Mitral Regurgitation (MR)

Definition

Classification

• Braunwald's Heart Disease

Etiology

• Bailey & Love's Short Practice of Surgery, 28th Ed.

Pathophysiology

Barash Clinical Anesthesia - Pathophysiology of MR: Acute (left) vs Chronic (right)

Acute MR

• The LV suddenly ejects blood back into a small, poorly compliant LA
• Abrupt rise in LA pressure → pulmonary venous hypertension → pulmonary oedema
• LV is effectively unloaded (reduced afterload), EF appears supranormal but forward stroke volume falls
• Causes: papillary muscle rupture post-MI, chordal rupture, acute endocarditis

Chronic Compensated MR

• Eccentric hypertrophy of LV develops (sarcomere replication in series)
• LA enlarges, increasing compliance → LA pressure normalized
• LV ejection fraction remains elevated due to reduced afterload and preserved contractile function
• Total stroke volume is increased; forward stroke volume approaches normal
• Patient may remain asymptomatic for years

Chronic Decompensated MR

• Progressive contractile dysfunction develops → ESV rises, EF falls
• Further LV dilation worsens regurgitation (annular dilatation, papillary muscle displacement → worse leaflet malcoaptation - a vicious cycle)
• Despite significant contractile dysfunction, EF may still appear "normal" due to the favorable loading conditions - EF underestimates true myocardial dysfunction
• Pulmonary congestion reappears; atrial fibrillation common with LA dilation
• Severe MR causes decreased survival whether symptomatic or not
• Goldman-Cecil Medicine, International Ed.

Bailey & Love - MR showing regurgitant jet into LA during systole, with raised LA pressure (120/↑ mmHg)

• Regurgitant orifice area
• LV-LA pressure gradient
• Systolic ejection time
• LA compliance

Clinical Features

Symptoms

• Acute MR: Acute onset pulmonary oedema, severe dyspnea, cardiogenic shock
• Mild chronic MR: Often asymptomatic
• Progressive chronic MR: Fatigue, exertional dyspnea, orthopnoea, palpitations (AF)
• Haemoptysis (with severe pulmonary hypertension)

Signs

• Apex: Displaced, heaving (volume-loaded LV); hyperdynamic apex beat
• Murmur: Pansystolic (holosystolic) murmur, best heard at apex, radiating to the axilla
• S3 gallop (volume overload)
• Signs of AF (irregularly irregular pulse) with LA dilatation
• Features of pulmonary hypertension in advanced disease (loud P2, RV heave)

Investigations

ECG

• P mitrale: bifid P waves (left atrial hypertrophy/dilatation)
• Left ventricular hypertrophy
• Atrial fibrillation (common with severe/longstanding disease)

Chest Radiograph

• Cardiomegaly (absent cardiomegaly suggests mild or acute MR)
• Prominent pulmonary vasculature
• LA enlargement (double shadow at right heart border; splaying of carina)

Echocardiography (Primary Investigation)

• TTE: Defines leaflet anatomy, LV size and function, LA size, estimates regurgitant severity
• Color-flow Doppler: Visualizes regurgitant jet; identifies jet direction, size, area
• Quantitative parameters:
  • Vena contracta width (width of narrowest part of regurgitant jet)
  • PISA (Proximal Isovelocity Surface Area): Calculates effective regurgitant orifice area (EROA) and regurgitant volume
  • Pulmonary vein systolic flow reversal (indicates severe MR)
• TEE: Superior detail of leaflet anatomy; essential when TTE is non-diagnostic or surgery is planned; 3D TEE provides precise anatomy for surgical repair planning
• Severe MR criteria: EROA ≥ 0.40 cm² (primary), regurgitant volume ≥ 60 mL, regurgitant fraction ≥ 50%

Cardiac MRI

• Most accurate quantification of regurgitant volume and fraction
• Increasingly used when echo is insufficient

Cardiac Catheterization

• For cases of diagnostic doubt regarding severity
• Coronary angiography mandatory in patients >40 years or with suspected coronary disease prior to surgery
• Textbook of Clinical Echocardiography; Goldman-Cecil Medicine; Bailey & Love

Management

Medical Therapy

• Goal: increase forward cardiac output, reduce regurgitant volume
• Arterial vasodilators (sodium nitroprusside): reduce SVR, preferentially increase aortic outflow, decrease regurgitant fraction - cannot use if hypotensive
• Intra-aortic balloon counterpulsation (IABP): used when vasodilators are contraindicated (hypotension) - increases forward output by reducing afterload and augmenting diastolic pressure
• Aim for urgent surgical correction

• Afterload reduction is not definitively indicated in chronic asymptomatic MR with preserved LV function, since afterload is typically not increased
• "Watchful waiting / active surveillance" is appropriate until development of: symptoms, LV dysfunction, new AF, or pulmonary hypertension
• ACE inhibitors/ARBs: used if hypertension co-exists or in secondary MR with LV dysfunction
• Rate control for AF; anticoagulation if AF present

