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Athlete's Heart and Cardiomyopathy
Istitute of Sport Science, Department of Medicine
Italian Olympic Committee
Long-term athletic conditioning is associated with cardiac morphologic changes, including increased left ventricular (LV) cavity dimension, wall thickness and mass. The extent to which LV dimension is increased in athletes is usually mild: several echocardiographic studies have shown that absolute left ventricular dimensions are increased in athletes in comparison to matched untrained controls by an average of 10% for cavity dimension and 15% for wall thickness. These absolute cardiac dimensions, although increased, usually remain within the accepted upper normal limits, and different in most cases from changes seen in patients with structural cardiac diseases, such as cardiomyopathies.
In elite athletes, however, left ventricular cavity dimensions and, in some instances, wall thicknesses may be markedly increased, well above the upper normal limits predicted by age and body size. Absolute left ventricular wall thickness may exceed > 13 mm, in a range compatible with primary pathologic hypertrophy, i.e. hypertrophic cardiomyopathy in about 2 % of elite athletes. Left ventricular cavity dilatation (end-diastolic transverse diameter may exceed 60 mm, in a range compatible with idiopathic dilated cardiomyopathy in about 15 % of elite athletes. In such circumstances, the morphologic features of the athlete's heart raise the differential diagnosis between an extreme physiologic adaptation to athletic conditioning and a pathologic cardiac condition. This differential diagnosis has implicit ethical, economic and legal implications, because the incorrect identification of a cardiac disease may lead to unnecessary withdrawal of an athlete from competition, thereby depriving that individual of the varied (including economic) benefits of sport. On the other hand, the correct diagnosis of certain cardiovascular diseases may be the basis for disqualification of athlete from competition, in a effort to minimize the risk of sudden cardiac death related to sport activity.
Differential diagnosis of athlete's heart and hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy is a primary cardiac disease, for which the most characteristic morphologic feature is a hypertrophied non-dilated left ventricle in absence of cardiac or systemic disease itself capable of producing left ventricular hypertrophy. The prevalence of this disease in the general population is estimated to be 0.2%. The differential diagnosis of athlete's heart and hypertrophic cardiomyopathy is of crucial importance, because sudden death may be the initial clinical event in young athletes with hypertrophic cardiomyopathy, often in relation to exertion. At present time there is no single approach that will definitively resolve this differential diagnosis in all instances, although several criteria appear useful in this regard, as summarized in Figure 1.
|Fig 1: Flow-chart showing criteria used to distinguishing hypertrophic cardiomyopathy (HCM) from athlete's heart when the left ventricular (LV) wall thickness is within the shaded gray zoneof overlap, consistent with both diagnoses.|
Left ventricular morphology (Figure 2):
|Fig. 2. Comparative echocardiographic images of left ventricular hypertrophy characteristics of hypertrophic cardiomyopathy (A, B) and athlete's heart (C, D). Parasternal long axis (A) and short axis (B) views and respective schematic drawings of the left ventricle, at the same calibration, from a 18-year-old with hypertrophic volleyball player with cardiomyopathy. In comparison, the same views and schematic drawings (C, D) from a 25-year-old elite rower with physiologic left ventricular hypertrophy. In the subject with hypertrophic cardiomyopathy, the maximum thickness is 18 mm in the anterior ventricular septum, but the posterior free wall is 8 mm, resulting in a markedly asymmmetric distribution of hypertrophy. In the rower, the maximum ventricular septal thickness is 15 mm, and there is a more symmetric distribution of hypertrophy. The left ventricular cavity is within normal limits (48 mm) in the patient, but is enlarged (58 mm) in the rower. Abbreviations: ALFW = antero-lateral free wall; AVS = anterior ventricular septum; MV = mitral valve; PFW / PW = posterior free wall; PVS = posterior ventricular septum; VS = ventricular septum.|
1) Wall thickening. The maximum wall thickness found in highly trained athletes is 15-16 mm, that likely represents the upper limit of physiologic left ventricular wall thickening. Instead, in patients with hypertrophic cardiomyopathy, including those who are asymptomatic and involved in athletic activities, the maximum wall thickness shows a broad range of values, 15 to 60 mm, and averages 22 mm. A minority of patients with hypertrophic cardiomyopathy, however, show relatively mild hypertrophy (wall thickness 13 to 15 mm) and, therefore, this single criterion may not differentiate physiologic from pathologic hypertrophy in all instances.
2) Distribution of hypertrophy. The distribution of hypertrophy in athlete's heart is sustantially symmetric and regular. Although the different segments of left ventricular wall may not be thickened to an identical degree (maximum wall is usually in the anterior ventricular septum), differences between contiguous segments of left ventricle are generally very small (< 2 mm) and the overall pattern of myocardial hypertrophy appears homogeneous. In patients with hypertrophic cardiomyopathy the distribution of hypertrophy is, in contrast, characteristically asymmetric and heterogeneous.
