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Right arrow Congenital - acyanotic

Ann Thorac Surg 2002;74:771-777
© 2002 The Society of Thoracic Surgeons

Original article: cardiovascular

Pericardial tissue valves and gore-tex conduits as an alternative for right ventricular outflow tract replacement in children

Bradley S. Allen, MD*a, Chawki El-Zein, MDa, Betina Cuneo, MDa, Joseph P. Cava, MDa, Mary Jane Barth, MDa, Michel N. Ilbawi, MDa

a Division of Cardiovascular Surgery, Heart Institute for Children, Hope Children’s Hospital, Oak Lawn, Illinois and the University of Illinois, Chicago, Illinois, USA

Accepted for publication May 7, 2002.

* Address reprint requests to Dr Allen, Heart Institute for Children, Hope Children’s Hospital, 4440 West 95th St, Oak Lawn, IL 60453 USA
e-mail: bradallen{at}thic.com


   Abstract
Top
 Abstract
Introduction
 Material and methods
 Results
 Comment
 References
 
Background. There is still no perfect conduit for reconstruction of the right ventricular outflow tract (RVOT) in children. Homografts are not always available in the appropriate size, and degenerate in a few years. This study evaluates the pericardial valve with Gore-Tex conduit as an alternative for RVOT construction.

Methods. From January 1, 1993, to September 30, 1999, a pericardial tissue valve was inserted in all patients undergoing RVOT reconstruction or pulmonary valve replacement (PVR) who were large enough to accommodate a tissue valve. In patients without a native main pulmonary artery, a new technique was used to construct an RV-PA conduit out of a flat sheet of Gore-Tex, as Dacron frequently leads to stenosis. Data were collected by retrospective review, follow-up echocardiograms, and assessment by a single cardiologist.

Results. There were 48 patients, 22 undergoing a PVR alone and 26 a RV-PA valved Gore-Tex conduit. Diagnosis included tetralogy of Fallot (n = 25); truncus arteriosis (n = 9); ventricular septal defect with PA (n = 5); DORV (n = 4); D-TGA with PS (n = 2); and 1 each IAA with sub AS, VSD with PI, and PS s/p Ross procedure. Patient age ranged from 3 to 33 years and 98% were reoperations. The valve sizes ranged from 19 to 33 mm and the median hospital length of stay was 4 days. There were 2 (4.2%) perioperative and 1 (2.1%) late deaths, none related to the valve or Gore-Tex conduit. At a follow-up of 15 to 86 months (mean 43 ± 16 months), all remaining 45 patients are New York Heart Association class I, all valves are functional, and no patient has required valve or conduit replacement or revision; more importantly, echocardiogram revealed no significant valve or conduit stenosis (mean gradient 16 ± 8 mm Hg) and no evidence of regurgitation or structural degeneration.

Conclusions. A pericardial tissue valve and Gore-Tex conduit provides a reliable alternative for RVOT reconstruction in pediatric patients. It is readily available, molds in the limited retrosternal space, and has outstanding intermediate results with no evidence of failure or deterioration up to 7 years after insertion.


   Introduction
Top
 Abstract
 Introduction
Material and methods
 Results
 Comment
 References
 
Reconstruction of the right ventricular outflow tract is needed in a wide variety of congenital heart diseases, both at the time of primary repair or later for replacement of existing valves or conduits [1–4]. Ideally, the conduit or valve needed for such reconstruction is formed of autologous tissue that grows, resists infection, lasts for the life span of the patient, and is readily available in all sizes. Such conduits, however, are not available and several alternatives have been used, none of which are without potential drawbacks. Dacron conduits were used for early repairs, but they were soon abandoned because of early calcification and obstruction [1, 2, 4–7]. Xenografts conduits were abandoned for the same reasons [1, 2, 4, 5]. This led to the introduction of pulmonary and aortic homografts, which remain the primary choice of most pediatric centers [1, 4, 8, 9]. Homografts, however, are not always available in the appropriate size and they still need to be replaced because of growth of the patient as well as conduit failure. Techniques of pulmonary valve repair that avoid the use of these suboptimal-valved conduits have been attempted with some success. A monocusp pulmonary valve has been constructed from autogenous pericardium or Gore-Tex patch and placed at the valve annulus [10–12]. This valvuloplasty technique has excellent early results but almost always fails by 24 months. Similarly, techniques that attempt at establishment of direct right ventricular pulmonary artery continuity may result in unguarded outflow tract or distortion of the pulmonary arteries.

