Repairing Degenerative Mitral Valve Disease
Keywords : Mitral valve repair, myxomatous mitral valve disease, degenerative mitral valve disease
Degenerative mitral valve disease is a common cause of mitral regurgitation and results in significant morbidity and mortality. Mitral valve repair is preferred over valve replacement given improvements in survival, left ventricular function, and freedom from reoperation. The purpose of this chapter is to provide surgeons with a comprehensive overview of various strategies available to successfully repair degenerative mitral valve disease. A brief overview of pertinent surgical anatomy is followed by a discussion on operative strategy and approach, with emphasis on minimally invasive techniques. Techniques to repair posterior, anterior, and bileaflet prolapse are discussed, along with some special scenarios. The chapter concludes with an overview on evaluating the repair, postoperative care, and pearls and pitfalls.
· Degenerative mitral valve disease, also called mitral valve prolapse or floppy mitral valve syndrome, is caused by myxomatous degeneration of the mitral valve tissue, whereby elastin and collagen bundles are disrupted, and proteoglycan deposition in the spongiosa results in leaflet thickening and redundancy.1 This, in turn, can cause impaired leaflet coaptation, chordal elongation or rupture, and annular dilation, resulting in mitral regurgitation.
· In the United States and other western countries, degenerative mitral valve disease is the most common cause of mitral regurgitation, with between 2% and 3% of adults suffering from at least moderate mitral regurgitation.2–6 Of these, approximately 10% develop significant mitral regurgitation requiring surgical intervention.7–10
· Mitral valve repair is the recommended treatment for degenerative mitral valve disease.11 Mitral valve repair, when compared to replacement, reproducibly improves survival, left ventricular function, and freedom from reoperation.12–21
· Despite the superiority of mitral valve repair over replacement, a large proportion of patients with degenerative mitral valve disease still undergo replacement.22,23 With experience, nearly any myxomatous mitral valve can be repaired, importantly with near 0% mortality rates.13,24–30
· In this chapter, various techniques for repairing degenerative mitral valve disease are presented. The goal is to provide surgeons with an expanded armamentarium for repairing the mitral valve.
Step 1. Surgical Anatomy
◆ The mitral valve, or left atrioventricular valve, is a dynamic and complex anatomic structure with a three-dimensional saddle shape that changes throughout the cardiac cycle. To perform mitral valve repair successfully, a comprehensive understanding of mitral valvular spatial geometry is compulsory. The mitral valve and its functional components make up the mitral valve apparatus, consisting of the atriovalvular junction and underlying annulus, the anterior (aortic) and posterior (mural) leaflets, and the subvalvular apparatus (Fig. 18.1A). The subvalvular apparatus consists of the chordae tendineae, along with their corresponding papillary muscles and underlying left ventricular wall.
Figure 18.1 (A) Short axis view of the mitral valve (MV) from the atrium. (B) Horizontal long axis cross section of the MV and left ventricle. (C) Mitral valve leaflet nomenclature.
· The atriovalvular junction (not to be confused with the atrioventricular junction) is the hinge connecting the atrium to the mitral leaflets; it can be easily identified by looking for the demarcation between the pink atrial myocardium and pale leaflets. Approximately 1 to 2 mm deep and external to the hinge is the mitral annulus, which is an ovoid ring of connective tissue anchoring the mitral leaflets to the fibrous skeleton of the heart. It also forms the atrioventricular junction between the left atrium and left ventricle (see Fig. 18.1B). It is important to note that only the hinge is visible to the surgeon; the deeper annulus cannot be seen. This relationship must be taken into consideration when placing annuloplasty sutures so as not to disrupt the hinge, which may impair leaflet motion.
· The annulus is often thought of as fixed, homogenous, and continuous; however, its consistency varies around the circumference of the mitral orifice, and its shape changes throughout the cardiac cycle. Overall, the annulus has a hyperbolic paraboloid (saddle) shape, with the midanterior and midposterior annular segments highest (farthest) from the apex and the anterolateral and posteromedial commissures (PC) at the lowest points.31
· The mitral valve annulus is connected to the aortic valve annulus at an angle of 120 degrees via the aortomitral curtain. The aortomitral curtain is flanked by the anterolateral (left) fibrous trigone and posteromedial (right) fibrous trigone, which along with the aortomitral curtain make up a particularly dense portion of the annulus where the anterior leaflet of the mitral valve attaches. This constitutes approximately 40% of the circumference of the annulus. The remaining 60% of the annulus suspends the posterior leaflet; this portion of the annulus is discontinuous and thinner, making it more prone to dilation.
· The mitral valve is naturally bicuspid, with a larger, semicircular anterior (aortic) leaflet and a smaller, quadrangular posterior (mural) leaflet (see Fig. 18.1C).
ü The anterior leaflet delineates the left ventricular inflow tract from the outflow tract. The anterior leaflet free edge is convex and without scallops.
