How to differentiate between a normal reduction in ejection fraction (EF) and viral myocarditis?

Differentiating Normal Reduction in Ejection Fraction from Viral Myocarditis

The key distinction is that physiologic athletic remodeling presents with normal or low-normal EF (rarely as low as 45%) accompanied by normal diastolic function, normal strain patterns (GLS -16% to -22%), and augmentation of EF with exercise, whereas viral myocarditis typically shows reduced EF with abnormal diastolic function, impaired strain (GLS worse than -16%), segmental wall motion abnormalities, and failure to augment EF with exercise. 1

Critical Distinguishing Features on Echocardiography

Athletic Heart (Physiologic)

• EF typically normal; elite endurance athletes may show mild reduction (as low as 45%) but this is rare 1
• Symmetric 4-chamber dilation with balanced enlargement 1
• Normal or supranormal diastolic function with rapid tissue Doppler velocities 1
• No regional wall motion abnormalities—coordinated, uniform contraction 1
• Symmetric wall thickening <12 mm (<15 mm in Black male athletes) 1
• GLS ranges from -16% to -22% 1
• Normal or augmented left atrial reservoir function 1

Viral Myocarditis (Pathologic)

• EF <50% is a red flag 1
• Segmental wall motion abnormalities in noncoronary distribution (classically lateral/inferolateral subepicardial) 1, 2
• Abnormal diastolic function: low tissue Doppler e' velocities for age or elevated E/e' ratio 1
• GLS worse than -16% indicates myocardial pathology 1
• Regional asymmetric wall thickening due to edema 1
• Reduced left atrial reservoir function 1
• Disproportionate LV dilation (LVEDD >70 mm men, >60 mm women) 1

Exercise Response: The Critical Differentiator

The most definitive distinction is exercise response: 1

• Athletic heart: Low-normal EF augments ≥10% with exercise 1
• Myocarditis: Failure to augment low-normal LVEF with exercise is highly suspicious for pathology 1

Advanced Imaging Markers

Global Longitudinal Strain (GLS)

• GLS >17% (more negative values like -18% to -22%) is reassuring for physiologic adaptation 1
• GLS worse than -16% (less negative, e.g., -14%) should raise concern for myocardial pathology 1
• In viral myocarditis, worsening GLS correlates with adverse outcomes and can detect subclinical dysfunction when LVEF appears normal 1

Right Ventricular Assessment

• Athletic heart: Similar degree of RV dilation to LV, coordinated wall motion, normal systolic function 1
• Myocarditis: RV dysfunction is common, with fractional area change <35%, RV-to-LV basal diameter ratio >1.0, or segmental abnormalities 1

Cardiac MRI Findings (When Indicated)

CMR is the most sensitive modality for identifying myocardial involvement: 1

• Native T1 or T2 >2 SDs above local reference mean indicates inflammation/edema 1
• ECV >30% suggests interstitial/extracellular space involvement 1
• Subepicardial or mid-myocardial late gadolinium enhancement (LGE) in noncoronary distribution is typical for myocarditis 1
• 2018 Lake Louise Criteria require both myocardial injury (elevated T1, ECV, or LGE) AND edema (elevated T2) for myocarditis diagnosis 1

Clinical Context and Biomarkers

Symptoms

• Athletic heart: Asymptomatic or proportionate exercise capacity 1
• Myocarditis: Disproportionate dyspnea on exertion, chest pain, palpitations, or postexertional fatigue 1

Important Caveat

Symptom intensity does NOT correlate well with LVEF severity or biomarker levels in myocarditis—patients may have severely reduced LVEF with minimal symptoms or vice versa 1, 2

Cardiac Biomarkers

• Elevated troponin (>99th percentile) indicates myocardial injury but correlates poorly with dysfunction severity 1, 2
• BNP/NT-proBNP elevation supports pathology but is not specific 1

Algorithmic Approach

1. Assess EF and chamber dimensions: Normal/low-normal EF with symmetric 4-chamber dilation suggests athletic heart; EF <50% with disproportionate dilation raises concern 1

2. Evaluate wall motion: Uniform contraction = athletic; segmental abnormalities = myocarditis 1

3. Measure GLS: Values -16% to -22% = reassuring; worse than -16% = pathologic 1

4. Assess diastolic function: Normal/supranormal tissue Doppler velocities = athletic; reduced e' or elevated E/e' = pathologic 1

5. Perform exercise testing if EF borderline: Augmentation ≥10% = athletic; failure to augment = myocarditis 1

6. Consider CMR if any red flags present: Elevated T1/T2 mapping and nonischemic LGE confirm myocarditis 1

Common Pitfalls

• Do not rely on EF alone—up to 15% of trained athletes have substantial LV enlargement with EF as low as 45% 1
• Most patients with viral myocarditis have normal LVEF initially, making strain imaging and diastolic assessment critical 1
• Isolated abnormal GLS requires reviewing primary data for accuracy before proceeding with additional testing 1
• RV dysfunction is often the predominant finding in viral myocarditis and may be missed if focus is solely on LV 1