The bovine pericardial tissue valve is a relatively new valve and compared with conventional porcine valves has improved flow characteristics and durability in the aortic position in adults [13, 14]. It has, however, never been studied primarily in the pediatric patient population nor on the right side of the heart where it may be more durable as a result of the reduced hemodynamic forces in the pulmonary circulation. Similarly, Gore-Tex conduits are less likely to develop significant pseudointima or early obstruction when compared with Dacron conduits [7, 15, 16]. These distinct advantages of pericardial valves and Gore-Tex conduits have led us to adopt their use as an alternative for right ventricular outflow obstruction. The main purpose of this study is to evaluate the functional performance of this composite conduit in pediatric patients.


   Material and methods
Top
 Abstract
 Introduction
 Material and methods
Results
 Comment
 References
 
Beginning in January 1993, a Carpentier-Edwards pericardial valve with or without a Gore-Tex conduit (W. L. Gore and Associates, Flagstaff, AZ) was used for pulmonary valve replacement or reconstruction of the right ventricular outflow tract in all pediatric patients who were large enough to accommodate the available sizes of this tissue valve. Data were collected by retrospective review of all charts, as well as clinical assessment by a single cardiologist. Follow-up serial echocardiographic examinations were performed to assess the valve and valved conduit for evidence of degeneration, calcification, stenosis, or regurgitation. A single cardiologist reviewed all echocardiograms. Peak instantaneous gradients across the valve (or conduit) was determined by doppler, and pulmonary insufficiency graded as either absent (grade 0), mild (grade 1), moderate (grade 2), or severe (grade 3). All but 1 patient had previously undergone total repair and the original diagnosis is listed in Table 1. The initial repair included use of a homograft for the RVOT construction in 26 patients, an infundibular patch with valvotomy in 10 patients and a transannular patch with a monocusp in 11 patients. Indications for valve or conduit replacement were severe pulmonary regurgitation, calcification and stenosis of the homograft, or a combination or stenosis and regurgitation. Data are presented as mean ± standard deviation of the mean, and Kaplan-Myer analysis used for survival and assessment of valve function. Postoperative valve or conduit failure was defined as peak instantaneous pressure gradient of >= 40 torr, or more than mild pulmonary valve regurgitation (grade 2 or more).


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  		Table 1. Original Diagnosis

 
Operative technique
Exposure was obtained using a redo median sternotomy incision with cardiopulmonary bypass and moderate hypothermia. The heart was protected using a modified integrated cardioplegic strategy [17, 18]. After cardiac arrest with cold antegrade blood cardioplegia, a left ventricular vent was placed through the superior pulmonary vein. Cardioplegia was given intermittently every 10 to 15 minutes during intracardiac repairs and a modified (nonpotassium) blood cardioplegia solution continuously infused whenever it did not impair visualization. In almost all cases, the pulmonary valve replacement as well as construction of the RV to PA Gore-Tex conduit could be performed with the heart continuously perfused with the modified solution. This results in essentially no myocardial ischemia during valve (conduit) insertion, as the heart is kept arrested and perfused. All patients received a warm substrate enriched cardioplegic reperfusate before removing the aortic clamp.

In patients with a native pulmonary artery, a transannular incision is performed. Valve sizers are used to determine the largest pericardial valve that can be inserted at the level of the pulmonary annulus. A wide elliptical patch of Gore-Tex is fashioned to enlarge the anterior wall of the pulmonary artery and RVOT. Starting distally, the patch is sutured to the edges of the PA incision up to the planned level of the valve insertion. The valve is then sutured to the native annulus posteriorly and to the Gore-Tex patch anteriorly with continuous nonabsorbable suture, and the patch insertion completed.

