Ann Thorac Surg 2008;85:2012-2018. doi:10.1016/j.athoracsur.2008.02.081
© 2008 The Society of Thoracic Surgeons
Original Articles: Adult Cardiac
Bicuspidization of the Unicuspid Aortic Valve: A New Reconstructive Approach
Hans-Joachim Schäfers, MDa,*,
Diana Aicher, MDa,
Svetlana Riodionycheva, MDa,
Angelika Lindinger, MDb,
Tanja Rädle-Hurst, MDb,
Frank Langer, MDa,
Hashim Abdul-Khaliq, MDb
a Department of Thoracic and Cardiovascular Surgery, University Hospitals of Saarland, Homburg/Saar, Germany
b Department of Pediatric Cardiology, University Hospitals of Saarland, Homburg/Saar, Germany
Accepted for publication February 21, 2008.
* Address correspondence to Dr Schäfers, Department of Thoracic and Cardiovascular Surgery, University Hospitals of Saarland, Homburg/Saar, 66421, Germany (Email: h-j.schaefers{at}uniklinikum-saarland.de).
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Abstract
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Background: Unicuspid anatomy of the aortic valve is infrequent but may require intervention by age 40 for severe regurgitation. We propose a new repair technique for the regurgitant unicuspid valve by converting it into a bicuspid aortic valve.
Methods: Between November 2003 and September 2007, 20 patients underwent regurgitant unicuspid aortic valve repair: 13 had aortic regurgitation (AR) and 7 had combined regurgitation and stenosis. Four patients had previously undergone balloon valvuloplasty for critical aortic stenosis. The aim of the repair was to construct a bicuspid valve with two normal commissures and unrestricted cusp motion. The fused cusp tissue was divided anteriorly and a new commissure of normal height was created. Noncoronary and right coronary cusps were extended with autologous pericardium. Concomitant operations included ascending aortic replacement in 7 and resection of subaortic stenosis in 1.
Results: No early or late deaths occurred. Intraoperative echocardiography revealed minimal or no AR in 19 patients. Follow-up was 4 to 47 months. One patient underwent valve re-repair for recurrent and progressive aortic regurgitation 3 years postoperatively. All other valves remained stable throughout the follow-up period. Freedom from relevant aortic insufficiency (
II) at 4 years was 77%; freedom from reoperation was 67%; and freedom from valve replacement was 100%.
Conclusions: The regurgitant unicuspid aortic valve can be repaired successfully and reproducibly by converting it into bicuspid anatomy. The functional results are comparable with those obtained in reconstructed bicuspid aortic valves. With this approach, replacement can be avoided in most patients with regurgitant unicuspid aortic valves.
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Introduction
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Unicuspid anatomy is an apparently rare variant of the aortic valve. It may occur as unicommissural or acommissural valve [1, 2] and has been observed in 0.02% of individuals undergoing echocardiography [3]. The unicommissural variant is characterized by only one fully developed commissure, commonly in a posterior location and thus equivalent to the commissure between noncoronary and left coronary cusps [1, 4]. There is congenital fusion between right and left coronary as well as right and noncoronary cusps.
An important and characteristic feature of this anatomy is the abnormally low height of the 2 rudimentary commissures [1, 4]. Interestingly, this anatomy was initially described for critical neonatal aortic stenosis [5] and later recognized as typical for unicuspid anatomy [4]. Commissural height as a characteristic feature is difficult to determine by echocardiography, and the morphologic characteristics may be overlooked at the time of aortic valve replacement; thus, the true prevalence is likely to be higher than currently assumed [3]. Indeed, unicuspid anatomy was found in 5% of stenotic aortic valves excised at the time of aortic valve replacement [6].
Many affected patients require intervention for severe stenosis in infancy or childhood [4, 5]. Others may remain hemodynamically stable for several years or decades before they require operation for severe regurgitation or calcified stenosis [6]. Valve dysfunction to the point of requiring surgical treatment seems to occur 10 to 20 years earlier than with bicuspid valves [6]. Aortic dilatation may be an associated finding as in bicuspid anatomy [7], and the presence of unicuspid anatomy predisposes to the development of aortic dissection more often and at a younger age than bicuspid anatomy [7].
