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Ann Thorac Surg 2002;74:684-688
© 2002 The Society of Thoracic Surgeons

Original article: cardiovascular

Stentless xenografts and homografts for right ventricular outflow tract reconstruction during the ross operation

Franz X. Schmid, MD*a, Andreas Keyser, MDa, Christoph Wiesenack, MDb, Stefan Holmer, MDc, Dietrich E. Birnbaum, MDa

a Department of department of Cardiothoracic and Vascular Surgery, University Hospital of Regensburg, Regensburg, Germany
b Department of Anesthesiology, University Hospital of Regensburg, Regensburg, Germany
c Department of Cardiology, University Hospital of Regensburg, Regensburg, Germany

Accepted for publication May 9, 2002.

* Address reprint requests to Dr Schmid, Department of Cardiothoracic and Vascular Surgery, University of Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany
e-mail: franz-xaver.schmid{at}klinik.uni.regensburg.de


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
Background. Shortage of homografts prompted us to replace the transplanted pulmonary trunk with stentless xenografts during the Ross procedure. The 5-year follow-up in comparison with pulmonary homografts is presented.

Methods. From April 1997 to March 2002, of 51 patients undergoing a modified Ross procedure 15 patients (age range 55 to 65 years, mean 59 ± 5) received a stentless xenograft, and 36 patients (15 to 56 years, mean 36 ± 11) a pulmonary homograft for right ventricular outflow tract (RVOT) reconstruction. Follow-up was complete for a mean of 3.1 years (range 6 to 60). Regularily performed echocardiography included determination of valve annulus, peak instantaneous gradient, leaflet performance, location of obstruction, and degree of regurgitation.

Results. There was 1 late death and 1 reoperation for homograft stenosis. The homograft annulus diameter decreased by a mean of 10% (range 3 to 10 mm; p < 0.01), and peak Doppler gradient increased significantly (p < 0.001). All patients except 1 had gradients less than 25 mm Hg. Gradients in xenograft patients were stable at a low level (6.5 ± 4.3 mm Hg to 8.8 ± 7.4 mm Hg at the latest follow-up). Mild pulmonary regurgitation was noted in 46.6% (xenografts) and 19.5% (homografts). Leaflet quality and mobility were maintained in all patients.

Conclusions. Pulmonary homografts underlie a process of annular reduction after the Ross procedure, which is usually not associated with graft stenosis. Mild pulmonary regurgitation is more common in xenografts than in homografts. RVOT reconstruction using stentless xenografts represents a satisfactory treatment modality for aged patients.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
From the very beginning the Ross operation includes inevitably the need for a satisfactory replacement of the transplanted pulmonary valve and artery [1]. In the majority of series pulmonary homografts are used exclusively. Their superior performance on the right side in comparison with aortic homografts in the long run has previously been documented [2]. Autograft aortic root replacement was introduced in 1986 and has gained increasing popularity especially in recent years [3–5]. Consequently, we have to foresee an increasing demand and in view of limited availability a growing shortage of pulmonary homograft conduits in the future. Porcine aortic root bioprosthetic conduits have recently been used with good early and midterm results in adults in the aortic position [6, 7].

