Intermediate follow-up of a composite stentless porcine valved conduit of bovine pericardium in the pulmonary circulation

Beyond Synthetics: Promising Outcomes With the Invengenx® Bovine Pericardial Patch for Ventricular Septal Defect Repair in a Young Pediatric Population

Ventricular septal defects (VSDs) are a prevalent congenital heart anomaly demanding safe and lasting interventions. This paper explores the application of Invengenx® bovine pericardial patch (Tisgenx, Irvine, California), a promising biomaterial, in VSD repair. We present two case studies: a seven-month-old infant and a three-year-old child undergoing VSD closure using autologous and bovine pericardial patches, respectively. Both patients tolerated the procedures well, experiencing no intra-operative complications and demonstrating excellent postoperative recovery. Echocardiography postoperatively showed no complications and improved clinical outcomes. Notably, the pericardial patches exhibited excellent integration and suture retention, highlighting their durability and compatibility with the growing heart. These cases establish the feasibility and effectiveness of the Invengenx® pericardial patch for VSD repair. The favorable outcomes in terms of safety and efficacy support the potential of this biomaterial as a valuable alternative in pediatric cardiac surgery, particularly for complex VSDs or patients with contraindications to synthetic patches. Further research is crucial to unlock the full potential of bovine pericardium as a durable and advantageous option for VSD repair in a broader range of pediatric patients.

Oral Use of Phenytoin to Reduce Calcification in Bovine Pericardium and Porcine Aortic Leaflets Implants in Rats

Introduction:

This study aims to test the effect of phenytoin as an inhibitor of the process of dystrophic calcification in bovine pericardium and porcine leaflets implanted in the subcutaneous tissue of rats.

Methods:

Isolated segments of biomaterials were implanted subcutaneously in young rats. The study groups received 500 mg phenytoin per kilogram of diet per day. After 90 days, samples were collected and quantitative calcification assessment by optical microscopy, radiological studies with mammography, and atomic emission spectrometry were performed.

Results:

Inflammatory reaction was a frequent finding in all groups when analyzed by optical microscopy. The calcium level assessed by atomic absorption spectrophotometry was significantly lower in the study groups using phenytoin compared to the control groups (control bovine pericardium group X=0.254±0.280 µg/mg; study bovine pericardium group X=0.063±0.025 µg/mg; control porcine aortic leaflets group X=0.640±0.226 µg/mg; study porcine aortic leaflets group X=0.056±0.021 µg/mg; P<0.05). Radiologic studies revealed a statistically significant difference between the groups treated with and without phenytoin (not only regarding the bovine pericardium but also the porcine leaflets).

Conclusion:

The results obtained suggest that phenytoin reduces the calcification process of bovine pericardium segments and porcine aortic leaflets in subdermal implants in rats; also, the incidence of calcification in bovine pericardium grafts was similar to that of porcine aortic leaflets.

Right ventricular outflow tract reconstruction with the Labcor® stentless valved pulmonary conduit

OBJECTIVES

The right ventricular outflow tract reconstruction is a common necessity in congenital cardiac surgery. As homograft availability is limited, alternatives need to be evaluated. The Labcor® conduit consists of a porcine tricomposite valve assembled inside a bovine pericardium tube. This study presents intermediate-term results for its utilization for right ventricular outflow tract reconstruction.

METHODS

Labcor conduits were implanted in 53 patients (February 2009-July 2016). We analysed perioperative data, freedom from conduit failure and risk factors for conduit dysfunction.

RESULTS

The most common diagnosis was Tetralogy of Fallot (n = 20, 37.7%). The median age at surgery was 10.0 [interquartile range (IQR) 4.9-14.3] years. Pulmonary artery plasty (n = 37, 69.8%) and augmentation of the right ventricular outflow tract (n = 16, 30.2%) were often part of the procedure. The median conduit size was 21 (range 11-25) mm. There was no in-hospital death. The median follow-up after surgery was 4.6 (IQR 3.4-5.6) years. Fourteen patients (27.5%) developed conduit failure with stenosis being the main cause. Freedom from conduit failure was 98.0% at 2 and 80.5% at 5 years. The median longevity of the conduit was 7.4 years (95% confidence interval 5.1-9.8 years). Younger age and smaller conduit size were related to conduit failure.

