1 Introduction

Although valve repair for aortic regurgitation (AR) has gained attention and the application of individual procedures is becoming standardized according to the pathophysiology of regurgitation, repair techniques for the bicuspid aortic valve (BAV) have not yet been standardized. The main reason for this is the diversity of BAV phenotypes. Even considering just the cusps, the level of diversity in the BAV is great as one must consider the presence/absence of a raphe, the types of fused cusps, and the orientation of the commissures. In addition, BAV/AR is frequently associated with dilatation of the aortoventricular junction (AVJ), Valsalva sinus, sinotubular junction (STJ), and the ascending aorta. Thus, there are rather few cases that can be managed well simply by treating the cusps alone. In this article, taking these factors into account, the BAV phenotype, its clinical significance, various repair techniques, and problems specific to BAV are discussed.

2 Historical Evolution

The history of BAV/AR repair is long, and free margin plication near the commissure was already reported in the 1960s. The origin of the current concept can be found from the AATS (American Association for Thoracic Surgery) lecture the “French correction” presented by Carpentier in 1983 [1]. The procedure applied was correction of the free margin length by triangular resection of the prolapsing cusp and plication of the aortic annulus (In this chapter, this term is assumed to denote the crown-shaped three-dimensional valve insertion line) by circular horizontal mattress suture. Concerning BAV, Cosgrove et al. [2] reported early outcomes in 21 of 28 cases (75%) of aortic valve repair in 1991. Technically, the procedure was a combination of raphe resection and triangular resection-suture of the fused cusp with Cabrol’s subcommissural annuloplasty [3]. These procedures are performed to repair a BAV as a bicuspid valve, and their basis remains the same although some modification has been added. However, the importance of intervention to AVJ dilatation has been reported from recent studies on long-term results [4,5,6], and several new strategies have been introduced [7, 8], including aggressive adaptation of valve-sparing aortic root replacement (VSARR) [9]. Quite recently, Schäfers’ group has reported that adding external suture annuloplasty to BAV repair improves freedom from reoperation at 5 years up to 93% compared with that of 73% in their early series [10].

In contrast, various techniques of tricuspidization have also been reported by several surgeons. Unlike the method to repair a BAV as a bicuspid valve, tricuspidization does not sacrifice the orifice area even if cusp plication is added to secure an effective height (eH). For this reason, there is room for consideration when the free margin length of the fused cusp is considerably longer than the non-fused cusp. Because another chapter discusses the procedure of tricuspidization, this article describes the techniques used to repair the BAV as a bicuspid valve.

3 Basis for Selecting the Operative Method

El Khoury’s classification [11] in accordance with Carpentier’s classification in mitral valves is effective for understanding the pathophysiology and selection of the operative method (see page 24 (Chap. 3)). For BAV, it is also necessary to understand the various phenotypes to logically select a surgical method. The phenotype is related not only with hemodynamics but also with genetics [12].

3.1 Cusp Morphology

The most convenient classification for the surgeon is that of Sievers and Schmidtke [13] (Fig. 10.1), which includes unicuspid valves. In this classification, the presence or absence and the number of raphes are indicated by type (0 means no raphe, 2 means a unicuspid valve), the fused cusp by a combination of L/R/N (left/right/non-coronary cusp), and the hemodynamic condition by S/I/B (stenosis/insufficiency/both). The most common is type 1 L/R, which includes two thirds of all cases, whereas the incidence of Type 0, which indicates a pure bicuspid valve configuration, is as low as 7%. This tendency is the same when dealing only with regurgitant valves.