Encouraged by promising midterm results for stentless aortic valves, especially in the elderly [8, 9], and prompted by lack of readily available homografts we have used stentless aortic porcine root cylinders as right ventricle-pulmonary artery (RV-PA) conduits for reconstruction of the right ventricular outflow tract during the Ross operation. This retrospective study reports and analyzes the early and midterm hemodynamic results in comparison with pulmonary homografts as obtained at our instituition.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patients
Between April 1997 and March 2002, 55 consecutive patients underwent a modified Ross procedure at our institution. The study group comprised 51 patients who had follow-up of at least 6 months after surgery. Demographics of the study patients are shown in Table 1. Mean peak systolic gradient across the RVOT and mean peak systolic right ventricular pressure were within normal range for all patients. The selection of our study groups was taken as a consequence of the patient’s age at which an autograft aortic valve replacement should be performed. Out of these 51 patients, 15 adults, from whom informed consent was obtained, underwent RVOT reconstruction using the Edwards Prima stentless aortic bioprosthesis (Model 2500P; Edwards Lifesciences S.A., Irvine, CA). There were 10 male patients and 5 female patients with a mean age of 59.6 ± 5.2 years (range 55 to 65). During the same period 36 patients (male:female ratio, 25:11) ranging in age from 15 to 56 years (mean 36.3 ± 11.7), received cryopreserved pulmonary conduits for reestablishment of RV-PA continuity. All homografts were supplied by EHB (European Homograft Bank, Brussels, Belgium). For each patient a pulmonary homograft or xenograft conduit was selected based on preoperative magnetic resonance imaging or echocardiographic estimation of the native pulmonary annulus.


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  		Table 1. Preoperative and Intraoperative Patient Data

 
The Ross operation was performed as an elective procedure in 48 patients (94%) and as an urgent procedure in 3 (6%). These included 2 patients with acute bacterial endocarditis. Xenografts were not used in this situation.

Operative technique
Under general anesthesia cardiopulmonary bypass was instituted through a medial sternal approach. Myocardial preservation was by crystalloid cardioplegia. The pulmonary autograft was always inserted into the aortic annulus by a free standing root replacement technique.

Before insertion of the stentless bioprosthesis its aortic coronary orifices were oversewn with 4-0 polypropylene suture. After complete removal of the native autograft annular ridge the Dacron (C. R. Bard, Haverhill, PA) reinforced inflow annulus of the root cylinder was anastomosed directly to the right ventricle so that the conduit would lie without kinking and that the valve component was placed as distal as possible to avoid compression once the sternum was closed. A hood covering the RV-xenograft continuity was not necessary. The outflow suture line was performed with a running technique with double-armed 4-0 polypropylene suture. Finally the xenograft was trimmed distally to be anastomosed to the host pulmonary artery confluence using also a 4-0 polypropylene running suture. The technique for implanting a conduit in the RVOT was the same for both groups.

The size of the xenograft valve implanted ranged from 25 to 29 mm, with a mean size of 27.4 ± 0.3 mm. With a mean valve size of 27.2 ± 1.7 mm (range 25 to 30 mm) for the homografts inserted, there was no difference in conduit diameter between groups.

Echocardiography
Transthoracic echocardiography was performed preoperatively, at the time of discharge from the hospital (within 2 weeks of operation), then between 3 to 6 months, at 12 months after operation, and yearly thereafter. Transthoracic M-mode, two-dimensional, color-flow, and Doppler echocardiogramms were obtained in all patients by the same experienced echocardiographers.

Each patient had complete review of at least three echocardiograms. Particular care was taken to obtain paired measurements for homograft/xenograft valve annulus during diastole, right ventricular cavity size relative to size, location of obstruction if present, and quality and mobility of homograft/xenograft leaflets. The modified Bernoulli equation was used to calculate peak and mean gradients. Degree of pulmonary regurgitation was graded as normal, mild (regurgitative jet and normal RV cavity size), and moderate (regurgitation and RV cavity enlargement).

Statistical methods
Results were expressed as mean ± standard deviation. Where appropriate, comparative analysis was performed using a paired t test or a Mann-Whitney U test. Statistical significance was considered at p less or equal to 0.05.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
Patient survival
There were no early deaths and 1 late death for an overall mortality of 1.8%. Six weeks after a successful autograft/xenograft procedure a 65-year-old man experienced hypovolemic shock and could not be resuscitated. Postmortem examination proved splenic rupture of unknown cause and must be considered as nonconduit related.

Additional morbidity included reexploration for bleeding in 1 homograft patient (1.9%) and pericardial effusion requiring drainage in another xenograft patient (1.9%).

