Operations for endocarditis are guided by some basic principles: optimal timing of surgery as discussed above, good exposure of the valve, radical debridement, optimal choice for reconstruction of the heart and repair or replacement of the valve, and adequate postoperative antibiotic treatment. Radical debridement with removal of all infected and necrotic tissue and foreign material is more difficult to accomplish in mitral cases with AV groove invasion and abscess formation, particularly when compared with aortic root infections. In addition, reconstruction after invasion of the AV groove and AV separation entails closing off the infected space, leaving it without drainage.
Native Mitral Valve Endocarditis
Intraoperative transesophageal echocardiography should be performed in all cases to evaluate the valve before commencing the procedure. Surgical treatment options for NVE affecting the mitral valve include valve replacement and valve repair. Although there is some experience with the mitral valve allograft for treatment of mitral valve endocarditis, there are too few data available to support this strategy.38
Most operations for NVE are best conducted through a full median sternotomy. Cannulation for cardiopulmonary bypass involves arterial return via the ascending aorta and bicaval cannulation for venous return. In case of large mobile vegetations, it is advisable to arrest the heart before placing a transatrial retrograde cardioplegia catheter. Protection is achieved using antegrade and retrograde substrate-enhanced cardioplegia.39
The mitral valve is exposed via a left atriotomy through the interatrial groove or transseptally. If the left atrium is small, an extended transseptal approach is employed. Once exposure of the mitral valve is accomplished, the valve is evaluated to assess for presence of paravalvular abscesses, intracardiac fistulae, or intervalvular fibrous body/ventricular involvement. Radical resection of all necrotic tissue is performed with a margin of normal tissue. All grossly infected tissue is removed without concern for the possibility of repair. Specimens are sent for microbiologic analysis and culture.
For NVE, our approach is to attempt repair if feasible. Mitral valve repair can be performed safely provided there is sufficient remaining tissue to allow valvular reconstruction without tension.40–44 In the event of extensive destruction of the subvalvular apparatus, prosthetic valve replacement is performed. Regardless of the mitral procedure performed, all patients with active infection receive 6 weeks of postoperative antibiotic therapy.
“Drop lesions” of the anterior leaflet encountered in association with aortic endocarditis can be repaired with autologous or glutaraldehyde-preserved pericardium.38 A patch of pericardium is fixed to the remaining tissue of the anterior leaflet with running polypropylene suture (Fig. 43-1). The smooth surface of the patch should face the atrium to decrease the risk of thromboembolic complications.37 More extensive destruction involving both the aortic valve and the anterior leaflet of the mitral valve can be repaired using a free-standing aortic root homograft with the anterior leaflet of the mitral valve still attached. The homograft's attached aortomitral curtain can be used to reconstruct the base of the native anterior mitral leaflet.37,45
Repair of anterior leaflet perforation by patch with autologous pericardium followed by annuloplasty.
Involvement of the free margin of the anterior leaflet can be managed with triangular resection and closure with interrupted fine sutures. Anterior leaflet chordal rupture can be repaired with chordal transposition from the posterior leaflet or with secondary chordal transfer to the free margin of the anterior leaflet. Artificial chordae may also be used to replace ruptured anterior leaflet chordae.
The middle scallop (P2 segment) of the posterior segment is frequently affected by the infectious process. Repair can be performed with quadrangular resection of the middle scallop, and a sliding repair is frequently required to close the gap between the remaining two scallops (Fig. 43-2). Extensive destruction of the posterior annulus requires removal of all devitalized tissue and annular reconstruction with autologous pericardium. Occasionally, repair of the annulus and the posterior leaflet can be accomplished with the same patch if chordal support to the leaflet is good. A running polypropylene suture is used on the ventricular, atrial, and valvular aspects of the patch. If replacement is required, a mechanical or bioprosthetic valve may then be inserted, affixing the prosthesis to the patch.45 It is important that the patch is generous enough to minimize tension on the sutures in ventricular muscle.
Quadrangular resection and sliding repair for posterior leaflet vegetation with ruptured chordae. (A, B) Segment of posterior leaflet is resected and a portion of leaflet detached from the annulus. (C) Leaflet remnants are sutured to the annulus, taking deep bites to reduce leaflet height. Leaflet edges are reapproximated in the center. Annuloplasty completes the repair.
The use of prosthetic ring annuloplasty in NVE is controversial. Favoring repair over replacement, we use a ring whenever the annulus is not infected.
Prosthetic Valve Endocarditis
Operations for PVE are reoperations, usually performed via a median sternotomy. An alternative approach is right anterolateral thoracotomy in the fourth intercostal space; this is particularly useful in patients with multiple previous sternotomies, bypass grafts near the sternum, or a history of mediastinal radiation and/or mediastinitis.46,47 However, a right thoracotomy for mitral reoperations allows limited access, sometimes denies aortic cross-clamping, and may be associated with a risk of stroke.
