cardiac mechanical function and adaptation. New mechanistic knowledge may shed the light on the clinical conundrum related to identifying the good athlete’s heart from the rare case in which the remodeling is bad.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References

Author notes