Mitral Valve Regurgitation - Ischemic Valvular Disease
Standard techniques of monitoring (arterial line, central venous access, Foley catheter...) are used in patients undergoing a combined mitral valve reconstruction and coronary bypass grafting. A Swan-Ganz catheter should be inserted in every patient. Initially a transesophageal echocardiogram should be performed. It is a key element to determine the functional type of mitral regurgitation and to assess left ventricular size and function. At the completion of cardiopulmonary bypass, it allows the surgeons to assess the quality of valve reconstruction, to detect residual air in left side cavities, and to monitor ventricular filling. An epiaortic scan of the ascending aorta is recommended to rule out the presence of atherosclerotic lesion prior to arterial cannulation.
Surgical approaches, cardio pulmonary bypass, and myocardial protection
Median sternotomy is the surgical approach of choice in patients undergoing combined mitral valve reconstruction and myocardial revascularization. In reoperative setting ( e.g. mitral valve surgery after previous coronary artery bypass grafting), a right thoracotomy approach is a viable alternative. Femoral vessels exposure is recommended if severe mediastinal adhesions are suspected (recent reoperation, multiple previous sternotomies, mediastinitis, and mediastinal radiation) and in patients with patent left internal mammary graft. Mitral valve surgery is classically performed with cannulation of both vena cava and the aorta, intermittent antegrade or a combined antegrade and retrograde cardioplegic arrest with cold blood high potassium cardioplegia for myocardial protection. Further myocardial protection can be obtained by moderate systemic hypothermia between 28-30C and local hypothermia with topical ice.
Exposure of the mitral valve and valve analysis
Following completion of coronary bypass grafting, the perfect exposition of the Mitral Valve Regurgitation is essential before undertaking any type of mitral valve surgery. The most commonly used approach is the interatrial approach through the Sondergaard's groove.
The valvular apparatus is inspected and then examined with a nerve hook in order to assess tissue pliability and to identify the functional type of mitral regurgitation. The anterior paracommissural scallop of the posterior leaflet (P1) constitutes the reference point. Applying traction to the free edge of other valvular segments and comparing them to P1 determines the extent of leaflet prolapse in patients with papillary muscle rupture. This technique is, however, not very reliable to assess the severity of leaflet tethering in the arrested heart. The presence and severity of annular dilatation/deformation is also evaluated. In postero-lateral myocardial infarction, this dilatation is asymmetrical, involving mostly the p2, p3 and posterior commissural area. In antero-septal infarction, the annulus is symmetrically dilated.
Mitral valve reconstructive Surgery
Type I mitral regurgitation
Type I mitral regurgitation is best treated with a remodeling annuloplasty. The ring is downsized by one size.
Type II mitral regurgitation
Mitral valve replacement with the preservation of the subvalvular apparatus is the surgical treatment of choice in patients with complete rupture of a papillary muscle.
Papillary muscle reimplantation can be attempted in selected patients, provided that necrosis of the supporting myocardial wall is limited and in the absence of akinetic or dyskinetic wall. The non-prolapsed area of the valve serves as a reference point to determine the site and level of implantation of the papillary muscle remnant. At this site a 5mm deep trench is created in the muscular wall. The papillary muscle remnant is trimmed in order to preserve only the fibrous cuff. The papillary muscle remnant is buried in the trench using interrupted 4/0 polypropylene sutures. The trench is then closed around the papillary muscle remnant using a figure of eight suture. The procedure should be completed with a remodeling annuloplasty.
Elongated papillary muscle can be treated by its plication or resection of its extra length followed by reconstitution of the continuity of the remaining segments. The procedure is completed with a slightly downsized ring annuloplasty to reduce the tension on the reconstructed valve. If the papillary muscle is too thin and the anatomic conditions are not favorable, Mitral Valve Regurgitation should be preferred.
Type IIIb mitral regurgitation
Remodeling annuloplasty using a downsized ring is the technique of choice in type IIIb dysfunction. The goals of valve reconstruction are: preserving leaflet mobility, restoring a large surface of coaptation by reducing the septo-lateral dimension, and stabilizing the annulus to ensure long-term stability.
From Carpentier A, Adams DH, Filsoufi F. Carpentier's Reconstructive Valve Surgery. Saunders (Elsevier), 2010.The prosthetic ring should be downsized by one size or two sizes depending on the severity of leaflet tethering. The use of double-row annuloplasty suture technique is recommended to reduce the risk of ring dehiscence.
From Carpentier A, Adams DH, Filsoufi F. Carpentier's Reconstructive Valve Surgery. Saunders (Elsevier), 2010 Additional procedure such as the resection of a large aneurysm or dyskinetic plaque may be necessary to enhance the results of valve reconstruction.
During the last decade, adjunct techniques including the closure of the indentation between p2-p3 segments, resection of secondary chordae, patch extension of the posterior leaflet and papillary muscle sling have been described to minimize the risk of residual or recurrent mitral regurgitation. Clinical experience with these procedures remains limited and there are no long-term data available.
Finally, it is important to stress that in selected patients particularly those with severe bileaflet tethering and enlarged left ventricle with an end diastolic diameter greater than 65 mm, mitral valve replacement with a bioprosthesis may be the surgical procedure of choice.