Cardiopulmonary bypass is instituted using the ascending aorta and bicaval cannulation. A transatrial retrograde cardioplegia cannula is used and myocardial protection is achieved using antegrade and retrograde cardioplegia.
The main issues in achieving mitral valve exposure are related to obtaining mobility of the right atrium and vena cavae.19 Our usual approach to obtain mitral valve exposure is to use an extended transseptal approach. If the left atrium is large and adhesions modest, a standard left atriotomy may be employed. Exposure may be enhanced by division of the superior vena cava and extending the left atriotomy toward the aortic root. This approach provides good exposure even when the left atrium is small.
Reconstruction of the Mitral Annulus
Once exposure of the mitral valve is obtained, the infected prosthesis is removed. Mitral valve PVE may produce an abscess cavity separating the left atrium, left ventricle, and prosthesis. In these situations the operation includes debridement of the annulus with subsequent annulus reconstruction using autologous or glutaraldehyde-fixed bovine pericardium (David technique).48,49 With this technique, a semicircular pericardial patch is used to reconstruct the annulus with one side of the patch sutured to the endocardium of the left ventricle and the other side to the left atrium. This patch closes off the cavity, which must be thoroughly debrided and sterilized before the patch is affixed. The new valve prosthesis is affixed to this reconstructed annulus (Fig. 43-3). The patch should be large in order to minimize tension on suture lines. In most situations with annular reconstruction we employ a bioprosthesis because of the larger and softer sewing ring and to avoid anticoagulation in the postoperative period.
(A) Prosthetic valve endocarditis with posterior perivalvular abscess. (B) The valve is removed and the abscess debrided. A pericardial patch sewn to the ventricle and atrium excludes the abscess cavity and reconstructs the annulus. (C) A new prosthesis is affixed to the pericardial patch and annulus. (Reproduced with permission from the Cleveland Clinic Foundation.)
An alternative technique for mitral annular reconstruction is the technique described by Carpentier and colleagues.50 This technique involves using figure-of-eight atrial and ventricular sutures to reconstruct the AV junction. Exerting traction on these sutures reduces the size of the annulus and closes the AV groove without injury to the circumflex vessels. The main potential disadvantage of this technique is that sutures may pull through stiff and noncompliant ventricular tissue.19 We have observed pseudoaneurysm formation after application of this technique.
Reconstruction of the Fibrous Trigones
Extension of PVE into the intervalular fibrosa/fibrous trigones may necessitate replacement of both mitral and aortic valves. This usually occurs in the setting of PVE affecting both the aortic and the mitral valves and seldom with isolated mitral valve endocarditis. Reconstruction of the intervalvular fibrosa as well as replacement of both the aortic and mitral valve are required (Fig. 43-4). In such circumstances the fibrous trigones may be reconstructed with autologous or bovine pericardium that is used to secure the new prosthesis.13,19 Perfect exposure is mandatory whether it is provided by the extended transseptal approach or by dividing the superior vena cava and extending the left atriotomy from anterior to the right superior pulmonary vein toward the dome of the left atrium. This approach allows debridement of the aortic and mitral valves, as well as the fibrous trigones. The prosthetic mitral valve is then sewn to the annulus posteriorly, medially, and laterally, and the superior portion of the mitral valve annulus is reconstructed with a pericardial patch that replaces the fibrous trigones. The valve is then sewn to the patch with horizontal mattress sutures. Once the mitral valve is secured in place, the aortic valve prosthesis is affixed to the aortic annulus. The pericardial patch is used to reconstruct the medial part of the aortic valve annulus. The aortic valve is then sewn to that patch.13,19 An alternative option is aortic valve and root allograft replacement in an anatomic position and orientation, suturing the intervalvular fibrosa/mitral valve of the allograft to the mitral valve prosthesis.
Reconstruction of the fibrous trigones. (A) Infection involves the mitral and aortic valves. Division of the superior vena cava facilitates exposure of the aortic valve, mitral valve, and fibrous trigones. (B) The new prosthetic mitral valve is sewn to the annulus posteriorly, medially, and laterally, but the superior portion of the mitral valve annulus is reconstructed by a pericardial patch that recreates the fibrous trigone. The valve is then sewn to this patch with horizontal mattress sutures. (C) Once the mitral valve prosthesis is in place, the aortic valve prosthesis is secured throughout most of the annulus. The pericardial patch reconstructs the medial part of the aortic valve annulus and the aortic valve is then sewn to the patch. (D) After the valve replacements are complete, the pericardial patch is extended to finish the closure of the aorta and the left atrium. (Reproduced with permission from the Cleveland Clinic Foundation.)