How do you differentiate between restrictive cardiomyopathy (RCM) and constrictive pericarditis (CP)?

Differentiating Restrictive Cardiomyopathy from Constrictive Pericarditis

Cardiac catheterization (option c) is the gold standard for differentiating restrictive cardiomyopathy from constrictive pericarditis when non-invasive methods are inconclusive, though cardiac MRI (option a) has emerged as the preferred first-line imaging modality for this distinction. 1, 2

Primary Diagnostic Approach

Cardiac MRI (Option a) - First-Line Imaging

Cardiac MRI is the most useful non-invasive test for distinguishing these conditions and should be performed before proceeding to invasive testing. 1, 3

• Pericardial thickness assessment: Thickened pericardium (>4mm) strongly suggests constrictive pericarditis, though normal thickness does not exclude it. 1
• Pericardial calcification detection: Identifies constrictive pericarditis rather than restrictive cardiomyopathy. 1
• Ventricular coupling evaluation: Real-time cine MRI during free breathing accurately assesses ventricular interdependence and septal bounce, which are hallmarks of constriction. 1
• Myocardial tissue characterization: Late gadolinium enhancement patterns can identify specific causes of restrictive cardiomyopathy (diffuse subendocardial enhancement in amyloidosis, patchy mid-wall enhancement in sarcoidosis). 1

Cardiac Catheterization (Option c) - Definitive Hemodynamic Assessment

When imaging is equivocal, cardiac catheterization provides definitive hemodynamic differentiation. 1, 2, 4

Key Hemodynamic Criteria Favoring Constrictive Pericarditis:

• End-diastolic pressure discordance: RVEDP-LVEDP difference <5 mmHg suggests constriction (85% predictive accuracy). 4
• RV systolic pressure: <50 mmHg favors constriction (70% predictive accuracy). 4
• RVEDP/RVSP ratio: ≥1/3 suggests constriction (76% predictive accuracy). 4
• When all three criteria are concordant, diagnostic accuracy exceeds 90%. 4

Additional Hemodynamic Features:

• Prominent Y descent: Characteristic of constrictive pericarditis, representing rapid early diastolic filling that abruptly halts. 2, 5
• Square root sign: "Dip-and-plateau" pattern in ventricular pressure tracings. 2
• Respiratory variation: >25% variation in ventricular filling across atrioventricular valves during respiration. 2
• Systolic area index: Novel parameter with 97% sensitivity and 100% predictive accuracy for constriction. 2

Hemodynamic Features Favoring Restrictive Cardiomyopathy:

• Elevated pulmonary artery systolic pressure: Typically >50 mmHg suggests restrictive cardiomyopathy rather than constriction. 2
• LVEDP exceeds RVEDP by >5 mmHg: Indicates myocardial disease. 4

Secondary Diagnostic Options

Endomyocardial Biopsy (Option d) - Role in Specific Scenarios

Biopsy is not used to differentiate constriction from restriction per se, but rather to identify specific treatable causes of restrictive cardiomyopathy, thereby avoiding unnecessary thoracotomy. 6

• Identifies specific restrictive cardiomyopathies: Amyloidosis, sarcoidosis, hemochromatosis, and other infiltrative diseases in 39% of patients with severe constrictive/restrictive physiology. 6
• Supports need for surgery: Normal or nonspecific biopsy findings in symptomatic patients increase likelihood of finding pericardial constriction at thoracotomy (77% in one series). 6
• Avoids unnecessary thoracotomy: When specific restrictive cardiomyopathy is identified, surgical exploration is contraindicated. 6
• May be ultimately required: For definitive diagnosis of infiltrative diseases when imaging is inconclusive. 1

Pericardiocentesis (Option b) - Not a Diagnostic Tool for This Distinction

Pericardiocentesis has no role in differentiating restrictive cardiomyopathy from constrictive pericarditis unless there is a significant pericardial effusion present. 1

• Only relevant for effusive-constrictive pericarditis: When pericardial effusion is present, monitoring pressures during pericardiocentesis can reveal persistent constriction after fluid removal. 1, 5
• Not applicable to chronic constriction: Most cases of constrictive pericarditis do not have significant effusions requiring drainage. 1

Clinical Algorithm

1. Start with cardiac MRI to assess pericardial thickness, calcification, ventricular coupling, and myocardial tissue characteristics. 1, 3

2. If MRI is diagnostic (clear pericardial abnormalities or specific myocardial disease pattern), proceed accordingly without catheterization. 1, 3

3. If MRI is equivocal, proceed to cardiac catheterization with comprehensive hemodynamic assessment including respiratory variation measurements. 2, 4, 7

4. If catheterization shows concordant criteria (all three hemodynamic parameters pointing to same diagnosis), confidence exceeds 90%. 4

5. If diagnosis remains uncertain after catheterization, consider endomyocardial biopsy to identify specific restrictive cardiomyopathies that would contraindicate surgery. 6

Critical Pitfall

One-fourth of patients cannot be classified by hemodynamic criteria alone, emphasizing the need for multimodality assessment combining imaging and invasive hemodynamics. 4, 7 The distinction is critical because constrictive pericarditis is surgically curable with pericardiectomy, while restrictive cardiomyopathy requires medical management or cardiac transplantation. 3, 8