A. Introduction. The mitral valve apparatus is composed of anterior and posterior leaflets, the mitral annulus, chordae tendinae, and papillary muscles. Degenerative, ischemic, rheumatic, and infectious (endocarditis) processes are responsible for the vast majority of mitral valve disease in adults (Table 14.1).
Mitral regurgitation (MR) can occur as a consequence of dysfunction of any one of these components. In primary MR, dysfunction of one or more of the components of the valve itself leads to valve incompetence with systolic regurgitation of blood from the left ventricle to the left atrium. In secondary MR, the valve leaflets and chordae are structurally normal; however, left ventricular dilatation and/or dysfunction (e.g., due to myocardial infarction or nonischemic cardiomyopathy) renders the valve incompetent. This incompetence is the result of displacement of the papillary muscles in the dilated left ventricle, which leads to leaflet tethering; associated annular dilatation may contribute to failure of leaflet coaptation.
Mitral stenosis (MS) is the result of processes (most commonly rheumatic) affecting the leaflets, annulus, and subvalvular apparatus. Thickening and fusion of the leaflets and chordae inhibit normal leaflet excursion during diastole (Table 14.1).
B. Indications for surgery
1. Acute Mitral Regurgitation: Patients with acute, severe MR usually require urgent surgical intervention. Leaflet perforation from endocarditis or chordal rupture may be causes of this disorder. However, this presentation is often the result of myocardial infarction resulting in papillary muscle dysfunction or rupture.
Hemodynamically stable patients benefit from afterload-reducing agents, which help to increase forward flow. In the patient with cardiogenic shock, inotropic and pressor support can often be detrimental, especially in the circumstance of ischemic disease. These agents increase myocardial oxygen demand and can thereby further exacerbate an acute coronary syndrome. If temporization is needed before surgery, intra-aortic balloon pump (IABP) or, occasionally, extracorporeal membranous oxygenation (ECMO) can be used in patients with a competent aortic valve.
2. Chronic Mitral Regurgitation
a. Symptomatic patients: The majority of patients with chronic moderately severe to severe primary MR that is symptomatic should be considered for surgery (Table 14.2).
In the case of chronic moderately severe to severe secondary MR, surgery should be considered for patients with refractory symptoms despite aggressive medical management. For patients with moderate to severe ischemic MR, it is suggested that valve repair or replacement be done concomitantly with coronary artery bypass graft (CABG) (Table 14.3).
b. Asymptomatic patients: In asymptomatic patients, the goal is to identify and monitor patients with severe MR and intervene before permanent left ventricular dysfunction or left ventricular dilatation. If a durable repair can be achieved at a center of excellence or there is new-onset atrial fibrillation or resting pulmonary hypertension, then it is reasonable to intervene in asymptomatic severe primary MR.
TABLE 14.2 Summary of AHA/ACC Recommendations in Chronic Primary Mitral Regurgitation
Level of Evidence
Class I
Mitral valve surgery is recommended for symptomatic patients with chronic severe primary MR and LVEF greater than 30%.
B
Mitral valve surgery is recommended for asymptomatic patients with chronic severe primary MR and left ventricular dysfunction (LVEF 30-60% and/or LVESD ≥40 mm).
Mitral valve repair is recommended in preference to mitral valve replacement when surgical treatment is indicated for patients with chronic severe primary MR limited to the posterior leaflet.
Mitral valve repair is recommended in preference to mitral valve replacement when surgical treatment is indicated for patients with chronic severe primary MR involving the anterior leaflet or both leaflets when a successful and durable repair can be accomplished.
Concomitant mitral valve repair or replacement is indicated in patients with chronic severe primary MR undergoing cardiac surgery for other indications.
Class IIa
Mitral valve repair is reasonable in asymptomatic patients with chronic severe primary MR with preserved left ventricular function (LVEF >60% and LVESD <40 mm) in whom the likelihood of a successful and durable repair without residual MR is >95% with an expected mortality rate of <1% when performed at a Heart Valve Center of Excellence.
B
Mitral valve repair is reasonable for asymptomatic patients with chronic severe nonrheumatic primary MR and preserved left ventricular function in whom there is a high likelihood of a successful and durable repair with (1) new onset of atrial fibrillation or (2) resting pulmonary hypertension (PA systolic arterial pressure >50 mm Hg).
B
Concomitant mitral valve repair is reasonable in patients with chronic moderate primary MR undergoing cardiac surgery for other indications.
C
Class IIb
Mitral valve surgery may be considered in symptomatic patients with chronic severe primary MR and LVEF ≤30%.
C
Mitral valve repair may be considered in patients with rheumatic mitral valve disease when surgical treatment is indicated if a durable and successful repair is likely or if the reliability of long-term anticoagulation management is questionable.
B
Transcatheter mitral valve repair may be considered for severely symptomatic patients (NYHA class III/IV) with chronic severe primary MR who have a reasonable life expectancy but a prohibitive surgical risk.
B
Class III
Mitral valve replacement should not be performed for treatment of isolated severe primary MR limited to less than one-half of the posterior leaflet unless mitral valve repair has been attempted and was unsuccessful.
C
AHA/ACC, American Heart Association/American College of Cardiology; LVEF, left ventricular ejection fraction; LVESD, left ventricular end-systolic diameter; MR, mitral regurgitation; NYHA, New York Heart Association; PA, pulmonary artery.
TABLE 14.3 Summary of AHA/ACC Recommendations in Chronic Severe Secondary Mitral Regurgitation
Level of Evidence
Class IIa
Mitral valve surgery is reasonable for patients with chronic severe secondary MR who are undergoing CABG or AVR.
C
Class IIb
Mitral valve surgery may be considered for severely symptomatic patients (NYHA class III/IV) with chronic severe secondary MR.
B
Mitral valve repair may be considered for patients with chronic moderate secondary MR (stage B) who are undergoing other cardiac surgery.
C
AHA/ACC, American Heart Association/American College of Cardiology; AVR, aortic valve replacement; CABG, coronary artery bypass graft; MR, mitral regurgitation; NYHA, New York Heart Association.
3. Mitral stenosis: Percutaneous mitral balloon commissurotomy (PMBC) is indicated for severe symptomatic MS. Surgical intervention should be considered in patients with severe symptomatic MS who are not candidates for PMBC or who are undergoing surgery for other cardiac lesions. See Chapter 4, Table 4.5 (“Indications for Intervention in Patients with Mitral Stenosis [MS] According to the 2014 ACC/AHA Guidelines”).
C. Contraindications. Patients who are too frail to tolerate an operation should not undergo surgical repair. This may be due to advanced age and comorbid conditions. The Society of Thoracic Surgeons (STS) risk score and EuroSCORE are assessment tools that can aid in identifying patients who are too high risk for surgery.
Though not an absolute contraindication, severe mitral annular calcification can make repair and replacement difficult and increase the risk for atrioventricular dissociation. Patients with severe pulmonary hypertension with associated right heart failure are at increased risk for poor outcomes with mitral valve surgery.
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