Patients who had a homograft or Dacron tube graft used during their original repair first had the conduit completely excised. Valve sizers are once again used to determine the largest pericardial valve that can be inserted. A large flat sheet of Gore-Tex is then wrapped around the valve sizer to form a tube, and the excess is removed (Fig 1). An extra 3 to 5 mm of redundancy is left in the circumference, as suturing always slightly gathers the patch. The proximal and distal ends are then trimmed at an angle, with the inside edges being the distance from the pulmonary artery to the right ventricle (Figs 1 and 2). The patch is first sutured distally to the posterior portion of the pulmonary artery and then proximally to the distal edge of the infundibular incision securing it in place (Fig 3). Next the pericardial valve is sutured in the Gore-Tex tube at the level of the original pulmonary valve using running polytetrafluoroethylene sutures (Fig 3). The remaining anterior portion of the pulmonary artery anastomosis is completed, and the edges of the patch are sutured together anteriorly creating a tube conduit (Fig 4). The same is then done of the right ventricular side, completing the conduit construction (Fig 5).



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  		Fig 1. Fashioning the Gore-Tex conduit. (A) A flat sheet of Gore-Tex is (B) wrapped around the appropriate valve sizer and the excess removed, leaving 3 to 5 mm of redundancy. (C) The Gore-Tex sheet is then folded, and the distal ends trimmed (at an angle), to make the conduit the appropriate length. The inside edges being the distance from the pulmonary artery to the right ventriculotomy. (D) The shaped Gore-Tex sheet (see text for details).

 


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  		Fig 2. The patch is secured to the pulmonary artery and right ventricle.

 


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  		Fig 3. The posterior portion of the pulmonary artery and right ventricular anastomosis is completed. The pericardial valve is then sutured to the Gore-Tex using running Prolene suture.

 


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  		Fig 4. The anterior portion of the pulmonary artery anastomosis is completed, and the edges of the patch sutured together creating a tube. The same is then done on the right ventricular side.

 


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  		Fig 5. The completed Gore-Tex pericardial valve tube conduit.

 

   Results
Top
 Abstract
 Introduction
 Material and methods
 Results
Comment
 References
 
From January 1, 1993, until September 30, 1999, 48 patients underwent pulmonary valve with or without RVOT conduit replacement. The age of the patients varied from 3 to 33 years (mean 11 ± 7) and weight from 14.5 to 104.5 kg (mean 37 ± 22 kg). Twenty-six patients (54%) had pulmonary valve replacement with a conduit used for reconstruction of the RV-PA conduit and 22 patients (46%) had their valve replaced with patch enlargement of the main pulmonary artery. Eighteen patients required a simultaneous procedure (Table 2). Valve sizes ranged from 19 to 33 mm (mean 26 ± 3 mm) and the bypass, cross clamp, and ischemic (time of no coronary perfusion) times were 172 ± 41, 98 ± 40, and 9 ± 8 minutes, respectively. The median length of hospital stay was 4 days (range 2 to 43) and 68% of patients (31 of 46) were discharged home on or before the fourth postoperative day.


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  		Table 2. Simultaneous Procedures

 
Early operative mortality occurred in 2 of 48 patients (4.1%). Both patients had undergone previous repair of truncus arteriosus and now required conduit replacement at 5 and 8 years of age. The first patient had severe atrial arrhythmias and RV dysfunction before surgery and failed to come off bypass secondary to RV failure. The second patient never regained consciousness and loss of neurologic function developed a few hours after surgery with no definite etiology. Computed tomography scan of the brain showed diffuse edema and poor cerebral perfusion. Late death occurred in 1 patient (2%) who died 6 months after surgery for reasons unrelated to the heart or conduit. One patient required exploration for postoperative bleeding and in another patient with ventricular arrhythmias before surgery respiratory and renal failure developed after surgery and the patient had to be maintained on amiodarone, lidocaine, and procainamide for ventricular arrhythmias; his hospital stay was 43 days.

