Can cardiac magnetic resonance (CMR) imaging results be used to determine the cause of cardiomyopathy?

Can CMR Determine the Cause of Cardiomyopathy?

Yes, cardiac magnetic resonance (CMR) imaging is highly effective at determining the underlying cause of cardiomyopathy and should be used as a first-line diagnostic tool when myocardial tissue characterization is needed to establish etiology. 1

Why CMR is Essential for Etiologic Diagnosis

CMR is generally considered appropriate when myocardial tissue characterization (scar, infiltrative disease, inflammation, etc.) is pivotal for the diagnosis, particularly when echocardiography fails to provide an accurate morpho-functional assessment. 1 The technique provides a "noninvasive, biopsy-like approach" that can verify pathognomonic imaging features of different cardiomyopathies. 1

Specific Diagnostic Capabilities by Cardiomyopathy Type

Inflammatory Cardiomyopathies:

• CMR may be considered as a first-line diagnostic tool for diagnostic workup of acute myocardial inflammation. 1
• The use of T1 and T2 mapping to detect myocardial inflammation is strongly suggested, as it has a positive impact on diagnostic accuracy. 1
• CMR is useful for identifying various chronic inflammatory conditions, ranging from chronic myocarditis to sarcoidosis to HIV disease. 1
• The 2018 Updated Lake Louise Criteria require at least one T2-based criterion (myocardial edema) AND at least one T1-based criterion (myocardial injury) for diagnosing myocarditis, with diagnostic accuracy of 78% sensitivity and 88% specificity. 1, 2

Arrhythmogenic Cardiomyopathy:

• CMR is indicated to support the diagnosis of arrhythmogenic cardiomyopathy together with ECG, histological and functional evaluation, both in early and advanced disease. 1
• Repeated cardiac imaging is needed to follow disease progression and for risk assessment of life-threatening ventricular arrhythmias. 1

Restrictive Cardiomyopathy:

• CMR is recommended for the diagnosis of restrictive cardiomyopathy through accurate assessment of cardiac chambers volume and mass, beside myocardial tissue characterization. 1
• T1 and T2* mapping may play a fundamental role in infiltrative cardiomyopathies and iron overload, respectively. 1

Dilated Cardiomyopathy:

• CMR is the gold standard for LV and RV quantification and should be considered when echocardiographic data is suboptimal, borderline, or doubtful. 1, 3
• CMR provides unique tissue characterization that can identify the underlying etiology through detection of myocardial edema, scarring, fibrosis, and infiltration. 1, 3
• The presence and pattern of late gadolinium enhancement (LGE) helps differentiate ischemic from non-ischemic causes. 4, 5

Hypertrophic Cardiomyopathy:

• CMR can provide additional information in prognostic stratification and therapeutic planning. 1
• CMR is recommended to assess the extent and distribution of hypertrophy and myocardial fibrosis prior to septal alcohol ablation or myectomy. 1

Algorithmic Approach to Using CMR for Etiologic Diagnosis

Step 1: Initial Assessment

• Perform echocardiography first to assess basic morphology and function. 1, 3
• If echocardiography provides clear diagnosis with adequate image quality, CMR may not be immediately necessary. 1

Step 2: CMR Indications

• Order CMR when: 1, 3
  • Etiology remains unclear after initial workup
  • Discrepancy exists between clinical presentation and echocardiographic findings
  • Tissue characterization is needed to distinguish between different cardiomyopathy types
  • Inflammatory, infiltrative, or storage disease is suspected
  • Precise quantification of ventricular volumes and function is required

Step 3: CMR Protocol Selection

• For suspected inflammatory disease: Use T2-weighted imaging or T2-mapping for edema, plus T1-mapping and late gadolinium enhancement for injury/fibrosis. 1, 2
• For suspected infiltrative disease: Use native T1 mapping and extracellular volume (ECV) quantification. 1, 6
• For suspected iron overload: Use T2* mapping. 1
• For all cases: Include late gadolinium enhancement to assess pattern and distribution of fibrosis/scar. 4, 5

Step 4: Pattern Recognition

• Subepicardial or mid-wall LGE in non-coronary distribution: Suggests myocarditis or non-ischemic cardiomyopathy. 1, 2
• Subendocardial or transmural LGE in coronary distribution: Indicates ischemic cardiomyopathy. 1, 2
• Diffuse LGE with elevated native T1: Suggests infiltrative disease (amyloidosis, sarcoidosis). 1, 6
• Elevated T2 signal with elevated T1: Indicates active inflammation. 1, 2

Critical Advantages Over Other Modalities

CMR has several formal advantages over endomyocardial biopsy: 1

• CMR can assess regions not accessible to biopsy (epicardium, pericardium). 1
• CMR avoids sampling error inherent to patchy disease distribution. 7
• CMR provides incremental data that may aid disease management. 1
• CMR can inform clinical decision making and avoid invasive procedures like coronary angiography and endomyocardial biopsies. 1

Native T1-mapping demonstrates the highest accuracy for diagnosing myocarditis, with 90% sensitivity, 91% specificity, and 91% accuracy. 2

Common Pitfalls to Avoid

Delaying CMR until after multiple other tests may postpone diagnosis and appropriate treatment. 3 When tissue characterization is needed to establish etiology, CMR should be ordered early in the diagnostic workup rather than as a last resort.

Do not rely solely on late gadolinium enhancement patterns. The combination of multiple CMR parameters (T1 mapping, T2 mapping, ECV, and LGE) provides superior diagnostic accuracy compared to any single parameter. 1, 2, 6

Timing matters for inflammatory cardiomyopathies. The course of myocardial inflammation limits optimal sensitivity for diagnostic imaging to a few weeks from presentation. 1 Order CMR promptly when myocarditis is suspected rather than waiting for symptoms to evolve.

In patients with severe renal dysfunction (eGFR <30 mL/min/1.73 m²), non-contrast CMR is reasonable for describing location, size, and hemodynamic effects, but may be less useful for tissue characterization. 2 Consider alternative approaches or weigh risks/benefits of gadolinium administration in this population.

Prognostic Value Beyond Diagnosis

CMR provides critical prognostic information beyond establishing etiology: 1, 2, 4

• Late gadolinium enhancement predicts subsequent risk of ventricular arrhythmias and cardiovascular death in biopsy-proven viral myocarditis. 2
• The presence and extent of LGE determine prognosis in many non-ischemic cardiomyopathies. 4
• Myocardial edema without LGE on CMR has been associated with improved recovery and outcomes in acute cases. 1