# Mitral Regurgitation: Degenerative Disease and Surgical Repair

## Overview

Degenerative mitral regurgitation (MR) is the most common indication for mitral valve surgery in the developed world. Surgical repair — rather than replacement — is the gold standard, offering superior long-term survival, preservation of ventricular function, and freedom from prosthesis-related complications. Repair rates exceeding 95% at experienced centers are now expected for degenerative disease.

## Carpentier Classification of Mitral Valve Pathology

### Functional Classification

The Carpentier classification organizes mitral valve pathology by leaflet motion. Type I describes normal leaflet motion with regurgitation caused by annular dilatation or leaflet perforation. Type II describes excess leaflet motion (prolapse), which is the most common mechanism in degenerative disease — the leaflet tip overrides the annular plane during systole due to chordal elongation, chordal rupture, or papillary muscle elongation. Type IIIa describes restricted leaflet motion in both systole and diastole, characteristic of rheumatic disease with leaflet thickening and chordal fusion. Type IIIb describes restricted motion in systole only, seen in functional or ischemic MR where ventricular remodeling tethers the leaflets.

### Segmental Anatomy (Carpentier Nomenclature)

The posterior leaflet is divided into three scallops: P1 (lateral), P2 (middle, the largest scallop), and P3 (medial). Corresponding segments of the anterior leaflet are designated A1, A2, and A3. The two commissures are anterolateral (between A1 and P1) and posteromedial (between A3 and P3). P2 prolapse is the most common lesion in degenerative MR, accounting for 60-70% of cases.

### Carpentier Classification Summary

| Type | Leaflet Motion | Mechanism | Typical Pathology |
|------|---------------|-----------|-------------------|
| I | Normal | Annular dilatation or leaflet perforation | Functional MR, endocarditis |
| II | Excess (prolapse) | Chordal elongation/rupture, papillary muscle elongation | Degenerative MR (FED, Barlow) |
| IIIa | Restricted (systole + diastole) | Leaflet thickening, chordal fusion | Rheumatic disease |
| IIIb | Restricted (systole only) | Ventricular remodeling, leaflet tethering | Functional/ischemic MR |

## Degenerative Mitral Valve Disease

### Fibroelastic Deficiency (FED)

FED is the most common form of degenerative disease in older patients (60-80 years). The leaflets are thin and translucent, with isolated segmental prolapse — typically a single ruptured chord to one segment (usually P2). It is generally straightforward to repair.

### Barlow Disease

Barlow disease occurs in younger patients (40-60 years) and is characterized by excess leaflet tissue with myxomatous thickening and redundancy, multi-segment prolapse or billowing, and annular dilatation with calcification. Repair is more complex, with a higher recurrence rate.

### FED vs. Barlow Disease Comparison

| Feature | Fibroelastic Deficiency (FED) | Barlow Disease |
|---------|-------------------------------|----------------|
| Age | 60-80 years | 40-60 years |
| Leaflet tissue | Thin, translucent | Thick, myxomatous, redundant |
| Prolapse pattern | Isolated single segment (usually P2) | Multi-segment, billowing |
| Annulus | Normal or mildly dilated | Dilated, often calcified |
| Typical mechanism | Single ruptured chord | Diffuse excess tissue |
| Repair complexity | Straightforward | Complex |
| Recurrence rate | Low | Higher |

### Forme Fruste

Forme fruste is intermediate between FED and Barlow, with myxomatous change limited to one or two segments and moderate tissue excess.

## Preoperative Assessment

### Echocardiography

TTE establishes severity grading, LV dimensions, LVEF, and pulmonary artery pressure. Severe MR is defined by vena contracta at or above 7 mm, EROA at or above 0.4 cm2, regurgitant volume at or above 60 mL, and regurgitant fraction at or above 50%. Intraoperative TEE provides precise identification of prolapsing segments, chordal pathology, annular dimensions, and jet direction. A critical point: the jet direction points away from the prolapsing leaflet. For example, posterior leaflet prolapse produces an anteriorly directed jet.