ü The posterior leaflet usually contains three distinct scallops—the anterolateral scallop (P1), the middle scallop (P2), and the posteromedial scallop (P3). The opposing portions of the anterior leaflet are termed the anterior segment (A1), the middle segment (A2), and the posterior segment (A3). The areas joining the anterior and posterior leaflets are the anterolateral commissure (AC) and the PC. This nomenclature facilitates descriptive noninvasive and surgical valve analysis.
ü The atrial surface of each leaflet is separated by two visible zones, the more proximal atrial zone, which is smooth and somewhat transparent, and the distal rough zone (also known as the zone of coaptation). The rough zone is the point at which the leaflets meet during systole. Most chordae tendineae insertion sites are located in the rough zone, giving this region a coarse and irregular appearance (hence, its namesake).
· The subvalvular apparatus consists of the chordae tendineae, the anterolateral papillary muscle, the posteromedial papillary muscle, and the free wall of the left ventricle. The subvalvular apparatus helps maintain valve function and integrity throughout the cardiac cycle. During diastole, as blood enters and the left ventricle distends, the papillary muscles and chordae pull the mitral leaflets open, allowing for maximal valve opening and efficient filling. During systole, the papillary muscles contract and shorten, maintaining optimal leaflet height and thereby ensuring a proper zone of coaptation at the level of the annulus to prevent leaflet prolapse.
ü Chordae tendineae connect the papillary muscle heads (or, in some cases, the ventricular wall) to the leaflets; they are divided into three groups—primary, secondary, and tertiary. Primary (marginal) chordae tendineae attach the papillary muscle heads to the leaflet margin; they are the thinnest of the chordae and serve to prevent leaflet prolapse. Secondary (intermediary) chordae attach the papillary muscle heads to the midsection of the ventricular surface of the leaflets; they are thicker than primary chordae and provide support to the leaflet tissue. Tertiary (basal) chordae are the thickest of the chordae types and connect the base of the leaflet or annulus to the papillary muscle head or ventricular wall; they are typically only found on the posterior and commissural leaflets.
◆ Arising between the middle and apical thirds of the left ventricle, two papillary muscles support the mitral valve, the anterolateral papillary muscle, and the posteromedial papillary muscle. Each papillary muscle supplies chordae to both anterior and posterior leaflets. The papillary muscles and their supporting left ventricular myocardium are critically important in maintaining optimal valvular function, as described previously. The anterolateral papillary muscle is typically solitary and receives blood from the left anterior descending artery and often a branch of the circumflex artery. The posteromedial papillary muscle usually has multiple heads and typically has a solitary blood source from either the circumflex artery or right coronary artery. Because of these anatomic differences, the posteromedial papillary muscle is more sensitive to ischemia and can rupture following a posterior myocardial infarction, leading to acute mitral regurgitation.
Step 2. Preoperative Considerations
· Degenerative mitral valve disease represents a spectrum ranging from fibroelastic deficiency, with limited elongated or ruptured chordae, to the Barlow syndrome, with extensive change, including redundant and billowing leaflets. The clinical presentation of patients with fibroelastic deficiency and Barlow syndrome is often unique. Patients with fibroelastic deficiency are often older and tend to have a relatively recent diagnosis of mitral disease without a history of a murmur.32 The leaflets are thin, and typically only one segment is prolapsed secondary to ruptured chords. On the other hand, patients with Barlow syndrome tend to be younger and have a long history of a murmur; these patients may have a family history of mitral valve disease, as well as marfanoid features.32 The leaflets are thickened and billowing, often with several prolapsing segments; calcification can be extensive, and atrialization of leaflets may be noted. Mitral regurgitation is also classified as acute or chronic and further subclassified into chronic and compensated or chronic and decompensated. Consideration of cause and chronicity are important preoperative considerations that affect operative planning and risk stratification.
· Echocardiography is essential prior to any planned mitral valve surgery because it provides important information about valve anatomy, disease lesions, and underlying cause. Three- dimensional echocardiography can also be a helpful adjunct in planning the repair prior to surgery. Additionally, echocardiography helps interrogate the other heart valves, biventricular function, atrial size, and estimates pulmonary artery systolic pressure.
Step 3. Operative Conduct
1. Surgical Approach
◆ The mitral valve is conventionally accessed through a median sternotomy (Fig. 18.2A). The median sternotomy provides excellent exposure to all structures of the heart and is favored for patients in whom multiple valves or concomitant surgeries (e.g., coronary bypass, aortic valve replacement) are planned with mitral valve repair. In this approach, standard central aortic and bicaval cannulation are preferred. Exposure of the mitral valve can be accomplished through several alternative approaches, as discussed in detail in the following.
