Infiltrative cardiomyopathy refers to a group of heart diseases where abnormal substances (e.g., amyloid proteins, iron, or sarcoid granulomas) deposit in the heart tissue, leading to structural and functional changes. These conditions often cause the ventricular walls to thicken or stiffen, impairing the heart’s ability to fill properly (diastolic dysfunction) and sometimes affecting its ability to pump (systolic dysfunction). Common examples include cardiac amyloidosis, sarcoidosis, and hemochromatosis.

The term “mass-voltage discrepancy” in this context likely relates to a diagnostic observation where the heart’s mass (e.g., wall thickness or overall myocardial mass) doesn’t align with expected findings based on other measures, such as electrocardiogram (ECG) voltage or chamber volume. This discrepancy is a hallmark of infiltrative cardiomyopathies, particularly cardiac amyloidosis, and can help differentiate them from other conditions like hypertrophic cardiomyopathy (HCM) or hypertensive heart disease.

Mass Volume Discrepancy in Infiltrative Cardiomyopathy

In a healthy heart or in conditions like HCM, increased myocardial mass (hypertrophy) typically correlates with higher ECG voltage due to more electrically active muscle tissue. However, in infiltrative cardiomyopathies, the deposited substances (e.g., amyloid fibrils) increase wall thickness—thus increasing mass—but don’t contribute to electrical activity. This often results in a paradoxical low or normal ECG voltage despite thickened walls seen on imaging (e.g., echocardiography or cardiac MRI). This mismatch is what’s referred to as a “mass-voltage discrepancy”.

Key Example: Cardiac Amyloidosis

• Mass Increase: Echocardiography or MRI shows thickened ventricular walls (increased left ventricular mass) due to amyloid infiltration in the extracellular space.
• Volume Discrepancy: The left ventricular cavity size often remains normal or small, unlike in dilated cardiomyopathies where chamber volume increases.
• ECG Findings: Low QRS voltage is classic, despite the apparent “hypertrophy” on imaging. This occurs because amyloid fibrils disrupt electrical conduction and don’t generate the expected voltage.
• Clinical Clue: This discrepancy—thick walls with low or discordant ECG voltage—raises suspicion for amyloidosis over HCM or hypertension-related hypertrophy.

Other Infiltrative Cardiomyopathies

• Sarcoidosis: May show wall thickening or dilation depending on the stage (inflammation vs. fibrosis). ECG voltage can vary, but conduction abnormalities (e.g., AV block) are more prominent than low voltage alone.
• Hemochromatosis: Iron deposition can increase wall thickness early on, but advanced stages may lead to dilation and systolic dysfunction. ECG voltage may not be low until late stages.

Diagnostic Implications

The mass-voltage discrepancy is a critical diagnostic clue:

• Echocardiography: Reveals increased wall thickness (mass) and restrictive filling patterns, but can’t distinguish infiltration from true hypertrophy without additional context.
• ECG: Low voltage in the presence of thick walls suggests infiltration rather than myocyte hypertrophy.
• Cardiac MRI: Late gadolinium enhancement (LGE) patterns (e.g., subendocardial in amyloidosis) and extracellular volume (ECV) measurements can confirm infiltration and quantify the extent.
• Clinical Correlation: Symptoms like low blood pressure, heart failure with preserved ejection fraction, or systemic signs (e.g., neuropathy in amyloidosis) further support the diagnosis.

Why It Matters

Recognizing this discrepancy shifts the diagnostic workup. For instance, in amyloidosis, you’d pursue serum free light chain analysis, bone scintigraphy (e.g., PYP scan for ATTR amyloidosis), or even endomyocardial biopsy, rather than assuming hypertension or HCM. Treatment differs significantly—e.g., tafamidis for ATTR amyloidosis vs. beta-blockers for HCM—so missing the discrepancy could lead to mismanagement.