### Indications for Surgery (ACC/AHA 2020)

Class I indications include symptomatic severe primary MR with LVEF above 30% and asymptomatic severe primary MR with LV dysfunction (LVEF 30-60% or LVESD at or above 40 mm). Class IIa indications include asymptomatic severe primary MR with preserved LV function when repair is highly likely (above 95% probability) and operative mortality is low (below 1%) at a Reference Center of Excellence, as well as asymptomatic severe MR with new-onset atrial fibrillation or resting pulmonary hypertension (PASP above 50 mmHg).

## Surgical Repair Techniques

### Principles of Repair (Carpentier's Triad)

Every mitral repair addresses three goals: restore normal leaflet motion (address prolapse or restriction), create a large surface of coaptation (ensure adequate leaflet apposition), and remodel the annulus (annuloplasty ring to support the repair).

### Posterior Leaflet Repair Techniques Comparison

| Technique | Indication | Advantages | Disadvantages |
|-----------|-----------|------------|---------------|
| Triangular resection | Limited P2 prolapse | Simple, reproducible | Removes leaflet tissue |
| Quadrangular resection + sliding annuloplasty | Broader P2 prolapse | Reduces posterior leaflet height (prevents SAM) | More complex; removes tissue |
| PTFE neochordae | Any segment prolapse | Preserves all tissue; larger coaptation surface | Requires papillary muscle access |
| Chordal transfer | Focal prolapse | Uses native tissue | Limited donor chord availability |
| Edge-to-edge (Alfieri) | Bailout technique | Simple | Creates double-orifice; stenosis risk |

### Posterior Leaflet Repair

Triangular resection excises a triangle of prolapsing tissue from the free edge and closes the leaflet edges with running suture — it is simple, reproducible, and effective for limited P2 prolapse. Quadrangular resection excises a rectangular segment of the prolapsing posterior leaflet and closes the gap, sometimes with a sliding annuloplasty that detaches the remaining leaflet segments from the annulus, slides them together, and reattaches them to reduce posterior leaflet height and prevent systolic anterior motion (SAM).

Non-resection techniques are increasingly preferred at many centers. PTFE neochordae (Gore-Tex sutures) are artificial chordae placed from the papillary muscle tip to the free edge of the prolapsing segment, preserving all leaflet tissue to maximize the coaptation surface. Chordal transfer moves a secondary chord from a non-prolapsing segment to support the prolapsing edge. The edge-to-edge repair (Alfieri stitch) sutures the free edges of A2 and P2 together, creating a double-orifice valve — used primarily as a bailout technique.

### Anterior Leaflet Repair

Anterior leaflet repair is more challenging because there is less tissue available for resection. PTFE neochordae are the preferred technique, with sutures anchored in the fibrous tip of the appropriate papillary muscle and two or more pairs placed to the prolapsing segment. Length is set to match non-prolapsing reference chordae. Chordal transfer from the posterior leaflet to support the anterior leaflet is another option. Chordal shortening has largely been abandoned due to higher recurrence rates.

### Commissural Repair

Commissural prolapse (anterolateral or posteromedial) can be addressed with commissural closure (plication), neochordae, or sliding commissuroplasty.

### Annuloplasty Ring

The annuloplasty ring is an essential component of every mitral repair — it stabilizes the annulus and prevents future dilatation. Complete rigid rings (such as the Carpentier-Edwards Physio) are the most popular, restoring normal annular shape and saddle geometry. Flexible bands (such as the Cosgrove-Edwards) preserve more annular dynamics. Semi-rigid rings offer a compromise. The ring is sized to the anterior leaflet area (intertrigonal distance), typically 28-34 mm. The ring should not be undersized (which causes SAM through restrictive annuloplasty) or oversized (which leads to inadequate coaptation).

<image>Step-by-step illustration of posterior leaflet (P2) mitral valve repair. Panel A shows the surgeon's view of the mitral valve with P2 prolapse due to ruptured chordae, with an anteriorly directed regurgitant jet indicated by an arrow. Panel B demonstrates quadrangular resection of the prolapsing P2 segment with the excised tissue shown. Panel C shows sliding annuloplasty with the remaining P1 and P3 segments detached and slid toward each other, then reattached to the annulus with interrupted sutures to reduce posterior leaflet height. Panel D shows the completed repair with a rigid annuloplasty ring in place and symmetric coaptation of the anterior and posterior leaflets. A small inset shows the alternative PTFE neochordae technique with Gore-Tex sutures running from the papillary muscle to the P2 free edge.</image>

## Systolic Anterior Motion (SAM)

### Mechanism

After repair, the posterior leaflet can be pushed anteriorly during systole, dragging the anterior leaflet toward the septum and creating dynamic LVOT obstruction (similar to hypertrophic obstructive cardiomyopathy) with recurrent MR. Risk factors include excessive posterior leaflet height (above 15 mm), a small LV cavity, a narrow aorto-mitral angle, and an undersized ring.