· A partial upper or lower sternotomy, or hemisternotomy, also permits access to the mitral valve (Fig. 18.2B, C). Whereas the lower hemisternotomy reduces the size of the skin incision and extent of sternal separation, the xiphisternal fascia must still be incised and is the area most prone to wound infection.
Figure 18.2 (A) Median sternotomy. (B) Partial upper sternotomy. (C) Partial lower sternotomy. (D) Right anterolateral minithoracotomy. (E) Intraoperative photograph of minimally invasive approach via right anterolateral minithoracotomy; note the use of smaller skin incisions for the placement of an endoscope, suction ports, cross-clamp, and retraction sutures.
· Our preferred minimally invasive approach is via a right anterolateral minithoracotomy (see Fig. 18.2D, E).33,34 This approach provides an excellent en face view of the mitral valve and spares dissection of the xiphisternal fascia. In patients who have undergone prior cardiac surgery, particularly aortic valve replacement, this minimally invasive approach can be particularly useful in not only avoiding a redo sternotomy, but also in visualizing the mitral valve when a previously placed aortic valve prosthesis prevents excessive manipulation of tissue.
· The patient is placed supine on the operating table, with an inflatable cushion placed under the right shoulder to elevate the right chest and rotate the patient slightly to the left. A 3- to 4-cm skin incision is made just above the nipple in male patients and in the inframammary crease in females. The thoracic cavity is entered through the third or fourth interspace. Additional small incisions facilitate placement of an endoscope, suction ports, working arm ports (for robotic surgery), and aortic cross-clamp. Retraction sutures can also be passed through tiny skin incisions using a suture passer, which creates a low-profile and clutter-free operative field.
· When using a right anterolateral minithoracotomy, we typically cannulate peripherally. The femoral artery and vein are cannulated via a small groin incision; the internal jugular vein is cannulated percutaneously with a 16 F cannula. Venous cannulae are positioned within the superior vena cava and inferior vena cava under echocardiographic guidance.
· We routinely use a transthoracic Chitwood clamp to cross-clamp the ascending aorta. An endoaortic occlusion balloon can also be used, although a significant learning curve exists during which the risk for aortic dissection and stroke are elevated. Finally, fibrillatory arrest strategies may be used in certain situations.35,36
◆ Once the patient has been cannulated, initiation of cardiopulmonary bypass can commence. Myocardial protection is extremely important, and our institution favors cold blood, high- potassium cardioplegia delivered in an intermittent antegrade or combined antegrade-retrograde fashion. Moderate systemic hypothermia and local topical hypothermia with topical slush are also applied.
◆ Alternative myocardial protection strategies exist and may be considered for certain patients. For example, a beating heart approach can be considered for patients with severe left ventricular dysfunction. For patients with severe atherosclerosis of the ascending aorta, ventricular fibrillatory arrest can also be used if cross-clamping the aorta is objectionable.
◆ It is important to consider the sequence of mitral valve surgery in the context of concomitant procedures. If concomitant coronary artery bypass is performed, distal anastomoses should be completed prior to mitral valve surgery; lifting the heart following mitral valve prosthesis implantation increases the risk of posterior ventricular rupture and possible atrioventricular groove disruption. If aortic valve replacement is required, the native aortic valve leaflets should be excised and the annulus débrided prior to mitral valve repair to avoid inadvertently cutting mitral annuloplasty or repair sutures. In addition, mitral valve repair should be completed prior to the replacement of the aortic valve as a prosthetic aortic valve can distort the mitral annulus and may complicate mitral valve repair. Tricuspid valve repair, if needed, should follow left-sided valve procedures and may be completed after aortic cross-clamp removal.
· Optimally exposing the mitral valve is critical to facilitate a successful repair. This can be achieved through several techniques, as described in the following.
· The most common approach to the mitral valve is the interatrial approach through Sondergaard’s groove, also known as rolling the groove (Fig. 18.3A). In this approach, the right and left atrial surfaces are carefully separated by dissecting through the fatty tissue anterior to the right superior and inferior pulmonary veins. It is important to start this incision on the left atrial body to avoid accidental injury to the pulmonary venous ostia. Carrying this incision too medially may result in an inadvertent right atriotomy. If encountered, caval tapes or vacuum-assisted venous return can help manage this issue.
· The right atrial transseptal approach is another common method to expose the mitral valve (see Fig. 18.3B). Bicaval cannulation with caval snaring helps obtain a bloodless field. A right atriotomy is made and extended posteriorly toward the left atrium. Atrial retractors or silk stay sutures can facilitate exposure of the septum. The fossa ovalis is identified, and an incision is made posteriorly to the patient’s right, being careful to leave enough septal tissue to close the incision at the conclusion of the case. This incision is carried inferiorly to the end of the fossa ovalis and superiorly to the muscular tissue, near the superior vena cava inlet. The interatrial septum is then retracted anteriorly to provide optimal visualization of the mitral valve. This approach is useful in patients who have previously undergone aortic valve replace- ment because exposure of the AC can otherwise be challenging. It also minimizes external suture lines and speeds de-airing when concomitant tricuspid valve interventions are planned.