CONCLUSIONS

Utilization of the Labcor conduit revealed acceptable intermediate-term results. The conduit appeared to be functioning sufficiently well within the first 5 years in the majority of patients. The higher rate of failure concerning smaller conduits might be associated with somatic outgrowth; however, conduit degeneration as common and long-term outcome still needs to be evaluated.

Small-sized conduits in the right ventricular outflow tract in young children: bicuspidalized homografts are a good alternative to standard conduits

OBJECTIVES

Downsizing a homograft (HG) through bicuspidalization has been used for more than 2 decades to overcome the shortage of small-sized conduits for reconstruction of the right ventricular outflow tract (RVOT) in young children. Our goal was to investigate the durability of bicuspidalized HGs compared with other small HGs.

METHODS

A retrospective analysis of 93 conduits ≤20 mm, implanted over 23 years, was performed. The end-points were survival, structural valve degeneration and conduit replacement. The conduits comprised 40 pulmonary HGs, 12 aortic HGs, 17 bicuspidalized HGs and 24 xenografts.

RESULTS

The median age, mean conduit diameter and z-value at implantation were 1.4 (interquartile range 0.3-3) years, 16.5 ± 2.7 mm and 2.8 ± 1.3, respectively. Valve position was heterotopic in 59 patients and orthotopic in 34 patients. At a mean follow-up period of 7.6 ± 5.9 years, the hospital survival rate was 89%. Freedom from explant at 5 and 10 years was 83 ± 5% and 52 ± 6%, respectively. Freedom from structural valve degeneration was 79 ± 5% at 5 years and 47 ± 6% at 10 years [68 ± 8% for pulmonary HG, 42 ± 16% for bicuspidalized HG, 31 ± 15% for aortic HG and 20 ± 9% for xenografts (log rank P < 0.001)]. Multivariable analysis indicated an increased risk for structural valve degeneration with smaller conduit size (hazard ratio 0.79, 95% confidence interval 0.67-0.94; P < 0.008), extra-anatomic position (hazard ratio 2.71, 95% confidence interval 1.33-5.50; P = 0.006) and the use of xenografts compared with non-downsized pulmonary HGs (hazard ratio 4.90, 95% confidence interval 2.23-10.76; P < 0.001).

CONCLUSIONS

Appropriately sized pulmonary HGs remain the most durable option for a right ventricular outflow tract conduit in young children. However, when a small pulmonary HG is unavailable, bicuspidalization offers a valid alternative, preferable to xenograft conduits, at mid-term follow-up.

Vascularisation for cardiac tissue engineering: the extracellular matrix

Cardiovascular diseases present a major socio-economic burden. One major problem underlying most cardiovascular and congenital heart diseases is the irreversible loss of contractile heart muscle cells, the cardiomyocytes. To reverse damage incurred by myocardial infarction or by surgical correction of cardiac malformations, the loss of cardiac tissue with a thickness of a few millimetres needs to be compensated. A promising approach to this issue is cardiac tissue engineering. In this review we focus on the problem of in vitro vascularisation as implantation of cardiac patches consisting of more than three layers of cardiomyocytes (> 100 μm thick) already results in necrosis. We explain the need for vascularisation and elaborate on the importance to include non-myocytes in order to generate functional vascularised cardiac tissue. We discuss the potential of extracellular matrix molecules in promoting vascularisation and introduce nephronectin as an example of a new promising candidate. Finally, we discuss current biomaterial- based approaches including micropatterning, electrospinning, 3D micro-manufacturing technology and porogens. Collectively, the current literature supports the notion that cardiac tissue engineering is a realistic option for future treatment of paediatric and adult patients with cardiac disease.

In search of a pediatric cardiac surgeon’s ‘Holy Grail’: the ideal pulmonary conduit

The limited lifespan of all currently available conduits leads to repeat operations and interventional procedures in many children. Each reoperation entails considerable risk to life, expenditure and compromised quality of life as the conduit degenerates. The ideal conduit should be available freely, inexpensive, require no anticoagulation, be resistant to infection, free from thromboembolism, have no gradients or regurgitation and have unlimited durability. This review explores various options as surgeons and researchers endeavor to develop the ideal conduit--which will fulfill all of the above-mentioned criteria. Various currently available conduits are analyzed. Special emphasis is given to tissue-engineered valves and percutaneous valve implantations.