Four patients were lost to follow-up. At the time of last physician visit and echocardoigram, all of these patients were asymptomatic, in NYHA class I, with no evidence of valve or conduit stenosis or regurgitation. Follow-up was complete in 41 of 45 patients (91%). The mean follow-up period was 43 ± 16 months with a range of 15 to 86 months. All patients were NYHA class I and no patient has required reoperation or reintervention. The actuarial freedom from valve replacement compared with two large series of homograph valves (Stark [4, 19] and Weipert [20]) is depicted in Figure 6. By echocardiography, the mean peak instantaneous gradient across the pericardial valve or conduit was 16 ± 8 mm Hg (range 0 to 34 mm Hg); 73% of patients (30 of 41) had a gradient of 0 to 20 mm Hg, 21% (9 of 41) a gradient of 21 to 30 mm Hg, 2% (1 of 41) a gradient of 31 to 40 mm Hg; no patient had a gradient of more than 40 mm Hg. Forty-nine percent of patients had no valvular insufficiency (grade 0), 51% had mild insufficiency (grade 1), and no patient had moderate (grade 2) or severe (grade 3) insufficiency.



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  		Fig 6. Actuarial freedom from valve explant in our patients compared to two large series (Stark [4, 19] and Weipert [20]) of homograft patients. Numbers in parenthesis indicate the actual number of patients at a given time point in each study.

 

   Comment
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
References
 
The most commonly used conduit for the reconstruction of the RVOT is the pulmonary or aortic homograft. The reported freedom from conduit replacement when a homograft is used is 50% to 90% at 5 years, and their performance has improved minimally, if any, with the recent improvement in homograft cryopreservation methods [1, 4, 8, 21–23]. The reason for failure is conduit degeneration and calcification resulting in stenosis or incompetence. Young age and small conduits have been found to be an important risk factor for early conduit failure in many series, whereas other have shown complexity of the underlying lesions, type of homograft, and previous operation to be proven risk factors [1, 4, 8, 20–25]. Despite the poor long-term performance and lack of availability of the appropriate size of homograft conduits they remain an important tool in the correction of many complex lesions.

The use of composite conduits made of Gore-Tex patch with bovine pericardial valve has several advantages. Pericardial valves are readily available and have stiff annulus, thus are less subject to compression or distortion by the overlying sternum, an important factor in the pathogenesis of accelerated degeneration. Their hemodynamic properties are excellent, and they do not need anticoagulation. They have improved durability and decreased incidence of calcification and degeneration, even on the left side of circulation where closure stress on the valve is increased [13, 14, 26]. Data in adults have shown that in the aortic position the pericardial valve has a 80% to 90% freedom from explant for structural dysfunction at 15 years of follow-up [13, 14, 26]. There is, however, a slightly faster degeneration rate in younger patients. Longer follow-up of our patients will therefore be needed to adequately assess the longevity of the pericardial valve in the pulmonary position, as the beneficial effects of reduced hemodynamic forces on the right side of the heart could be offset by the accelerated rate of degeneration in younger patients. Similarly, the Gore-Tex conduit is readily available, more pliable and has less risk of peel formation, stenosis or calcification than any other available material, especially Dacron, which has a high incidence of accelerated neointimal formation [2, 7, 15, 16].

The technical modifications applied in this series, namely tailoring of the conduit insitu, allows for accurate construction of the patch to fit the gap between the right ventricle and pulmonary arteries. This intraoperative construction minimizes conduit kinking or distortion, which could predispose to turbulence and consequent valve degeneration. It incorporates proximal right and left pulmonary artery enlargements, thus averting distal stenosis, which increases the stress on the valve leaflets and could lead to early failure. It avoids the use of any part of the previous placed homograft, which is almost always calcified or friable. It also enlarges the right ventricular outflow and enables the use of a larger size valve, minimizing the need for future enlargement as the child grows. This should theoretically make the bioprosthesis longevity, rather than the conduit diameter, the limiting factor that determines the need for replacement.

In spite of the excellent functional longevity of the Gore-Tex composite conduits, they have a few drawbacks. The pericardial valve is not available in small sizes precluding its use in small infants and children. Disproportionate enlargement of the outflow tract may lead to pathophysiology of an aneurysm and increases the right ventricular stroke work. Moreover, an oversized valve may compress the underlying coronary arteries. Hemostasis might be a problem, especially in the heparinized patient. However, use of smaller needles may minimize continuous oozing from needle holes. These conduits also require longer aortic cross clamp and bypass time for construction. However, the use of a modified integrated cardioplegic strategy which utilizes continuous cold (nonpotassium) cardioplegic infusions during valve and conduit construction minimizes myocardial ischemia, and facilitates conduit construction by keeping the heart arrested [17, 18]. In this series, continuous perfusion was possible for almost the entire cross clamp interval, resulting in a mean myocardial ischemic time of only 9 minutes. Continuous coronary perfusion is also possible with fibrillatory arrest or a beating empty heart, but these methods have inherent drawbacks. Fibrillation often leads to subendocardial ischemia, especially in the setting of ventricular hypertrophy. A beating empty heart may be well perfused, but has the potential of an air embolus if there is a residual small unrecognized shunt.