• Heart failure medical therapy (ACE inhibitors, beta-blockers, diuretics for symptom control)
• Does not delay surgery if criteria are met

Surgical Therapy

1. Severe MR with symptoms (NYHA II-IV)
2. Severe MR with LV dysfunction (EF ≤ 60% or LV end-systolic diameter ≥ 40 mm)
3. New-onset atrial fibrillation attributable to MR
4. Pulmonary hypertension (PA systolic pressure > 50 mmHg at rest or > 60 mmHg with exercise)
5. Severe MR in patients undergoing cardiac surgery for another indication
6. Asymptomatic severe MR with high likelihood of successful repair at an experienced center

• Valve repair is preferred when technically feasible:
  • Lower operative mortality (~2% vs ~6% for replacement)
  • Lower rate of endocarditis
  • Better preserved LV function post-operatively
  • Avoids lifelong anticoagulation (if bioprosthetic replacement used)
  • Better long-term EF and survival
• When repair is not feasible: valve replacement with preservation of subvalvular apparatus (chordal-sparing) is preferred
• For severe ischemic MR: replacement shows less residual MR and less severe heart failure vs. repair at 1-2 years, though clinical outcomes are equivalent
• Bailey & Love; Goldman-Cecil Medicine; Braunwald's Heart Disease; Symptom to Diagnosis 4th Ed.

Transcatheter / Percutaneous Therapy

• MitraClip (TEER - Transcatheter Edge-to-Edge Repair): Replicates the Alfieri stitch - clips P2 and A2 segments of posterior and anterior leaflets together, creating a double-orifice mitral valve
  • FDA approved for: primary (degenerative) MR with prohibitive surgical risk; secondary MR in heart failure patients with LV dysfunction despite optimal medical therapy (based on COAPT trial)
  • EVEREST II: randomized comparison vs. surgery showed MitraClip is safer but less effective at reducing MR
  • Performed via transseptal approach under TEE guidance
• Other emerging devices: annuloplasty rings, leaflet augmentation, and transcatheter MVR devices (TMVR)
• Braunwald's Heart Disease

Anesthetic Considerations (for MR Patients Undergoing Surgery)

• Barash Clinical Anesthesia, 9th Ed.

Natural History and Prognosis

• Severe MR is associated with decreased survival whether symptomatic or not
• Within 5 years of detecting severe MR: ~50% of patients develop LV dysfunction, AF, or heart failure requiring surgery
• In asymptomatic patients with flail leaflets: mortality risk increases with increasing LV end-systolic diameter
• Patients with secondary MR have worse prognosis, reflecting underlying LV dysfunction compounded by additional volume overload
• Surgery (especially repair) improves both symptoms and survival when performed before irreversible LV dysfunction develops
• Braunwald's Heart Disease; Goldman-Cecil Medicine

Surgical Repair of Mitral Regurgitation

Why Repair Over Replacement?

• Lower operative mortality (~1-3% vs ~6% for replacement)
• Better preservation of LV function post-operatively (maintains the subvalvular apparatus)
• Avoids prosthesis-related complications: no lifelong anticoagulation, lower risk of prosthetic valve endocarditis, no structural valve deterioration
• Reoperation rates <10% at 10 years when postoperative echo shows mild or absent MR
• Improved long-term event-free survival and quality of life
• Sabiston Textbook of Surgery 11th Ed.; Bailey & Love 28th Ed.

Carpentier's Functional Classification (Foundation of Repair Planning)

• Sabiston Textbook of Surgery - From Carpentier A, J Thorac Cardiovasc Surg 1983

Operative Setup and Exposure

1. Cardiopulmonary bypass (CPB) with cardioplegic arrest
2. Mitral valve exposed via:
   • Opening the left atrium in the Waterston groove (most common), OR
   • Transseptal approach - opening right atrium then interatrial septum
3. Systematic valve assessment:
   • Nerve hooks probe each segment of anterior and posterior leaflets
   • Assess leaflet height, prolapse vs. tethering, leaflet structure
   • Examine subvalvular apparatus: ruptured, elongated, or fused primary and secondary chords; papillary muscle status and position
   • Water (saline) test: saline flushed into LV cavity identifies and marks prolapsing segments by showing where leaflets fail to coapt

• Fuster & Hurst's The Heart, 15th Ed.

