Mitral Valve Replacement Chordal Preservation

Fig. 6.7a. Mitral valve exposure. Standard mitral exposure. Left atriotomy begins just anterior to right superior pulmonary vein. This affords excellent exposure of the mitral valve in most cases.

Transseptal Incision Mitral

Fig. 6.7b. Dubost mitral exposure. A bi-atrial, transseptal incision is made going through the interatrial septum at the fossa ovalis. Bicaval can-nulation and snares are required.

Fossa Ovalis

the intra-annular position of the valve prevents the cordae and annulus from impinging on the leaflets of the mechanical valve. Furthermore, if a suture breaks, the pledget can be easily retrieved. (Some, however, support seating the valve in the supra-annular position, i.e. by placing the pledgetted sutures from the ventricular up into the atrial side. This results in a sturdy seating arrangement resulting in a higher burst pressure).

Porcine Valve Replacement

Fig. 6.8. Mitral valve replacement. (a) Traction is placed on the anterior leaflet of the mitral valve to gain exposure of the 12 o'clock position. (b) Annular sutures are placed sequentially, starting at the 12 o'clock position. Traction on this stitch will improve visualization of the annulus. Plegetted sutures are placed from atrial to ventricular aspect. (c) Sutures are placed through the valve sewing ring and the valve seated. (d) Seated mitral prosthesis. The vent is passed through the valve into the left ventricle.

Fig. 6.8. Mitral valve replacement. (a) Traction is placed on the anterior leaflet of the mitral valve to gain exposure of the 12 o'clock position. (b) Annular sutures are placed sequentially, starting at the 12 o'clock position. Traction on this stitch will improve visualization of the annulus. Plegetted sutures are placed from atrial to ventricular aspect. (c) Sutures are placed through the valve sewing ring and the valve seated. (d) Seated mitral prosthesis. The vent is passed through the valve into the left ventricle.

Excision of the valve continues down to the commissures and in general, the posterior leaflet of the mitral valve is preserved so as to retain the chordae and preserve left ventricular geometry. If this cannot be done because of heavy calcification or fibrosis, then the posterior leaflet too should be excised. The sutures are then placed into the sewing ring of the St. Jude's valve. The leaflets should be positioned perpendicular to the interventricular septum as this allows for more clearance from the leaflets. Figure 6.9 shows that the clearance from the leaflet edge is greater when the valve is seated perpendicular to the annulus rather than parallel to the annulus.

It should be noted that for a porcine or bovine bioprosthesis, the stitches are likewise placed from the atrial to the ventricular side. The stents in the case of bioprostheses are positioned at the 10 o'clock to 2 o'clock position to prevent impingement of the left ventricular outflow tract. The widest cusp on the porcine bioprosthesis is placed adjacent to the septum (Fig. 6.10).

During the entire process of mitral valve replacement, care is taken to prevent injury of the circumflex and coronary sinus, AV node/bundle of His, and the noncoronary cusp left coronary cusp.

With the mitral valve seated in place, a left atrial vent is then placed across the mitral valve leaflets into the left ventricle, and the left atrium is then closed. Prior to finishing the left atrial closure, the left ventricular vent is shut off and 10 cm of pressure applied to the lungs to purge air. Then once the left atrium is closed, the left ventricular vent is restarted as is the aortic root vent, and the aortic cross-clamp is released with the patient in Trendelenburg. A needle and syringe are used to aspirate air from the dome of the left atrium and left ventricular apex, and weaning from coronary artery bypass is achieved as previously described.

Several technical points are worthy of mention. The surgeon stands on the right hand side for this, as with all cardiac surgical procedures. The first assistant initially holds the mitral valve retractor. Once the valve is excised and the suture is placed, the first assistant gives the mitral valve retractor to a nurse or second assistant who stands on the left side of the first assistant. The third assistant stands on the right side of the primary surgeon. Thus the first assistant has both hands free

Fig. 6.9a. Clearance of St. Jude valve leaflets. Minimal clearance of [1] (i.e. leaflets oriented perpendicular to septum) is greater than [2] (i.e. parallel to septum). b. Correct orientation of St. Jude valves in aortic and mitral positions with leaflets perpendicular to septum.