· Several less conventional approaches to exposing the mitral valve exist, although these are used uncommonly and typically only in specific clinical scenarios. The left atrial dome approach, wherein the roof of the left atrium between the aorta and superior vena cava is incised, provides an excellent direct view of the mitral valve; however, the incision itself is quite small and leaves limited working room (see Fig. 18.3C). Additionally, extreme care must be taken in closing this incision because controlling bleeding in this area is quite challenging after the patient has been weaned from cardiopulmonary bypass. This approach can be combined with the transseptal approach in an expanded transseptal/left atrial dome approach to maximize mitral valve exposure if necessary. In the case of a left ventricular aneurysm repair, the mitral valve can be approached in a transventricular manner; an off-pump coronary stabilizer is helpful in adequately exposing the mitral valve in this situation (see Fig. 18.3D).37,38 A transaortic approach can also be used in cases of aortomitral endocarditis (see Fig. 18.3D).38,39
· Once the mitral valve has been exposed, the next step to a successful repair is careful analysis of the valve to determine the specific mechanism of mitral regurgitation.
Figure 18.3 (A) Exposure through Sondergaard’s groove. (B) Transseptal approach for mitral valve exposure. (C) Exposure of the mitral valve through the dome of the left atrium. (D) Transaortic approach in the case of infective endocarditis.
· Nearly all patients with chronic mitral regurgitation develop some degree of annular dilation and, as such, nearly all patients undergoing repair for chronic mitral regurgitation derive benefit from ring annuloplasty. It is our practice to perform a ring annuloplasty in all patients undergoing mitral valve repair.
· Ring annuloplasty also improves the durability of mitral valve repair because it prevents further annular dilation and late mitral regurgitation.
· The posterior annulus is typically the annular segment that dilates in chronic mitral regurgitation, and thus some surgeons prefer incomplete annuloplasty rings or posterior annuloplasty bands. Although this approach can effectively prevent late annular dilation, care must be taken to anchor the band to the fibrous trigones adequately. We prefer complete annuloplasty rings that are contoured to the physiologic saddle shape of the native, healthy mitral valve annulus, which more reliably prevents adverse annular remodeling following repair.
· Our general approach is first to place annuloplasty sutures because this helps retract the mitral valve and improves visualization. Following annuloplasty suture placement, obvious valvular defects are repaired, followed by annuloplasty ring placement. If regurgitation remains, additional repair techniques can be carried out.
· Annuloplasty sutures are placed circumferentially around the annulus. The needle should enter and exit the tissue just outside the atriovalvular junction, passing through the annulus. The curve of the needle should be followed, which will generate appropriately sized bites of approximately 10 mm (Fig. 18.4A). The space between separate sutures should be approximately 2 mm. Care must be taken not to injure surrounding tissue inadvertently. When placing annuloplasty sutures in the anterior annulus, one must be careful to avoid catching the noncoronary cusp of the aortic valve. The circumflex coronary artery can be injured if sutures are placed too deeply near the AC and toward the posterior annulus (see Fig. 18.4B).
· Properly sizing the mitral annulus is important to prevent adverse consequences. Overly restrictive annuloplasty rings can result in systolic anterior motion (SAM) of the mitral valve or iatrogenic functional mitral stenosis.
· Ring sizing is based on intercommissural distance and the surface area of the anterior mitral leaflet (see Fig. 18.4C). With this in mind, if the free edge of the anterior leaflet extends 2 to 4 mm beyond the inferior aspect of the annuloplasty ring sizer, the surgeon should choose a ring that is one size larger to prevent the risk of SAM of the mitral valve.40
· When passing sutures through the annuloplasty ring, equal suture distances should be taken along the anterior aspect of the ring because the anterior annulus seldom dilates. However, less travel on the posterior aspect of the annuloplasty ring should be taken to correct posterior annular dilation (see Fig. 18.4D). Take note of the markings on the annuloplasty ring; the commissures are typically marked to assist you in spacing sutures properly. Count the number of sutures that must be placed through the anterior and posterior portions of the ring and space them accordingly. When placing sutures through the annuloplasty ring, only pass the needle through the designated sewing band and not through the metal skeleton.
· Posterior leaflet prolapse and/or flail are the most common lesions in patients with degenerative mitral regurgitation. Traditionally, resection of the prolapsed leaflet was performed; however, nonresectional techniques are increasingly being used.
· Triangular resection is a common technique that can be effectively used when the amount of tissue to be resected is not extensive (Fig. 18.5). This technique is also useful in the setting of isolated segment flail. First, stay sutures are placed around normal chordae flanking the prolapsed segment of the leaflet; this helps delineate the area of prolapse and adequately expose the leaflet. Next, the area of prolapse is excised with two diagonal incisions toward the annulus, which form a triangular area of resection. Using polypropylene sutures, the leaflet free edges on each side of the resection are reapproximated.
