In this study, performed in male master athletes, mainly involved in lifelong endurance and competitive sports, structural cardiac adaptations were frequent. These changes affected all cardiac chambers and were more pronounced in athletes involved in endurance sporting disciplines, with high intensity and high volume of exercise. Importantly, this data reinforces the concept that the characteristics of exercise are major determinants of cardiac remodeling, also in master athletes.
Physiological cardiac adaptations induced by regular exercise training encompasses morphological, functional and electrical changes, routinely designed as ‘athletes’ heart’. This cardiac remodeling is influenced by individual and anthropometric characteristics, such as gender, ethnicity or BSA, and several exercise-related characteristics.1 Thus, during athlete’s evaluation it is important to consider these factors. Though in young athletes several studies describing with detail the cardiac adaptations to exercise have been published in the last years, data regarding older and master athletes are scarce and controversial.16
Structural changes
The long-term practice of competitive endurance sports produces an overall pattern of cardiac remodeling characterized by a balanced and homogeneous increase in the dimensions of the cardiac chambers.17 In 1975, Morganroth et al18 described by TTE the relationship between type of exercise and LV remodeling, showing a greater LVM due to greater LVEDV in athletes involved in dynamic exercise. In the current study, although the majority (more than two thirds) of the athletes had LV volumes above the reference, its number decreased substantially when adjusted to BSA, reinforcing the advantage of the use of indexed values. LV geometry it was changed in approximately half of the athletes, mainly due to eccentric hypertrophy. Similar findings were showed by Utomi at al19 in a cohort of athletes engaged in dynamic sports, with predominance of normal LV geometry and eccentric hypertrophy. In a study performed by Ryffel et al20 on a population of male adult competitive athletes, the adaptive responses to endurance exercise differed according to the age of onset of training. Athletes that started at a younger age had more frequently an eccentric pattern, while athletes that started exercise at an older age showed more frequently a concentric hypertrophy. Elite and recreational athletes have a similar geometric pattern, but the last showed a lower degree of LV hypertrophy, in consideration of the lower intensity of exercise. Conversely, athletes that started regular exercise at middle age had lower increase in LV cavity size and higher increase in LVWT, which may result in a relative concentric pattern of LV hypertrophy. The sports starting age and the number of years of continuous endurance training should also be considered and may lead to a better understanding of structural cardiac adaptations. Finocchiaro et al21 reported that athlete’s gender also affects the LV remodeling phenotype in endurance athletes, with a more common concentric pattern among male and eccentric pattern among female athletes. However, as the study was performed in young athletes and in the current study only male athletes were included, this association was not possible to prove.
RV enlargement was also common in most of the athletes. Physiological adaptations in the RV are frequently observed in athletes, especially in those involved in lifelong high-level endurance exercise. The RV chamber size seems to increase during the competitive season in top-level athletes, without association with a reduction in RV function or myocardial deformation and occurs in close association with changes on LV, suggesting physiological remodeling.22 In this context, the potential for erroneous diagnosis of arrhythmogenic cardiomyopathy is considerably greater.9
LA dilation was evident in more than half of the athletes included. This adaptation was described in several previous studies, but most of them used linear dimensions and not indexed volumes, as recommended and performed in our study. LA remodeling in competitive athletes may be regarded as a physiologic adaptation to exercise conditioning, largely without adverse clinical consequences.23 In a recent meta-analysis, Cuspidi et al24 suggests that the adaptation of LA to intensive exercise is characterized by a marked increase in LAV, being more pronounced in the athletes involved in high-dynamic/high-static exercise. Elite athletes have larger LA dimensions compared with controls when evaluated by either LA diameter or volume corrected for BSA, with the largest average diameters reported in endurance athletes.25
Only one athlete had aorta segments dimensions above the reference values. Although it has been reported an association between athletic training small increase in aorta dimensions, this difference is clinically nonsignificant.26 Dilation of aorta in athletes is uncommon, unlikely to represent a feature of athlete’s heart, and most probably an expression of a pathological condition, requiring close clinical surveillance.27
The structural adaptations observed were significantly associated with several characteristics of exercise. LV remodelling was more common in high intensity sports and athletes exercising more hours/week, while RV dilation in endurance sports and athletes with higher volume of exercise. Specifically, regarding the volume of exercise, there was a significant linear correlation with structural adaptations in the four cavities. The pattern and magnitude of physiologically adaptations also vary with the nature of sports training. Data from large athlete populations assessed with multivariate analysis show that 75% of variability in LV cavity size is attributable to factors including type of sport, gender and age, but BSA was the largest of these components.28
Functional changes
Only a minority of athletes showed a reduced LVEF at rest. Although uncommon, this finding has been previously described in different populations of endurance athletes.29 On the other hand, a significant percentage of athletes (22%) had an abnormal GLS. The impact of exercise training on LV systolic mechanics remains unclear, but this finding was also previously published, in a study in which the GLS was reduced in 31% of the athletes studied, more frequently in those involved in high level exercise. The reduction of GLS was associated with a normal/enhanced diastolic performance and larger LV volumes, which can justify the lower needs of systolic deformation to eject the same stroke volume than athletes with smaller volumes.30 In this seting, the values of GLS in our study also seem to belong to the spectrum of healthy physiology cardiac remodeling. In line with this assumption is the presence of normal diastolic function in all athletes, which may represent a beneficial effect of regular exercise, enhancing LV diastolic function and counteracting its reduction associated with normal ageing.2
Physiological versus pathological adaptations
Despite the fact that cardiac adaptations have been described as physiological and reversible in the majority of the athletes, the eventual development of pathological events after lifelong exercise training is an actual issue on debate.31 In a study performed by Pelliccia et al,32 among 114 young Olympic endurance athletes, no cardiac diseases were diagnosed after up to 17 years of intense and uninterrupted endurance training. However, in a different study of elite male athletes with large cardiac dimensions, followed over 5.6 years of deconditioning period, the resolution of cavity enlargement was incomplete in some athletes, which could not rule out future clinical implications.33 In the current study, during a mean continuous exercise training of 17±10 years, no pathological adaptations were identified, but no deconditioning was performed.
The ‘athlete’s heart’ is easily differentiated from pathological conditions in the majority of the cases, but some athletes present changes in the ‘grey zone’, in which a comprehensive evaluation of several clinical and complementary date should be valorized.34 TTE assumes a main role in evaluation and characterization of the cardiac adaptations in athletes and the differential diagnosis from several pathological conditions. Although not recommended for pre-participation screening of athletes, some authors propose TTE in specific ages, especially a first exam during adolescence to rule out structural heart conditions associated with sudden cardiac death not detected by electrocardiogram, and a second exam from the age of 30–35 years, when athletes become master, to evaluate pathological cardiac remodeling to exercise, late onset cardiomyopathies and wall motion abnormalities due to myocarditis or coronary artery disease.35
Limitations
Some study limitations should be highlighted. The data do not apply to women and may not be representative of all sports modalities, as recruitment bias cannot be excluded. The sample size may be underpowered to test the methodology used. As the study was cross-sectional, some factors with potential influence in cardiac adaptations, such as past performance enhancing substances abuse, were difficult to collect. The absence of a control group limits the clarification of the influence of the exercise-related characteristics in cardiac remodeling.