Surgery of native and prosthetic mitral valve endocarditis may be challenging and requires great experience with mitral reconstructive and reoperative cardiac procedures respectively. A systematic approach using the following principals should be applied to optimize surgical results.
1) Intra-operative transesophageal echocardiography should be performed in every patient. Initially, it is used to identify the functional type of mitral regurgitation and to assess the extent of valvular and intracardiac lesions. At the completion of the procedure, transesophageal echocardiography is critical to evaluate the quality of repair, or the function of a prosthetic valve. It is also essential to assess the quality of deairing of the left-sided chambers and to study left ventricular function.
2) Cardiac manipulation before aortic-cross clamping should be minimized to prevent detachment and systemic embolization of vegetations. This is particularly important whenever vegetations are large, mobile and friable.
3) A careful valve analysis should be performed to confirm the echocardiographic data and to make a complete inventory of all lesions: leaflet abscess or perforation, vegetations, annular abscess, and chordae rupture. In patients with prosthetic valve endocarditis, vegetations, annular abscess and valve dehiscence are common findings.
From Carpentier A, Adams DH, Filsoufi F. Carpentier's Reconstructive Valve Surgery. Saunders (Elsevier), 2010
4) Radical resection of all infected and necrotic tissues is mandatory with 1-2 mm margin of normal tissue. An infected prosthetic valve should be removed completely. Multiple specimens including vegetations and valvular debris should be sent for further microbiologic analysis. Local application of an anti-septic solution is strongly recommended.
5) The aortic valve may need to be inspected to rule out the extension of infection to the aortic root and the potential localization of secondary lesions on the aortic leaflets.
Native mitral valve endocarditis
After the exposure of the mitral valve, all macroscopically infected tissues are widely excised without any concern about the possibility of repair. Once the debridement is performed, reconstructive surgery using Carpentier's technique should be considered. The feasibility of mitral repair depends on the availability of healthy tissue following debridement. In the event of entire leaflet involvement or extensive destruction of subvalvular apparatus, prosthetic valve replacement is performed using standard techniques. Because multiple studies have failed to identify differences in the reoccurrence of infection between mechanical and bioprosthetic valves, standard criteria should be applied for valve selection.
Mitral valve reconstruction can be carried out safely in multiple anatomic presentations provided sufficient leaflet tissue remains available to allow valvular reconstruction without excessive tension on the suture lines.
Leaflet perforation or detachment
After adequate debridement, the leaflet defect is repaired with a patch of autologous pericardium. A piece of pericardium is preserved in glutaraldehyde 0.625% for 10 minutes and then rinsed in a saline solution for 15 minutes. The patch is sutured to the remaining valvular tissue with a monofilament suture. The smooth surface of the pericardium is oriented toward the atrium to decrease the potential risk of thromboembolic complications. Occasionally a large surface area of the anterior leaflet is destroyed in double aortic and mitral valve endocarditis. If an aortic homograft is used to reconstruct the aortic root, the homograft's attached aorto-mitral curtain and the anterior leaflet can be used to reconstruct the mitral valve.
Chordae rupture with posterior leaflet prolapse
The middle scallop of the posterior segment (P2 segment) is often involved in the infectious process with one or several chordae rupture. A quadrangular resection of P2 segment is performed. Annular plication or sliding leaflet plasty technique is used depending upon the extent of P2 resection. The same principle applies for infective endocarditis affecting the P1 or P3 segment. Following leaflet reconstruction, the implantation of a prosthetic ring is strongly recommended.
Chordae rupture with anterior leaflet prolapse
Limited infection of the free margin of the anterior leaflet is best treated with a triangular resection followed by a primary repair with interrupted polypropylene suture. Using this technique, leaflet resection should not involve more than 10% of the surface area of the anterior leaflet. In the event of chordae rupture, chordae transposition of the secondary chordae of the anterior leaflet to the free margin or from the posterior leaflet may be required to provide adequate support. The support of the free margin can also be restored with artificial chordae, although the use of living tissue is preferable in an infectious context.
Chordae rupture with commissural prolapse
Whenever the commissure is involved, the prolapsed area is resected and reconstructed using the annular plication or sliding leaflet plasty technique.
In the setting of mitral valve endocarditis, prosthetic ring annuloplasty following reconstruction remains controversial. In patients with acute endocarditis without annular dilatation or deformation, the use of a prosthetic ring can be avoided. However, in the presence of chronic mitral regurgitation and dilated annulus, prosthetic ring annuloplasty should be utilized to restore a large surface of coaptation, remodel the annulus and ensure long-term durability of the repair.
Prosthetic mitral valve endocarditis
Reoperative mitral valve surgery can be performed through a redo sternotomy or right anterolateral thoracotomy.
Redo sternotomy is preferred if concomitant procedures such as coronary artery bypass grafting and/or aortic valve surgery are required. Right anterolateral thoracotomy is the approach of choice if the patient has undergone multiple previous sternotomies, or presents with patent grafts, or if suspicion of severe mediastinal adhesions (recent sternotomy, mediastinitis, and mediastinal radiation). The right thoracotomy approach is relatively contraindicated in the following situations: previous right-sided chest surgery, severe chronic obstructive pulmonary disease, or moderate to severe aortic regurgitation.