Fig. 6.9a. Clearance of St. Jude valve leaflets. Minimal clearance of [1] (i.e. leaflets oriented perpendicular to septum) is greater than [2] (i.e. parallel to septum). b. Correct orientation of St. Jude valves in aortic and mitral positions with leaflets perpendicular to septum.

Fig. 6.10. Technical detail of suture orientation for porcine tissue valve. The widest prosthetic cusp [(A) to (B)] is oriented from (A) to (B) on the mitral annulus, corresponding to the left ventricular outflow tract under the aortic valve.

and with his left hand holds the valve, and with his right hand holds a needle driver. The surgeon drives the sutures through the sewing ring and the first assistant grasps the needles in the sewing ring and pulls them out and inserts them into the fingers of his left hand which is holding the valve. At each one-third of the way around the circumference of the valve, the threads are clamped and then cut by the second and third assistants. The third assistant on the surgeons right hand side loads the needle which is given to him by the surgeon, (i.e. the second half of each pair) in a backhand manner. An organized consistent approach by the surgeon, first, second and third assistants and scrub nurse makes the procedure run smoothly.

Approaches to the Mitral Valve

The standard approach is an incision just posterior to the inter-atrial groove into the left atrium, anterior to the right superior pulmonary vein (Fig. 6.7a). This approach is acceptable in nearly all cases as long as there has been adequate mobilization of the right superior pulmonary vein, superior and inferior vena cava and traction stitches have been placed in the anterior leaflet of the mitral valve to bring the annulus into view. If these maneuvers fail then other techniques are described but rarely needed. This includes the Dubost bi-atrial, transseptal approach to the mitral valve which includes an incision into the right atrium, left atrium, and through the inter-atrial septum to gain improved exposure of the mitral valve (Fig. 6.7b). Another approach is through the dome of the left atrium. Yet another approach is a left thoracotomy to gain access to the left atrial appendage with cannulation of the femoral artery and placement of another cannula in the right ventricular outflow tract into the right ventricle. The mitral valve can also be approached via a left ventricular aneurysm and replacing the valve from the ventricular aspect. Another approach is a right thoracotomy with standard cannula-tion giving improved exposure of the left atrium. Another method is through transsection of the superior vena cava and retraction inferior and laterally of the cava to gain access to the dome of the left atrium. Mitral valve replacement has also been approached through the aortic root via the aortic valve.

Atrioventricular Disruption

Atrioventricular groove disruption is a horrifying complication which may occur after mitral valve replacement. This occurs because of a separation between the atria and the ventricle in the back of the heart. It may be due to a heavily calcified mitral valve annulus which cracks when the mitral valve is placed, or it may be due to heavily pulling on the heart to deair the apex of the left ventricle. This axial torsion on the heart may actually tear the atrioventricular septum at the point that the ridge of the mitral valve attaches to it. This is exactly in the region of the circumflex coronary artery and coronary sinus, complicating things further. If a sudden gush of blood comes from the back of the heart after mitral valve replacement, one must assume an AV disruption. Although the chance of survival is limited at this point, several rapid maneuvers may be helpful in trying to salvage the patient. Cardiopulmonary pulmonary bypass must be reinstituted immedi-

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102 Cardiothoracic Surgery ately. A cross-clamp is applied and plegia given. The left atrium is opened and the prosthetic valve is removed. Pledgetted sutures are used to repair the AV disruption from both within and outside the heart. Figure 6.11 shows the sutures placed on the outside of the heart. One must be extremely careful to avoid injury to the circumflex coronary artery and coronary sinus. Atrioventricular stability may be extremely tenuous. An episode of hypertension or other acute increase in afterload may result in a blow-out of a tentative atrioventricular groove.