Bovine valved jugular vein (Contegra™) to reconstruct the right ventricular outflow tract

The right ventricular outflow tract (RVOT) is the part of the circulation located between the right ventricle and the bifurcation of the pulmonary artery. The most cranial part of the right ventriculum infundibulum, the pulmonary anulus, the valve and finally the main trunk of the pulmonary artery are the most important structures. The RVOT is frequently affected in congenital heart diseases, either isolated, or in combination with other cardiac malformations. Current techniques for surgical correction of anomalies of the RVOT include repair and/or replacement of the pulmonary valve often combined with sub- or supravalvular reconstruction. The use of extracardiac conduits (homografts, stented or stentless xenografts) to re-establish continuity between the pulmonary ventricle and pulmonary artery has been an important advance in repair of complex congenital malformations. The Contegra (Medtronic) conduit was introduced as a xenograft tissue for RVOT reconstruction. This conduit has some advantages over homografts including availability for pediatric and adult patient sizes and proximal and distal cuffs allowing for extended reconstruction. The principal late problem related to extracardiac conduit operations is the inevitable need for one or more conduit replacements due to patient somatic growth or progressive conduit degeneration and calcification leading to stenosis.

Evaluation of a tissue-engineered bovine pericardial patch in paediatric patients with congenital cardiac anomalies: initial experience with the ADAPT-treated CardioCel(R) patch

OBJECTIVES

This study evaluated the safety, efficacy and clinical performance of the tissue-engineered ADAPT® bovine pericardial patch (ABPP) in paediatric patients with a range of congenital cardiac anomalies.

METHODS

In this single-centre, prospective, non-randomized clinical study, paediatric patients underwent surgery for insertion of the ABPP. Primary efficacy measures included early (<30 day) morbidity; incidence of device-related complications; haemodynamic performance derived from echocardiography assessment at 6- and 12-month follow-up and magnetic resonance imaging findings in 10 randomly selected patients at 12 months. Secondary measures included device-handling characteristics; shape and sizing characteristics and perioperative implant complications. The Aristotle complexity scoring system was used to score the complexity level of all surgical procedures. Patients completing the 12-month study were eligible to enter a long-term evaluation study.

RESULTS

Between April 2008 and September 2009, the ABPP was used in 30 paediatric patients. In the 30-day postoperative period, no graft-related morbidity was observed. In total, there were 5 deaths (2 in the 30-day postoperative period and 3 within the first 6 postoperative months). All deaths were deemed due to comorbid non-graft-related events. Echocardiography assessment at 6 and 12 months revealed intact anatomical and haemodynamically stable repairs without any visible calcification of the patch. Magnetic resonance imaging assessment in 10 patients at 12 months revealed no signs of calcification. Fisher's exact test demonstrated that patients undergoing more complex, higher risk surgical repairs (Aristotle complexity score >8) were significantly more likely to die (P = 0.0055, 58% survival compared with 100% survival for less complex surgical repairs). In 19 patients, echocardiographic data were available at 18-36 months with no evidence of device calcification, infection, thromboembolic events or device failure.

CONCLUSIONS

This study demonstrates the safety and efficacy of this engineered bovine pericardial patch as a cardiovascular substitute for surgical repair of both simple and more complex congenital cardiac defects.

Right Ventricular Outflow Tract Reconstruction With Contegra Monocuspid Transannular Patch in Tetralogy of Fallot

BACKGROUND

Pediatric diminutive right ventricular outflow tract (RVOT) reconstruction with homografts or porcine xenografts remains challenging because of limited availability, early degeneration, tissue ingrowth, and child growth. The objective of this study was to assess whether Contegra valved bovine conduit, implanted as monocuspid transannular patch, might be an interesting alternative to overcome these problems.

METHODS

We reconstructed the RVOT of 12 patients with tetralogy of Fallot, by the use of a Contegra conduit, tailored as a monocuspid valved transannular patch. The patients were 4 females and 8 males, with a mean age of 12.8 +/- 15.1 months and a mean weight of 7.2 +/- 1.9 kg. The mean pulmonary artery annulus size was 8.2 +/- 1.6 mm.