· If the area of redundant leaflet tissue to be resected is more extensive, a quadrangular resection may be needed (Fig. 18.6A). As in triangular resection, stay sutures are placed around normal chordae to flank the area of resection. Next, two perpendicular incisions are made from the leaflet free margin toward the annulus, removing a quadrangular segment of leaflet. Using 2-0 sutures, an annular plication stitch is placed spanning the gap between the resected leaflet. Tension is placed on this suture and an additional simple interrupted or figure-of-eight annular suture is placed, bringing the leaflet free edges close enough for reapproximation with running polypropylene sutures. These annular stitches do not require reinforcement because the prosthetic annuloplasty ring will serve this purpose.
Figure 18.5 Triangular resection.
· In situations in which a large part of posterior leaflet must be resected, or when the posterior leaflet height must be reduced, a sliding leaflet plasty can be performed after quadrangular resection (Fig. 18.6B). The P1 and P3 segments are detached from the annulus with two additional incisions. Using running polypropylene sutures, P1 and P3 are reapproximated to the annulus, with more travel along the annulus than the leaflet tissue to allow for medial translocation. If the gap between leaflets is large, or if they cannot be approximated without tension, annular plication may be required, being cautious not to kink the circumflex coronary artery with overly aggressive bites.
|Figure 18.6 (A) Quadrangular resection with annular plication. (B) Quadrangular resection with sliding leaflet plasty|
· An alternative to the sliding leaflet plasty in cases of large and redundant leaflets is leaflet height reduction (see Fig. 18.7).40 First, the leaflet is partially detached from the annulus. Next, a curvilinear crescent-shaped portion of the leaflet corresponding to the detached edge is excised. The leaflet is reattached to the annulus with running monofilament sutures. Following leaflet height adjustment, the line of coaptation may need to be adjusted using artificial neochords, which are described in further detail in the following sections. Leaflet height reduction can also be used on the anterior leaflet and is especially helpful in the prevention or treatment of SAM of the mitral valve.
· Posterior leaflet height can also be reduced using the butterfly technique, which also avoids annular plication and may reduce the risk of SAM (Fig. 18.8).41 The prolapsed segment of posterior leaflet is first excised with a triangular resection, followed by a second triangular resection mirroring the first. The free edges of resected tissue are then reapproximated with polypropylene sutures. In addition to avoiding annular plication, this technique often allows for the implantation of a larger annuloplasty ring.
Figure 18.7 Posterior leaflet height reduction.
Figure 18.8 Butterfly technique.
· The so-called haircut technique is another nonresectional method of correcting posterior leaflet redundancy and/or prolapse without compromising annular continuity (Fig. 18.9).42 In this technique, a prolapsed P2 segment with multiple ruptured chords is trimmed, or given a haircut, at approximately the same height as the adjacent P1 and P2 segments. If possible, viable chords are salvaged for reimplantation later in the procedure. Next, the P1-P2 and P2-P3 clefts are closed. The preserved chords are reattached to the free edge of the P2 segment; if no chordae are salvageable, transfer of secondary chords can be performed, or neochords can be placed. A smooth posterior coaptation surface is restored along with valve competency as a result of the haircut. This method is particularly useful in the setting of annular calcification or diminutive P1 and P3 scallops.
Figure 18.9 Haircut technique.
· The simplified nonresectional leaflet remodeling technique, a modification of the McGoon plication repair, can also be used to create a smooth, nonprolapsed coaptation surface (Fig. 18.10).43,44 The free edge of the prolapsed leaflet segment is inverted into the left ventricle, imbricating redundant leaflet tissue in a triangular shape. The leaflet folds on each side of the imbricated segment are approximated, creating a smooth posterior coaptation surface. Importantly, the inverted segment forms a triangular shape (analogous to a triangular resection), with a narrower amount of inverted tissue closer to the annulus to preserve annular continuity.
Figure 18.10 Nonresectional leaflet remodeling technique.
· One of the limitations of the simplified nonresectional leaflet remodeling technique is the theoretical possibility that the posterior leaflet, which remains mobile and somewhat redundant, can move anteriorly, resulting in SAM of the mitral valve. To account for this possibility, the posterior ventricular anchoring neochordoplasty technique was developed (Fig. 18.11).45 This technique is a modification of the earlier described simplified nonresectional leaflet remodeling technique, in which the free edge of the prolapsed leaflet segment is inverted into the left ventricle. However, it is attached and anchored to the ventricular wall using a single polytet- rafluoroethylene (PTFE) suture. This anchoring suture is placed 3 to 4 mm deep and tied loosely, being careful not to place undue tension on the ventricular wall, causing necrosis and possible late neochord failure. The same anchoring suture is used to reapproximate the leaflet folds on each side of imbricated leaflet segment. This technique effectively remodels the posterior leaflet while simultaneously anchoring the posterior leaflet, reducing the risk of SAM.
