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Ann Thorac Surg 2005;79:1662-1667
© 2005 The Society of Thoracic Surgeons

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Original articles: Cardiovascular

Is There a Role for Mechanical Valved Conduits in the Pulmonary Position?

^a Department of Pediatric Cardiothoracic Surgery, Wilhelmina Children's Hospital, Utrecht, The Netherlands
^b Department of Cardiothoracic Surgery, German Heart Center at the Technical University Munich, Munich, Germany

Accepted for publication October 28, 2004.

^_* Address reprint requests to Dr Haas, Wilhelmina Children's Hospital, UMC Utrecht, Department of Pediatric Cardiothoracic Surgery, Room KG 01.319.0, PO Box 85090, 3508 AB Utrecht, The Netherlands (E-mail: f.haas{at}wkz.azu.nl).

	Abstract

Top Abstract Introduction Material and Methods Results Comment References

 
BACKGROUND: The use of allografts or xenografts is the treatment of choice for pulmonary valve replacement. However, the limited durability is responsible for multiple reoperations associated with increased morbidity. In search of a definitive solution, the implantation of a mechanical valved conduit might be an option in highly selected patients. This study evaluated short-term results after pulmonary valve replacement with a mechanical valved conduit.

METHODS: Fourteen patients underwent pulmonary valve replacement with a mechanical valved conduit. All patients had a mean of 3.0 ± 1.2 previous operations. Seven patients were previously operated on for tetralogy of Fallot, 3 patients for pulmonary atresia, 3 patients for common arterial trunk, and 1 patient for subaortic stenosis.

RESULTS: All patients survived the operation and are currently well. At follow-up (11 to 63 months), all but 2 patients showed normal right ventricular function, with a mean gradient of 14 ± 9 mm Hg (range, 4 to 30 mm Hg) across the pulmonary valve. At follow-up, there was no evidence of valve failure or tissue growth within the valve annulus. All patients are receiving anticoagulants to maintain an international normalized ratio of 3.0 to 4.5.

CONCLUSIONS: In highly selected patients, the use of a mechanical valved conduit in the pulmonary position leads to satisfactory results. To avoid a predictable reoperation after multiple right ventricular outflow tract reconstruction, and therefore reoperation-related morbidity, the implantation of a mechanical prosthesis as a lifelong solution requires consideration. Selection criteria for this permanent solution should include older age, multiple previous operations, and patient compliance with anticoagulant therapy.

	Introduction

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This article has been selected for the open discussion forum on the CTSNet Web Site: www.ctsnet.org.discuss

 

For many years, homografts or xenografts have been an important tool in reconstruction of the right ventricular (RV) outflow tract. Despite gradual deterioration of any implant, long-term follow-up data in large collectives have shown good results with regard to complication rate and durability [1, 2]. However, because of progressive degeneration with time, biologic valved conduits do not represent a permanent solution for children and adolescents with complex congenital heart defects. Repeat operations are characterized by specific technical problems, with increased morbidity and mortality in adults and in the pediatric population [3–5]. To avoid a predictable reoperation after RV outflow tract reconstruction with valved biologic conduits, implantation of a mechanical valved conduit as a lifelong solution might be an option in selected cases. We evaluated our short-term results after pulmonary valve replacement with a bileaflet mechanical valved conduit.

	Material and Methods

Top Abstract Introduction Material and Methods Results Comment References

 
From November 1998 to November 2003, a mechanical pulmonary valve replacement with a bileaflet valved conduit (St. Jude Medical, St. Paul, MN), was performed in 14 patients at the German Heart Center Munich. All patients have had previous reconstruction of the RV outflow tract, consisting of allograft or xenograft implantation in 11 patients and a transannular patch in 3. The underlying diagnoses of these 14 patients were tetralogy of Fallot in 7, pulmonary atresia with ventricular septal defect in 3, common arterial trunk in 3, and severe subaortic stenosis with subsequent Ross procedure in 1 patient. Four patients suffered from pulmonary hypertension before mechanical pulmonary valve replacement. Twelve patients showed decreased RV function, and 4 patients had reduced left ventricular function in cineangiography. Furthermore, 3 patients presented with severe tricuspid regurgitation, and additional severe aortic regurgitation was seen in 3 patients. Hemodynamic characteristics and preoperative and operative data are shown in Table 1. Mean age at operation was 24.8 ± 9.2 years (range, 10 to 38 years). All patients had a mean of 3.0 ± 1.2 previous operations by means of a median sternotomy (range, 2 to 5). Indications for operation were classified as, first, symptomatic patients with right heart failure and moderate to severe pulmonary valve dysfunction (n = 6); second, asymptomatic patients with moderate to severe pulmonary valve dysfunction and evidence of significant RV dysfunction by cineangiography (n = 4); and third, patients undergoing reoperation mainly for associated lesions such as tricuspid valve incompetence or aortic valve regurgitation in the presence of significant pulmonary valve dysfunction (n = 4). In patients who had previously undergone RV–pulmonary artery conduit placement, conduit exchange was indicated when the pressure gradient between the RV and the pulmonary artery exceeded 50 mm Hg, or when the RV exhibited signs of volume overload [6]. Selection criteria for prosthetic valve replacement were based on (1) older age, to avoid outgrowth of the prosthesis; (2) multiple previous operations with an increased reoperation-related morbidity; (3) current use of anticoagulants; and (4) patient compliance with anticoagulant therapy.