RESULTS

The Contegra tissue was suitable for suturing and for reconstruction of even severely hypoplasic RVOT. We did not observe any sign of conduit or valve degeneration during the follow-up of 28.1 +/- 17.1 months. There were no early or late deaths, and no device-related adverse events. A peak transvalvular gradient of 36.5 +/- 4.7 mm Hg was measured by echocardiography in 4 patients postoperatively, and it decreased during the follow-up to 20 +/- 7.6 mm Hg. Pulmonary valve incompetence was grade 3 in 2 patients and grade 4 in 2 patients.

CONCLUSIONS

The Contegra monocuspid transannular patch is widely applicable to RVOT reconstruction with satisfactory midterm results, particularly in patients with small pulmonary annulus. Its main advantage is to reduce the potential risk of supravalvular stenosis due to the narrowing at the distal suture line, as demonstrated when used as conduits, especially in the smaller sizes.

Simultaneous Enlargement of the Pulmonary Annulus and the Pulmonary Cusp with Autologous Pericardium in Right Ventricular Outflow Tract Reconstruction

BACKGROUND

Surgical repair of obstructive lesions of the right ventricular outflow tract (RVOT) commonly creates pulmonary valve incompetence, which continues to stimulate research for the optimal materials and surgical techniques to reconstruct RVOT. In this study, we present the early results with simultaneous enlargement of the pulmonary annulus and the pulmonary cusp with a transannular patch of autologous pericardium in RVOT reconstruction.

PATIENTS AND METHODS

From January 2003 to December 2005, the surgical technique of simultaneous enlargement of the pulmonary annulus and the pulmonary cusp was used in 32 patients who had complex congenital heart anomalies with pulmonary artery hypoplasia. The functional status of the patients was followed up in the cardiologic clinic of our institute. The motion of the newly constructed valve and the degree of pulmonary insufficiency were evaluated by echocardiography before discharge and at 2-6 months, 12 months, and 36 months postoperatively.

RESULTS

Early death occurred in one patient (3.1%). Postoperative complications occurred in six patients but they recovered uneventfully. During the follow-up, 28 of 31 operative survivors were in New York Heart Association functional class I without medication and the other three were in class II. Seventeen patients had no or trivial pulmonary regurgitation; mild regurgitation was present in 12 patients, and moderate regurgitation was seen in 2 patients. None of these patients needed reoperation and echocardiography showed good motion of the reconstructed valve.

CONCLUSIONS

The surgical technique of simultaneous enlargement of the pulmonary annulus and the pulmonary cusp with a transannular patch of autologous pericardium is a safe, reliable, and effective way for RVOT reconstruction. Satisfactory early results have been achieved; however, long-term follow-up is necessary to determine the true value of this technique.

Evaluation of downsized homograft conduits for right ventricle–to–pulmonary artery reconstruction

OBJECTIVE

Although homograft conduits are frequently used to establish right ventricle-to-pulmonary artery continuity, the limited availability of small-size homografts is a significant constraint in pediatric cardiac surgery. We compared the performance of standard homograft conduits with that of surgically reduced bicuspid homograft conduits in patients undergoing repair of truncus arteriosus.

METHODS

Forty infants undergoing complete repair of truncus arteriosus with either standard homografts (n = 26) or reduced-size bicuspid homografts (n = 14) were evaluated.

RESULTS

The median downsized conduit diameter (13 mm) was similar to the standard homograft diameter (12 mm, P = .52). There were 6 early deaths and 5 late deaths, representing an overall 30-day mortality of 15% and a 5-year mortality of 25%. No deaths were directly related to homograft dysfunction. Four (29%) downsized conduits and 8 (31%) standard conduits required replacement at a median interval of 18.5 months and 42.4 months, respectively. Catheter-based interventions were required in 5 (36%) patients in the downsized group and in 3 (12%) patients in the standard group. There was no difference in freedom from surgical or catheter-based reintervention between the 2 groups (P = .42). Freedom from conduit failure (severe conduit stenosis, moderate or greater regurgitation) was 55.9% and 17.2% at 3 years in the downsized and standard groups, respectively.

CONCLUSION

The surgically downsized homograft is an excellent option when an appropriate-sized homograft is not available and might prevent morbidity associated with the use of an oversized conduit.