Fig. 10.1
figure 1

The Sievers classification

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Sabet et al. [14] refer to the spatial orientation of the commissures. The arrangement of 180/180° is found in 5% of commissures, and 1/3 of them have no raphe. However, only 2% have an arrangement of 120/240°. The most common is the so-called 150/210° configuration, which accounts for 92%. In a study simulating the stress on the cusps according to the cusp configuration [15], stress on the 180/180° Sievers type 0 valve was shown to be lower than that on the 150/210° type 1 L/R valve. The average age at the time of BAV/AR surgery is younger than that for BAV/AS [14, 16], and the frequency of calcification is also reported to be lower in BAV/AR [14]. As the degree of cusp calcification depends upon the stress and time elapsed, such knowledge about stress is important not only for estimating the natural history of the BAV but also for considering the prognosis of the repaired valve. Aicher et al. reported that the long-term durability of the repaired BAV is favorable when the smaller angle of the commissures is more than 160° [4].

3.2 Aortopathy

Otto and colleagues [17] examined the relation between aortic shape and aortic valve morphology, which was based on the conventional classification of BAV: the anterior-posterior (type 1) cusp orientation, in which the right and the left cusps were fused, and the right-left cusp orientation. They classified the latter further into type 2, in which the right and the non-coronary cusps were fused, and the rarer type 3, in which the left and the non-coronary cusps were fused. The shape of the aorta was classified into N (normal), in which the STJ exists and the sinus is larger than the ascending aorta, A (ascending dilatation), in which the ascending aorta is larger than the sinus, and E (sinus effacement), in which the STJ is not present. Type 1 represents 80% of BAV, and 60% of them have an N-shaped aorta, whereas in type 2, the A shape comprises more than half. For both types 1 and 2, the E-shape aorta is rare (Table 10.1). In contrast, Fazel et al. [18] classified the pattern of aortic dilatation into four clusters: aortic root alone (cluster I, 13%), tubular ascending aorta alone (cluster II, 14%), tubular portion and transverse arch (cluster III, 28%) and aortic root and tubular portion with tapering across the transverse arch (cluster IV, 45%). The important thing here is that dilatation of the aortic root was present in up to 60% of cases, and a bovine arch was found in one third of them. This means that the N shape of Otto and colleagues does not indicate an aorta without root dilatation but only shows that the aortic root is larger than the ascending aorta.

Table 10.1 Phenotype of aortopathy (Otto)
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Changes in the aortic annulus accompanying the aortopathy also differ greatly between aortic stenosis (AS) and AR among BAV. Sabet et al. [14] reported that annular dilatation (possibly indicating AVJ dilatation) in AR was recognized in approximately half of the cases, which was higher than that in AS (11%). Sadee et al. [16] reported that root dilatation was recognized in about 1/3 of their cases, and its presence increased the risk of the occurrence of AR by a factor of 4. Thus, aortopathy is closely involved in the occurrence of BAV/AR.

4 Decision Making in BAV Repair

4.1 Root Replacement or Not

Ascending aortic dilatation in BAV aortopathy is thought to be associated with hemodynamic factors and tissue vulnerability including a gene-related problem. For this reason, the threshold diameter for therapeutic intervention has been set smaller than that for a tricuspid aortic valve, and in the ESC (European Society of Cardiology) guideline [19], it is 45 mm at the time of aortic valve surgery. However, a recent study has reported that the diameter of the ascending aorta at the onset of aortic dissection was 10 mm larger in the BAV [20], and the validity of early surgical intervention was reconsidered. Also for the aortic root, analysis of long-term prognosis after aortic valve replacement and separate repair of the ascending aorta without root replacement has shown the stability of the remaining native aortic root [21]. However, the phenotype of BAV was not considered in these reports. More recently, Sievers et al. [22] reported that in stenotic BAVs, aortic dilatation was more localized to the ascending aorta, whereas BAVs with AR were associated with a more extensive aortopathy involving the root.

From the viewpoint of the long-term durability of valve repair, the importance of intervention to AVJ dilatation has been pointed out [4,5,6], and VSARR tends to be aggressively implemented even for lesions that do not meet the diameter-based criteria [9]. In VSARR, unlike various attempts to reduce and stabilize the AVJ without root replacement, the spatial orientation of the commissures can be freely modified, which may be another benefit of VSARR. However, surgical stress on the patients is greater than that of ascending aorta replacement, and the validity of the “unnecessary” intervention to the small root has been argued.

