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Mitral Valve Replacement


Mitral Valve Replacement
Keywords : mitral valve, mitral valve replacement
Step 1. Anatomy
·    The mitral valve is a complex structure comprised of an anterior and posterior leaflet that is connected to the left ventricle via attachments to papillary muscles through the chordae tendineae.

·  It is anchored to the mitral annulus, which is in close relation to the circumflex coronary artery laterally, coronary sinus medially, and aortic valve anteriorly.
·    Shown in Fig. 19.1 is the mitral annulus in a lateral view, along with view of the mitral valve from the top of the heart showing its proximity to the aortic and tricuspid valves.


Step 2. Access to the Mitral Valve
·    Exposure of the mitral valve must be optimized to facilitate efficient and effective surgery. Although not described in detail, complete drainage of the right atrium must be achieved prior to arresting the heart and opening the left atrium.
·  Left atriotomy via Sondergaard’s groove: The interatrial plane is dissected to separate a portion of the right atrium that overhangs the left atrium toward the septum. This incision is extended superiorly toward the left atrial roof. It is extended inferiorly anterior to the inferior pulmonary veins, but posterior to the inferior vena cava (Fig. 19.2).

·   Extended vertical transseptal biatriotomy: The right atrium is opened from the right atrial appendage toward the inferior vena cava. The interatrial septum is then incised down to the fossa ovalis and extended cephalad onto the dome of the left atrium. This approach is particularly useful in the setting of reoperative valve surgery with an aortic valve prosthesis in place (Fig. 19.3)

·    Khonsari biatriotomy: This extends from the right atrial appendage toward the right superior pulmonary vein to expose the interatrial septum, which is then incised transversely through the fossa ovalis (Fig. 19.4)


Step 3. Suture Placement for Mitral Valve Replacement
·     Continuous suture: This approach to anchoring a prosthesis is typically performed when the mitral annulus is tough and fibrous without much annular calcification. The major advantage of this technique relates to surgical speed, which may be advantageous in robotic or minimally invasive mitral surgery. This is performed with a 3-0 Prolene or Gore-Tex sutures (Fig. 19.5).

·  Interrupted sutures without pledgets: This technique is performed in the setting of mitral annular calcification or following failed prosthesis removal at the time of reoperative mitral replacement. The major advantage of this technique is that the sewing cuff of the mitral prosthesis will be seated precisely within the plane of the mitral annulus, without any distortion. This is performed with 3-0 Ethibond sutures (Fig. 19.6).

·  Interrupted sutures with pledgets: These sutures can be placed from the atrium toward the ventricle (pledgets sitting on the atrial surface of the mitral valve) or vice versa (pledgets sitting on the ventricular surface of the mitral valve; Fig. 19.7).
·    Although both approaches can be applied for bioprosthetic or mechanical valve replacement, it is advantageous to place pledgets on the atrial surface when using a mechanical valve. This minimizes the risk of pledget embolization into the left ventricle if a suture tears during tying.

Step 4. Prosthesis Orientation
·    Bioprosthesis: The largest leaflet cusp should face the left ventricular outflow tract to prevent outflow obstruction (Fig. 19.8).

·  Mechanical prosthesis: Modern bileaflet valves are positioned in an antianatomic position with the pivot guards orientated in an anterior-posterior direction (Fig. 19.9).


Step 5. Chordal Preservation
Maintenance of the ventricular-annular continuity at the time of mitral valve replacement has been associated with more favorable ventricle remodeling and better survival compared to nonchordal sparing valve replacement.

1. Preservation of the Posterior Leaflet
· The most common approach to chordal preservation involves complete resection of the anterior leaflet in which the posterior leaflet is retained. Replacement sutures are placed through the annulus and through a portion of the posterior leaflet (Fig. 19.10).3
· Some have also described resection of the central portion of the posterior leaflet, with reattachment of the posterior leaflet free edge with the valve replacement sutures.