Adverse Mid-Term Outcome Following RVOT Reconstruction Using the Contegra Valved Bovine Jugular Vein

BACKGROUND

Current techniques for repair of the right ventricular outflow tract (RVOT) may require interposition of a valved conduit between the right ventricle and the pulmonary artery bifurcation. Recently, the Contegra conduit (Medtronic, Inc.) was introduced as an alternative xenograft tissue for RVOT reconstruction. Promising early hemodynamic and clinical results have been reported so far, but still less is known about mid-term adverse outcome.

METHODS

A total of 38 Contegra valved conduits (12 to 22 mm) were implanted from October 1999 to June 2004, in 36 children less than 5 years old and in 2 patients 8 and 21 years old. Diagnosis included the following: tetralogy of Fallot (n = 21); pulmonary atresia (n = 4); double outlet right ventricle + pulmonary stenosis (n = 3); d-transposition of the great arteries, ventricular septal defect, and pulmonary stenosis (n = 3); truncus arteriosus (n = 3); and other complex malformations (n = 4).

RESULTS

There was no mortality following initial surgery and no valved-conduit-related early morbidity. Early postoperative echocardiographic assessment after 3 months demonstrated favorable hemodynamics in all patients. However, during further follow-up, 5 conduits had to be replaced because of severe stenosis at the level of the distal anastomosis (2 of them had moderate to severe dilatation of the conduit proximally to the valve). Excessive intimal peel formation and severe perigraft scarring reaction were observed in all cases. One child died before surgery.

CONCLUSIONS

The Contegra valved conduit is an interesting concept for reconstruction of the RVOT. However, because of unpredictable incidence of supravalvar stenosis during mid-term results, we cannot recommend routine use of this material.

Early Results of the Bovine Jugular Vein Graft Used for Reconstruction of the Right Ventricular Outflow Tract

BACKGROUND

This study is an assessment of early results of bovine jugular vein grafts (BJV) used to reconstruct the right ventricular outflow tract.

METHODS

Ninety-three consecutive BJV implantations performed between May 2001 and August 2003 were included in this study. The median age was 7.2 years. Indications included various forms of tetralogy of Fallot and pulmonary atresia (56 patients), aortic valve disease requiring a Ross procedure (21 patients), truncus arteriosus (8 patients), d-transposition of the great arteries with ventricular septal defect and pulmonary stenosis (5 patients) and miscellaneous (3 patients). Additional plasty of the intrapericardial pulmonary arteries was performed in 41 patients. Follow-up was complete with a mean duration of 20.3 +/- 5.8 months.

RESULTS

There were 3 patients (3.2%) with early deaths and 2(2.2%) with late deaths, but none were related to the bovine jugular vein grafts. Twelve bovine jugular vein grafts needed reintervention; 11 were due to development of a stenotic membrane at the anastomosis site and one was due to somatic outgrowth of the child (10 conduit replacements and two balloon dilatations). Overall freedom from reintervention was 91.6% and 83.5% at 12 and 24 months, respectively. Small size (< or = 14 mm) conduits show respective rates of 80.7% and 63.6%, whereas larger sizes were 98% and 96%, free from reintervention at 12 and 24 months.

CONCLUSIONS

Bovine jugular vein grafts, when used for reconstruction of the right ventricular outflow tract, showed good early-term results. Attrition of small size bovine jugular vein grafts, due to development of a stenotic process at the anastomotic site needs to be closely observed. Longer follow-up is needed to allow a more definitive comparison with other established options.

Problems with the right ventricular outflow tract: a review of morphologic features and current therapeutic options

Repair of complex malformations that necessitate restoration of continuity between the right ventricle and the pulmonary arteries can now safely be performed with low morbidity and mortality. Major concerns still remain on the long-term outlook for these patients, and about the durability of the different prostheses used to restore that continuity, whether during initial correction or at the time of reintervention for failure of the conduit or pulmonary regurgitation. In this review, we discuss the salient morphologic features of the right ventricular outflow tract, and then focus on the indications for early and late intervention, current therapeutic options, and outcomes.

Conduit selection for right ventricular outflow tract reconstruction: contemporary options and outcomes

Reconstruction of the right ventricular outflow tract, with the establishment of an unobstructed pathway between the right ventricle and the pulmonary arteries, is a task that the congenital heart surgeon frequently faces. In situations where this outflow tract is congenitally absent, or the pulmonary valve has been used to replace a dysfunctional left ventricular outflow tract, a conduit is usually required to establish pulmonary blood flow. Cryopreserved homografts are currently favored for this, though these nonviable valved allografts have certain limitations. The following review will further define the problem of right ventricular outflow tract reconstruction, with an emphasis on conduit selection and possible alternatives to conduit repair.

