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Ann Thorac Surg 2001;71:S365-S367
© 2001 The Society of Thoracic Surgeons

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Autografts, allografts, and biological valves in children

Performance of allografts and xenografts for right ventricular outflow tract reconstruction

^a Department of Cardio-thoracic Surgery, German Heart Center at the Technical University, Munich, Germany

Address reprint requests to Dr Lange, Deutsches Herzzentrum München, Lazarettstr 36, 80636 München, Germany
e-mail: lange{at}dhm.mhn.de

Presented at the VIII International Symposium on Cardiac Bioprostheses, Cancun, Mexico, Nov 3–5, 2000.

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. We compared the long-term durability of allografts and xenografts implanted for reconstruction of the right ventricular outflow tract.

Methods. A total of 401 patients were studied from January 1974 to June 2000 (145 xeno- and 256 allografts), follow-up being 98% complete. We analyzed freedom from reoperation and allograft specific factors that may indicate degeneration.

Results. The age at implantation was 2 days to 31 years (median 4.0 years). Conduit exchange rate was similar (p = 0.2) for conduit diameters less than 15 mm (41% ± 9% for allografts, 30% ± 6% for xenografts), but significantly different (p = 0.02) for diameters of 15 mm or larger (60% ± 8% for allografts, 30% ± 10% for xenografts). Diagnosis-related 20-year survival analysis showed a significantly (p = 0.01) better survival of patients with tetralogy of Fallot/pulmonary atresia (83% ± 5%) and Rastelli-type surgery (81% ± 8%) compared with patients with truncus arteriosus communis (69% ± 8%). ABO-compatibility, preservation method, and aortic or pulmonary allograft could not be identified as risk factors for allograft longevity.

Conclusions. For smaller diameters (less than 15 mm), allografts exhibit no advantage over xenografts, whereas in larger diameters (15 mm or larger) allografts are the conduit of choice for the right ventricular outflow tract.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Allograft valves have been implanted in humans for nearly four decades, since their first implantation by Donald Ross [1] and Barrat-Boyes [2] in 1962. A few years later glutaraldehyde-preserved xenograft porcine valves in a woven Dacron tube also became available [3]. At our institution, antibiotic preservation of allografts was introduced in 1974 and cryopreservation made allograft banking available since 1991. In this retrospective study we compared the long-term performance of allografts and xenografts. For the allografts we specifically addressed the influence of donor graft origin (aortic versus pulmonary), blood group compatibility, antibiotic versus cryopreserved storage, and valve diameter at initial implantation on long-term conduit performance.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Only patients with right ventricular outflow tract (RVOT) reconstruction and surviving more than 90 days were included. Thus a total of 401 patients with pulmonary atresia (PA, n = 133), tetralogy of Fallot (TOF) with pulmonary valve insufficiency (n = 83) or tetralogy of Fallot (TOF) with atresia (n = 13), or truncus arteriosus communis (n = 105), or patients who had undergone Rastelli-type surgery (double-outlet right ventricle with pulmonary stenosis, n = 21; or transposition of the great arteries with pulmonary stenosis, n = 46) were studied.

These patients received as their first valved conduit 145 porcine xenografts and 256 allografts. The follow-up was complete in 98% (2,593 patient years). The age of the patients at the time of the first valved conduit implantation ranged from 2 days to 31 years (median 4.0 years); 29% (n = 119) of the patients were less than 1 year of age at initial conduit implantation.

We analyzed freedom from reoperation after xeno- or allograft implantation for two groups, with graft diameters less than 15 mm and 15 mm or more, respectively. Furthermore, the following intrinsic factors that may influence longevity of allografts were studied: preservation techniques (antibiotic versus cryopreserved), origin of the allograft (pulmonary versus aortic), and blood group compatibility.