· The use of artificial neochords can also be helpful in the repair of posterior leaflet prolapse. Techniques for neochord placement are discussed in detail in the following section on anterior leaflet prolapse; these principles are entirely applicable to posterior leaflet prolapse as well.
◆ In degenerative mitral valve disease, pathology of the anterior mitral leaflet is far less common than that of the posterior leaflet, accounting for fewer than 15% of cases. Even in cases of bileaflet prolapse, often only posterior leaflet intervention is required for a satisfactory repair.46 Despite this, there are circumstances that require repair of the anterior mitral leaflet, and the following sections describe techniques commonly used in this setting. We prefer to preserve as much leaflet tissue as possible by using chordal techniques on the anterior leaflet. Of note, most of the following techniques can also be used on the posterior leaflet and can be especially helpful in cases with insufficient leaflet tissue.
Figure 18.11 Posterior ventricular anchoring neochordoplasty (PVAN) technique.
· In the rare case of a billowing and redundant anterior leaflet, a very limited triangular resection can be considered, as described earlier.47 We prefer to limit resections of the anterior leaflet to no greater than 10% of the total leaflet surface area. More extensive resections reduce the area of coaptation and decrease the durability of valve repair.
· If anterior leaflet prolapse is present, and an area of adjacent, normal posterior leaflet tissue with intact chordae of appropriate length is available, a chordal transposition can be performed (Fig. 18.12). A 2- to 3-mm-wide strip of adjacent normal posterior leaflet with the attached chordae is resected free from the posterior leaflet, careful to keep the attached chordae intact. With polypropylene sutures, the segment of posterior leaflet is secured to the anterior leaflet, thereby transferring functional chordae to the anterior leaflet. The posterior leaflet defect is repaired with polypropylene sutures. There is no need for neochord measurements and adjustments, which is the primary advantage of chordal transposition. However, this technique requires that a normal segment of posterior leaflet be sacrificed.
· When a diseased valve lacks enough normal chordae to function properly, and chordal transposition is not possible, artificial neochordae placement can be helpful. However, this technique can be challenging for several reasons. Determining optimal neochordae length can be difficult and requires careful measurement. Once an optimal length has been determined, keeping the PTFE sutures at this length is also not always easy because this material is prone to slippage. Finally, adequate exposure of the papillary muscle heads and underside of the mitral valve leaflets is not always possible. Despite these challenges, there are several strategies that can be used to use artificial neochordae successfully in mitral valve repair. Multiple neochords may be required and, in practice, we prefer to place chordae in pairs to balance out the forces on the prolapsed segment and improve durability.
· The first strategy to create an effective artificial neochord is termed the loop technique (Fig. 18.13). First, the correct plane of apposition should be determined, usually from an adjacent, nonprolapsing valve segment. Using a pair of calipers or other measuring device, the distance between this plane and the papillary muscle head is determined. Next, keeping the calipers at the same setting, a PTFE loop is created over the measuring instrument, tying a knot over a pledget to secure the suture at this distance. Next, each needle is passed through the pledget an additional two times to lock the loop distance and prevent sliding. After this has been completed, the needles are passed from anterior to posterior through the corresponding papillary muscle and tied over another pledget. The loop is now secured to the papillary muscle; to secure the loop to the leaflet, a second PTFE suture attaches the loop to the prolapsed leaflet, with the knot oriented toward the ventricular cavity.
· The second method of placing artificial neochordae is known as the freehand technique. In this method, a PTFE suture is passed through the papillary muscle and then through the edge of the prolapsed leaflet segment. This suture is clamped and set aside while an annuloplasty ring is implanted. Following annuloplasty, the ventricle is pressurized using a saline-filled bulb syringe. Then, the PTFE suture is tied and secured at the level at which optimal coaptation occurs, resulting in elimination or minimization of visible regurgitation through the valve. This technique is faster and very simple, but requires the surgeon to be able to judge the appropriate neochord length accurately and ostensibly tie a large air knot securely, without slipping. Adjacent papillary muscles with chordae of normal length can sometimes be used as a reference point.
Figure 18.12 Chordal transposition.
Figure 18.13 Neochord placement.
