Three procedures are routinely practiced for the relief of MS: BMV, open commissurotomy (OMV), and MVR. In some areas, closed commissurotomy (CMV) is still practiced quite effectively and does not entail the cost of the catheters and balloons needed for BMV. Because BMV is less morbid and carries a lower mortality than surgery, the timing for BMV is more liberal than for the surgical procedures at both ends of the clinical spectrum. It may be applied for mild symptoms caused by severe MS or in late-stage disease in patients at high risk for surgery from various comorbidities. Advanced symptoms worsen prognosis (Fig. 50–6), and thus BMV or surgery should be performed before the patients reaches New York Heart Association (NYHA) class III.80 Additionally, pulmonary hypertension defined as a peak systolic pressure > 50 mm Hg at rest also worsens prognosis and increases surgical risk.81 Thus mechanical relief of obstruction should ideally take place before this degree of severity has developed.
Survival according to therapy and symptomatic status for patients with mitral stenosis is shown. New York Heart Association classes II, III, and IV are roughly equivalent to Olesen groups B, C, and D, respectively. Reproduced with permission from Roy SB, Gopinath N: Mitral Stenosis. Circulation. 1968 July;38(1 Suppl):68-76 .80
BMV was first performed by Inoue in 1984,82 followed by Lock in 1985.83 BMV is the procedure of choice for relieving MS,30 with surgery being reserved only for patients who are not candidates for BMV. It is recommended for the following groups of patients30: (1) symptomatic patients (class II-IV) with severe MS (MVA ≤ 1.5 cm2) (class 1 indication) or asymptomatic patients with very severe MS (MVA ≤ 1.0 cm2) (class 2a indication) with a favorable valve morphology in the absence of LA thrombus and moderate-to-severe MR; (2) asymptomatic patients with severe MS (MVA ≤ 1.5 cm2) with new-onset AF and suitable valve anatomy (class 2b indication); (3) symptomatic patients with MVA > 1.5 cm2 and hemodynamically significant MS during exercise (mean mitral valve gradient > 15, PCWP > 25 mm Hg, class 2b indication; and (4) severely symptomatic patients (NYHA class III-IV) with severe MS (MVA ≤ 1.5 cm2) with suboptimal valve anatomy and high risk for surgery (class 2b indication).
The steps for BMV are demonstrated in Fig. 50–7. First, a transseptal puncture is performed (Fig. 50–7A), and the inter-atrial septum is dilated with a dilator (Fig. 50–7B). A balloon is then advanced across the septum, into the LA across the mitral valve. Stepwise inflation causes commissures separation (Fig. 50–7C, D; Fig. 50–5B), permitting a dramatic increase in leaflet motion and valve area. BMV can be performed using a hourglass-shaped balloon (triple lumen Inoue balloon82 or double lumen Accura balloon84,85), a single83 or double peripheral angioplasty balloon,86 or a reusable valvulotome.87 Although the three techniques produce a similar outcome,86,88 currently the hourglass-shaped balloons are preferred. The procedure should be performed by experienced, skilled operators. The mortality is approximately 1% in experienced centers. Other complications include severe MR requiring surgery (2%), embolic events (1%), and cardiac perforation (1%).10 Retrograde BMV without transseptal puncture using a steerable guidewire is an alternative to conventional BMV.89,90
The steps for balloon mitral valvotomy are shown. A. Transeptal puncture. B. Dilatation of interatrial septum with dilator. C. Balloon inflation creating a waist at the site of the stenosis. D. Full balloon inflation with giving of waist.
