Mitral Regurgitation (Adult Master Topic)

1. Overview

Mitral Regurgitation (MR) is a valvular heart disease characterised by the abnormal backward flow of blood from the left ventricle (LV) into the left atrium (LA) during systole. It is the most common valvular disorder worldwide, affecting ~2% of the total population and up to 10% of those > 75 years. [1]

MR is broadly classified into Primary (Organic)—due to intrinsic disease of the valve apparatus (leaflets, chordae, or papillary muscles)—and Secondary (Functional)—resulting from LV or LA remodelling that prevents effective coaptation. The clinical signature of chronic MR is an insidious progression of dyspnoea and AF, while Acute MR is a surgical emergency presenting as catastrophic "Flash" pulmonary oedema. [2]

Management has been revolutionised by the COAPT trial, which established the role of Transcatheter Edge-to-Edge Repair (TEER/MitraClip) for secondary MR. The 2024 standards prioritize early surgical repair for primary MR to prevent irreversible LV dysfunction, even in asymptomatic patients. [3]

2. Epidemiology

The Global Spectrum

• High-Income Countries: Degenerative (Myxomatous) MR is the leading cause (e.g. Mitral Valve Prolapse).
• LMICs: Rheumatic Heart Disease remains the primary driver of MR.
• Post-MI: Ischaemic MR occurs in up to 20% of patients after an inferior MI due to papillary muscle dysfunction. [4]

Incidence and Mortality

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3. Aetiology & Pathophysiology

⚠️ THE 7-STEP MOLECULAR MECHANISM (Primary/Degenerative)

1. VIC Disruption: In myxomatous disease, Valve Interstitial Cells (VICs) are activated, often due to mechanical strain or TGF-β dysregulation.
2. Proteoglycan Accumulation: Activated VICs over-produce glycosaminoglycans and proteoglycans (dermatan sulphate). This thickens the Spongiosa layer of the leaflet.
3. Collagen Fragmentation: Matrix Metalloproteinases (MMP-1 and MMP-2) degrade the structural Type I collagen in the Fibrosa layer, weakening the valve’s core.
4. Chordal Elongation/Rupture: Weakened collagen leads to the stretching and eventual snap of the Chordae Tendineae. This allows the leaflet to "flail" into the LA during systole.
5. Regurgitant Volumetric Load: The LV must pump both the systemic stroke volume and the regurgitant volume. This leads to Eccentric Hypertrophy (dilated, compliant LV).
6. LA Remodelling: The LA dilates to accommodate the high-pressure jet. This stretch triggers electrical remodelling and Atrial Fibrillation.
7. Pulmonary Venous Congestion: Eventually, the LA and LV become non-compliant. Back-pressure rises into the pulmonary veins, causing Pulmonary Hypertension and Right Heart Failure. [5, 6, 7]

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4. Clinical Presentation

Chronic MR (The Silent Progression)

• Symptoms: Dyspnoea on exertion, fatigue, and palpitations (AF).
• Signs:
  • Displaced Apex Beat: Indicative of LV dilatation.
  • Pansystolic Murmur: High-pitched, blowing, loudest at the apex, radiating to the Axilla.
  • Soft S1: Due to poor leaflet coaptation. [8]

Acute MR (The Emergency)

• Presentation: Sudden-onset "Flash" pulmonary oedema.
• Paradox: The murmur may be short and quiet because the LA is small and non-compliant, leading to a rapid equalization of LV and LA pressures.
• Cause: Papillary muscle rupture (Post-MI) or Infective Endocarditis. [9]

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5. Investigations

Echocardiography: The Severity Criteria

Severe MR is defined by:

• Regurgitant Volume: ≥60 mL/beat.
• Regurgitant Fraction: ≥50%.
• Effective Regurgitant Orifice Area (EROA): ≥40 mm² (≥20 mm² for secondary MR).
• Vena Contracta Width: > 7 mm. [10]

Advanced Imaging

• Cardiac MRI: The most accurate non-invasive tool for quantifying regurgitant volume when Echo is equivocal.
• Transoesophageal Echo (TOE): Essential for planning surgical repair (identifies the specific Scallop/Segment of the leaflet involved).

