Two-dimensional transthoracal echocardiography is the principal diagnostic tool for clinical recognition of many cardiac pathologies. While being a cornerstone in the diagnosis and follow-up of HCM, it can also detect other relevant abnormalities possibly responsible for SCD in young athletes, such as left ventricular dysfunction (e.g. due to myocarditis or dilated cardiomyopathy), valvular heart disease and aortic root dilatation. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is often difficult to diagnose by echocardiography alone. If this condition is suspected, a cardiac MRI is generally considered to be a better investigation tool. Although echocardiography may raise strong suspicion of congenital coronary anomalies (mainly the left main coronary artery from the right sinus of Valsalva) in selected young athletes, CT angiography, magnetic resonance imaging (MRI) or even coronary arteriography are usually necessary to diagnose this entity.
- Athlete’s Heart vs HCM
As with ECG screening, echocardiography in trained athletes carries the potential for false-positive results, which may arise from borderline values for left ventricular wall thicknesses and cavity size mainly in the differentiation of physiological adaptations from HCM. Also, it has to be emphasised that echocardiography is more strongly affected by the individual expertise of the examiner than any of the other examinations mentioned above. 21,22
In the vast majority of competitive athletes, absolute left ventricular wall thickness is normal or only mildly increased (≤12mm). However, in some athletes, the increase in left ventricular wall thickness may be more substantial (up to 16mm), which makes HCM likely. The echocardiographic hallmark of HCM is a hypertrophic and non-dilated left ventricle in the absence of other cardiac or systemic disease that could cause the hypertrophy. Although, in general, patients with HCM show a marked increase in left ventricular wall thickness (average wall thickness reported in most echocardiographic studies is ≈20mm, ranging to >30mm), an important minority of patients with HCM, especially young, adolescent patients <18 years of age, show relatively mild left ventricular hypertrophy with a wall thickness in the range of ≈12 to 15mm. In this diagnostic “grey area” only careful analysis of several echocardiographic characteristics, in addition to clinical and electrocardiographic features, permits the diagnosis. In rare cases, only close follow-up or even detraining (with no loss in wall thickness after a few months) leads to the correct diagnosis. A regression of left ventricular hypertrophy after athletic deconditioning (of at least three months) demonstrates the physiological origin of wall thickening from athletic training alone. A decrease in left ventricular wall thickness is usually not observed in HCM.
Left ventricular hypertrophy appears to be rather homogeneous in healthy athletes (even if there can be a predominantly thickened anterior septum) with differences in wall thickness of only 1-2mm between segments. By contrast, in patients with HCM the pattern of wall thickening is often heterogenous and asymmetric with the anterior portion of the septum (or other particular segments) being the region of maximal hypertrophy. Moreover, in HCM contiguous segments of the left ventricle show strikingly different wall thicknesses with abrupt transition between such areas. Note that in black athletes of West African origin reference values for wall thickness might be 1-2mm higher than in Caucasians. 23,24
Considering left ventricular cavity size improves specificity of the echocardiographic diagnosis of HCM: more than one third of highly trained elite male athletes (particularly those with a relevant endurance component as part of their sport and those with above-average body dimensions) show an enlarged left ventricular end-diastolic cavity dimension (>55mm). Conversely, the end-diastolic cavity dimension is small in most patients with HCM (often <45mm depending on their body dimensions).
The left ventricular diastolic filling pattern further helps to distinguish HCM from physiologic changes in athletes: most patients with HCM, including those with relatively mild hypertrophy, show abnormal Doppler diastolic filling patterns of the left ventricle, whereas trained athletes have invariably demonstrated normal left ventricular filling patterns. Tissue velocity imaging (TVI) may be able to detect such deviations from the norm at an earlier stage.
- Female athletes
- Highly trained healthy female athletes rarely show left ventricular wall thicknesses that lie within the “grey area”, which means that a female player with “borderline” left ventricular wall thickness (in the presence of normal cavity size) is even more likely to have HCM. For an appropriate diagnostic approach to female football players it is thus wise to rely upon gender-specific reference values.
- Usually, distinguishing an “athlete’s heart” from cardiopathies other than HCM is not very difficult: even when there are increases in left ventricular end-diastolic cavity dimensions exceeding the “normal range” of 53-58 mm (<3.2cm/m² in women and <3.1cm/m² in men), the absence of left ventricular systolic dysfunction is usually sufficient to distinguish this physiological ventricular enlargement induced by training from that due to dilated cardiomyopathy. Also, relating the cavity size to the (objective) ergometric capacity is usually helpful in making this decision.
Because highly trained athletes may sometimes demonstrate right ventricular enlargement, the need for differential diagnosis between an athlete’s heart and right ventricular cardiomyopathy may arise. Differentiation by echocardiography alone may be difficult because of technical limitations in imaging right ventricular structures and assessing its function in these athletes. Magnetic resonance imaging (MRI) may improve the non-invasive diagnosis of this condition, demonstrating the pathophysiological hallmark of fibro-fatty replacement of myocardium. Diameters of the aorta (particularly in suspected Marfan syndrome) have to be referenced to individual conditions (age, body surface area, height, etc.).