Surgical Repair Techniques

1. Ring Annuloplasty (Performed in EVERY Repair)

• Reduce annular diameter and restore normal annular geometry
• Restore the natural saddle-shape (3D) of the mitral annulus
• Enhance leaflet coaptation in all segments
• Stabilize and prevent future annular dilation (protects repair durability)

• Complete vs. partial (open) rings
• Flexible vs. semi-rigid vs. rigid
• Flat vs. 3D contoured (saddle-shaped)
• Sizing is based on measuring the height and surface area of the anterior leaflet

Bailey & Love - Operative view: Carpentier-Edwards annuloplasty ring seated on the mitral annulus

2. Posterior Leaflet Resection (for Type II - Posterior Leaflet Prolapse/Flail)

• A rectangular segment of the prolapsing posterior leaflet is excised
• The leaflet edges are sutured back together
• A sliding plasty may be added: relaxing incisions along the posterior leaflet base allow the leaflet to slide, reducing tension on the repair and decreasing posterior leaflet height
• Sliding plasty reduces the risk of SAM (see complications below)

• Smaller, more conservative resection of the prolapsing tip
• Increasingly preferred over quadrangular resection as it conserves more leaflet tissue

• Reduces posterior leaflet height after resection
• Prevents post-repair SAM (systolic anterior motion)

3. Neochordae Implantation (PTFE Chordal Replacement)

• Artificial chordae created from Gore-Tex (PTFE) sutures (CV-4 or CV-5)
• Sized to the appropriate height (measured from the annulus to the free leaflet edge at correct coaptation)
• One end attached to the papillary muscle head, the other to the free edge of the prolapsing leaflet
• Provides stable long-term leaflet support and prevents recurrent prolapse
• Advantages over resection: preserves leaflet tissue, lower risk of SAM, more versatile (can address multiple segments, anterior leaflet prolapse)
• Can be done with pre-looped PTFE "chordal loops" for standardization

4. Chordal Transfer (for Anterior Leaflet Prolapse)

• A secondary chord from the posterior leaflet (which has redundant chordae) is transferred to support the prolapsing free edge of the anterior leaflet
• Useful when neochordae are not preferred or in experienced centers as an alternative

5. Edge-to-Edge (Alfieri) Suture

• The free edges of the anterior and posterior leaflets at the site of prolapse/malcoaptation are sutured together, creating a double-orifice valve
• Replicates the surgical basis of the transcatheter MitraClip
• Used as a primary technique for commissural prolapse or as a "bail-out" if other techniques fail
• Must always be combined with annuloplasty ring

6. Leaflet Augmentation (Patch Repair)

• Leaflet defects (perforations from endocarditis, retracted rheumatic leaflets) are repaired using autologous pericardium or bovine pericardial patches
• Used in Type IV pathology (endocarditis, rheumatic disease, severe annular calcification)
• For rheumatic disease (Type IIIa): leaflet mobilization with pericardial augmentation to increase leaflet area and improve coaptation

7. Subvalvular Repair Techniques (for Secondary/Ischemic MR - Type IIIb)

• Papillary muscle approximation ("sling" procedure): sutures or bands drawn between the two papillary muscle heads to reapproximate them and reduce lateral tethering
• Papillary muscle repositioning: addresses the primary cause of tethering
• However, ring annuloplasty alone (undersized/downsized ring) has high recurrence rates (59% moderate-severe MR at 2 years) - this is why chordal-sparing replacement may be preferred for secondary MR (ACC/AHA 2020 guidelines: Class IIb)

Summary of Repair Techniques by Carpentier Type

Fuster & Hurst's The Heart - Repair techniques: (A) Quadrangular resection & sliding plasty, (B) Chordal replacement (neochordae), (C) Triangular resection

Pathoanatomic Grading System (Alreshidan/Herron)

• Fuster & Hurst's The Heart 15th Ed. - From Alreshidan M et al., Semin CardioThorac Vasc Anesth 2019

Intraoperative Assessment of Repair Success

1. Saline water test (after repair, before coming off CPB): saline injected into LV to check leaflet coaptation
2. Intraoperative TEE (mandatory before weaning from bypass):
   • Must demonstrate mild or no residual MR for repair to be deemed successful
   • Adequate leaflet coaptation height and surface
   • No systolic anterior motion (SAM) of the anterior leaflet
   • No significant mitral stenosis (adequate valve opening area)
   • If residual moderate or severe MR: repair must be revised or conversion to replacement

• Fuster & Hurst's The Heart 15th Ed.

Key Complication: Systolic Anterior Motion (SAM)

• Increase preload and afterload (fluid loading)
• Negative inotropy (reduce/stop inotropes)
• Beta-blockers (negative chronotropy)
• If irreversible: return to bypass for corrective surgery - larger annuloplasty ring and/or reduction of posterior leaflet height (Alfieri stitch or re-resection)
• Fuster & Hurst's The Heart 15th Ed.

Outcomes

When Replacement is Preferred Over Repair

• Severe annular calcification (MAC) precluding ring placement
• Extensive rheumatic disease with subvalvular fusion not amenable to repair
• Severe secondary (ischemic) MR - chordal-sparing replacement has superior MR reduction vs. ring annuloplasty alone (ACC/AHA Class IIb)
• Failed prior repair
• Complex anatomy at non-expert center (repair durability requires surgical experience)