What does an abnormal cardiac Magnetic Resonance Imaging (MRI) with fat infiltration indicate?

From the Guidelines

An abnormal cardiac Magnetic Resonance Imaging (MRI) with fat infiltration is highly indicative of Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), a condition characterized by the replacement of ventricular myocardium with fibrous and fatty tissue, leading to ventricular dysfunction and tachyarrhythmias 1.

Key Findings

• Fat infiltration in the right ventricle (RV) is a common finding in ARVC, occurring in up to 88% of patients, and is often associated with fibro-fatty replacement of the myocardium 1.
• The presence of fat infiltration, along with other criteria such as RV regional dysfunction, reduced RV ejection fraction, and enlarged indexed RV end-diastole volume, can be used to diagnose ARVC 1.
• Left ventricular (LV) involvement can also occur, typically in the subepicardium or mid-myocardium, and may be associated with a higher risk of ventricular arrhythmias 1.
• Cardiac MRI is a valuable tool for detecting ARVC, with high spatial resolution and non-invasive tissue characterization capabilities, allowing for the assessment of subtle RV regional functional and structural wall abnormalities 1.

Diagnostic Considerations

• The diagnosis of ARVC is a composite of clinical, electrocardiographic, arrhythmic, histological, functional, and structural features, and cardiac MRI plays a role in assessing the latter two aspects 1.
• Great caution must be employed when interpreting cardiac MRI results, as a normal electrocardiogram (ECG) and Holter monitoring with an abnormal cardiac MRI exam is uncommon in ARVC patients 1.
• The use of late gadolinium enhancement (LGE) and gradient echo with fat saturation technique can help detect myocardial fibro-fatty replacement, but this aspect is not included in the Task Force Criteria (TFC) 2010 as a diagnostic criterion due to lack of standardization and control population 1.

From the Research

Abnormal Cardiac MRI with Fat Infiltration

An abnormal cardiac Magnetic Resonance Imaging (MRI) with fat infiltration can indicate several conditions, including:

• Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) 2, 3
• Healed myocardial infarction (MI) 3
• Cardiac lipoma, lipomatous hypertrophy of the interatrial septum, tuberous sclerosis complex, dilated cardiomyopathy, and cardiomyopathy with muscular dystrophy 3
• Right ventricular fatty infiltration with an abnormal ECG, which may not necessarily fulfill the criteria for ARVC 4
• Myocardial scar, which can play a central role in the genesis and maintenance of re-entrant arrhythmias 5

Differentiating Pathologic from Physiologic Fatty Infiltration

To differentiate pathologic from physiologic fatty infiltration, it is essential to consider:

• Patient age: physiologic myocardial fat develops with aging 3
• Characteristic locations of myocardial fat: pathologic conditions often have specific locations, such as the RV outflow tract and free wall in ARVC 3
• Myocardial thickness: pathologic conditions often have thinning of the myocardium 3
• Ventricular size: pathologic conditions often have enlargement of the ventricle 3
• Wall motion abnormality and late gadolinium enhancement at MR imaging: these findings can help narrow the diagnosis 3, 6

Diagnostic Value of Cardiac MRI

Cardiac MRI can provide valuable information about myocardial structural abnormalities, such as:

• Myocardial fatty replacement 5
• Myocardial oedema 5
• Necrosis/fibrosis 5
• Fat suppression can enhance the interpretation of intramyocardial fatty infiltration 6