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Ann Thorac Surg 1998;66:1337-1342
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Should a bicuspid aortic valve be replaced in the presence of subvalvar or supravalvar aortic stenosis?

^a Division of Cardiothoracic Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
^b Division of Pediatric Cardiology, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA

Address reprint requests to Dr Delius, UC Davis Medical Center, 4301 X St, #2250, Sacramento, CA 95817

Presented at the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 26–28, 1998.

	Abstract

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Background. A bicuspid aortic valve is commonly associated with other levels of left ventricular outflow tract obstruction. Providing the bicuspid aortic valve is competent and nonobstructive, repair of subvalvar or supravalvar stenosis usually focuses on the obstructive lesions, leaving the valve in situ. The aim of this report was to examine the impact of a bicuspid aortic valve on the risk of reoperation for patients undergoing operation for subvalvar or supravalvar aortic stenosis.

Methods. Since 1976, 47 patients with supravalvar or subvalvar aortic stenosis have undergone repair. The median follow-up is 5.1 years (range, 2 months to 20.1 years). Sixteen patients (34%) had a bicuspid aortic valve that was competent and nonobstructive, and 31 (66%) had a tricuspid aortic valve.

Results. Reoperation was required in 9 patients (56%) with a bicuspid aortic valve, in each involving aortic valve replacement with an autograft (3), homograft (2), or prosthesis (4). Six patients (19%) with a tricuspid aortic valve required reoperation, yet only 1 required aortic valve replacement. The freedom from valve replacement was 43% (70% confidence interval, 31% to 55%) in the bicuspid aortic valve group versus 100% (70% confidence interval, 94% to 99.5%) in the tricuspid group at 5 years (p = 0.0001). The freedom from any reoperation at 5 years was 43% (70% confidence interval, 31% to 55%) in patients with a bicuspid aortic valve versus 86% (70% confidence interval, 80% to 93%) in the tricuspid group (p = 0.02).

Conclusions. The data suggest that patients with subvalvar or supravalvar aortic stenosis and a bicuspid valve may be better palliated with a more definitive operation such as the Ross or Ross-Konno procedure.

	Introduction

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With the possible exception of mitral valve prolapse, a congenital bicuspid aortic valve is the most common congenital heart malformation, affecting approximately 1% of the population [1]. Studies have shown that sclerosis of the bicuspid aortic valve begins in the second decade of life, with some degree of aortic stenosis developing in 72% of these patients by the fifth and sixth decades of life [1, 2]. Endocarditis also occurs in approximately 10% of these patients [3]. However, a significant proportion of patients with a bicuspid aortic valve never require intervention [3, 4], making prophylactic valve replacement unreasonable. On the other hand, if an operation on the aortic root is required for other reasons, the decision to replace the aortic valve becomes more difficult. A recent report of patients from this institution undergoing repair of supravalvar aortic stenosis showed that the primary risk factor for reoperation was the presence of a bicuspid aortic valve and the most common reoperation required was valve replacement [5]. It seems feasible that the presence of other lesions of the left ventricular outflow tract might also alter the natural history of bicuspid aortic valve. The aim of this report was to extend our observations regarding the impact of bicuspid aortic valve to additional patients with supravalvar aortic stenosis and also to patients with subvalvar stenosis.

	Material and methods

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Patient population
Between January 1976 and June 1997, 47 patients with subvalvar (n = 28 patients) or supravalvar (n = 19 patients) aortic stenosis have undergone surgical correction. Some of the patients with supravalvar obstruction were included in a previous report from this institution [5]. Sixteen of these 47 patients (34%) had a bicuspid aortic valve (group I) that was competent and nonobstructive, and 31 (66%) had a competent nonstenotic tricuspid aortic valve (group II). There were no patients during this time period who had a significantly incompetent or obstructive aortic valve and supravalvar or subvalvar aortic stenosis at initial presentation or operation. Seven of the 19 patients with supravalvar stenosis (37%) were in group I. Nine of the 28 patients with subvalvar stenosis (32%) were also included in group I. Among the patients with supravalvar aortic stenosis, 1 had the diffuse form and the remainder had the discrete form. Discrete subvalvar stenosis was present in 25 patients, whereas 3 had the tunnel form. Associated cardiac diagnoses are shown in Table 1. Indications for operation included symptoms (exercise intolerance, 12; angina, 3; syncope, 2) or a gradient across the left ventricular outflow tract greater than 50 mm Hg. The diagnosis and pressure gradients were established by preoperative cardiac catheterization and angiocardiography in all patients. Catherization data documented the absence of obstruction at the valvar level in each patient in this report. Immediate postoperative peak gradients were measured in the operating room in all patients by direct needle puncture after weaning from cardiopulmonary bypass. Echocardiography with continuous-wave Doppler flow analysis was used for long-term follow-up. Selected patients underwent subsequent cardiac catheterization; in most cases, the indication for follow-up catheterization was the development of symptoms, a predicted gradient across the left ventricular outflow tract greater than 50 mm Hg by continuous-wave Doppler analysis, or evidence of increasing aortic insufficiency.