2. Anterior Leaflet Preservation
·    This has been described with excision of a central trapezoidal segment of the anterior leaflet. The remaining tissue is taken by the valve suture. Others have described using Prolene sutures to reapproximate the remaining leaflet tissue to the annulus before valve suture placement (Fig. 19.11A).4
·   Others have also described complete detachment of the anterior leaflet with resection of the middle portion of the leaflet. The remaining leaflet tissue is that reapproximated to the anterolateral and posteromedial commissures, respectively.5
·   Initially described for implantation of a tilting disk mechanical prosthesis, reattachment of the detached anterior leaflet to the posterior annulus has been used by some.
·   The Khonsari I technique is applied for rheumatic valves in which the primary chordate are destroyed and subvalvular apparatus are thickened. In this technique, second-order chords are preserved in bundles and then reattached radially to the annulus in their anatomic position using pledgetted valve sutures.6,7

3. Neochordae Placement
  Polytetrafluoroethylene sutures are placed on the papillary muscles and attached to the mitral annulus at 2, 5, 7, and 10 o’clock positions (Fig. 19.12).


Step 6. Annular Reconstruction
·   In patients with destruction of the posterior annulus, secondary endocarditis, or following radical débridement in patients with severe annular calcification, a pericardial patch is sewn into the left ventricle cavity with Prolene sutures. Valve sutures are then secured to the patch before the atrial surface is reapproximated (Fig. 19.13).

Step 7. Mitral Annular Calcification
·    Mitral annular calcification is common and represents a challenging cardiac lesion.
·    Mitral annular calcification in younger patients with degenerative disease tends to involve the posterior annulus (Fig. 19.14). In these patients, the calcification is dense and can be removed en bloc, with subsequent reconstruction of the annulus, described previously.
· In patients with a history of renal dysfunction requiring renal replacement therapy, or mediastinal irradiation, or those of advanced age, the calcification of the mitral annulus may be friable, with extension into the ventricle cavity.
·    In these patients, valve explants may be challenging. I recommend that resection begin with the anterior leaflet, thereby facilitating visualization of the subvalvular structures. Importantly, this aids in the identification of the mitral annulus, which may not be obvious. Débridement of the annulus is performed with sharp dissection using a no. 11 blade and bluntly with a rongeur. Mitral replacement with interrupted suture placement is useful because it allows the mitral prosthesis to be seated within the mitral annulus. Also, interrupted suture placement may mitigate tension on the annulus, which can result in calcium fracturing when tying.

·   For impenetrable calcium involving the portion of the mitral annulus from the 12 to 3 o’clock positions, sutures may be placed across the interatrial septum via the right atrium. Impenetrable calcium involving the mitral annulus from the 9 to 12 o’clock positions may require suture placement externally on the left atrial roof onto the mitral annulus (Fig. 19.15).
·  Another strategy for mitral prosthesis implantation involves the intraatrial insertion of the prosthesis, as described by Gandjbakhch.8 In this technique, a Dacron collar is sewn onto a valve prosthesis. An inner row of interrupted pledgetted valve sutures (pledgets on the atrial surface) are placed before the free end of the collar is sewn to the left atrium with running Prolene sutures.


References
·   Guiraudon GM, Ofiesh JG, Kaushik R. Extended vertical transatrial septal approach to the mitral valve. Ann Thorac Surg. 1991;52(5):1058–1060; discussion 1060–1062.
·    Khonsari S, Sintek CF. Transatrial approach revisited. Ann Thorac Surg. 1990;50:1002.
·    Feikes HL, Daugharthy JB, Perry JE, et al. Preservation of all chordae tendinae and papillary muscles during mitral valve replacement with a tilting disc valve. J Cardiac Surg. 1990;2:81.
·    David TE. Mitral valve replacement with preservation of chordae tendinae: Rationale and technical consideration. Ann Thorac Surg. 1986;41:680.
·    Miki S, Kusuhara K, Ueda Y, et al. Mitral valve replacement with preservation of chordae tendinae and papillary muscles. Ann Thorac Surg. 1988;45:28.
·    Okita Y, Miki S, Ueda Y, Tahata T, Sakai T, Matsuyama K. Mitral valve replacement with maintenance of mitral annulopapillary muscle continuity in patients with mitral stenosis. J Thorac Cardiovasc Surg. 1994;108:42–51.
·    Wasir H, Choudhary SK, Airan B, Srivastava S, Kumar AS. Mitral valve replacement with chordal preservation in a rheumatic population. J Heart Valve Dis. 2001;10:84–89.
·    Nataf P, Pavie A, Jault F, Bors V, Cabrol C, Gandjbakhch I. Intraatrial insertion of a mitral prosthesis in a destroyed or calcified mitral annulus. Ann Thorac Surg. 1994;58(1):163–167.