TSRA Content:
Authors: Mona Kakavand, MD, and Lin Chen, BA
This is a revision and update from the previous edition of the TSRA Primer in Cardiothoracic Surgery written by, Stephanie Mick, MD, and Fatuma Kromah, MD.
The proper functioning of the mitral valve (MV) depends on the coordinated, adequate function and state of the annulus, leaflets, chordae, papillary muscles, left atrium and left ventricle. If the function of any of these components is impaired, there is an increased likelihood of valve dysfunction, which can cause the valve to become either stenotic (mitral stenosis - MS) or regurgitant (mitral regurgitation - MR).
Anatomical Considerations
The optimal tool for assessing the mitral valve is a transesophageal echocardiogram (TEE) which can be used to confirm findings of mitral valve dysfunction, integrity, area, character of regurgitant flow/jet and transvalvular gradient prior to intervention. Understanding each component is essential in order to understand the techniques involved in repair or replacement.
Annulus:
Assess for dilatation, calcification, mobility, contraction, and deformities.
Anterior and posterior leaflet scallops (A1-3 and P1-3):
Assess for prolapse, flail, restriction, thickening, pliability, coaptation, vegetations, and cleft deformity.
Chordae tendineae:
These chords attach the mitral leaflets to the papillary muscles or the left ventricular free wall, enabling leaflet coaptation and ventricular contraction. Evaluate for elongation, redundancy, shortening, thickening, fusion, or rupture.
Papillary muscles:
Assess the anterolateral and posteromedial muscles for elongation or rupture, usually secondary to infarction.
Left ventricle:
The LV via the chordae and papillary muscles pulls the mitral valve leaflets during systole, thereby maintaining the line of coaptation and valve competency. LV dilation disrupts normal function and leaflet coaptation.
Mitral Valve Regurgitation (MR)
The pathophysiology associated with MR is chronic LV volume overload leading to eccentric hypertrophy and dilation of the LV. Initially, stroke volume is preserved, but eventually, LV function declines, causing increased LV end systolic volume, elevated LA and LV pressures. This ultimately leads to pulmonary edema and heart failure as the ejected volume flows backwards into the LA as a compensatory mechanism.
The Carpentier Classification classifies regurgitant lesions in terms of the associated leaflet and chordal motion:
Type I (normal leaflet motion):
Anterior and posterior leaflets fail to coapt completely (e.g., annular dilatation, leaflet perforation)
Type II (excessive leaflet motion):
One or both leaflets overshoot/override the other (i.e prolapse). This can be due to ruptured cord or papillary muscle or myxomatous degeneration aka "floppy mitral valve"
Type III (restricted leaflet motion):
One or both leaflets fail to coapt due to tethering.
- Illa: restricted opening (e.g., rheumatic disease, with chordal thickening/shortening)
- IIIb restricted closure (e.g. ischemic cardiomyopathy when tethering of leaflets is increased by outward displacement of papillary muscle)
Surgical Indications for MR:
*In this primer, only Class I indications are listed. Consult reference for more indications
Class I Indications for MV Surgery (Surgery is Recommended)
- Symptomatic patients with severe MR regardless of LV function
- Asymptomatic patients with chronic severe MR and LV dysfunction (EF ≤60%, +/- ESD ≥ 40 mm)
- MV repair is recommended over MV replacement in the majority of patients with severe chronic MR and they should be treated in centers experienced in MV repair
Mitral Valve Stenosis (MS)
The pathophysiology of MS is restricted LV inflow resulting in increased LA pressures. There is back pressure on the pulmonary circulation causing dyspnea and eventually pulmonary hypertension, RV failure and subsequent LV failure. This is a progressive process that can take 10 - 20 years before becoming symptomatic. The most common cause is rheumatic fever - with rarer causes including endocardial fibroelastosis, carcinoid syndrome, pulmonary vein stenosis and left atrial myxoma.
Surgical Indications: ACC/ AHA Guidelines for Mitral Stenosis
Class I Recommendations for MV Surgery: Surgery is Recommended
- MV repair with acceptable operative risk in severely symptomatic patients (NYHA III-IV) with severe MS only if percutaneous mitral balloon valvotomy (PMBC) is unavailable, if valve morphology is not favorable for balloon or patient has failed a previous PMBC, if there is more than 2+ MR coexists with MS , and if there is left atrial thrombus that persists despite anticoagulation.
Mitral Valve Repair/"Plasty'' (MVr) & Replacement (MVR)
Three operations exist to fix the mitral valve: MV repair/plasty (MVr), MV Replacement (MVR) with preservation of the subvalvular apparatus, and MVR with removal of the subvalvular apparatus. Each approach has pros and cons, and the indications for each procedure are therefore slightly different.
