Athlete’s heart – Cardiology Basics

Athlete’s heart – Cardiology Basics

Athlete’s heart is thickening of the heart muscle due to constant training in response to increased circulatory demand. Athlete’s heart is not dangerous, it is a physiological adaptation of the heart to training and increased load. It is associated with a slow heart rate, called athlete’s bradycardia.

The slower resting heart rate is a protective mechanism to prevent undue rise with exercise as normally heart rate increases with intensity of exercise. There is an increase in the size of the chambers of the heart and increased efficacy of pumping to meet the high demand during endurance exercise.

The enlargement of heart was recognized in cross country skiers as early as the 19th century. Athlete’s heart usually occurs in endurance athletes and may also occur in heavy weight lifters.
Thickening of the heart muscle can be documented by ultrasound imaging of the heart known as echocardiogram. There could be alterations in the ECG as well.

Importance of athlete’s heart from the medical point of view is to differentiate it from a genetic heart muscle disorder known as hypertrophic cardiomyopathy. That disease is also characterised by abnormal thickening of heart muscle.

Hypertrophic cardiomyopathy is the commonest cause of sudden cardiac death in young athletes and differentiation from athlete’s heart is very important. Simplest way to differentiate hypertrophic cardiomyopathy from athlete’s heart is to stop training for a period and observe for decrease in the thickness of heart muscle.

While decrease in thickness of heart muscle occurs in athlete’s heart after stopping training, there is no such decrease in hypertrophic cardiomyopathy as it is a genetically mediated heart disease.

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.

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.

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. ECG abnormalities are often associated with endurance sports like cycling, rowing/canoeing and cross-country skiing.

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 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.