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6. Management: Repair vs. Replace

1. Primary MR (Surgical)

• Gold Standard: Mitral Valve Repair is vastly superior to replacement (preserves the subvalvular apparatus and avoids lifelong anticoagulation).
• Indication: Symptomatic severe MR OR asymptomatic if LVEF less than 60% or LVESD > 40mm. [11]

2. Secondary MR (Medical first)

• Pillar 1: Optimized GDMT (ACEi, BB, MRA, SGLT2i).
• Pillar 2: CRT if QRS > 130ms.
• Pillar 3: MitraClip (TEER) if symptomatic despite the above (COAPT trial evidence). [12]

3. Acute MR

• Emergency: Immediate surgical referral.
• Bridge: Intra-aortic Balloon Pump (IABP) to reduce afterload and improve forward flow while awaiting surgery.

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7. Evidence: Landmark Trials

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8. Single Best Answer (SBA) Questions

Question 1

A 55-year-old male with severe degenerative MR (flail P2 segment) is asymptomatic. His LVEF has dropped from 68% to 58% over the last year. What is the most appropriate management?

• A) Start Ramipril and review in 6 months
• B) Repeat Echo in 12 months
• C) Refer for Mitral Valve Repair
• D) Refer for Mitral Valve Replacement
• E) Perform a Treadmill Stress Test
• Answer: C. In primary MR, the surgical threshold is lower (LVEF less than 60% or LVESD > 40mm) because the LVEF "overestimates" true function. If function is falling, surgery is indicated even if the patient is asymptomatic.

Question 2

What is the primary haemodynamic benefit of an Intra-aortic Balloon Pump (IABP) in a patient with acute papillary muscle rupture and mitral regurgitation?

• A) Increased preload
• B) Reduction in afterload, increasing forward stroke volume
• C) Direct compression of the mitral valve
• D) Prevention of atrial fibrillation
• E) Reduction in pulmonary venous pressure via suction
• Answer: B. By deflating just before systole, the IABP reduces the resistance the LV must pump against (afterload), which encourages blood to flow out of the Aorta rather than back through the incompetent Mitral valve.

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9. Viva Scenario: The "Axilla" Radiation

Examiner: "Where does a mitral regurgitation murmur radiate to, and are there any exceptions?"

Candidate:

1. Classic Radiation: Most MR murmurs radiate to the Axilla.
2. The Exception: In cases of Posterior Leaflet Prolapse, the regurgitant jet is directed anteriorly against the interatrial septum, causing the murmur to radiate to the Base of the Heart and Carotids (mimicking Aortic Stenosis).
3. Anterior Leaflet: Conversely, anterior leaflet prolapse sends the jet posteriorly, radiating to the back or spine.
4. Clinical Importance: Understanding jet direction is crucial for the surgeon and for correctly identifying the valve lesion on clinical examination.

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10. Patient Explanation

"Your mitral valve is a one-way 'flap-door' in your heart that should close tightly to keep blood moving forward. In your case, the door is 'leaky,' allowing blood to splash back into the lungs with every beat. Over time, this makes your heart stretch and get tired. For your type of leak, we aim to 'repair' the door using keyhole or open-heart surgery, which is much better than replacing it entirely, as it keeps your heart's natural shape."

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11. References

1. Vahanian A, et al. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2022. [PMID: 34453165]
2. Stone GW, et al. Transcatheter Mitral-Valve Repair in Patients with Heart Failure (COAPT). N Engl J Med. 2018. [PMID: 30280640]
3. Otto CM, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease. Circulation. 2021. [PMID: 33332150]
4. Obadia JF, et al. Percutaneous Repair or Medical Treatment for Secondary Mitral Regurgitation (MITRA-FR). N Engl J Med. 2018. [PMID: 30145927]
5. Delling FN, et al. Evolution of Mitral Regurgitation and Left Atrial Thickness. Circulation. 2014. [PMID: 24657193]

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Last Updated: 2026-01-05 | MedVellum Editorial Team