3) Left ventricular cavity. In athletes with physiologic wall thickening, left ventricular cavity is also consistently enlarged (end-diastolic cavity diameter > 55 mm). The left ventricular cavity shape appears normal, with the mitral valve normally positioned within the cavity and no evidence of left ventricular outflow tract obstruction. In patients with hypertrophic cardiomyopathy, including those who are asymptomatic, left ventricular cavity dimension is small or within normal limits (end-diastolic cavity diameter often < 45 mm. Therefore, in some cases, it is possible to resolve the diagnostic ambiguity of borderline wall thickening in athletes on the basis of left ventricular cavity dimension, when either < 45 or > 55 mm. However, when absolute cavity dimension falls between these two extremes, this criterion does not reliably discriminate between physiologic and pathologic hypertrophy.
4) Dynamic changes in left ventricular hypertrophy. Serial echocardiographic studies have shown dynamic changes in left ventricular wall thickness associated with variations in intensity of training. Of note, in elite and highly-trained rowers examined both at the peak conditioning (when maximum wall thickness averaged 13-15 mm) and after 3 months of deconditioning, was documented a significant reduction in wall thickness (by 2 to 5 mm, mean 3). In hypertrophic cardiomyopathy, no substantial changes in wall thickness would be expected to occur in response to changes in the level of physical activity. Consequently, a brief period of forced deconditioning combined with serial echocardiographic studies may be a useful diagnostic to distinguish physiologic from primary pathologic hypertrophy.
Left ventricular filling
Indexes of left ventricular filling may be useful in distinguishing athlete's heart from hypertrophic cardiomyopathy. Trained athletes with phisiologic LV hypertrophy consistently show normal left ventricular filling pattern In contrast, abnormalities in relaxation and filling have been described as characteristic features of hypertrophic cardiomyopathy, and are present in up to 80% of patient. In hypertrophic cardiomyopathy, diastolic dysfunction is not strictly related to the severity of left ventricular hypertrophy, and may be present in cases with only mild hypertrophy and no symptoms, that most likely require differential diagnosis form athlete's heart. The most frequent abnormalities are a slowed deceleration of early diastolic flow velocity associated with increased late (atrial) peak flow velocity and reversed ratio of early-to-late diastolic peak flow velocity.
Type of sport
Knowledge of the characteristics of athletic training may be helpful in identifying physiologic and pathologic hypertrophy. Marked left ventricular wall thickening is virtually limited to elite, highly-trained athletes engaged in endurance disciplines (primarily rowing, canoeing and cycling). Consequently, absolute increase of left ventricular wall thickness (> 13 mm) in an athlete training in most other sporting disciplines is unlikely to represent the effect of conditioning alone.
Gender itself may be a useful criterion for discriminating physiologic from pathologic hypertrophy. Physiologic left ventricular wall thickening (>13 mm) is virtually confined to male athletes. On the other hand, men and women with hypertrophic cardiomyopathy do not differ with regard to morphologic expression of the disease, either in terms of maximum wall thickness (mean: 22 mm in both sexes), distribution of left ventricular hypertrophy and number of hypertrophied segments involved. This feature largely reflects the fact that hypertrophic cardiomyopathy is a primary, genetically determined, myocardial disease. Therefore, the finding of borderline wall thickness (i.e., 13-15 mm) in a female athlete is unlikely to be the consequence of athletic conditioning itself and is more likely the expression of pathologic cardiac condition.
In athletes with physiologic left ventricular hypertrophy, a variety of electrocardiographic abnormalities can be found, not uncommonly mimicking those seen in patients with hypertrophic cardiomyopathy, such as markedly increased QRS voltage, T wave inversion and abnormal Q waves. In hypertrophic cardiomyopathy, the 12-lead electrocardiogram is abnormal in the vast majority of patients (> 90 % of cases), showing a wide variety of patterns, which are often bizarre. However, no particular electrocardiographic pattern is specific for the hypertrophic cardiomyopathy and in the individual subject the 12-lead electrocardiogram may not consistently discriminate between athlete's heart and pathologic hypertrophy.
Familial transmission and genetic screening
The most definitive evidence for the presence of hypertrophic cardiomyopathy in an athlete with an increase in wall thickness comes from the demonstration of this disease in a relative. Therefore, echocardiographic screening for affected family members represent a potential method for resolving this diagnostic uncertainty. However, absence of echocardiographic evidence for hypertrophic cardiomyopathy in family members does not exclude occurrence of the sporadic form.