Reoperation
One patient required reoperation for significant homograft stenosis when a pulsed Doppler gradient of 64 mm Hg had developed. Intervention by balloon dilatation proved unsuccessful and a stentless xenograft was inserted at 19 months after the primary operation to replace the stenosed homograft. At reoperation the leaflets were noted to be quite mobile although obstruction was associated with wall calcification and contraction. Freedom from actuarial reoperation is 93% for homografts and 100% for xenografts, respectively (p = not significant).

Autograft valve function
At a median follow-up of 3.1 years for both groups (range 6 months to 4.9 years), the most recent echocardiogram revealed no/trivial aortic insufficiency (AI) in 26 patients (72%), mild AI in 9 patients (25%), and moderate AI in 1 patient (3%) for the homograft group; and no/trivial AI in 13 patients (87%), and mild AI in 2 patients (13%) for the xenograft group, respectively. The majority of patients (96%) are in excellent clinical condition (New York Heart Association class I and II).

Pulmonary homograft and xenograft status
Compared with early postoperative data, mean homograft annulus size was decreased by 4.2 ± 3.7 mm (range 3 to 10 mm). In terms of percentage change, annulus dimension was decreased by a mean of 10% (range 0% to 30%; p < 0.01). An increase in annulus size was not noted. In xenograft patients changes in neopulmonary annulus diameters did not occur due to a fabric mediated fixed dimension of the proximal sewing ring.

Mean peak Doppler gradients of homografts increased significantly from 9.8 ± 6.7 mm Hg (early postoperatively) to 18.2 ± 7.9 mm Hg (at 6 to 12 months postoperatively), and 18.9 ± 12.3 mm Hg (latest examination; p < 0.001; Fig 1). In total, 32 patients (89%) demonstrated peak Doppler gradients less than 20 mm Hg, 3 (9.3%) developed gradients between 20 and 30 mm Hg, and 1 patient required homograft replacement owing to a rapidly increasing gradient up to 64 mm Hg. During follow-up RVOT gradients in xenograft patients were stable at low, near normal resting levels of 6.5 ± 4.3 mm Hg, 8.6 ± 5.7 mm Hg, and 8.8 ± 7.4 mm Hg, respectively.



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  		Fig 1. Mean peak Doppler gradients across the right ventricular outflow tract (RVOT) during follow-up (fu) for patients receiving pulmonary homografts and stentless xenograft conduits. (Open bars = homografts; hatched bars = xenografts.)

 
Significant pulmonary regurgitation developed more often in xenografts than in homografts (Table 2). Mild or moderate xenograft valvular insufficiency was noted in 8 of 15 patients (53.4%). Both 6 to 12 months postoperatively and at the latest follow-up investigation 20% of patients with xenograft RVOT reconstruction demonstrated valvar insufficiency graded moderate (n = 3). In patients with homografts for RV-PA continuity significant pulmonary regurgitation was noted in 5.6% (2 of 36 patients), but was not classified as more than moderate in any patient. All patients are in good clinical condition and are not scheduled for reoperation. Leaflet integrity and mobility was maintained in all patients in both groups throughout the observational period.


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  		Table 2. Echocardiographic Results at the Latest Follow-Up

 

   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
Valve surgery goes along with the search for an ideal valve substitute and the search is continual and pertinent. The Ross operation is now increasingly accepted a reliable alternative to mechanical, biological, and homograft valves for aortic valve replacement and is considered the valve of choice for young and middle-aged patients at a number of institutions [3, 4, 5, 10]. This study confirms that excellent midterm functional results can be achieved. 97% of our patients had no or mild autograft regurgitation and physiologic gradients at a median follow-up of 3.1 years (Fig 2). If autograft valve failure occurs, it usually occurs early due to technical problems [4]. The procedure can be performed even in high risk and older patients with a low overall mortality (1.8%).



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  		Fig 2. Percentage of neopulmonary regurgitation (homografts versus stentless xenografts) during follow-up (fu).