Randomized trials have shown BMV to be superior to CMV, with a larger postprocedure valve area when the two procedures were compared in patients with valves suitable for BMV,91,92,93,94 and similar results have been shown for BMV and OMV.95 Although successful BMV is usually defined as a postprocedure valve area > 1.5 cm2 (without > grade 2 MR), valve area often exceeds 1.8 cm2 and is durable for a decade or more. There is an immediate reduction in transmitral gradient, LA mean pressure, and PA pressure. Even patients with systemic or suprasystemic PA pressure have an immediate significant drop in PA pressure after successful BMV.96 Reduction in PA pressure is associated with improvement in tricuspid regurgitation (TR) in some, but not all, patients. Successful BMV has been shown to reduce systemic embolism,49 but does not appear to revert AF.66 Long-term studies with follow-up for up to 20 years are available.97,98 Among 912 patients with a median age of 48 years,97 cardiovascular survival without reintervention and cardiovascular survival without surgery was 38% and 46%, respectively, at 20 years. For patients aged < 50 years, the figures were 45% and 57%, respectively.97 The overall survival and cardiovascular survival at 20 years was 75% and 85%, respectively.97 In another study of 547 patients with a mean age of 31 years,98 freedom from restenosis at 10 and 19 years was 78% and 26%, respectively.
The BMV technique and hardware has remained essentially unchanged over the past three decades, but the indications of BMV have expanded to encompass patients with calcified valves, severe submitral disease, LA/LAA clot, moderate MR (grade 2), mitral valve restenosis (post BMV/CMV/OMV/MVR), pregnancy, children, and those with difficult anatomy (anomalous inferior vena cava connections, dextrocardia, kyphoscoliosis).
Relief of MS by surgery may be done either by CMV, OMV, or MVR. CMV, via transatrial or transventricular route, is still practiced successfully in many developing countries. However, the results of BMV are superior to CMV, with lower morbidity. As such, CMV is indicated only if BMV is not available. OMV is done under cardiopulmonary bypass and enables direct visual inspection of the mitral valve, enabling direct splitting of commissures, splitting of fused chordae tendinae and papillary muscles, and debridement of calcific deposits. LA thrombi may be removed and the LAA amputated to reduce future thromboembolic events. Further, moderate to severe TR can be repaired. The results are dependent on the surgical skills, and the main advantage of OMV is that it avoids a prosthetic valve. When extensive calcification and severe subvalvular disease make BMV/OMV unfeasible, MVR is the surgical treatment of choice. The indication for MVR are as follows30: (1) severely symptomatic patients (NYHA class III/IV) with severe MS (MVA < 1.5 cm2) who are not high risk for surgery and who are not candidates for, or have failed, previous BMV (class 1 indication); (2) severe MS (MVA < 1.5 cm2) undergoing other cardiac surgery (eg, aortic valve surgery, coronary artery bypass grafting) (class 2a indication); and (3) mitral valve surgery and LAA excision may be considered for patients with severe MS (MVA ≤ 1.5 cm2, stages C and D) with recurrent embolic events despite adequate anticoagulation (class 2b indication). Further, patients with moderate to severe TR do better after surgery that includes a tricuspid valve repair.99 Given the morbidity and mortality associated with MVR and the potential long-term complications associated with a prosthetic valve (prosthetic valve thrombosis, infective endocarditis, prosthesis mismatch, bleeding complications with anticoagulation), the threshold for MVR is higher than for BMV and is limited to NYHA class III and IV patients. The operative mortality is 3% to 8%, but it may reach as high as 10% to 20% with NYHA class IV patients.100 Therefore the patient should not be allowed to reach NYHA class IV during postponement of surgery. Even if the patient does present in NYHA class IV, surgery should not be denied, as the outlook without surgery is very poor. BMV can be an alternative in such cases after careful discussion.30 The type of valve inserted will depend on the patient’s age and the risk of anticoagulation, but is increasingly more dictated by patient choice. However, if the patient has long-standing AF and must be anticoagulated anyway, a mechanical valve may be inserted. On the other hand, a young patient in sinus rhythm may opt for a bioprosthetic valve to avoid the hazards of anticoagulation, with an understanding of the need for future redo surgery for valve deterioration. If AF is less chronic, a maze procedure may be used at the time of MVR,64 although its success in a purely rheumatic population is less certain than in a nonrheumatic population. Although it is often hoped that relief of MS will result in restoration of sinus rhythm, AF in MS is due not only to increased LA size but also to rheumatic scarring and histologic changes in the LA.101 Thus, relief of mitral obstruction may65 or may not prevent AF102 or allow for return to sinus rhythm.