It is rather difficult to compare the present series with those in the literature. The criteria for replacement of a failing conduit or valve varies among different institutions making the definition of the end point, namely conduit failure less uniform [1, 4, 9, 23, 25]. Significant stenosis or regurgitation indicating conduit failure are often well tolerated by the healthy right ventricle. Therefore, the use of heart failure symptoms to define conduit failure prolongs artificially the functional life of the conduit. Balloon valvuloplasty has also been used to artificially prolong the functional performance of different conduits at the expense of producing significant regurgitation. Various studies have shown that delay in the treatment of residual pulmonary stenosis, especially when associated with regurgitation is quite detrimental [3, 27–30]. It accelerates right ventricular dysfunction and predisposes to ventricular arrhythmias. Moreover, the delay in conduit or valve replacement may lead to permanent myocardial fibrosis and the absence of any demonstrable postoperative improvement in hemodynamic performance or exercise variables. To avoid these sequelae, some surgeons advocate an early and aggressive approach to dysfunctional conduits, especially with the very low operative mortality associated with right ventricular to pulmonary artery conduit replacement. It is therefore important that future comparisons of the functional life of different valves or conduits in the RVOT be based on a standardized definition of what constitutes conduit failure.

The intermediate results obtained from the use of Gore-Tex pericardial valve conduits in this series compares very favorably with any other form of conduits used. Freedom from reoperation or conduit failure has been 100% at a mean follow-up of 4.3 years and as long as 7 years after surgery. By comparison, two large series of homograft valves by Stark and Weipert [4, 19, 20] demonstrate a substantially higher rate of conduit replacement (Fig 6). The mean age in these reports was slightly younger than in our patients and approximately 15% were less than 1 year of age. Nevertheless, with mean ages of 6.8 years (Stark) and 6.5 years (Weipert) these series are probably reflective of our patients. Moreover, Stark did not find young age to be a risk factor in his series of 405 patients. In contrast, univariant analysis demonstrated older age to be a risk factor for replacement, and multivariant analysis found reoperation (second conduit) to be the highest predictor of conduit failure [4, 19]. The excellent performance of the pericardial valve conduits therefore becomes even more apparent if one considers that 47 of 48 (98%) of patients receiving a pericardial valve had at least one earlier valve or conduit replacement. Furthermore, our results are in spite of the strict criteria we used to define conduit failure (pressure gradient > 40 mm Hg or more than mild pulmonary valve regurgitation), which are in marked contrast to more liberal criteria of conduit replacement usually reported in other series, such as those of Stark and Weipert [4, 8, 9, 19, 20, 22, 25]. A recent study by Baskett and associates [21] underscores the importance of this distinction. In this study, freedom from homograft replacement was 90% at 50 months, whereas utilizing the same strict conservative criteria applied in our series 44% of homograft valves had failed by 26 months.

Newer approaches to right ventricular outflow construction may provide alternatives with as good an outcome as the one reported in this series. The stentless bioprosthesis has provided excellent early and intermediate results when used in the aortic position [31]. Their use, however, has not been tested in pediatric patients or in the pulmonary position. Similarly, a bovine pulmonary valve conduit or valved jugular vein has been used to reconstruct right ventricular outflow tract in limited number of patients which encouraging early results [32, 33]. Further evaluation of these alternatives may be needed before they gain wide acceptance.

In summary, the present study shows excellent intermediate results for right ventricle-to-pulmonary artery conduit reconstruction using a pericardial valve with or without a Gore-Tex conduit. Clearly, long-term follow-up is needed to assess the longevity of the RVOT pericardial bioprosthesis in the pediatric age group, and to determine the ultimate role of this reconstruction of conduit replacement.


   References
Top
 Abstract
 Introduction
 Material and methods
 Results
 Comment
 References
 

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