· The double orifice edge-to-edge repair, also known as the Alfieri stitch, is a technique that can be used to repair anterior, posterior, or bileaflet prolapse (Fig. 18.14).48 In this technique, using a figure-of-eight polypropylene stitch, the prolapsing segment of leaflet is tied to its opposite leaflet segment. This creates a double-orifice mitral valve. The position of this stitch varies, depending on the amount of redundant leaflet tissue; a valve with an excess of tissue will require a deeper stitch to prevent SAM. If leaflet tissue is thin and frail, reinforcing the stitch with autologous pericardium or pledgets may be required. To prevent iatrogenic mitral stenosis, at least 2.5 cm2 of total valve area is required, which can be measured with Hegar dilators
Figure 18.14 Alfieri stitch—double orifice edge-to-edge repair.
· Commissural prolapse can be repaired with or without resection. The simplest method to correct commissural prolapse is to obliterate the commissure with a running polypropylene suture, inverting the prolapsed segment of leaflet (Fig. 18.15A). Alternatively, triangular resection can be performed if the amount of prolapse is limited, involving 5 mm or less of the commissural edge (see Fig. 18.15B).40 If a more substantial area of prolapse exists, a quadrangular resection with sliding plasty of the adjacent paracommissural segments is performed (see Fig. 18.15C). It is helpful to restore the neocommissure’s area of coaptation with inverting sutures.
· If papillary muscle rupture is the cause of commissural prolapse, the papillary muscle should be reattached to the ventricular wall to restore appropriate commissural height. To reattach a ruptured papillary muscle, necrotic tissue must first be excised, typically leaving only the fibrous head of the papillary muscle attached to the chordae. The remaining papillary muscle head is then grasped and retracted caudally until it meets the ventricular wall at a point where leaflet height is restored; this point is marked. Next, an 8- to 10-mm incision is made in the ventricular wall at a depth of no more than 5 mm, avoiding coronary vasculature. Using 4-0 monofilament sutures, buried horizontal mattress sutures are used to anchor the residual papillary muscle head into the ventricular wall.
· In the case of papillary muscle elongation, a papillary muscle sliding plasty or papillary muscle-shortening procedure can be performed. In cases in which only some of the chordae attached to a papillary muscle are elongated, the papillary muscle can be incised longitudinally. The segment of papillary muscle attached to the elongated chords is then slid downward and secured at a lower level to the normal portion of papillary muscle, using one or two interrupted monofilament sutures. The suture should not pass through the chordae. The distance that the papillary muscle segment is slid downward should equal the distance of leaflet prolapse. A papillary muscle-shortening procedure is another option, whereby a wedge of papillary muscle is resected from the papillary muscle segment with chordal elongation. The wedge defect is closed with interrupted monofilament sutures. If an entire papillary muscle has chordal elongation, the abnormal papillary muscle can be anchored to an adjacent papillary muscle of normal height.
◆ Calcification of the mitral annulus often makes valve repair more challenging and can lead to paravalvular leak, dehiscence, and atrioventricular groove disruption. For effective repair, the calcified tissue should be débrided. In most cases, the calcified tissue is encased in a capsule of fibrotic tissue, which allows for en bloc resection. Following débridement, annular reconstruction is typically required, although it may be possible, using pituitary rongeurs, to débride enough of the calcified tissue carefully and selectively to provide adequate leaflet mobility and coaptation, without the need for annular reconstruction.49 For annular reconstruction, various techniques have been described.
◆ Tirone David and colleagues have described a technique using bovine pericardium to reconstruct the annulus.50–52 In cases of posterior annular reconstruction, a 2-cm wide semicircular patch is created. Using 3-0 polypropylene sutures in a continuous running fashion, the left ventricular endocardium is sutured to one side of the patch, and the other side is secured to the left atrial wall. Next, the detached portion of the leaflet is sutured to the patch at the level of the annulus. A circumferential pericardial patch can be used for complete annular reconstruction, with an annuloplasty ring being used to attach the leaflets to the patch, providing rigidity.
Figure 18.15 Correcting commissural prolapse. (A) Commissure obliteration by inversion of prolapsed segment. (B) Triangular resection of prolapsed segment. (C) Quadrangular resection for larger prolapsed segment.
◆ Carpentier et al. have advocated for the use of figure-of-eight atrioventricular mattress sutures for annular reconstruction to minimize the amount of foreign material used (Fig. 18.16).53 In addition, the use of figure-of-eight mattress sutures serve to decrease annular size and displace the circumflex vessels away from the annular reconstruction. First, a braided 2-0 suture is passed through the atrial edge, followed by the ventricular edge, being mindful of the circumflex coronary artery. Depth of the ventricular bites should be approximately one-third of the ventricular thickness. Next, with approximately 1 cm of travel, the suture is again passed through the ventricular edge and then returned up through the atrial edge, with the free ends of suture being on the atrial side. When tightening the suture and closing the atrioventricular junction, the assistant uses forceps to pull the atrial edge downward. The same sutures are used for annuloplasty ring placement later in the operation. Next, 4-0 polyester sutures in a continuous running fashion are used to reinforce the neoatrioventricular junction and prevent paravalvular blood flow from separating the neoatrioventricular junction. The leaflets are reattached to the neoannulus with running 4-0 polypropylene sutures. Finally, the free ends of the figure-of-eight mattress sutures are used to attach an annuloplasty ring, completing the repair. Carpentier and associates53 have stressed the importance of being extremely delicate when lowering the annuloplasty ring, applying only the desired amount of tension on the suture. When tying the suture, the sutures should not be pulled upward; rather, the finger should push the annuloplasty ring downward.