Although stenotic unicuspid valves are treated by valvotomy [8, 9], regurgitant unicuspid aortic valves are commonly replaced [10, 11]. Aortic valve replacement (AVR) is also performed for unicuspid valves that have become regurgitant as a consequence of surgical or balloon valvuloplasty [12]. An AVR with mechanical substitutes provides adequate hemodynamic results but fixes the annulus to a given size. Freedom from reoperation after mechanical AVR in pediatric patients is only 85% to 90% at 10 years [13]. Also, AVR with a pulmonary autograft carries a risk of reoperation of approximately 10% at 10 years [14], either on the autograft or the right ventricular conduit. A reconstructive approach could avoid the problems associated with the two replacement options.
Repair has been performed for congenital aortic valve anomalies previously, either by individualized correction of defects after balloon valvuloplasty or by creating a tricuspid aortic valve [11, 15–21]. Long-term data are sparse, and it is unclear what proportion of unicuspid aortic valves could be preserved rather than replaced.
From previous experience with aortic valve repair, we have learned that valve competence and stability are better achieved in bicuspid rather than tricuspid valves [22]. On the basis of this experience, we decided to create a bicuspid design in repairing unicuspid aortic valves. Because a key difference between unicuspid and bicuspid anatomy is the presence of 2 commissures of normal height in bicuspid anatomy, construction of a second normal commissure was to be a key part of the reconstructive procedure. We describe the surgical technique and the early results.
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Material and Methods
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Of 327 patients with aortic regurgitation undergoing aortic valve operations between November 2003 and September 2007 in our institution, 20 (6.1%) were treated for a regurgitant unicuspid and unicommissural aortic valve. In the same period, an additional 3 patients were initially thought to have a bicuspid valve and were treated by simple division of fused cusp tissue; they were excluded from further analysis. The remaining 20 were treated by the same operative technique and are the subject of the current investigation. Clinical and echocardiographic data were collected prospectively. The study was presented to the Institutional Review Board, which waived the need for patient consent for data presented in an anonymized fashion.
The mean age of patients was 26 ± 13 years (range, 3 to 49 years), and 14 were male. Four individuals had previously undergone balloon valvuloplasty for congenital aortic stenosis.
The primary indication for operation in 17 patients was aortic regurgitation with symptoms of heart failure or prognostic indicators of impending left ventricular failure. In patients 7, 11, and 18 (Table 1), aortic dilatation (> 2.5 cm/m2) was the main indication for operation. Four patients had aortic regurgitation (AR) grade IV, 17 had grade III, and 2 had grade II. The mean indexed left ventricular end-diastolic diameter was 24 to 66 mm/m2, and the mean peak systolic gradient was 23 to 69 mm Hg. Aortic dilatation, defined as a maximum aortic diameter exceeding 5 cm, was present in 7 instances.
Operative Technique
The chest was opened by a median sternotomy, and the patient was placed on cardiopulmonary bypass using aortic and right atrial cannulation. The aorta was opened by a transverse aortotomy approximately 5 to 10 mm above the level of the sinotubular narrowing, if present. In patients with aortic dilatation, a longitudinal incision was made initially and the aorta transected horizontally 5 mm above the height of the posterior commissure. Blood cardioplegia was given directly into the coronary ostia. All patients had rudimentary anterior (noncoronary/right coronary) and the left lateral (left coronary/right coronary) commissures; that is, they were below the level of the right coronary ostium, and thus 5 to 15 mm lower than the posterior commissure. The posterior commissure was or normal height in all. The aim of the valve procedure was to create a bicuspid configuration with 2 commissures of normal height and corresponding cusp dimensions (Fig 1).
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Fig 1. Schematic drawing of aortic cusp insertion lines of (A) a unicuspid vs (B) a bicuspid aortic valve. (LC = left coronary cusp; NC = noncoronary cusp; RC = right coronary cusp.)