 
In addition to remaining concern about the long-term durability of the autograft root there is residual anxiety on the right ventricular side. The functional performance of the RV-pulmonary artery conduit may predict late morbidity and the need for reoperation. Homograft valves are subject to calcification and structural degeneration in the long term. Raanani and associates [11] have identified younger donor age, smaller homograft size, and shorter duration of cryopreservation as independent risk factors for late homograft stenosis. The pathophysiologic mechanism of homograft failure is not well understood and has been described as immunologic phenomena. Variable occurrence of viable donor cells has been reported even in cryopreserved homografts [12, 13]. Most of our patients demonstrated a significant decrease of the homograft diameter. Unlike the study of Meliones and colleagues [14], who described gradients at the valve level and echocardiographic investigations by Matsuki and colleagues [10], who identified the distal anatomosis as the site of gradients, we realized relative narrowing and wall thickening in the whole length of the homograft. Consistent with findings of others [11, 15] reduction of the homograft diameter was not associated with the development of significant obstruction or any clinical problem. As the reason for development of early stenosis is considered immunologic we would not recommend and do not practice replacement by a second homograft in the situation of significant homograft stenosis.

A number of alternative options for right ventricular outflow tract reconstruction have been considered, namely cryopreserved and fresh aortic and pulmonary homografts, conduits of the patient’s own living pericardium or fascia lata, and xenograft valves inserted within a Dacron conduit. Nowadays, it is out of discussion that pulmonary homografts provide the best proven long-term performance [16]. We continue to use pulmonary homografts as extracardiac conduits when available.

Our rationale for studying stentless xenografts for reconstruction of the right ventricular outflow tract during autograft aortic valve replacement came about because of shortage of suitable pulmonary homografts. Their improved hemodynamic profile in comparison to stented valves gives rise to expect subsequent superior structural durability. The Prima stentless aortic bioprosthesis offers the advantages of excellent hemodynamic characteristics, lack of postoperative anticoagulation, and a low rate of thrombosis and thromboembolic events. Its low pressure fixation of both the root and leaflets are thought to produce both strength and flexibility of tissues while maintaining the natural valve geometry and sinus configuration [17]. Nevertheless its potential to delay calcification and early structural valve degeneration has still to be proven. In our study as long as 5 years after implantation, the prosthesis has proved to be dependable and has provided satisfactory freedom from valve-related complications. This finding is in line with a number of analyses of intermediate and long-term outcomes after aortic valve replacement using stentless xenograft valves. Long-term observations suggest that the rate of primary tissue failure may be at least equivalent to stented xenografts [8, 9]. The attrition rate of stented valves increases 10 years after implant but similar or even superior results can be anticipated for stentless xenografts placed in the right side of the heart when exposed to significantly decreased hemodynamic strain and stress. Indeed, follow-up in our patients is too limited to conclude on durability of the stentless xenograft conduits compared with alternative options for RVOT reconstruction.

Significant xenograft valve regurgitation has been recorded in the present study. Interestingly, functional valve deterioration was not due to structural leaflet failure. Leaflets seen at echocardiography showed no sign of thickening or shrinkage and demonstrated normal leaflet motion. The stentless conduit is more compressible than a stented prosthesis whereas homografts are more pliable than xenografts. The impact of complete closure of the pericardium, as it is a routine procedure in our practice, and sternal compression on conduit performance in the RVOT remain unanswered questions. Overall, structural deterioration appears to be a rare event in our series because 97.2% of the homograft valves and 100% of the xenografts were free from structural failure at 5 years.

Limitations of the study
The major limitation of the study is that patients were not randomized to receive a different type of valve prosthesis. Patients receiving homografts were younger than those in the study group with xenografts and might not have been an accurate basis for comparison, although selection criteria were very strict and most of the clinical variables were not different between the population groups. Finally, the relative small group of patients considered indicates a low statistical power but the accuracy of follow-up has prevented us from concluding a larger study in a relatively short period of time. The information obtained from the study may be sufficient to initiate a large randomized trial comparing different valve substitutes.