After mitral valve exposure, the infected prosthesis and surrounding tissues must be excised. Left ventricular cavity should be inspected carefully to remove all infected tissues. In the presence of an annular abscess, a complete sharp excision of all infected tissues must be performed. Following annular debridement, the mitral annulus should be reconstructed prior to the insertion of a new prosthetic valve.
Mitral annular reconstruction using figure-of-eight mattress atrial and ventricular sutures (Carpentier technique) With this technique, the atrioventricular junction is constructed by a series of figure-of-eight 2-0 braided mattress sutures placed into the atrial and ventricular edges. These sutures are brought out on the atrial side. The ventricular bites of theses sutures should only involve one third of the thickness of the myocardial wall and be as wide as possible, taking advantage of any fibrous tissue present on the surface of the myocardium. Exerting traction on these sutures reduces the size of the annulus and closes the atrioventricular groove without injury to the circumflex vessels. The closure of the atrioventricular groove is facilitated by downward displacement of the atrial edge toward the ventricular edge with forceps. By means of this technique the circumflex vessels and surrounding fat are displaced outward and the atrioventricular junction is restored as a firm fibrous structure available for valve replacement.
Another alternative is "sliding atrium technique" also described by Carpentier. This technique is particularly indicated whenever the infectious process extends to the ventricular myocardium. In this setting, following debridement, a large area of ventricular myocardium is without fibrous tissue coverage. The atrial edge is mobilized to create a 2-3 cm flap which is used to cover the nude myocardial area. The fat and connective tissue surrounding the circumflex vessels are left attached to the ventricular side. Subsequently figure-of-eight mattress sutures are used as described above.
Mitral annular reconstruction using autologous or glutaraldehyde fixed bovine pericardium (David technique) In patients with posterior annular destruction a semicircular shaped pericardial patch is used to reconstruct the annulus. While ensuring the patch is large enough to completely cover the defect, one side of the patch is sutured to the endocardium of the left ventricle and the other side is used to secure the prosthetic valve.
In those with complete annular destruction, a circumferential patch is tailored to create a new annular structure. After mitral annular reconstruction, mitral valve replacement is performed using standard techniques.
All patients should be treated with intravenous antibiotics for a minimum of four to six weeks. The duration of antibiotic therapy should be extended in patients with prosthetic valve infection with virulent microorganisms (e.g. Staphylococcus aureus, fungal infection). If blood cultures were positive at the time of surgery, they should be repeated postoperatively until negative results are obtained. Predischarge echocardiography is recommended to assess valvular function and to rule out an early perivalvular leak which may occur in patients who underwent annular reconstruction for abscess. Additional work-up may be necessary to identify the potential source of infection (e.g. gastrointestinal work up in patients with streptococcus infection). Long-term follow up with repeat echocardiography is necessary particularly in patients at high risk of recurrence (e.g. intravenous drug abusers, persistence of health -care associated factors and prosthetic mitral endocarditis).
Over the last two decades, the operative mortality associated with the surgical treatment of mitral endocarditis has significantly decreased. Recent clinical studies typically report an operative mortality ranging between 0-20% including both native and prosthetic mitral endocarditis. Several factors including advances in antimicrobial therapy, patient selection, myocardial protection, and surgical techniques have all likely contributed in improving surgical outcomes. Prosthetic valve endocarditis remains associated with a much higher operative mortality rate than native valve endocarditis. Other factors associated with increased hospital mortality include: advanced age, double valve endocarditis, hemodynamic compromise with cardiogenic shock, preoperative end stage organ dysfunction such as renal or liver dysfunction, and fungal and MRSA endocarditis. Interestingly, the activity of mitral endocarditis (i.e. active vs. healed) does not appear to impact on short or long-term survival, and therefore it is not of primary concern in the decision making process regarding the timing of surgery.
In patients with native mitral valve endocarditis ,valve reconstruction is preferable to valve replacement whenever feasible, as repair is associated with a lower hospital mortality and improved long-term survival. Several recent series have documented outstanding results with valve repair in the setting of mitral endocarditis, with operative mortality rates ranging between 0-9%. The rate of postoperative stroke is between 0 to 3%. Currently in experienced centers, a reconstructive rate ranging between 50 to 80 % is expected provided that the patient is referred for surgery in timely fashion before extensive valvular destruction occurs. In terms of infection free survival, mitral valve reconstruction is associated with a less than 1% per year re-infection rate, and appears to be preferable to mitral valve replacement. Preserving native mitral valve tissue by means of repair and avoiding a valve prosthesis in the setting of active infection most likely accounts for this observation. A systematic review of the literature has shown that the rates of hospital mortality, reoperation, late recurrence of endocarditis, and strokes were significantly less after mitral valve reconstruction compared to mitral replacement.
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