Mitral Valve Surgery: A Pathoanatomic Approach
Vinay Badhwar
Jahnavi Kakuturu
Chris C. Cook
INTRODUCTION
The most prevalent adult valvular heart disease is mitral valve (MV) disease, and its most common presentation is regurgitation.1 Mitral stenosis (MS) is associated with fusion or calcification of the leaflets preventing their adequate opening or closing throughout the cardiac cycle. Mitral regurgitation (MR) may be primary, secondary, or mixed.2 Primary MR is an abnormality of the leaflets or subvalvular chordal apparatus. Secondary MR occurs because of the restriction of leaflet motion, with or without mitral annular dilatation, secondary to ventricular, and papillary muscle pathology. Mixed MR occurs when pathoanatomic features of primary and secondary MR coexist in the same patient. Strategies and techniques of surgical correction of MV disease are tailored to treat the precise pathoanatomy.
Untreated severe primary MR is associated with significant longitudinal morbidity including a 30% incidence of atrial fibrillation and 63% incidence of heart failure.3 Similar sequela accompany severe MS. Once the presence of severe MR has been established, MV surgery is indicated to prevent further left ventricular dilatation and symptoms of heart failure, even in asymptomatic patients. For patients with severe MS who are not candidates for percutaneous mitral balloon commissurotomy (PMBC), mitral valve replacement (MVR) is necessary to treat pulmonary hypertension, symptoms of dyspnea and fatigue, and prevention of secondary right ventricular dysfunction. Whenever anatomically possible and appropriate, MV repair should be performed as it may confer a survival advantage over MVR of 12% to 21% at 15 years.4,5 This chapter will review the indications and pathoanatomic approach to current MV surgery.
INDICATIONS
For patients with severe primary MR without symptoms or with symptoms but without ventricular compromise, early surgical intervention compared with watchful waiting confers superior 10-year survival (86% vs 69%, respectively), with repair rates in high-volume centers exceeding 95% and a mortality of less than 1%.6 Techniques of MV surgery have shifted from prosthetic MVR as the principle therapy for all pathology, to one based on the primary strategy of MV repair whenever possible, which has been applied with increasing consistency for the last 25 years. A recent analysis of the Society of Thoracic Surgeons (STS) Adult Cardiac Surgery Database revealed that 17,907 isolated nonredo MV surgeries were performed across the United States, a 24% increase over 5 years previously, the majority of which were MV repair with an overall repair rate for primary MR of 82.5%.7 Durability of MV repair is generally excellent with a freedom from reoperation rate of 94% at 10 years.8 The surgical approach to isolated MV operations has also changed, with 23% of patients in the STS study having received minimally invasive thoracotomy or robotic techniques.7 Current indications for MV surgery are based largely on these principles, as well as similar findings in the literature that have been summarized by the 2020 American College of Cardiology (ACC)/American Heart Association (AHA) Clinical Practice Guidelines released in December 2020 and highlighted later.9
For severe MS, defined by an MV area of less than or equal 1.5 cm2, diastolic pressure half time of greater than or equal to 150 ms, and pulmonary artery systolic pressures greater than 50 mm Hg, MVR is the principle therapy for nonrheumatic calcific pathology and symptoms.9 For patients with symptomatic severe rheumatic MS who have failed PMBC or deemed not a candidate for it, MV surgery is a Class 1 recommendation.
For primary MR, MV surgery is a Class 1 recommendation for symptomatic severe MR regardless of left ventricular (LV) function or asymptomatic patients with an LV ejection fraction (LVEF) less than or equal 60% or LV end-systolic dimension (ESD) greater than or equal to 40 mm by echocardiography. It is further a Class 1 recommendation that MV repair is performed whenever possible for primary MR. For patients with preserved LVEF and focal degenerative MV disease involving less than half of the posterior leaflet only, MVR is considered Class 3, or harmful. For asymptomatic patients with normal LVEF greater than 60%, MV repair is a Class 2a indication provided a durable repair can be provided greater than 95% of the time at a mortality rate of less than 1%. For asymptomatic patients with preserved LVEF but LV dilatation or recent decline in LVEF, MV surgery is a Class 2b recommendation. Finally, for patients of high or prohibitive risk for MV surgery, transcatheter edge-to-edge repair (TEER) is considered a Class 2a recommendation (Algorithm 88.1).9
For rheumatic MR (primary or mixed), associated with symptoms, MV repair is a Class 2b recommendation provided it is performed in an experienced comprehensive valve center.