Conclusions
Right ventricular outflow tract reconstruction during the Ross operation with stentless xenografts is a satisfactory treatment modality for aged patients in that it offers excellent hemodynamic performance, freedom from valve deterioration, and anticoagulant therapy. Moreover, it added to uniform improvement in functional status. It follows that stentless xenograft conduits are as effective as pulmonary homografts in this situation. Although a longer follow-up is required the data reported here suggest that patients older than 55 years may have stentless xenograft implants in the RVOT with a low rate of clinical complications and a favorable prospect of long-term performance.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Ross D.N. Replacement of aortic and pulmonary valves with a pulmonary autograft. Lancet 1967;2:956-958.[Medline]
  2. Bando K., Danielson G.K., Schaff H.W., et al. Outcome of aortic and pulmonary homografts for right ventricular reconstruction. J Thorac Cardiovasc Surg 1995;109:509-517.[Abstract/Free Full Text]
  3. Elkins R.C. The Ross operation: a 12-year experience. Ann Thorac Surg 1999;68:S14-S18.
  4. Oury J.H., Hiro S.P., Maxwell M., et al. The Ross procedure: current registry results. Ann Thorac Surg 1998;66:S162-S165.
  5. Stelzer P., Weinrauch S., Tranbaugh R.F., et al. Ten years of experience with the modified Ross procedure. J Thorac Cardiovasc Surg 1998;115:1091-1100.[Abstract/Free Full Text]
  6. Dosche K., Vanermen H. Experience with the Edwards Prima stentless aortic bioprosthesis: a 2-year review. J Heart Valve Dis 1995;4(Suppl 1):85-89.
  7. Doty D.B., Cafferty A., Cartier P., et al. Aortic valve replacement with Medtronic freestyle bioprosthesis: a 5-year result. Semin Thorac Cardiovasc Surg 1999;11(Suppl 1):35-41.[Medline]
  8. Westaby S., Huysmans H.A., David T.E. Stentless aortic bioprosthesis: compelling data from the second international symposium. Ann Thorac Surg 1998;65:235-240.[Abstract/Free Full Text]
  9. David T.E., Feindel C.M., Scully H.E., Bos J., Rakowski H. Aortic valve replacement with stentless porcine aortic valves: a ten-year experience. J Heart Valve Dis 1998;7:250-254.[Medline]
  10. Matsuki O., Okita Y., Almeida R.S., et al. Two decades experience with aortic valve replacement with the pulmonary autograft. J Thorac Cardiovasc Surg 1988;95:705-711.[Abstract]
  11. Raanani E., Yau T.M., David T.E., et al. Risk factors for late pulmonary homograft stenosis after the Ross procedure. Ann Thorac Surg 2000;70:1953-1957.[Abstract/Free Full Text]
  12. Lang S.J., Giordano M.S., Cardon-Cardo C., Summers B.D., Staiano-Coico L., Hajjar D.P. Biochemical and cellular characterization of cardiac valve tissue after cryopreservation or antibiotic preservation. J Thorac Cardiovasc Surg 1994;108:63-67.[Abstract/Free Full Text]
  13. Kadner A., Chen R.H., Mitchell R.N., Adams D.H. Homograft crossmatching is unnecessary due to the absence of blood group antigens. Ann Thorac Surg 2001;71:S349-S352.[Abstract/Free Full Text]
  14. Meliones J.N., Snider A.R., Bove E.L., et al. Doppler evaluation of homograft valved conduits in children. Am J Cardiol 1989;64:354-358.[Medline]
  15. Al Halees Z. Right ventricle to pulmonary artery connection after the Ross procedure: is it really a concern?. Ann Thorac Surg 2002;73:343-344.[Free Full Text]
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  17. Sabbah H.N., Hamid M.S., Stein P.D. Estimation of mechanical stresses on closed cusps of porcine bioprosthetic valves: effects of stiffening, calcium and focal thinning. Am J Cardiol 1985;55:1091-1096.[Medline]



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