MITRAL VALVE EXPOSURE
After extracorporeal circulation has been instituted, adequate exposure of the mitral valve is mandatory to perform a safe and effective operation. Pericardial adhesions, if present, are released up to the apex.
The interatrial approach is used in most instances ( Fig. 7-1 ). It provides better access to the mitral valve than the classic direct atrial approach and less damage than Dubost’s biatrial transseptal approach. The interatrial groove is dissected and the two atria are divided up to the fossa ovalis (a) . This dissection exposes the roof of the left atrium, which is incised after the heart has been arrested by cardioplegia (b) . The incision is extended superiorly to 1 cm from the superior vena cava, and inferiorly to midway between the right inferior pulmonary vein and the inferior vena cava (c, d) . If the right atrium is opened inadvertently, it is closed later when left atrial closure is performed.
Maximal exposure of the left atrium is obtained using the self-retaining sternal retractor ( Fig. 7-2 ). The upper blade is positioned first. Its curvature is pushed upwards with the right thumb while the left hand hooks the blade to the sternal retractor. The lower blade is then positioned by pushing its curvature upwards with the left thumb while its straight portion is hooked using the right hand. A lateral blade is available to improve the exposure of the posterior aspect of the mitral valve if necessary.
If exposure of the mitral valve remains suboptimal, several additional maneuvers may be useful:
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All pericardial adhesions are released.
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The vena cavae are dissected from the pericardial tissue and upwards traction is placed on the caval tapes.
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The left atrial incision is extended between the inferior vena cava and the right inferior pulmonary vein.
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A 1-cm incision perpendicular to the atrial incision is added involving the right atrium vertically and the septum transversally up to the fossa ovalis (insets) . This adjunct technique replaces the classic Dubost biatrial incision ( Fig. 7-1, e, insets ).
Once the atrium is fully opened and the mitral valve exposed, a left atrial vent is placed to drain the pulmonary venous return.
To obtain optimal exposure, a transseptal approach may be indicated in cases with previous aortic valve replacement, a small left atrium, or the presense of severe adhesions between the right atrium and the pericardium ( Fig. 7-3 ). This approach is also favored in patients with a giant left atrium to obtain easier access to the mitral valve and to position the incision in an area of high-velocity blood flow, thus minimizing the risk of clot formation. After a craniocaudal (longitudinal) right atriotomy (a) , the septum is incised through the fossa ovalis toward the space between the coronary sinus and the orifice of the inferior vena cava (b) . Inverted mattress sutures are placed to hold the septal edge (c) , which is then retracted with blades (d) .
VALVE ANALYSIS
The aim of mitral valve analysis is to confirm or modify the preoperative echocardiographic findings, the functional type, and the segmental localization. Then, a full inventory of the lesions is undertaken. The left atrium is carefully inspected. Endocardial thickening, thrombus formation, calcification, or jet lesions are noted. Jet lesions are important as they indicate a leaflet prolapse opposite to the jet or a restricted leaflet motion on the side of the jet ( Fig. 7-3, d ). The mitral annulus is then examined first to evaluate the degree of annular dilatation and its symmetrical or asymmetrical shape, and to recognize occasional calcifications or fibrin deposits. The leaflets are examined with two nerve hooks to proceed to a “functional analysis” of all the leaflet segments in an organized manner ( Fig. 7-4 ). Tissue pliability and leaflet motion are analyzed, beginning at the P1 segment and proceeding clockwise. The free edge of P1 typically serves as “the reference point,” since P1 is more rarely affected by abnormal leaflet motion than other leaflet segments.
Valve analysis of all leaflet segments is carried out in an organized manner using P1 as a “reference point” in most instances.
The normal leaflet motion of P1 should be confirmed, however, by pulling its free edge upwards with a nerve hook. The free edge should not override the plane of the mitral orifice nor be tethered by short chordae or a displaced papillary muscle. Using another hook, the remaining valvular segments are examined in a sequential manner and compared to P1 to determine whether they are prolapsed or restricted. The “segmental functional analysis” is the “Fil d’Ariane” *
* See Glossary .
of mitral valve reconstructive surgery. It allows recognition and localization of the dysfunctions, analysis of the lesions, and selection of the appropriate reconstructive techniques. Whenever P1 motion is abnormal, another segment should be identified to serve as the reference point. Whenever a prolapse involves all the leaflet segments, one segment should be corrected first with the annulus serving as the reference point, and the remaining segments should be corrected using the corrected segment as the reference point.Exposure of the Subvalvular Apparatus
Proper exposure of the subvalvular apparatus is necessary whenever valvular reconstruction involves one or two papillary muscles. Traction sutures are first placed around the main chordae of the anterior leaflet ( Fig. 7-5 ). The posterior leaflet is gently retracted using the atraumatic retractor. In most instances, the anterior papillary muscle is easily visualized. Exposure of the posterior papillary muscle is more difficult and requires placement of an atraumatic retractor in the P3 region. The head of the posterior papillary muscle is grasped and pulled upwards using Rezzano forceps. This maneuver exposes muscular and fibrous bands that attach the base of the papillary muscle to the ventricular wall. A papillary muscle clamp is then used to further expose the papillary muscle. The clamp is placed laterally to the papillary muscle across the fibrous bands, carefully avoiding its base (inset) .
