Athlete’s heart denotes structural, functional and electrical remodeling seen in trained athletes. It is a physiological adaptation helping athletes perform physical tasks better than non-athletes . Though most of the findings in athlete’s heart are related to the left ventricle, changes do occur in the right ventricle as well.
Effect of exercise on the left ventricle
During aerobic exercise which is isotonic, the heart rate and stroke volume increases. Systemic vascular resistance falls, but slight to moderate increase in blood pressure can occur due to the increased cardiac output. As the cardiac output increases, it is a mostly a volume overload situation and left ventricle can develop eccentric hypertrophy with enlargement of cavity and proportionate increase in wall thickness. Isometric exercise or weight training on the other hand causes only slight increase in cardiac output due to increase in heart rate. But there is significant rise in blood pressure leading to pressure overload to the left ventricle. This causes concentric left ventricular hypertrophy in which increase in wall thickness predominates, without much increase in cavity size. These cardiac adaptations tend to normalize left ventricular wall stress .
A study evaluating 947 elite, highly trained athletes has reported echocardiographic left ventricular dimensions . Highest left ventricular wall thickness noted was 16 mm. Wall thickness of 13 mm or more were noted in only 16 of the 947 athletes. All these persons had enlarged left ventricular end diastolic dimensions ranging from 55 to 63 mm. The hypertrophy was noted only in rowers, canoeists and cyclists.
Enlargement of the left ventricular cavity, increased wall thickness and increased trabeculations in athlete’s heart will have to be differentiated from conditions like dilated cardiomyopathy, hypertrophic cardiomyopathy and isolated left ventricular non-compaction .
Effect of exercise on the right ventricle
Due to limitations of echocardiogram in evaluating the right ventricle, magnetic resonance imaging study of the right ventricle along with that of the left ventricle has been reported . Twenty one male endurance athletes were compared with untrained controlled subjects. Similar changes in left and right ventricular mass, volume and function were noted in endurance athletes. Authors concluded that the athlete’s heart is a balanced enlarged heart. ECG and imaging changes noted in endurance athletes may overlap with findings in arrhythmogenic right ventricular cardiomyopathy .
ECG changes in athlete’s heart
Athlete’s bradycardia due to increased parasympathetic tone and decreased sympathetic tone is a well known observation. Though sinus bradycardia is usual, other abnormalities like sinus arrhythmia, sinus arrest, wandering atrial pacemaker and coronary sinus rhythm have been described. First degree and second degree Mobitz type I atrioventricular block may be seen occasionally. Increase in QRS voltages satisfying criteria for left or right ventricular hypertrophy can be present. J point elevation and early repolarization pattern has been reported. Biphasic T waves and T wave inversions can occur in athlete’s heart syndrome . Most of the ECG changes due to increased parasympathetic tone disappear on exercise ECG, usually indicating their benign nature.
In a study of 1005 athletes 14% had distinctly abnormal ECG pattern. 26% had mildly abnormal pattern and 60% had normal or minor alterations in ECG . Structural cardiac abnormalities were identified in 5% of athletes in this study. Larger left ventricular end diastolic dimensions and wall thickness were associated with abnormalities in ECG. ECG abnormalities were associated with endurance sports like cycling, rowing/canoeing and cross-country skiing. Study had 75% males and abnormal ECGs were associated with male gender and age below 20 years. A curious finding was that 5% of athletes had significantly abnormal or bizarre ECG patterns without evidence of structural cardiovascular abnormalities or increase in cardiac dimensions.
Multimodality imaging for athlete’s heart
A multimodality imaging approach to differentiate physiological changes due to athlete’s heart from significant cardiac ailment has been suggested by an expert consensus from the European Association of Cardiovascular Imaging . ECG, echocardiography and cardiac magnetic resonance (CMR) imaging with late gadolinium enhancing are important investigative modalities to be used. These are useful in suspected myocardial diseases like cardiomyopathy and myocarditis. When there is a suspicion of coronary artery disease, exercise ECG and exercise stress echocardiography have been suggested. Nuclear cardiology imaging, cardiac computed tomography and CMR may be needed in selected cases. As there is radiation exposure, considering the young age of most athletes, use of cardiac CT and nuclear cardiology imaging should be limited to athletes with unclear stress echocardiography or CMR.