What is mitral regurgitation?

Mitral Regurgitation

Mitral regurgitation (MR) is the abnormal backflow of blood from the left ventricle into the left atrium during systole due to improper closure of the mitral valve, which can lead to left ventricular overload, dysfunction, and ultimately heart failure if left untreated. 1

Types and Mechanisms

Mitral regurgitation can be classified into two main categories:

Primary (Organic) MR

• Caused by intrinsic abnormalities of the mitral valve apparatus
• Common causes include:
  • Degenerative disease (most common in developed countries)
    • Mitral valve prolapse
    • Fibroelastic degeneration
    • Barlow's disease
  • Rheumatic heart disease (more common in developing countries)
  • Endocarditis
  • Ruptured papillary muscle (acute, following myocardial infarction)
  • Congenital abnormalities

Secondary (Functional) MR

• Occurs despite a structurally normal valve
• Results from left ventricular dysfunction causing:
  • Papillary muscle displacement
  • Mitral annular dilation
  • Leaflet tethering
• Common causes include:
  • Ischemic heart disease (95% of cases show Type IIIb dysfunction) 1
  • Dilated cardiomyopathy
  • Left atrial dilation (atrial functional MR)

Carpentier's Classification of MR Mechanisms

Based on leaflet motion: 1

• Type I: Normal leaflet motion (annular dilation, leaflet perforation)
• Type II: Excessive leaflet motion (prolapse, flail leaflet)
• Type III: Restrictive leaflet motion
  • Type IIIa: Restriction during diastole and systole (rheumatic)
  • Type IIIb: Restriction during systole (ischemic/functional)

Clinical Presentation

• Asymptomatic in early stages
• Progressive symptoms as disease advances:
  • Exertional dyspnea
  • Fatigue
  • Palpitations
  • Symptoms of heart failure in advanced cases
• Characteristic murmur: Holosystolic, radiating to the axilla
• In acute severe MR: Pulmonary edema and cardiogenic shock may occur 2

Diagnostic Evaluation

Echocardiography is the primary diagnostic tool: 1

• Transthoracic echocardiography (TTE):

  • Assesses valve morphology and function
  • Quantifies severity using multiple parameters
  • Evaluates left ventricular size and function
  • Measures left atrial dimensions

• Severity assessment parameters:

  • Qualitative: Jet size, vena contracta width, pulmonary vein flow pattern
  • Quantitative:
    • Effective regurgitant orifice area (EROA)
    • Regurgitant volume (RVol)
    • Regurgitant fraction (RF)

• Transesophageal echocardiography (TEE):

  • Better visualization of valve morphology
  • More accurate assessment in complex cases
  • Essential for procedural planning

Severity Grading

MR severity is determined by integrating multiple parameters: 1

• Mild MR: EROA <0.2 cm², RVol <30 mL
• Moderate MR: EROA 0.2-0.39 cm², RVol 30-59 mL
• Severe MR: EROA ≥0.4 cm², RVol ≥60 mL

Important caveat: In secondary MR, lower thresholds may indicate severe MR (EROA ≥0.2 cm², RVol ≥30 mL) due to the concept of "disproportionate MR" 1

Pitfalls in Assessment

• Eccentric jets: May underestimate severity if only jet area is used 1
• Non-holosystolic MR: Late systolic or biphasic MR can lead to overestimation if PISA method is used at peak 1
• Atrial fibrillation: Causes variability in measurements
• Inconsistent findings: When echocardiographic findings don't match clinical presentation, additional imaging (TEE or CMR) is recommended 1

Natural History and Prognosis

• Yearly mortality rates for patients over 50 years: 3
  • Moderate organic MR: ~3%
  • Severe organic MR: ~6%
• Progression is often insidious due to left atrial enlargement compensating for increasing regurgitant volume
• Eventually leads to left ventricular overload, dysfunction, and heart failure if untreated

Treatment Approaches

Medical Therapy

• Limited role in primary MR
• In secondary MR:
  • Guideline-directed medical therapy (GDMT) for heart failure is the first step 1
  • Includes ACE inhibitors, beta-blockers, ARNIs, SGLT2 inhibitors

Interventional Treatment

• Surgical options:

  • Mitral valve repair (preferred when feasible)
  • Mitral valve replacement
  • Valve repair reduces mortality by approximately 70% compared to medical therapy in severe organic MR 3

• Transcatheter options:

  • Mitral transcatheter edge-to-edge repair (mTEER/MitraClip)
  • First-line therapy for patients with heart failure and significant secondary MR despite maximal GDMT 1

Key Considerations in Management

• Timing of intervention is critical:

  • Early intervention in asymptomatic patients with severe MR shows better outcomes
  • Best results are obtained in centers with high repair rates (≥80-90%) and low operative mortality (<1%) 3

• For secondary MR:

  • Optimize GDMT first
  • Consider transcatheter intervention if MR persists despite optimal medical therapy 1

• For primary MR:

  • Surgical repair is preferred when feasible
  • Early intervention before symptom onset may be warranted in specialized centers

Clinical Pearls

• Always ensure concordance between physical examination findings and echocardiographic results 1
• Be cautious of underestimation of MR severity with eccentric jets
• Consider the concept of proportionate vs. disproportionate MR in secondary MR 1
• Integrate multiple parameters when assessing MR severity rather than relying on a single measurement