Operations were performed using standard techniques. The right ventricle was opened by a vertical incision, thereby exposing a ventricular septal defect if necessary. In cases of interpositioning, an allograft conduit optimal valve function was achieved by performing a proximal patch-roof, which extends the gap for closure. The patch material was Gore-Tex (W. L. Gore and Associates, Flagstaff, AZ) or double velour-woven Dacron. Using an aortic allograft, an attempt was made to form the roof with the dissected rest of the anterior mitral leaflet. In cases of interpositioning a xenograft conduit (Hancock, Medtronic, Minneapolis, MN) at the ventricular end of the Dacron tube was cut obliquely and a Dacron roof was formed, covering the ventriculotomy.

Aortic and pulmonary valve allografts were procured from healthy donors within 48 hours after death. One hundred ninety-eight allografts were antibiotically preserved. Since January 1991, a new cryopreservation procedure was used for standardized uniform cooling [4]. Conduit exchange was indicated when the pressure gradient between the right ventricle and the pulmonary artery exceeded 50 mm Hg or when the right ventricle exhibited signs of volume overload [5, 6].

All data related to survival and reoperation for valve dysfunction were analyzed by the method of Kaplan and Meier, differences were evaluated with the log-rank test. Patients at risk are the number of patients who are exposed at any particular time. A multivariate Cox regression analysis was conducted to evaluate the simultaneous effects of age at initial implantation, initial conduit diameter, and xeno- versus allograft durability.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
There was no significant difference in the distribution of xenografts and allografts (p = 0.72) for different diagnosis. At first implantation the median diameter for xenografts was 14 mm (range 8 to 27 mm) and for allografts 19 mm (range 8 to 30 mm). Xenograft patients were slightly younger (mean age 5.8 years, SEM 0.5, range 1 day to 27.3 years; for allografts: mean age 6.7 years, SEM 0.4, range 2 days to 31.3 years).

Graft-related patient survival probability at 20 years (Fig 1) was 82.0% ± 4.0% after allograft implantation and 77.0% ± 5.0% after xenograft implantation (p = 0.85). Diagnosis related survival was significantly different (p = 0.01) for PA/TOF patients (83.0% ± 5.0%) and patients with Rastelli-type surgery (81.0% ± 8.0%) as compared with truncus arteriosus communis patients (69.0% ± 8.0%).

View larger version (18K): [in this window] [in a new window]   Fig 1. Kaplan–Meier function for overall survival (p = 0.85). Allograft (- - - -) versus xenograft (——). Numbers in brackets (top = allograft, bottom = xenograft patients) indicate patients at risk at the beginning and after 5, 10, 15, and 20 years of observation.

For conduits less than 15 mm (Fig 2A) the median freedom from conduit replacement was not significantly different (p = 0.20) for allografts 8.5 (95% confidence interval [CI] 6.7, 10.2) years compared with xenografts 6.6 (95% CI 5.7, 7.5) years. Ten years after implantation, the probability for conduit exchange was 41% ± 9% for allografts and 30% ± 6% for xenograft conduits.

View larger version (42K): [in this window] [in a new window]   Fig 2. (A) Freedom from valved conduit replacement with implanted diameters less than 15 mm (p = 0.20). Allograft (- - - -) versus xenograft (——). Numbers in brackets (top = allograft, bottom = xenograft patients) indicate patients at risk at the beginning and after 5, 10, and 15 years of observation. (B) Freedom from valved biological conduit replacement with implanted diameters of 15 mm or larger (p = 0.02).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
In the present study, the primary aim was to identify determinants of allograft and xenograft conduit deterioration. As end points for conduit failure, either conduit replacement for any reason or death of the patient with that conduit in place was determined. Early postoperative conduit failure rarely accounts for significant morbidity or mortality [7], therefore only data from conduits still in place 90 days after their first insertion were included for this study.