· The repair should be evaluated at multiple time points during the operation so that the surgeon may modify the repair strategy. At a minimum, the repair should be tested after leaflet repair or neochord placement but prior to annuloplasty ring placement. Once the annuloplasty ring has been placed, but prior to tying the sutures, the repair should be evaluated again. Once the repair procedure has been completed, the valve is evaluated one final time prior to weaning from cardiopulmonary bypass.
· The saline test is an excellent method to assess the quality of a repair (Fig. 18.17A). First, with the aortic root vent unclamped, the left ventricle is filled with saline to evacuate air and prevent coronary artery air embolism. After successful evacuation of air, the aortic root vent is clamped, and a bulb syringe is used again to inject pressurized saline into the left ventricle through the mitral valve. The mitral valve should prevent the pressurized saline from leaking retrograde. The surgeon should also see a symmetric line of coaptation parallel to the posterior aspect of the annuloplasty ring. The coaptation line ideally should be a safe distance away from the left ventricular outflow tract to prevent SAM of the mitral valve.
· To evaluate the repair further, the ink test can be used (see Fig. 18.17B). With the left ventricle pressurized during the saline test (as previously mentioned), a marking pen is used to trace the coaptation line. The line of coaptation should ideally be 4 to 10 mm deep. If the depth is less than 4 mm, further correction should be performed, which may include resection of restrictive chordae, downsizing the annuloplasty ring, or cleft closure techniques. If the depth is greater than 10 mm, the patient may be at increased risk of developing SAM of the mitral valve, and the surgeon should consider reducing posterior leaflet height.
· Transesophageal echocardiography should be used as a final test of the quality of valvular repair after the patient has been separated from cardiopulmonary bypass, but prior to decannulation.
Step 4. Postoperative Care
· Left atrial enlargement is extremely common due to the pathophysiology of mitral regurgitation; as such, atrial fibrillation is common before and after surgery in patients with mitral regurgitation. Atrial fibrillation prophylaxis is important.
· Careful attention should be paid to the possibility of the patient developing SAM of the mitral valve, which is a complication of mitral valve repair occurring in up to 10% of patients.54 SAM is most often caused when a redundant posterior leaflet shifts the plane of leaflet coaptation anteriorly, which then displaces the anterior leaflet into the left ventricular outflow tract, resulting in obstruction and late systolic mitral regurgitation.
· In addition to redundant posterior leaflet tissue, SAM can also be caused by failing to reduce the posterior leaflet height adequately or undersizing the annuloplasty ring and is occasionally due to anterior leaflet pathology.
· Most cases of postrepair SAM, when mild or moderate, can be managed conservatively. They generally resolve in the weeks to months following repair when ventriculoaortic gradients normalize, and left ventricular outflow tract remodeling occurs.54
· When managing patients with SAM conservatively, maintaining adequate filling of the left ventricle is critically important to prevent left ventricular outflow tract collapse. Ventricular underfilling is prevented by maintaining preload through volume resuscitation, increasing afterload with alpha agonists, and preserving diastolic filling with heart rate reduction, either via beta blockade or by decreasing the temporary pacemaker rate. Inotropes should be minimized, if possible, to prevent hyperdynamic contraction of the left ventricle.
· If the previous maneuvers are unsuccessful in treating postrepair SAM, the patient must undergo re-repair to correct the underlying lesion; valve replacement is very rarely indicated.
Figure 18.17 (A) Saline test. (B) Ink test.
· Careful evaluation of the valve to determine the precise lesion causing regurgitation is the most important step of the operation because it guides all other decisions with regard to repairing the valve.
· Excellent exposure is necessary for successful repair of complex valvular lesions. Multiple maneuvers can be used to improve exposure. For example, after performing the pericardiotomy, remove the retractor and suture the pericardium to the right side of the skin incision before replacing the retractor; this rotates the heart and optimizes exposure of the mitral valve. Leftward traction on the caval snares can also assist in rotating the heart and optimizing exposure.
· When placing annuloplasty sutures, we start with the 6 o’clock suture. This can then be used for traction when placing subsequent annuloplasty stitches.
· Proper sizing of the annuloplasty ring is critical. Overly restrictive annuloplasty rings can result in SAM of the mitral valve or iatrogenic functional mitral stenosis.
· To de-air more expeditiously, turn off the left ventricular vent early during closure of the left side of the heart while having the perfusionist add blood to the patient’s circulation.