4.2 Patient Selection

In the long-term follow-up of a BAV that is repaired as a bicuspid valve, an increase in the pressure gradient can be a problem [8], in addition to the recurrence of AR (see the next section of this article). In this respect, the presence of a pre-operative pressure gradient and a high degree of thickening/calcification of the cusps is not preferable. The latter also acts disadvantageously in cusp coaptation and reduces the geometric height (gH) from the fusion of transverse fine wrinkles of the cusp tissue. To solve the problem of cusp sclerosis and low gH, pericardium may be used to extend [23] or augment the cusps in addition to resection of the thickened part. However, the use of pericardium is a negative prognostic factor for the long-term durability of the repair [4]. Thus, it would be ideal to select lesions that do not have advanced sclerosis that restricts valve opening.

5 Problems Intrinsic to BAV Repair as a Bicuspid Valve

In repairing the BAV as a bicuspid valve, securing both an adequate valve orifice area and durability of the repair are incompatible. This is a unique problem not found in tricuspidization.

5.1 Effective Height

Aicher and colleagues showed the importance of eH in the long-term results of aortic valve repair and reported that a higher eH is necessary in the BAV than in the tricuspid aortic valve, and the reoperation-free rate was high when the eH was 9 mm or more [4]. To gain eH, central plication may also be needed for the non-fused cusp. In the case of the BAV, however, as the relative length of the cusp free margin to the STJ diameter becomes shorter, the opening of the cusp becomes increasingly restricted. In other words, securing both eH and an adequate valve orifice area is incompatible, and thus, it is important to determine the point of compromise. An appropriate value of eH depends on gH, and it should not be decided alone. Establishment of criteria that can be adapted even for Japanese, who are much smaller compared with Western people, will be appreciated. I personally set the target value of eH to be 45% of gH.

5.2 Spatial Orientation of the Commissures

Aicher and colleagues recommend placing commissures at 180/180° [4], the purpose of which is to improve the opening of the fused cusp. It may also be possible to alleviate secondary calcification of the cusp due to the reduction of stress. However, as the opening of the non-fused cusp is directed towards the restriction when converting 150/210° valves into 180/180° (simple mathematics), a question about the net effect on the valve orifice area is raised. Vallabhajosyula and colleagues [24] reported that the pressure gradient of a BAV repaired at 150/210° is lower than that at 180/180°. In the simulation by Jermihov et al. as well [15], the valve orifice area of a perfectly symmetrical 180/180° valve was smaller than that of a 150/210° valve. In addition, even if raphe excision and triangular resection were added to a Sievers type 1 valve, there are two nadirs in the fused cusp and a perfectly symmetrical valve is not formed. Stress on this type of valve has not been studied. To create a perfectly symmetric BAV, the method of Gleason [25] can be performed, in which the fused cusp is detached from the annulus, the raphe is resected, a symmetric cusp is reconstructed with pericardium, and the cusp is sutured deeper into the left ventricular outflow tract (Fig. 10.2). When the pericardial patch is used at the hinge part, however, due to the difference in mechanical properties between the pericardium and the cusp tissue, only the native cusp part may move, and the opening of the pericardial part may be restricted, which may further compromise the durability of the pericardial patch itself. Thus, the orientation of the commissures is also an unsolved problem inherent in the procedure of repairing the BAV as a bicuspid valve.

Fig. 10.2
figure 2

The Gleason method

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6 Operative Technique

6.1 Repair of the Fused Cusp

Because the fused cusp is usually redundant and prolapsed, the raphe that restricts the cusp motion is resected and a central plication is added to the free edge. I use 6-0 monofilament sutures and make the free margin length equal to that of the non-fused cusp. Each suture is placed to shorten the free margin by 2 mm. When large plication is required, triangular resection or plication [26] of the cusp body is required to correct the slackness of the cusp belly and achieve good coaptation. I add it when more than two stitches are required for central plication. When marked thickening and sclerosis of the fused part are present, triangular resection is better. It is desirable that the point of central plication faces the Arantius body of the non-fused cusp. Paracentral plication may also be used if central plication is impossible due to thickening of this part and resection of the thickened part will not leave enough free-margin length.