In our patient population there was no difference in overall patient survival probability (Fig 1) regardless of the use of an allo- or xenograft conduit as the initial graft. Analyzing diagnosis-related survival, significantly better survival was seen for the TOF/PA and Rastelli-type surgery group as compared with the truncus arteriosus communis group [8]. However, survival was independent of the choice of conduit, such as allo- or xenograft.

Analyzing the data for patients with graft diameters less than 15 mm (Fig 2A) and 15 mm or larger (Fig 2B), the shortest reoperation-free interval was observed in patients who were corrected as infants with conduits smaller than 15 mm. After correction, these children outgrow the implanted conduit, before degeneration occurs [4, 5]. Therefore, for the age group of less than 1 year, it seems to be justified to implant xenografts, especially when small allograft conduits are not available. Some authors [9] even advocate the use of xenografts for small diameters, because they suggest that the prosthetic material facilitates later conduit changes. In contrast, for large conduits the advantage in using allografts is obvious. Only 28% of allograft conduits compared with 63% of the xenograft conduits had to be replaced at 10 years. This finding is still significant in the multivariate Cox regression analysis (Table 1).

Hence, when the graft diameter is less than 15 mm, replacement will be necessary in nearly all patients for outgrowth even before degeneration occurs, and therefore xenografts may be used alternatively. For diameters of 15 mm or more, allograft conduits perform significantly better as xenografts, whereas allograft-specific limitations had no influence. Despite gradual deterioration, allograft conduits remain an important tool in the reconstruction of the RVOT with an excellent 20-year patient survival record.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

1. Ross D.N. Homograft replacement of the aortic valve. Lancet 1962;II:487.
2. Barratt-Boyes B.G. Homograft aortic valve replacement in aortic incompetence and stenosis. Thorax 1964;19:131-150.
3. Bowman F.O., Hancock W.D., Malm J.R. A valve containing Dacron prothesis. Arch Surg 1973;107:724.[Abstract/Free Full Text]
4. Homann M., Haehnel J.C., Mendler N., et al. Reconstruction of the RVOT with valved biological conduits: 25 years experience with allografts and xenografts. Eur J Cardiothorac Surg 2000;17:624-630.[Abstract/Free Full Text]
5. Weipert J., Meisner H., Mendler N., et al. Allograft implantation in pediatric cardiac surgery: Surgical experience from 1982 to 1994. Ann Thorac Surg 1995;60:S101-S104.
6. Weipert J., Haehnel J.C., Meisner H. Outcome of pulmonary and aortic allografts for reconstruction of the right ventricular outflow tract in congenital cardiac surgery. In: Yankah A.C., Yacoub H., Hetzer R., eds. Cardiac valve allografts. Darmstadt: Steinkopf, 1997:275-280.
7. Stark J., Bull C., Stajevic M., Jothi M., Elliott M., de Leval M. Fate of subpulmonary homograft conduits: determinants of late homograft failure. J Thorac Cardiovasc Surg 1998;115:506-516.[Abstract/Free Full Text]
8. Schreiber C., Eicken A., Balling G., et al. Single center experience on primary correction of common arterial trunk: overall survival and freedom from reoperation after more than 15 years. Eur J Cardiothorac Surg 2000;18:68-73.[Abstract/Free Full Text]
9. Sano S., Karl T.R., Mee R.B.B. Extracardiac valved conduits in the pulmonary circuit. Ann Thorac Surg 1991;52:285-290.[Abstract]
10. Bando K., Danielson G.K., Schaff H.V., Mair D.D., Julsrud P.R., Puga F.J. Outcome of pulmonary and aortic homografts for right ventricular outflow tract reconstruction. J Thorac Cardiovasc Surg 1995;109:509-517.[Abstract/Free Full Text]
11. Clarke D.R., Bishop D.A. Allograft reconstruction of the right ventricular outflow tract: technique and results. In: Yankah A.C., Yacoub M.H., Hetzer R., eds. Cardiac valve allografts. Science and practice. New York: Springer, 1997:263-274.

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