Complete follow-up was available in 46 of 47 patients. The median follow-up for all patients was 5.1 years (range, 2 months to 20 years). One patient with a tricuspid aortic valve was lost to follow-up but was asymptomatic and doing well at 3 years after the initial operation; this patient was included in this report. The median length of follow-up was 9.8 years (range, 2 months to 18.5 years) in group I and 5.0 years (range, 4 months to 20 years) in group II.

Operative techniques
No patient in this report had any surgical intervention to the aortic valve at the initial operation. Operative techniques used for patients with supravalvar aortic stenosis have been described in detail in earlier reports [5, 6]. Briefly, all patients underwent repair using an inverted Y incision as originally described by Doty and associates [6]. Four patients also had a patch placed in the left sinus of Valsalva [7].

Patients with the discrete form of subaortic stenosis (n = 25) underwent transaortic membrane excision and concomitant myectomy or myotomy. Patients with the tunnel form of subaortic stenosis underwent myectomy (n = 2) or a valve-sparing modified Konno procedure (n = 1).

Statistics
Actuarial analyses were used to estimate survival, freedom from reoperation, and freedom from valve replacement. The log rank test was used to compare outcomes between the bicuspid and tricuspid groups. Relative risk analysis was used to determine the impact of the presence of a bicuspid aortic valve on the risk of subsequent aortic valve replacement. Fisher’s exact test was used to compare the likelihood of subsequent aortic valve replacement in patients with a bicuspid or tricuspid aortic valve. Comparison of hemodynamic data was performed with Student’s t test. For each test a p value equal to or less than 0.05 was considered statistically significant; p values greater than 0.2 are noted as not significant.

	Results

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Survival
The actuarial estimate of survival at 10 years was 100% in group I and 93% (70% confidence interval [CI], 89% to 97%) in group II (not significant) (Fig 1). There were three late deaths, two in group I and one in group II. Two patients died of heart failure at 7 and 19 years after the initial operation. One patient died of hemorrhage intraoperatively at reoperation 14 years after the initial operation.

View larger version (14K): [in this window] [in a new window]   Fig 1. Actuarial survival for patients who have undergone primary repair of subvalvar or supravalvar aortic stenosis (not significant). Error bar indicates 70% confidence interval. Numbers of patients at risk are in parentheses.

Reoperations
Seventeen reoperations were performed in 15 patients. The reoperations performed and the indications for reoperation are shown in Table 2. Reoperation was required in 9 patients (56%) in group I, all of whom required aortic valve replacement with an autograft (n = 3), homograft (n = 2), or prosthesis (n = 4). Although some degree of aortic insufficiency was present in 5 of these patients, aortic stenosis was the primary pathophysiologic lesion in every patient in group I, even those with subvalvar stenosis as the primary lesion. All valves demonstrated fusion of the commissures and varying (albeit significant) degrees of calcification. Six patients (19%) in group II required reoperation, only 1 of which involved aortic valve replacement at 7 years after the initial operation.

View larger version (17K): [in this window] [in a new window]   Fig 2. Actuarial freedom from any reoperation for patients with a bicuspid or tricuspid aortic valve who have undergone primary repair of subvalvar or supravalvar aortic stenosis (p = 0.02). Error bar indicates 70% confidence interval. Numbers of patients at risk are in parentheses.

View larger version (20K): [in this window] [in a new window]   Fig 3. Actuarial freedom from valve replacement for patients with a bicuspid or tricuspid aortic valve who have undergone primary repair of subvalvar or supravalvar aortic stenosis (p = 0.0001). Error bar indicates 70% confidence interval. Numbers of patients at risk are in parentheses.

	Comment

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The management of the patient with a functional bicuspid aortic valve becomes more complicated when there are concomitant cardiac lesions. A recent exchange of opinions on the Internet-based Open Heart Forum regarding a patient with a functional bicuspid aortic valve and an ascending aortic aneurysm highlights the difficult decision-making involved in managing these patients; opinions were evenly split as to whether prophylactic aortic valve replacement was indicated at the time of aneurysm replacement to prevent reoperation. Bicuspid aortic valves are commonly associated with other congenital lesions, particularly aortic arch obstruction and obstruction of the left ventricular outflow tract [8]. Bicuspid aortic valves have been noted in 25% to 41% [5, 9, 10] of patients with supravalvar aortic stenosis and 9% to 20% [11, 12] of patients with subvalvar aortic stenosis.