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A stay suture was placed in the posterior commissure, and a second stay suture was placed at the identical height above the rudimentary anterior commissure in the location of the new commissure, that is, close to the right coronary ostium and a few millimeters above it. Additional stay sutures were placed to obtain good exposure (Fig 2). The fused cusp tissue was incised toward the anterior commissure up to the aortic wall and detached from the aortic insertion for 5 to 10 mm on both sides (Fig 3). The cusp tissue was thus divided into a noncoronary and a fused cusp, similar to the anatomy of a bicuspid valve. If calcification or dense fibrosis was present in the adjacent tissue of noncoronary or rudimentary right coronary cusp, the affected part of the cusp was excised. Thickened but pliable cusp tissue was retained.
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Fig 2. Schematic drawing of a typical unicuspid aortic valve as seen by the surgeon. The posterior commissure is of normal height, and the anterior (rudimentary) commissure is abnormally low. The commissure between rudimentary right and left cusps is also lower than normal. These two rudimentary commissures are lower than the coronary ostia. (ANT = anterior; LCO = left coronary ostium; RCO = right coronary ostium.)
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Fig 3. The fused cusp tissue is incised towards the anterior commissure and then detached from the aortic insertion for a few millimeters along the dotted lines.
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Autologous pericardium was excised and spread on a piece of cardboard using hemoclips. It was placed in glutaraldehyde (2%) for 2 minutes and rinsed in saline for 2 to 4 minutes afterwards. Two triangular pieces of pericardium were cut to fill the gap between the noncoronary cusp and the new commissure. Using a continuous 5-0 Prolene suture (Ethicon, Somerville, NJ), the patch was sutured into place, from the noncoronary cusp to the commissure (Fig 4). A second triangular patch was then prepared and sutured into the defect of the fused cusp so that it was in the position of the rudimentary right coronary cusp (Fig 5). If a defect after balloon valvuloplasty was present, the patch was configured to also accommodate the cusp defect. As for the noncoronary cusp, the aortic insertion of the patch started in the original cusp insertion and then curved towards the new commissure.
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Fig 4. For reconstruction using pericardial patches, the suture lines (straight line) in the anterior aortic root will curve cranially to create a second commissure of normal height.
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Fig 5. The cusps are augmented with triangular pieces of pericardium (shaded) reaching from native cusp tissue to the new commissure. The result is a bicuspid aortic valve with 2 commissures of normal height.
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The length of the free margin of the newly created noncoronary cusp was adjusted to achieve nearly normal configuration. In the past 2 years this was done by measurement of effective height and aiming for 8 mm in pediatric and 10 mm in adult patients. The length of the free margin of the new fused cusp was then adjusted to be at an identical height with that of the noncoronary cusp. Subcommissural root plication was not performed.
If additional aortic replacement was required (supracommissural in all instances, n = 7), the valve procedure was performed first and a limited length of the graft (2 to 3 cm) was then sutured to the aortic root. The geometry of the reconstructed valve was examined again by measurement of effective height. If necessary, the free margins of the 2 cusps were shortened to maintain the effective height of the noncoronary cusp that had been chosen for the patient. Aortic replacement, if necessary, was then completed with a second graft. One patient underwent resection of a subaortic stenosis before valve repair.
All patients were studied intraoperatively using transesophageal echocardiography. The degree of aortic regurgitation was assessed primarily by the size of the regurgitant jet determined by color Doppler and the downward slope of the continuous wave Doppler [23]. All patients were studied at least once before discharge, between postoperative days 5 and 7. Further echocardiographic studies were performed at 3, 6, and 12 months and yearly thereafter. Mean follow-up was 16 ± 13 months (range, 4 to 47 months) and complete in all patients, for a cumulative follow-up of 27 patient-years.
All data are presented as mean ± standard deviation. Statistical analysis included comparison of parametric and continuous variables between preoperative and postoperative data using one-way analysis of variance. Kaplan-Meier curves were calculated for freedom of relevant regurgitation, freedom from reoperation, and freedom from valve replacement using Prism software (GraphPad Inc, San Diego, CA). A value of p < 0.05 was considered statistically significant.
