What are the causes of mitral valve fibrosis seen as late gadolinium enhancement (LGE) on cardiac MRI?

Causes of Mitral Valve Fibrosis on Late Gadolinium Enhancement (LGE)

Mitral valve fibrosis detected by LGE on cardiac MRI occurs primarily in two distinct contexts: (1) papillary muscle and basal inferolateral wall fibrosis in mitral valve prolapse with mitral annular disjunction (the "arrhythmic MVP" phenotype), and (2) left ventricular myocardial fibrosis secondary to chronic mitral regurgitation from any cause, representing maladaptive remodeling. 1, 2, 3

Primary Mitral Valve Prolapse-Related Fibrosis

The most clinically significant pattern involves papillary muscle and basal inferolateral wall fibrosis in patients with mitral valve prolapse (MVP), particularly when mitral annular disjunction (MAD) is present 1, 4, 2, 3. This represents the "arrhythmic MVP" phenotype:

• Papillary muscle fibrosis occurs in 36% of patients with severe arrhythmic events versus only 9% without arrhythmias (p=0.03) 4
• LGE in papillary muscles carries an odds ratio of 4.09 (95% CI 1.28-13.05) for ventricular arrhythmias 4
• The fibrosis typically appears as focal mid-to-subendocardial enhancement in the basal inferolateral wall, in continuity with the disjunctive posterior annulus 2
• Longitudinal MAD distance also correlates with arrhythmia risk (OR 1.16,95% CI 1.02-1.33) 4

Critical diagnostic pitfall: This subtle basal inferolateral fibrosis is frequently missed on conventional bright-blood LGE imaging because the subendocardial scar blends with the adjacent bright blood pool. Dark-blood PSIR LGE sequences significantly improve detection sensitivity and should be included in dedicated MVP protocols 2, 3.

Secondary Myocardial Fibrosis from Chronic Mitral Regurgitation

Patients with moderate-to-severe chronic primary MR develop both replacement fibrosis (detected by LGE) and diffuse interstitial fibrosis (detected by T1 mapping), even when they don't yet meet surgical criteria 5, 6:

• 31% of patients with at least moderate primary MR show LGE, presenting as either infarct pattern, mid-wall fibrosis, or combined patterns 6
• Patients with LGE have significantly larger LV dimensions (end-systolic diameter 39±4 vs 34±5 mm, p=0.002) 6
• Replacement fibrosis (HR=1.83, p<0.01) and interstitial fibrosis (HR=1.61, p<0.01) independently predict mortality and need for mitral valve replacement 5
• LGE-positive patients have 78.5% incidence of adverse outcomes versus much lower rates in LGE-negative patients 5

Fibrosis in Specific Cardiomyopathies Affecting the Mitral Apparatus

Hypertrophic Cardiomyopathy (HCM)

• Papillary muscle abnormalities and fibrosis occur frequently and require different surgical management 7, 8, 9
• LGE is seen in 50-80% of HCM patients, with extensive LGE >15% of LV mass marking high sudden death risk 9
• Left atrial fibrosis is associated with HCM and atrial fibrillation 7, 8

Ischemic Cardiomyopathy

• The burden of replacement fibrosis by LGE predicts both clinical events and severity of ischemic MR 1
• Papillary muscle fibrosis from ischemia is a recognized cause of ventricular arrhythmias 10

Dilated Cardiomyopathy

• About one-third of DCM patients show mid-wall LGE, which is a strong independent predictor of all-cause mortality, cardiovascular death/transplantation, and sudden cardiac death 11

Other Causes

Papillary muscle fibrosis can occur in cardiac amyloidosis, cardiac sarcoidosis, and other infiltrative cardiomyopathies 10.

Practical Imaging Approach

For suspected arrhythmic MVP:

1. Perform cine imaging to identify prolapse and measure MAD (≥3mm is significant)
2. Include both conventional bright-blood AND dark-blood PSIR LGE sequences at identical slice prescriptions 2
3. Carefully scrutinize the basal inferolateral wall and papillary muscles
4. Use T1 mapping to detect diffuse interstitial fibrosis indicating early dysfunction 3, 12

For chronic MR assessment:

1. Quantify MR severity using phase-contrast flow imaging (more accurate than echo in this setting) 1
2. Assess both replacement fibrosis (LGE) and interstitial fibrosis (native T1, ECV) 5
3. Evaluate LV volumes, function, and early remodeling markers like global longitudinal strain 1, 12

The presence of myocardial fibrosis in either context has major prognostic implications and should influence decisions regarding arrhythmia surveillance, ICD consideration, and timing of surgical intervention 1, 4, 3, 5.