In recent years, a variety of genetic defects have been found in association with familial hypertrophic cardiomyopathy and have raised the possibility of DNA-diagnosis in athletes with borderline hypertrophy. Most of the disease-causing mutations have been identified in genes located on chromosomes 1, 11, 14 and 15; these genes encode the sarcomere proteins cardiac troponin-T, myosin binding protein-C, beta-myosin heavy chain and alfa-tropomyosin, respectively. Furthermore, a large number of mutations for each of these abnormal genes have been described. In most cases, different families have been shown to have different mutations, and some of these have been associated with an unfavourable natural history and clinical course In consideration of the substantial genetic heterogeneity of hypertrophic cardiomyopathy and the relatively complex, time-consuming and expensive techniques necessary for the genetic screening, identification of the disease-causing mutations is, at present, quite laborious and not routinely available for clinical practice.
Differential diagnosis of athlete's heart and idiopathic dilated cardiomyopathy
Idiopathic dilated cardiomyopathy is a primary myocardial disease characterized by left ventricular dilatation and systolic dysfunction. The prevalence of this cardiac disorder has been estimated to be 0.4 % in the general population. Left ventricular cavity dimensions show a broad range of absolute values and in a few instances the degree of dilatation may be minimal. The magnitude of impairment in left ventricular systolic function is also broad, and in the early stages of the disease may be minimal.
On the other hand, left ventricular cavity dimension may be markedly enlarged (end-diastolic transverse diameter > 60 mm) in a sizeable proportion of highly-trained athletes (about 15%). In these individuals, therefore the differential diagnosis between idiopathic dilated cardiomyopathy and physiological left ventricular enlargement of athlete's heart may raise.
Left ventricular morphology (Figure 3)
|Fig. 3. Comparative echocardiographic images of left ventricular dilatation in idiopathic dilated cardiomyopathy (a) and athlete's heart (b). Parasternal, short axis and M-mode tracing of the left ventricle from a 20-year-old asymptomatic patient with idiopatic dilated cardiomyoapthy (a). In comparison, the same views at the same calibration, from a 26-year-old elite rower, who was a participant at the Olympic Games (b). In both the patient and the elite athlete, the left ventricular cavity is dilated to the same extent (67 mm); however, the ventricular septum and free wall are relatively thin (8 mm) and show a reduced systolic motion in the patient, but are increased (up to 13 mm) and show a normal systolic motion in the rower. In the patient, the mitral valve and papillary muscles are superiorly located; in the athlete, the mitral valve is normally located within the left ventricular cavity.|
In athletes, physiologic left ventricular cavity enlargement is associated with enlargement of the right ventricular and atrial chambers, as an expression of a global cardiac remodeling. In elite athletes, the maximum left ventricular end-diastolic cavity dimension does not exceed 70 mm, that likely represents the upper limit of physiologic left ventricular enlargement. In patients with dilated cardiomyopathy, on the other hand, dilatation of both ventricles is common, but left ventricular enlargement usually predominates and may be substantial, as an expression of primary myocardial disease. The enlarged left ventricular cavity in athletes maintains the normal ellipsoid shape, while LV cavity in patients with dilated cardiomyopathy usually achieves a more spherical shape, in association with impaired contractility and deterioration of the clinical status. Indeed, in dilated cardiomyopathy, mitral regurgitation is common, due to dilatation and distortion of the mitral ring. Left ventricular wall thickness may be within normal range in both instances, but relative wall thickness is usually (mildly) increased only in the athletes heart.
Left ventricular function
In athletes with physiological left ventricular dilatation, global systolic function is normal, and regional wall motion abnormalities are absent. Therefore, in an athlete with left ventricular cavity dilatation, evidence of systolic dysfunction is the most reliable criterion for differentiating athlete's heart from primary pathologic condition, such as idiopathic dilated cardiomyopathy.
Type of sport
In assessing whether an enlarged left ventricular cavity in an athlete represents a physiological or pathologic condition, knowledge of the athlete's training may also be useful. Long-term, intensive training in largely aerobic disciplines (primarily cycling, cross-country skiing, canoeing, rowing and soccer) has been shown to represent the strongest determinant for p hysiologic enlargement of left ventricular cavity.
A wide range of electrocardiographic alterations have been described in association with both physiologic left ventricular dilatation and idiopathic dilated cardiomyopathy. However, no particular pattern is specific for idiopathic dilated cardiomyopathy and, in the individual athlete, the analysis of 12-lead electrocardiogram may not reliably discriminate between athlete's heart and this pathologic condition.
* Assumed to be the nonobstructive form of HCM in this discussion, since the presence of substantial mitral valve systolic motion would confirm, per se, the diagnosis of HCM.
+May involve a variety of abnormalities, including heterogeneous distribution of left ventricular hypertrophy (LVH) in which the asymmetry is prominent, and adjacent regions may be of greatly different thicknesses, with sharp transition evident between segments; also, patterns in which the anterior ventricular septum is spared from the hypertrophic process and the region of predominant thickening may be in the posterior portion of the septum or anterolateral or posterior free wall.
F.M. Di Paolo
R. De Luca
Istitute of Sport Science, Department of Medicine
Italian Olympic Committee, Rome, Italy