View larger version (11K): [in this window] [in a new window]   Fig 1. Preparation of the bileaflet valved conduit. The distal part of the conduit was cut just above the valve level and was then sutured to the prosthetic ring, proximally (arrow). This "new" proximal part was cut obliquely, thus creating a "roof" to cover the ventriculotomy.

View larger version (15K): [in this window] [in a new window]   Fig 2. Ideal positioning of the valved conduit. The prosthesis was always attempted to be placed in a 90-degree position relative to the ventricular septum.

	Results

Top Abstract Introduction Material and Methods Results Comment References

 
All patients survived the operation and were discharged in an improved clinical condition. Three patients had to be reoperated on for postoperative bleeding within the first 5 days, and 1 patient underwent thoracotomy for revision of a transatrial pacemaker lead after 22 days. The postoperative course in the remaining patients was uneventful. They are receiving anticoagulants (warfarin sodium, acenocoumarol) to maintain an international normalized ratio (INR) of 3.0 to 4.5. Self-management is performed in 8 patients. During follow-up, 3 patients were readmitted to the hospital because of atrial tachycardia, suspected endocarditis, and epistaxis in 1 patient each. No patient showed signs of thromboembolism or suffered from hemolytic anemia. The cardiac-to-thoracic ratio did not change significantly during follow-up. Echocardiography demonstrated normal RV function in all but 2 patients. Both patients had presented with severely depressed RV function preoperatively, and although a marked clinical improvement was obvious, complete recovery of RV function was not achieved. At follow-up, 7 patients were asymptomatic, 5 patients were categorized to New York Heart Association functional class II, and only 1 patient to class III. Although 10 patients reported a marked physical improvement, 2 patients reported minor improvement, and only 1 patient could not detect any subjective change. Doppler flow studies demonstrated only mild pressure gradients across the bileaflet mechanical conduit, with a mean of 14 ± 9 mm Hg (range, 4 to 30 mm Hg). There was no evidence of valve failure, or neointimal growth within the valve annulus or the conduit itself.

	Comment

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The increasing population of grown-up congenital heart patients with multiple previous operations has stimulated us to provide a more definitive surgical repair. This retrospective analysis of our experience with a mechanical valved conduit in the pulmonary position confirms that this procedure can be considered as a safe alternative to the well-established allograft or xenograft implantation. Implantation of a mechanical valved conduit comprises only approximately 3% from a total of more than 400 allograft or xenograft implantations at our institution [1]. This small percentage emphasizes the highly selected nature of this particular group of patients.

Although early mortality for isolated RV–pulmonary artery conduit replacement decreased during recent years [7], severe cardiac laceration and air embolism were recently reported in 5.2% of patients, who had undergone one to three reoperations [5]. Unpublished data from our institution have shown an incidence of 9.7% for severe cardiac or pulmonary laceration in patients operated on from four to nine times, although careful surgical technique and judicious use of elective femorofemoral bypass had been used. The reduction of the potential risk at reoperation, and an improved quality of life associated with a more definitive surgical repair, give reasons for the consideration of a mechanical valved conduit in the pulmonary position.

In this study, pulmonary valve replacement was performed successfully without any early and late mortality. Most patients reported a marked physical improvement at last follow-up, and RV function had improved to normal on echocardiography in all but 2 patients. The high proportion of patients exhibiting a normal RV function on postoperative echocardiography can be explained by the fact that pulmonary valve replacement had been performed before severe RV dysfunction developed, thus maintaining adequate RV contractility postoperatively. A competent prosthetic valve, with a low pressure gradient, without progressive deterioration, as reported for homografts or xenografts [1, 2], may additionally account for a maintained normal RV function. The incomplete improvement of New York Heart Association functional class during follow-up in 6 of our patients is at least partially caused by additional comorbidity, such as severe atrioventricular valve insufficiency, aortic valve insufficiency, impaired left ventricular function, or the occurrence of pulmonary hypertension.

Four main criteria were used in the decision-making process for a mechanical valved conduit. First, older age to avoid outgrowth of the prosthesis; second, multiple previous operations with an increased reoperation-related morbidity; third, current use of anticoagulants; and fourth, patient compliance with anticoagulant therapy.

Older age represented one criterion, although, a mechanical valved conduit was also implanted in 2 patients aged 10 and 12 years. The high number of previous operations in one and a chest deformity with a suspected high risk of reoperation in the other resulted in the choice for a mechanical prosthesis, although somatic growth has not yet been completed. Whether these patients eventually develop a patient-prosthesis mismatch later in life has to be determined. The criterion of multiple reoperations alone is probably not sufficient for the selection process in some patients. Those patients who underwent only two previous operations were either currently treated with anticoagulants owing to a mechanical valve in the aortic position or they had to undergo mechanical valve replacement as an additional procedure. Specific anatomic conditions such as chest deformities, occlusion of the femoral vessels, or the extensive attachment of the heart or the great vessels to the sternum contributed to the decision for the use of a mechanical valve in the pulmonary position. Women of childbearing age for whom anticoagulants would create difficulty and noncompliant patients should be excluded.