MVr:
This is the operation of choice when MV morphology is suitable for repair and appropriate surgical skill and expertise are available. Since no prosthesis is used, it avoids the risk of chronic anticoagulation or late post-op prosthetic valve failure. MVr preserves the subvalvular apparatus, leading to better postoperative LV function and survival, but is technically more demanding than MVR and may require longer CPB times.
MVR with Subvalvular Apparatus Preservation:
Assures postoperative MV competence, preserves LV function, improved postoperative survival compared with total MVR. Disadvantages include the progressive deterioration inherent to tissue valves and the need for anticoagulation (i.e. mechanical valves)
MVR with Resection of the Subvalvular Apparatus:
Should be avoided except when the native valve and apparatus are so distorted that the apparatus cannot be spared (e.g. rheumatic disease or endocarditis affecting the chords). Resection of the subvalvular apparatus leads to altered geometrics and altered contraction patterns of the left ventricle due to alteration of the papillary muscle attachments. The LV generally contracts in a twisting motion, which can be altered if the subvalvular apparatus is removed.
Repair Techniques
Resection:
Posterior leaflet quadrangular or triangular resection is an option for mitral insufficiency secondary to prolapse of a segment of the posterior mitral valve leaflet (most commonly P2). The P2 scallop is resected. P1 and P3 segments are then partially detached from the annulus and reattached to each other and the posterior annulus.
Sliding valvuloplasty:
A leaflet advancement technique used in patients with excessive posterior leaflet tissue (usually P2 segment) often in conjunction with a quadrangular resection involves detachment of the posterior mitral leaflet from the annulus for a distance of 1-2 cm toward each commissure and re-approximation of the base of the leaflet to the mitral annulus, thereby “sliding" the remaining valvular segments (P1 and P3) to cover the area of resected P2 segment. Helps prevent systolic anterior motion (SAM), which leads to LV outflow tract obstruction.
Reduction annuloplasty:
- Ring annuloplasty may be flexible or rigid, complete, or incomplete, and is required to support the mitral valve repair. This may be utilized when there is normal leaflet motion, but the annulus is dilated, leading to improper coaptation (e.g. as in ischemic functional mitral regurgitation). It can also be used to correct/stabilize annular dilatation while preventing further dilation by increasing coaptation of the anterior and posterior leaflets.
- Folding valvuloplasty is where the leading edge of a prolapsed or redundant leaflet is imbricated, thereby reducing the leaflet height.
Artificial chord:
Implantation is used for correction of anterior or posterior leaflet prolapse by utilizing 5-0 PTFE or GoreTex suture. The distance from the leaflet to the fibrous portion of the papillary muscle is measured and the neochordae is then sutured in a mattress fashion.
Patch repair:
Used in the event of a small leaflet perforation. The perforation is meticulously debrided of fibrinous and infected material.
Commissuroplasty:
For a prolapsed valve with chordal rupture or severely elongated segments of A1 and A3. Polypropylene horizontal mattress sutures obliterate the commissure at each side of the existing pathology thereby stabilizing regurgitation through the anterior mitral leaflet defect.
Anatomical Structures at Risk
The MV is surrounded by structures that can inadvertently be injured or damaged by excessive dissection or placement of deep sutures during repair or replacement.
Left circumflex coronary artery:
Traverses laterally around the mitral annulus in the posterior AV groove and can be injured by sutures placed beyond the annulovalvular junction.
AV node and artery and bundle of His:
Runs parallel and close to the anterior MV leaflet near the posteromedial commissure and the right fibrous or posteromedial trigone.
Left and non-coronary cusps of the aortic valve:
Anterior MV leaflet is in fibrous continuity with the left and non-coronary aortic cusps. The bundle of His is also near the posterior fibrous trigone.
Coronary sinus:
Runs in the medial segment of the AV groove adjacent to the posterior leaflet.
Systolic Anterior Motion (SAM)
SAM occurs when the tips of the MV leaflets are displaced anteriorly into the LVOT causing MR and LVOT obstruction. The best prevention is avoiding excess anterior MV leaflet tissue or excessive height of posterior MV leaflet. SAM is exacerbated by hypovolemia, excess inotropes, and tachycardia. Treat SAM by keeping the patient “slow, tight, and full.”
MV Prosthesis
Mitral Rings:
May be complete or partial and rigid, semi-rigid or flexible. They help correct annular dilation, prevent further dilation, increase leaflet coaptation, and reinforce annular suture lines.