Aortic valve pathology has been noted to affect the risk of reoperation and even survival in patients with supravalvar aortic stenosis [5, 9, 10]. A prior report from this institution demonstrated that only the presence of a bicuspid aortic valve was a risk factor for reoperation [5]. A large series from the Mayo Clinic also showed that associated aortic valve disease correlated strongly with late death and the need for reoperation [9].

Most reports discussing the risk of reoperation in patients undergoing relief of subaortic obstruction have focused on anatomic subtypes (tunnel versus discrete) and technical details (eg, myectomy, myotomy). Patients with subaortic stenosis have a substantial risk of reintervention. Moses and associates [13] described an adverse event-free survival (defined as death, reoperation, residual gradient >50 mm Hg, endocarditis, or complete heart block) of only 43% at 4 years in patients with the discrete form of subvalvar stenosis, which is the most favorable anatomic subtype. Although most reoperations in patients with subvalvar stenosis are the result of recurrent subaortic stenosis [14, 15], a substantial number are performed because of aortic valve pathology. Aortic valve replacement was required in 21% to 27% of patients with subvalvar stenosis due to unspecified aortic valve lesions in other reports [16, 17]. In most cases aortic valve replacement is caused by the aortic insufficiency that can result from subvalvar stenosis. Little is known about the impact of a bicuspid aortic valve in this population. Although most patients in this report had isolated recurrent subvalvar stenosis as their primary indication for reoperation, 44% of patients requiring reoperation also required valve replacement. Each of these patients originally had a bicuspid aortic valve. Interestingly, all of these patients had stenosis rather than regurgitation as the predominant physiologic lesion, although some degree of regurgitation was present in most.

Bicuspid valves only rarely become stenotic or incompetent in early life [18]. It is the onset of acquired disease, usually resulting from fusion of the commissures from the periphery to the center, that produces problems in valvar function [18, 19]. As noted earlier, valvar stenosis or incompetence requiring valve replacement usually does not develop until well into adulthood. Patients undergoing repair of supravalvar or subvalvar stenosis usually have a significant improvement in their left ventricular outflow tract gradients, although complete eradication of the gradient is unusual [5, 9, 11, 13]. It has also been suggested that patients with subvalvar obstruction often have comparatively small aortic roots, possibly also contributing to residual postoperative gradients [20]. These persistent gradients are not usually physiologically significant, and many patients have symptomatic improvement or resolution of left ventricular hypertrophy after repair. However, almost all patients have a persistent murmur, suggesting that turbulent flow is present across the left ventricular outflow tract [13]. Calcification of the bicuspid aortic valve is thought to be caused by mechanical wear and tear [4, 19]. It seems feasible that turbulence resulting from mild residual left ventricular tract obstruction may hasten degeneration of the bicuspid aortic valve and lead to premature calcification with resulting stenosis or regurgitation.

Replacement of the aortic root with a pulmonary autograft has been increasingly applied to children with aortic valve pathology [21–23]. The pulmonary autograft has the advantage of being native tissue, which is resistant to infection and capable of growth [23]. Most pulmonary autografts are currently implanted as an aortic root, although this is subject to surgeon expertise and preference. Pulmonary autograft implantation also has been combined with a Konno procedure to provide effective relief of subvalvar stenosis as well [21, 24]. The freedom from reoperation in experienced hands has been reported as 92% ± 4% at 7 years [23], which is significantly better than the 5-year freedom from reoperation of 43% in this series of patients with a bicuspid valve and subvalvar or supravalvar stenosis. Autograft reconstruction of the left ventricular outflow tract should be considered a palliative operation because replacement of the homograft used to reconstruct the right ventricular outflow tract is often necessary. However, the length of palliation achieved with this approach appears to be superior to that we have observed by following a policy of leaving a bicuspid valve in situ when other lesions of the left ventricular outflow tract are repaired.

In conclusion, lesions of the left ventricular outflow tract are often associated with bicuspid aortic valves. Degeneration of the bicuspid valve appears to be markedly accelerated if other lesions of the left ventricular tract are present; more than 50% of patients require reoperation within 5 years of the initial repair of these associated lesions. Patients with subvalvar or supravalvar aortic stenosis and a bicuspid aortic valve may be better palliated with a more definitive operation such as a Ross or Ross-Konno procedure.

	Acknowledgments

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We thank M. Bridget Zimmerman, PhD, for her assistance with statistical analysis and Vicki Hudachek for helping to prepare the manuscript.

	References

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