What test confirms the cause of heart failure with low voltage ECG (electrocardiogram) and concentric thickening on echocardiogram?

Cardiac MRI with Late Gadolinium Enhancement

In an elderly patient with heart failure, low voltage ECG, and concentric thickening on echocardiography, cardiac MRI with late gadolinium enhancement is the test that confirms the underlying cause, as this clinical triad strongly suggests cardiac amyloidosis or another infiltrative cardiomyopathy.

Why This Clinical Presentation Demands Tissue Characterization

The combination you describe is a classic red flag:

• Low voltage ECG with concentric thickening creates a diagnostic paradox—the ECG shows reduced electrical amplitude despite increased myocardial mass 1
• This discordance is pathognomonic for infiltrative disease, particularly cardiac amyloidosis 2
• Standard echocardiography can identify the structural abnormality but cannot determine the specific etiology 1

The Diagnostic Algorithm for Unknown Etiology Heart Failure

When heart failure etiology remains unclear after initial echocardiography, guidelines recommend advanced imaging for myocardial characterization 1:

First-Line Tissue Characterization

• Cardiac MRI with contrast (late gadolinium enhancement) is the definitive test for distinguishing infiltrative cardiomyopathies from other causes of concentric hypertrophy 1
• MRI provides unique information about tissue composition, fibrosis patterns, and infiltration that echocardiography cannot 3, 2
• The pattern of late gadolinium enhancement differentiates amyloidosis (diffuse subendocardial or transmural) from hypertrophic cardiomyopathy (patchy mid-wall) from other etiologies 2

Why Other Tests Are Insufficient

• Echocardiography alone cannot determine the cause of concentric thickening—it shows morphology but not tissue composition 1, 4
• Coronary angiography evaluates ischemic disease but won't identify infiltrative processes 1
• Chest CT has limited utility for cardiac tissue characterization and is primarily for extracardiac findings 1

Critical Diagnostic Considerations

The Infiltrative Disease Differential

In your clinical scenario, the primary considerations are:

• Cardiac amyloidosis (most likely given age and clinical triad) 2
• Hypertrophic cardiomyopathy (though typically presents earlier in life)
• Fabry disease (rare, but important not to miss)
• Sarcoidosis (can cause both infiltration and conduction abnormalities) 1

MRI's Unique Diagnostic Capabilities

• Late gadolinium enhancement patterns are highly specific for different cardiomyopathies 3, 2
• MRI quantifies myocardial mass, volumes, and function more accurately than echocardiography 3
• T1 mapping and extracellular volume quantification can detect early infiltration before overt hypertrophy develops 2

Common Pitfalls to Avoid

Do not assume hypertensive heart disease simply because the patient is elderly—the low voltage ECG excludes this diagnosis 1. Hypertensive hypertrophy causes high voltage ECG patterns, not low voltage.

Do not delay MRI while pursuing endomyocardial biopsy first—MRI is non-invasive and often diagnostic, reserving biopsy for cases where MRI is inconclusive or contraindicated 3, 2.

Do not accept "heart failure with preserved ejection fraction" as a final diagnosis without determining the underlying cause—this is explicitly discouraged by guidelines 1.

When Endomyocardial Biopsy Is Needed

If MRI is contraindicated (pacemaker, severe renal dysfunction precluding gadolinium) or if MRI findings are equivocal, endomyocardial biopsy becomes necessary for definitive tissue diagnosis 5. However, MRI should be the first-line confirmatory test in this clinical scenario 1, 3.