Up to now, the placement of a mechanical valve in the pulmonary position has not gained widespread acceptance. This is mainly the result of anecdotal reports of severe thromboembolic complications and severe bleeding complications [8–12], which date back to the late 1980s. However, at that time both mechanical valve types and, more importantly, anticoagulation regimen were different or were not even applied [8, 10, 13]. Although a mechanical valve in the pulmonary position may occasionally function long-term without anticoagulation [14], the reported high incidence of valve thrombosis without anticoagulation underlines the need for adequate anticoagulation. Well-known criteria for anticoagulation for all mechanical valves in all other positions than the pulmonary one exist [15]. Although to date no evidenced-based recommendations on the therapeutic range of INR are provided, we currently favor an INR of 3.0 to 4.5. One theory for the need of a more aggressive anticoagulation regimen in right-sided mechanical valve replacement is the low-pressure and relatively slow-flow situation. This justifies a high level of anticoagulation. Additionally, all patients of the present study had intracardiac conditions that favor thrombus formation, ie, enlargement of the right or left atrium, atrial fibrillation, impaired left ventricular or RV function, and congestive heart failure, which exclude a lower intensity target. With our regimen, only 1 patient experienced epistaxis during follow-up. A recently performed randomized study has also shown that the rate of major bleeding is not statistically different between a targeted INR of 2.0 to 3.0 and a targeted INR of 3.0 to 4.5 [16]. In our opinion, patients are not at higher risk for major bleeding with the INR kept within this target range. Systematic patient education and monitoring as well as self-management of anticoagulation therapy reduces the variation in the INR, thereby leading to a possibly lower frequency of bleeding complications and thromboembolism.

In the present study, 3 of 14 patients underwent reoperations within the first 5 days for postoperative bleeding. This high incidence is likely to be caused by the well-known association between length of operation, multiple reoperations, and postoperative bleeding complications. The mean operative time was 364 ± 101 minutes, and the patients underwent a mean of 3.0 ± 1.2 previous operations. Owing to the fact that anticoagulation with warfarin or acenocoumarol was started after the patient's chest tubes were removed, the possible association between oral anticoagulation treatment and postoperative bleeding can be ruled out.

Recently, it has been reported that tilting-disc valves in the pulmonary position may perform better than bileaflet valves [17]. This has led these authors to hypothesize about the possible advantages of structural features of monodisc valves. However, an attempt to categorize prostheses by design seems inappropriate [18]. Reviewing the current literature, the reported thromboses of bileaflet valves were frequently accompanied with an insufficient anticoagulation regimen, rather than owing to any clinical or structural drawback [8, 10, 13].

Still, anticoagulation carries a risk for thromboembolic events, which is reported to be approximately 3% to 4% in adults and children [19, 20]. However, because of the high lytic activity of the lung, minor thromboembolism may not cause clinical significance. All these anticoagulation-related drawbacks should be taken into account when considering a more definitive solution in patients with multiple inevitable reoperations.

Study Limitations
This study comprises a highly selected small series of patients with heterogeneous causes, in whom a mechanical valved conduit was placed in the pulmonary position. Although the patient cohort is small and reliable statistics cannot be drawn, it is the largest series ever published. With the increasing population of grown-up congenital heart patients who have often had previous operations by means of a median sternotomy, the option of a mechanical valved conduit in the pulmonary position may gain greater importance in the future.

This study shows the applicability of mechanical prosthesis with encouraging results. Whether or not lifelong anticoagulation carries a lower risk than the surgical morbidity and mortality of multiple allograft and xenograft replacements will only be determined by long-term follow-up. However, the reduction of the potential risk of further reoperations and improvement of cost effectiveness may justify the consideration of a mechanical prosthesis in highly selected patients.

Conclusions
To avoid a predictable reoperation after RV outflow tract reconstruction with allografts or xenografts, and therefore reoperation-related morbidity, the implantation of a mechanical valved conduit as a possible lifelong solution might be an option in selected patients. Although this retrospective analysis comprises only a small number of patients, the results are encouraging. At our institution, selection criteria for a mechanical valved conduit in the pulmonary position are based on, first, older age, to avoid outgrowth of the prosthesis; second, multiple previous operations with an increased reoperation-related morbidity; third, current use of anticoagulants; and fourth, patient compliance with anticoagulant therapy.

	References

Top Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Full Text (PDF) Online Discussion Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Felix Haas Christian Schreiber Martin Kostolny Klaus Holper Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Haas, F. Articles by Lange, R. Search for Related Content PubMed PubMed Citation Articles by Haas, F. Articles by Lange, R. Related Collections Congenital - acyanotic