How do we distinguish athlete's heart from Hypertrophic Obstructive Cardiomyopathy (HOCM)?

From the Guidelines

Distinguishing athlete's heart from hypertrophic obstructive cardiomyopathy (HOCM) can be achieved by using a combination of diagnostic modalities, with cardiac MRI being a key tool, as it provides comprehensive information on morphology, location, distribution, and extent of hypertrophy and fibrosis, and can distinguish HOCM from athlete's heart with high accuracy 1.

Key Differences

The key differences between athlete's heart and HOCM include:

• Symmetric left ventricular hypertrophy in athlete's heart, typically less than 13mm in males and 12mm in females, whereas HOCM often presents with asymmetric septal hypertrophy exceeding these thresholds
• Normal diastolic function, no left ventricular outflow tract obstruction, and proportional chamber enlargement in athlete's heart, whereas HOCM shows diastolic dysfunction, possible outflow obstruction, and disproportionate septal thickening
• Normal ECG findings or benign changes like sinus bradycardia in athletes, while HOCM often shows pathological Q waves, ST-segment abnormalities, and T-wave inversions
• Clinical evaluation, including symptoms and family history, can also help differentiate between the two conditions

Diagnostic Approach

A comprehensive diagnostic approach should include:

• Echocardiography to evaluate left ventricular hypertrophy, diastolic function, and outflow tract obstruction
• Cardiac MRI to provide detailed information on morphology, location, distribution, and extent of hypertrophy and fibrosis, and to distinguish HOCM from athlete's heart
• Genetic testing to identify genetic mutations associated with HOCM
• Exercise testing to evaluate symptoms and cardiac function during exertion
• Deconditioning to assess regression of left ventricular hypertrophy in athlete's heart

Importance of Cardiac MRI

Cardiac MRI is a crucial diagnostic tool in distinguishing HOCM from athlete's heart, as it can:

• Provide comprehensive information on morphology, location, distribution, and extent of hypertrophy and fibrosis
• Distinguish HOCM from athlete's heart with high accuracy
• Identify areas of segmental hypertrophy, which may be missed or underestimated with echocardiography
• Quantify myocardial thickness, which is an important prognostic indicator for myectomy
• Evaluate papillary muscle abnormalities, which require different surgical management
• Screen family members with myocardial crypts, elongated mitral leaflets, delayed relaxation, high EF, and LGE seen in gene-positive, phenotype-negative patients 1.

From the Research

Distinguishing Athlete's Heart from HOCM

To distinguish athlete's heart from hypertrophic cardiomyopathy (HOCM), several methods can be employed, including:

• Clinical examination
• Electrocardiography (ECG) to identify non-specific changes
• Echocardiography as the primary method for differentiation
• Cardiac Magnetic Resonance (CMR) imaging for novel parameters with discriminative capacity
• Metabolic exercise testing
• Histological studies of endomyocardial biopsies
• Genetic testing

Echocardiography Findings

Echocardiography can help differentiate between athlete's heart and HOCM by identifying:

• Eccentric biventricular hypertrophy with wall thicknesses under 15 mm and a moderately dilated left ventricle (LVEDD up to 58 mm) in athlete's heart
• Asymmetric left ventricular hypertrophy with a reduced LV-diameter in HOCM
• Left ventricular outflow tract obstruction in up to 70% of HOCM cases during stress echocardiography
• Normal diastolic function with increased early diastolic filling in athlete's heart, whereas diastolic dysfunction occurs in the majority of HOCM patients 2

Advanced Imaging Techniques

Advanced imaging techniques, such as:

• Tissue and Doppler imaging
• Speckle tracking
• Cardiac Magnetic Resonance (CMR) imaging can aid in the differentiation of athlete's heart from HOCM, particularly in 'gray-zone' hypertrophy cases 3, 4

Electrocardiogram (ECG) Findings

The ECG can be used to diagnose and manage HOCM, and may help differentiate it from athlete's heart, although athlete's heart can mimic HOCM on ECG 5, 6

• Abnormal ECG patterns can be found in 40% of athletes, but structural cardiac diseases are identified in only 5%
• ECG alterations may be the consequence of athletic conditioning itself, rather than underlying cardiac disease 6