For secondary MR, ongoing controversy remains as to the optimal treatment at the optimal time given its dynamic nature and the impact on the degree of LV dysfunction on both short-term and long-term outcomes.10,11,12,13 Consistent across all
planned MV interventions is the role of guideline-directed medical therapy (GDMT) on optimizing loading conditions before MV surgery or TEER.9,10,11,12,13 As such, all patients presenting with secondary MR should have initial attempts at GDMT optimization, preferably with a heart failure specialist.9 For patients with symptomatic severe secondary MR, MV surgery is a Class 2a recommendation when coronary artery bypass grafting (CABG) is performed for myocardial ischemia. MV surgery also holds a Class 2b recommendation for MR secondary to annular dilatation and atrial fibrillation (or atrial MR), and symptomatic severe MR due to LVEF less than 50%. Although some patients may benefit from MV repair techniques, chord-sparing MVR for secondary MR may be reasonable in certain individuals, and it carries a Class 2b recommendation (Algorithm 88.2).9
planned MV interventions is the role of guideline-directed medical therapy (GDMT) on optimizing loading conditions before MV surgery or TEER.9,10,11,12,13 As such, all patients presenting with secondary MR should have initial attempts at GDMT optimization, preferably with a heart failure specialist.9 For patients with symptomatic severe secondary MR, MV surgery is a Class 2a recommendation when coronary artery bypass grafting (CABG) is performed for myocardial ischemia. MV surgery also holds a Class 2b recommendation for MR secondary to annular dilatation and atrial fibrillation (or atrial MR), and symptomatic severe MR due to LVEF less than 50%. Although some patients may benefit from MV repair techniques, chord-sparing MVR for secondary MR may be reasonable in certain individuals, and it carries a Class 2b recommendation (Algorithm 88.2).9
 ALGORITHM 88.1 Guidelines for the management of primary mitral regurgitation. COR, class of recommendation CVC, cardiovascular center; ERO, effective regurgitant orifice area; ESD, end-systolic volume; LV, left ventricular; LVEF, left ventricular ejection fraction; MR, mitral regurgitation; MV, mitral valve; RF, regurgitant fraction RVol, regurgitant volume; VC, vena contracta; y, year. (Reprinted from Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. J Am Coll Cardiol. 2021;77(4):e25-e197. Copyright © 2021 by the American College of Cardiology Foundation and the American Heart Association, Inc. With permission.) |
ANATOMIC CONSIDERATIONS
For the MV surgeon, it is essential to have a working mastery of echocardiographic structural interpretation, for it is the prediction of pathoanatomic mechanisms and the identification of potential anatomic pitfalls that provides the guidance for surgical strategy.14 Quantitative parameters consistent with severe MR should be identified before anesthetic induction and include a vena contracta width greater than 7 mm, effective regurgitant orifice area greater than 40 mm2, regurgitant volume greater than 60 mL, regurgitant fraction greater than 50%, or the presence of a flail leaflet or ruptured chorda.2 Important for surgical planning is the two-dimensional (2D) or three-dimensional (3D) identification of surgically relevant items such as clefts, annular/leaflet calcification, perforations, or possible coexistent chordal tethering that may impact the tailoring of the precise steps to achieve a successful surgical outcome.
Pathoanatomy at every level of the mitral apparatus may coexist in the same patient, and the preoperative or intraoperative imaging must be carefully reviewed so that the MV surgeon may make an effort to develop the surgical plan before making incision. This is of particular importance when the mechanism is anything more than focal single scallop disease. The MV apparatus is subdivided into the annulus, anterior and posterior leaflets, and the subvalvular chordae tendineae
and papillary muscles. The posterior leaflet is subdivided from lateral to medial into P1, P2, and P3 segments, with corresponding A1, A2, and A3 segments of the anterior leaflet. The anterior leaflet constitutes two-thirds of the valve orifice area and one-third of the annular circumference, while the posterior leaflet constitutes one-third of the valve area and two-thirds of the circumference. The subvalvular apparatus is composed of the anterolateral and posteromedial papillary muscles that give rise to primary chords attached to the free edge of the leaflet, secondary chords attached to the mid-leaflet ventricular surface, and tertiary chords attached to base of the leaflet.
and papillary muscles. The posterior leaflet is subdivided from lateral to medial into P1, P2, and P3 segments, with corresponding A1, A2, and A3 segments of the anterior leaflet. The anterior leaflet constitutes two-thirds of the valve orifice area and one-third of the annular circumference, while the posterior leaflet constitutes one-third of the valve area and two-thirds of the circumference. The subvalvular apparatus is composed of the anterolateral and posteromedial papillary muscles that give rise to primary chords attached to the free edge of the leaflet, secondary chords attached to the mid-leaflet ventricular surface, and tertiary chords attached to base of the leaflet.
 ALGORITHM 88.2 Guidelines for the management of secondary mitral regurgitation. *Chordal-sparing MV replacement may be reasonable to choose over downsized annuloplasty repair. AF, atrial fibrillation; CABG, coronary artery bypass grafting; COR, class of recommendation; ERO, effective regurgitant orifice area; GDMT, guideline-directed medical therapy; HF, heart failure; LVEF, left ventricular ejection fraction; LVESD, left ventricular end-systolic volume; MR, mitral regurgitation; MV, mitral valve; PASP, pulmonary artery systolic pressure; RF, regurgitant fraction; RVol, regurgitant volume Rx, treatment. (Reprinted from Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. J Am Coll Cardiol. 2021;77(4):e25-e197. Copyright © 2021 by the American College of Cardiology Foundation and the American Heart Association, Inc. With permission.) |
The Carpentier classification is most commonly used to define leaflet motion to describe the possible etiology of MR.2,15 Type 1 is normal leaflet motion, and the MR may be due to congenital clefts, endocarditis/perforation, or annular dilation. Type 2 is excessive leaflet motion, and it is associated with primary degenerative leaflet prolapse or flail leaflet accompanied with chordal rupture. Type 3 is restricted leaflet motion. Type 3A occurs when leaflet motion is restricted in systole and diastole such as with rheumatic disease or radiation, and Type 3B occurs when leaflet motion is restricted in systole only such as with ischemic or nonischemic ventricular secondary MR. Type 3B secondary MR may further be subclassified into grades of severity (1-4) based on the amount of annular dilation, amount of leaflet tethering, and LVEF (Table 88.1).12,13
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