If the gH is not high enough, extension by pericardium [23] can also be added. Shaving the thickened cusp on the aortic surface may also gain approximately 2 mm of gH (I call this procedure “unrolling”). In the case of prolapse due to fenestration rupture, a pericardial patch is generally a preferred method of repair [27]. Free edge suspension by a continuous ePTFE (expanded polytetrafluoroethylene) suture [28] is currently used mainly to reinforce the fenestration, and its application to correct prolapse has become less frequent.

6.2 Treatment for the Non-fused Cusp

If the eH is low, central plication is added to achieve the target value. It is important to avoid symmetrical prolapse, especially when VSARR is performed.

6.3 Procedures for the Aortic Annulus and Root

Cabrol’s subcommissural annuloplasty proved to be insufficient to ensure good long-term outcomes [4,5,6]. Circular plication of the AVJ using suture, a Dacron strip, or a specially designed ring and aggressive application of VSARR [9] are thus increasingly used. The former can be classified into internal and external methods, but the details are given in another chapter. Svensson et al. [8] reported a method of root plication that detaches the commissures and fixes them at a higher level for patients with mild root dilatation (Fig. 10.3). Although the Cabrol method is not suitable for AVJ correction, it is useful to correct the commissural gap in conjunction with a figure-of-eight suture [8].

Fig. 10.3
figure 3

The Svensson method

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7 My Tips

The sequence of individual procedures is important in the repair of the BAV, and if there is enlargement of the aortic annulus, I will handle this first because the target value of eH is influenced by the AVJ diameter (and also by the changes in the shape of the sinus of Valsalva and the STJ diameter in the case of VSARR). When VSARR is not performed, I currently use an external Dacron strip for AVJ reduction. In doing so, I transect the aorta at the level of the STJ for dissection of the root down to the level of the AVJ. The target AVJ diameter is determined according to the gH, but at least 20 mm is secured. In actual practice, a 26-mm Dacron vascular prosthesis is most frequently used. Central plication of the non-fused cusp, if necessary, is then performed until the eH reaches the target value (gH—1/2AVJ or more). Using this as a reference, the central plication and triangular resection (or plication) of the fused cusp are performed. In the case of triangular plication, traction of the central plication suture facilitates determination of the triangular suture line. After placing several mattress sutures on the cusp body, a running suture is added up to the free edge, with resection of the excess cusp tissue performed when necessary (Fig. 10.4).

Fig. 10.4
figure 4

A case of BAV repair without VSARR. (1) External Dacron strip for AVJ reduction/stabilization. (2) Adjustment of eH of the non-fused cusp with central plication. (3) Adjustment of free margin length of the fused cusp with central plication for correction of prolapse. (4) Triangular resection to remove thickened cusp tissue and to correct slackness of the cusp belly. (5) Suturing the cut end of the cusp body

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8 Results

As the current long-term performance of the tissue valve in the aortic position has continued to improve, valve repair must be evaluated by the long-term results. Ten-year results have only been reported by experts such as the Cleveland Clinic group [8], Mayo Clinic group [29], and the Schäfers [7] and El Khoury [30] groups. Although reoperation-free survival at 10 years is close to 90% for the El Khoury group and around 80% by for Cleveland Clinic and Schäfers groups, it is not necessarily ideal as indicated by the 49% rate from the Mayo Clinic group. Even in the David group’s 8-year results [31], although their reoperation-free rate is 82%, the rate of freedom from AR of grade 3 or more is as low as 44%. These results are sufficiently compelling, however, for young people with poor long-term durability of tissue valves.

9 Conclusion

Long-term outcomes of BAV repair still has room for improvement, and many innovative techniques or strategies are being introduced. It is expected that the effects of these innovations will be validated in further studies.