Mitral Valve Repair

Mitral valve repair is becoming more and more common because of the advantages inherent in repairing the patient's own native mitral valve. It prevents the coagulation disorders necessary with coumadinization for mechanical valves and prevents the necessity for reoperation for bioprosthetic valve failure. The indications for mitral valve repair for mitral regurgitation include ruptured chordae to the posterior leaflet usually from myxomatous degeneration, or less commonly ischemia. Another indication is ischemic cardiomyopathy causing dilation of the mitral valve ring, in which case an annular ring (Duran ring) is placed. Another reason is myxomatous degeneration resulting in dilation of the annulus and redundancy of the leaflets. Another type of mitral valve repair is commissurotomy in the case of commissural fusion. This is only worthwhile if the leaflets themselves are pliable and not very thickened and the leaflet edges are intact without being rolled or deformed. The chordae and papillary muscles must be relatively normal. Chordal rupture to the anterior leaflet may also be repaired in some instances by chordal transfer from the posterior leaflet to the anterior leaflet (via quadrangular excision of the posterior leaflet and repair). It should be said that mitral valve repair, with the exception of commissurotomy, should always be accompanied by an annuloplasty since this supports the repair and will help prevent future dilation. Generally, a Duran ring, which is a complete ring, is used rather than a Carpentier ring which is an incomplete ring. The Carpentier ring is more

Fig. 6.11. Repair of atrioventricular rupture following mitral valve replacement. Plegetted sutures are positioned around the circumflex artery and coronary sinus.

Fig. 6.11. Repair of atrioventricular rupture following mitral valve replacement. Plegetted sutures are positioned around the circumflex artery and coronary sinus.

Groove Rupture Repair

rigid than the flexible Duran ring and is not as mobile with the annular movements of the normal cardiac cycle.

It is very important when doing the initial assessment of the mitral valve in a contemplative repair to do a careful evaluation of the valve. This involves assessing the amount of leaflet fibrosis, commissural fusion, leaflet edge rolling, and chordae and papillary muscles, since this will determine whether repair is possible and the type of repair. Figure 6.12a-d describes the technical considerations of several types of mitral valve repairs.

One of the complications of mitral valve repair includes systolic anterior motion (SAM) of the anterior leaflet of the mitral valve. This can lead to left ventricular outflow obstruction from displacement of the anterior leaflet toward the septum with systole. Besides left ventricular outflow obstruction, SAM can also lead to severe mitral regurgitation. The phenomenon may occur when there is redundant tissue in a prolapsing mitral valve. After repair and annuloplasty, a redundant posterior leaflet fills the annuloplasty ring and results in coaptation of the posterior leaflet near the middle of the anterior leaflet rather than on its free edge. This shifts the anterior leaflet toward the ventricular septum, obstructing left ventricular outflow and distorting normal coaptation leading to mitral regurgitation.

SAM worsens with ionotropic support whereas beta blockade may be helpful. Afterload reduction, as with the use of IABP, alo worsens SAM. Surgical maneuvers to treat SAM include myomectomy and septal resection although this entails additional risk and does not treat the underlying problem. Direct approaches includes replacement of the mitral valve with a prosthesis. Another method to prevent or treat SAM is to reduce the height of the posterior leaflet in valve repair. This can be done by a sliding repair to detach and reposition a portion of the posterior leaflet to shorten its height. The resulting coaptation of the mitral leaflets is nearer tot he leaflet edges, preventing posterior displacement of the anterior leaflet.

Fig. 6.12. Mitral valve repair. Systematic valve evaluation includes assessing the leaflets, commissures, chordae and papillary muscles. (a) Commissurotomy. Fused commissures are incised. Papillary muscle incision is frequently needed for complete mobility after a commissurotomy.
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