Athlete’s Heart

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• History of athletic training and performance

• Enhanced exercise ability (maximum oxygen uptake > 40 mL/kg/min)

• Resting bradycardia, sinus arrhythmia, or atrioventricular conduction delays that disappear with exercise

• Increased chamber sizes and left ventricular (LV) mass noted on echocardiography, with normal diastolic function.

• LV wall–to–volume ratio in diastole < 0.15 mm/m²/mL by cardiac MRI

• Normal B-type natriuretic peptide levels

GENERAL CONSIDERATIONS

• The basic cardiac response to exercise training is myocardial hypertrophy, which may or may not involve chamber enlargement, depending on the type of training

• Pure isotonic (endurance) training results in the most chamber enlargement

• Pure isometric (strength) training results in the greatest degree of LV wall thickening

• Exercise training also results in increased resting parasympathetic tone, resulting in resting bradycardia and other phenomena such as Mobitz I second-degree atrioventricular (AV) block

• LV systolic and diastolic function is normal in the athlete’s heart even if hypertrophy is marked

• The challenge for the clinician is distinguishing cardiac disease from normal cardiac adaptation to exercise training, especially in the former athlete in whom some of the cardiac effects of training may persist

• In general, the morphologic cardiac effects of training are reversible with cessation of exercise

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Well-trained athletes are usually asymptomatic but may have symptoms that are suggestive of cardiac disease (eg, chest pain or dyspnea) for other reasons, such as respiratory infection

• Prolonged isotonic training occasionally leads to orthostatic dizziness and syncope, most commonly immediately after endurance exercise

• The hallmark of the athlete is an ability to perform exercise at a high level

PHYSICAL EXAM FINDINGS

• Slow pulse rate at rest, which may be as low as 30 bpm in endurance athletes

• Enlarged apical impulse

• S₃ or S₄ sounds

• Early systolic flow murmur at the base of the heart, which may disappear with the patient upright

DIFFERENTIAL DIAGNOSIS

• Pathologic LV volume increase (ie, dilated cardiomyopathy)

• Pathologic LV hypertrophy, especially hypertrophic cardiomyopathy

• Pathologic bradycardia

• Coronary artery disease

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• Creatinine kinase and troponin may be elevated after vigorous prolonged exercise

ELECTROCARDIOGRAPHY

• Sinus bradycardia, sinus arrhythmia, first-degree AV block, Mobitz I second-degree AV block, and junctional rhythm

• Incomplete right bundle branch block

• Early repolarization in leads V3–6

• Biphasic or inverted T waves in V3–4

• Peaked upright T waves in V3–6

• Signs of LV or right ventricular or atrial hypertrophy

• Myocardial infarction patterns (Q waves) due to chamber hypertrophy

IMAGING STUDIES

• Chest x-ray: may show cardiomegaly. This finding supported the first reports of athlete’s heart in the nineteenth century

• Echocardiography: may ...