### Prevention

SAM is prevented by sliding annuloplasty to reduce posterior leaflet height, avoiding undersizing the annuloplasty ring, and adequate resection of excess tissue.

### Intraoperative Management of SAM

If SAM develops after repair, initial management includes volume loading (increase preload), discontinuing inotropes, and administering phenylephrine (increase afterload). If SAM persists despite medical management, the repair must be revised to further reduce posterior leaflet height, upsize the ring, or consider replacement.

## Quality Metrics and Outcomes

### Repair Rate

Centers of excellence achieve greater than 95% repair rates for degenerative MR. The STS benchmark specifies that the repair rate for posterior leaflet prolapse should exceed 90%. Repair rate is a publicly reported quality metric.

### Operative Mortality

Isolated degenerative MR repair carries less than 1% mortality at experienced centers, significantly lower than mitral valve replacement (2-5%).

### Long-Term Results

Freedom from reoperation is 90-95% at 10 years for degenerative repair. Long-term survival approaches that of the age-matched general population. Recurrent MR (moderate or greater) occurs in 5-10% at 10 years.

<image>Carpentier segmental anatomy of the mitral valve as seen from the surgeon's perspective (left atrial view). The anterior leaflet is divided into A1 (lateral), A2 (middle), and A3 (medial) segments. The posterior leaflet is divided into P1 (lateral), P2 (middle, largest scallop), and P3 (medial) segments. The anterolateral and posteromedial commissures are labeled. The aortic valve is visible through the aortic-mitral curtain above the anterior leaflet. The anterolateral and posteromedial papillary muscles are shown with their chordal attachments to the respective leaflet segments. Color coding indicates the most common prolapse locations in degenerative disease.</image>

## Clinical Pearls

P2 prolapse is the "bread and butter" of mitral valve repair, and every CT surgery resident must master its repair through resection and/or neochordae techniques. The jet direction on TEE points away from the prolapsing segment — an anteriorly directed jet means posterior leaflet prolapse, and vice versa. Annuloplasty ring implantation is mandatory in every mitral repair; repair without a ring has unacceptable recurrence rates from progressive annular dilatation. SAM is a preventable complication: reduce posterior leaflet height below 15 mm and do not undersize the ring. Neochordae (PTFE) are increasingly replacing resection techniques because they preserve leaflet tissue and create a larger coaptation surface. Repair rates above 95% for degenerative MR are achievable and expected at experienced centers — patients with degenerative MR should be referred to surgeons with high repair rates. The threshold for early surgery in asymptomatic severe MR has shifted, with Class IIa guidelines now supporting surgery when repair likelihood exceeds 95% and mortality is below 1%, even without symptoms or LV dysfunction. Barlow disease is more complex to repair than FED — anticipate multi-segment prolapse, annular calcification, and longer cross-clamp times.

## References

- **Carpentier A, Adams DH, Filsoufi F.** *Carpentier's Reconstructive Valve Surgery.* Saunders/Elsevier; 2010.
- **Otto CM, Nishimura RA, Bonow RO, et al.** 2020 ACC/AHA Guideline for Valvular Heart Disease. *Circulation.* 2021;143(5):e72-e227.
- **David TE, Armstrong S, McCrindle BW, Manlhiot C.** Late outcomes of mitral valve repair for mitral regurgitation due to degenerative disease. *Circulation.* 2013;127(14):1485-1492.
- **Goldstone AB, Chikwe J, Pinney SP, et al.** Incidence, epidemiology, and prognosis of residual pulmonary hypertension after mitral valve repair for degenerative mitral regurgitation. *J Am Heart Assoc.* 2020;9(7):e015402.
- **Adams DH, Rosenhek R, Falk V.** Degenerative mitral valve regurgitation: best practice revolution. *Eur Heart J.* 2010;31(16):1958-1966.