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Results
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The planned repair procedures were completed in all instances, and no patient required intraoperative conversion to replacement. Mean myocardial ischemic time was 59 ± 9 minutes. Aortic regurgitation was grade II in 1 patient and less in all other patients. No patients died early or presented with AV block. Transthoracic echocardiography before discharge documented stable valve function in all patients (Table 1). The mean peak systolic gradient was 31 ± 7 mm Hg (range, 25 to 38 mm Hg) initially and decreased subsequently during a 3-month period. The current mean peak gradient is 24 ± 8 mm Hg (Table 1). In 12 patients, the mean aortic valve orifice area determined intraoperatively was 2.0 ± 0.2 cm2/m2 (range, 1.5 to 2.5 cm2/m2).
All patients were followed up and are alive and well. During further follow-up, no thromboembolic complications occurred and no incidence of endocarditis occurred. Aortic regurgitation increased in 4 of the 20 patients and remained stable in the remaining patients (Table 1). Correspondingly, left ventricular end-diastolic dimensions have remained stable in almost all patients during the observational period. Peak systolic gradients have remained stable during the current observation period, and there has been no evidence of calcification of the pericardium or degeneration of native cusp tissue.
Patient 3, who had aortic regurgitation and subaortic stenosis (Table 1), presented 3 years postoperatively with an increasing outflow tract gradient in conjunction with regurgitation grade II to III. He underwent reoperation, with repeated outflow tract enlargement. At this time the aortic valve was assessed again and was determined to be regurgitant due to inadequate height of the neocommissure as well as inadequate effective height. The valve was re-repaired using the same principle, and the commissure was elevated by additional 6 mm. His valve function has been good and stable since.
At 4 years, freedom from grade II or more aortic regurgitation was 77% and freedom from reoperation was 67%. Since the valve requiring reintervention was re-repaired, freedom from valve replacement at 4 years was 100%.
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Comment
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Unicuspid and unicommissural anatomy of the aortic valve is a seemingly rare entity. Although this variant can be identified by echocardiography [3], the differences between unicuspid and bicuspid anatomy are sometime subtle and may be overlooked and the valve misjudged as bicuspid. In determining actual valve morphology preoperatively by echocardiography, we have observed not only the asymmetric opening pattern [3] but also a characteristic configuration with an abnormally low height difference between cusp margin and aortic insertion in long-axis views. The anatomic recognition is much easier for the surgeon, who can more clearly identify commissural height. Normal aortic valve commissures (in the absence of root dilatation) are located above the coronary ostia, but the rudimentary commissures of unicuspid valves are always lower than the ostia, in particular, lower than that of the right coronary [4, 5]. In previous studies, the incidence was 5% in stenotic aortic valves requiring operation [6], and our current numbers are in a similar range, with approximately 6% of patients treated for aortic regurgitation. In fact, our impression is that the incidence may even be higher in young adults with calcified aortic stenosis. Not all surgeons make an effort to recognize the morphologic characteristics of the unicuspid aortic valve before they excise it, and one of the references on repair of congenital aortic anomalies includes an image of a unicuspid valve classified as bicuspid [11].
Some previously performed repairs of regurgitant aortic valves in pediatric patients have followed balloon valvuloplasty of congenital stenosis, and a certain (but unknown) proportion of unicuspid valves with altered morphology may have been present [15–18]. An individualized approach was chosen in these patients [15–18], and restoration of "normal," that is, tricuspid aortic valve geometry, using pericardium was preferred [17]. The reports do not state in what proportion of patients repair rather than replacement was possible, and tricuspidization was found to be a risk factor for repair failure [18]. Tricuspidization has been proposed for repair of bicuspid valves by other groups [19–21], but was obviously possible only in a limited number of patients. Several intraoperative conversions to AVR for repair failure have been reported [20]. Another group has reported the successful creation of tricuspid aortic valves using pericardium, although few repairs were performed for congenital causes [24].
The limitations in feasibility and not always optimal results of tricuspidization of a congenitally malformed valve are not surprising. Bacha and colleagues [16] contributed their good repair results to the avoidance of attempting to create a tricuspid aortic valve. The construction of a tricuspid valve with native cusp tissue or pericardium is a geometrically challenging procedure. In addition, it does not accommodate the asymmetry of the aortic root seen in many of these congenital anomalies, including commissural height and intercommissural distance. Tricuspidization is thus bound to be of limited applicability in unicuspid aortic valves until better definitions of cusp dimensions are available. By contrast, our current approach of bicuspidization appears comparatively simple. It can be seen as a mere extension of surgical valvotomy, with the key difference of creating a new commissure. It also builds on the experience with partial cusp repair in reconstruction of the dysfunctioning bicuspid aortic valve, in which adequate valve function has been easier to obtain in bicuspid rather than tricuspid valves [22]. The fact that we have been able to apply the technique in all consecutive regurgitant valves and there have been no intraoperative conversions supports the feasibility and reproducibility of the concept.