Medtronic freestyle valve for right ventricular reconstruction in pediatric ross operations

BACKGROUND

The use of homograft conduits to reconstruct right ventricle (RV) to pulmonary artery (PA) connections is an essential component of the Ross operation. Homograft availability and cost may be problematic when considering the Ross operation. We elected in January 1998 to utilize commercially available xenografts as an alternative to homografts for RV/PA reconstruction in the pediatric Ross operation. Our early results using the Medtronic Freestyle valve (Medtronic, Minneapolis, MN) for RV/PA reconstruction are presented.

METHODS

We reviewed our database for all Ross operations performed on children since January 1998. A total of 16 patients were identified. Eleven children received a Medtronic Freestyle valve, 2 children received a homograft, and 3 children received another type of xenograft. Echocardiographic evaluation of all children who received the Medtronic Freestyle valve was performed at hospital discharge and at two subsequent outpatient evaluations.

RESULTS

The median peak instantaneous pressure gradient across the xenograft was 16 +/- 9 mm Hg (immediately after surgery before hospital discharge); 22 +/- 20 mm Hg at 23 +/- 11 months (first postdischarge follow-up); and 27 +/- 20 mm Hg at 35 +/- 9 months (second postdischarge follow-up). Linear regression analysis revealed an increasing pressure gradient with time (R(2)-adjusted = 0.44, p < 0.0001). At the same three observation points, the xenograft annulus diameter decreased: 25 +/- 1.2 mm; 19 +/- 4.3 mm; and 20 +/- 1.8 mm. Linear regression analysis revealed a decreasing annulus diameter with time (R(2)-adjusted = 0.41, p < 0.0001).

CONCLUSIONS

The Medtronic Freestyle valve provides a possible alternative to homografts for the reconstruction of the RV/PA connection in the pediatric Ross operation. Long-term follow-up is necessary to evaluate this xenograft as an alternative to the homograft.

Late results of the peel operation for replacement of failing extracardiac conduits

BACKGROUND

Pulmonary ventricle to pulmonary artery conduits have made repairing many complex congenital cardiac anomalies possible. Late patient outcome is adversely affected by the hemodynamic consequences of conduit failure and the need for reoperation for conduit replacement.

METHODS

We retrospectively reviewed 102 patients (65 males, 37 females) who underwent operation with autologous tissue reconstruction ("peel operation") between May 1983 and November 2001, in which a prosthetic roof was placed over the fibrous bed of the explanted conduit. Ages ranged from 5 to 58 years old (median age 19 years old). Explanted conduits were Hancock (n = 54), homograft (n = 21), Tascon (n = 11), and other (n = 16). The conduit roof was constructed with pericardium (n = 91) and other (n = 11). A prosthetic pulmonary valve was utilized in 68 patients: porcine in 65 patients and mechanical in 3 patients. A nonvalved reconstruction was performed in 34 patients. Concomitant cardiac procedures were performed in 66 patients.

RESULTS

Early mortality overall was 2% (n = 2) and was 0% for patients who underwent isolated conduit replacement (n = 36). Mean follow-up was 7.6 years (maximum, 19 years). Overall survival at 10 and 15 years was 91% (84.7, 97.2) and 76% (62.8, 91.7), respectively. Nine patients required reoperation related to the peel operation: regurgitation in nonvalved conduit (n = 7); moderate pulmonary bioprosthesis stenosis and regurgitation with atrial arrhythmia (n = 1); and pulmonary bioprosthesis endocarditis (n = 1). Overall survivorship free of reoperation for peel reconstruction failure at 10 and 15 years was 90.7% (82.6, 99.6) and 82% (69.4, 97.0), respectively. Survivorship free of reoperation for patients with a prosthetic valve was 93.7%, and for those with no prosthetic valve was 80.0% at 15 years (p = 0.57). At late follow-up, 89% of patients were in New York Heart Association functional class I or II.

CONCLUSIONS

The peel operation simplifies conduit replacement, can be performed with low risk, and provides a generous-sized flow pathway. In our experience late results demonstrate a lower freedom from reoperation than conventional prosthetic or homograft conduits.