The hemodynamic results of the bicuspidizing repair in our patients are very satisfactory. Postoperative systolic gradients were slightly higher than seen in tricuspid valves but still in a very acceptable range for a patient population in which subaortic stenosis was present in some individuals and ring diameter tended to be low for body size. Most important, the proportion of residual mild and moderate regurgitation was lower than what has been reported for tricuspidization [18, 21]. As a consequence, freedom from reoperation is low, although follow-up is still short. Of interest was that 1 of the 3 patients with unicuspid valves treated by division of fused cusp tissue (not analyzed in this report) required reoperation within 1.5 years.
It is our impression that the functional results are the consequence of an aortic valve configuration that is close to normal for a bicuspid valve. Important technical prerequisites for good postrepair geometry of the aortic valve seem to be the aortic incision and cusp configuration. We always use a simple horizontal incision to avoid unnecessary alteration of root geometry. From repair of bicuspid valves we have learned that simple symmetry of the cusps is not sufficient, but nearly normal geometry must be obtained for a stable medium- and long-term result [25]. Because the different dimensions that determine cusp geometry are difficult or impossible to measure intraoperatively, we have introduced effective cusp height as a surrogate indicator [26]. The use of this indicator has made the operation more reproducible and less dependent on subjective judgment. The only patient who has required reintervention so far was operated on early in the series. In retrospect, the valve had insufficient effective height due to insufficient commissural height and symmetric prolapse, that is, insufficient effective height. At re-repair this was corrected by increasing commissural height and normalizing cusp configuration, with resultant normalized function.
It may be argued that the design of a bicuspid aortic valve has a limited prognosis with potential failure, and the invariable development of stenosis has been proposed [27]. On the other hand, we have seen bicuspid valves in patients aged older than 70 whose only abnormality was regurgitation. As with bicuspid anatomy, unicuspid aortic valves not only develop severe valve dysfunction but are also associated with aortic dilatation in more than 50% of the affected individuals [7]. Some of our patients required operation primarily for elimination of aortic aneurysm. It is uncertain whether it is reasonable to apply the bicuspidizing repair also to unicuspid aortic valves in this setting if the regurgitation is only mild. Although no clear data are available to justify valve repair in this setting, common sense indicates that this is more reasonable than leaving a completely malformed valve behind.
We have been satisfied with the functional results of the current reconstructive approach, but questions remain to be answered in the future. Little is known about the durability of the pericardium used for cusp extension. Autologous pericardium seems superior to heterologous [24], but limited information is available on the ideal protocol of pretreatment with glutaraldehyde. In the pediatric patients, it will be important to know whether the native structures of aortic valve and root grow with the patient, and it is unclear what will happen to the cusp configuration with increasing age. Thus, further follow-up will be necessary.
The exact mechanics regarding cusp stress and strain are unknown. Possibly further studies, including geometric simulations, should identify the best configuration for the repair of these congenitally malformed valves. Finally, it remains to be shown whether this type of repair can also be applied to stenotic unicuspid valves with marked calcification. At this point we have no experience with repair of acommissural unicuspid valves.
We conclude that with the bicuspidization procedure, most, if not all, regurgitant unicuspid aortic valves should be amenable to repair if unicommissural anatomy is present. The functional early results are good, and the approach has been applicable in all patients we have treated thus far. In fact, the principles of the procedure—elevation of the commissure and augmentation of the cusps—may also be applicable to surgical valvotomy in stenotic unicuspid valves, allowing for a more aggressive valvotomy while minimizing the risk of consecutive regurgitation [12]. Further follow-up and additional studies will be necessary to define the role of this procedure in the future.
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References
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Abstract
Introduction
