Prosthetic Conduit Research Articles

Replacement of in situ saphenous venous aneurysms with arterial autografts

Background Aneurysm formation in arterialized autologous saphenous veins is an unusual complication of in situ femoral popliteal bypass procedures. Methods In a personal series of 207 in situ saphenous femoral popliteal bypass operations, three nonanastomatic venous aneurysms occurred. All three venous aneurysms occurred in male patients who had no adequate autologous vein available as an interposition graft. The use of eversion endarterectomized superficial femoral artery is reported as a substitute interposition graft with long-term results. Results In the 3 male patients in this series, nonanastomatic aneurysms developed in their in situ saphenous femoral popliteal bypass grafts. The venous aneurysms developed between 5 and 8 years after the original surgical procedure. No adequate vein was available as a replacement for the excised venous aneurysm. Prosthetic conduit was not used owing to the remote possibility of a subclinical infection. A segment of eversion thromboendarectomized superficial femoral artery removed from the same leg was used as a replacement interposition graft in each patient. The in situ venous graft with the autologous interposition thromboendarterectomized superficial femoral artery remained patent until each patient's death 4 to 7 years after the venous aneurysm replacement. Conclusions A short segment of endarectomized superficial femoral artery has been found to be a novel solution for the treatment of isolated saphenous vein graft aneurysms when no suitable vein is available. These patients should be maintained on lifelong aspirin therapy owing to the thrombogenic potential of endarectomized artery.

Establishing right ventricle-pulmonary artery continuity by autologous tissue: an alternative approach for prosthetic conduit repair

BackgroundIn conventional conduit operations, longevity has been essentially limited by the inevitable need for conduit replacement. This study was undertaken to compare long-term results of the use of equine pericardial conduits, autologous pericardial conduits, and direct anastomosis repair. MethodsBetween 1982 and 2001, 366 patients underwent primary establishment of right ventricle-pulmonary artery continuity at our institution. The mean age at the time of operation was 6.2 years (range, 4 days to 28 years) and mean weight was 17.2 kg (range, 1.6 to 61 kg). Three different repair techniques were used for connection: hand-made valved equine pericardial conduits (n = 179), autologous pericardial conduits (n = 71), and direct anastomosis without a conduit (n = 116). Mean follow-up period for early survivors was 8.6 years in the equine group, 6.1 years in the direct anastomosis group, and 5.1 years in the autologous pericardium group. ResultsDirect anastomosis repair (p = 0.0002) was associated with significantly better freedom from late events (conduit replacement or late death) than equine pericardial conduits. The hazard ratio was less with the autologous pericardium conduit than with the equine pericardium, but the difference was not statistically significant (p = 0.2122). Younger age at operation, and postoperative pressure ratio from right to left ventricle were also predictors of conduit longevity. ConclusionsTo decrease the probability of late events, direct anastomosis is an encouraging technique compared with traditional equine pericardium extracardiac conduit repair. An autologous pericardial conduit, because of its benefits, would be an alternative when direct anastomosis is not suitable.

Commentary by Specialist Editor

T procedure, devised to palliate childrenwith a univentricular heart or other complex cardiac defects not amenable to biventricular repair, was first reported in 1971 by Francis Fontan.1 In the intervening years since then there have been many technical changes and modifications, some of which have proved to be useful advances. These surgical improvements, togetherwithbetter patient preparation and improved selection for the procedure, have led to progressively better results. The most recent major surgical change has been the introduction of the extra-cardiac conduit, described by Puga and coworkers in 1988 2 and by Marcellettti et al. in 1990.3 This procedure has been widely used by paediatric cardiac surgeons since the mid-1990s, usually with a prosthetic conduit placed from the IVC to the pulmonary arteries, and occasionally with a homograft tube. This technique has several advantages compared to previous techniques—separation of the higher pressure column of venous blood from the systemic atrium, hence avoiding right atrial distention, minimization of suture lines on the atrium, and provision of more laminar flow from the IVC to the pulmonary arteries with less turbulence and energy loss. In particular, it is hoped that this technique will reduce the incidenceof late atrial arrhythmias, and the resultant risk of thrombo-embolic events arising from the left atrium, and the associated decline in functional status associated with the arrhythmia. However, the conduit lacks growth capacity and continues to have thrombo-embolic potential itself. In this edition of the journal, Chowdhury et al. report a technique for construction of an extra-cardiac conduit, using pedicled pericardium, which is intended to address some of the possible limitations of the conventional extracardiac conduit.4 It attempts to overcome the two remaining limitations of the extra-cardiac method, the lack of

The Efficacy of Robot-assisted Versus Conventional Laparoscopic Vascular Anastomoses in an Experimental Model

Background. Robot-assisted surgery is thought to facilitate complex laparoscopic movements, enhancing advanced laparoscopic procedures.Objective. To evaluate the benefit of robotic assistance for laparoscopic vascular surgery.Design. Experimental study using prosthetic conduits in a laparoscopic training box.Methods. Two surgeons each performed 40 laparoscopic vascular anastomoses alternating with and without robotic assistance. A Zeus-Aesop surgical Robotic system™ with 3-D visualisation was used. Each surgeon made 40 anastomoses in total, using different prostheses (5 mm PTFE and 16 mm Dacron) and suture material (Prolene and PTFE). A time-action analysis was performed to evaluate surgical performance. Primary efficacy parameters were quality and leakage of the anastomosis, total time and total number of actions.Results. Equal quality scores and anastomotic leakage were achieved with both techniques. Robotic assistance resulted in significant longer suture and knot tying time and significant more actions were needed compared to the manual laparoscopic procedures. Significant more failures occurred during the robot-assisted procedures.Conclusion. In this study, robotic (Zeus-Aesop) assistance did not improve the laparoscopic performance of the surgeon whilst making vascular anastomoses.

Right ventricle-pulmonary artery shunt in first-stage palliation of hypoplastic left heart syndrome

This article reviews our experience using a prosthetic conduit between the right ventricle (RV) and the pulmonary artery (PA), in lieu of the more traditional aortopulmonary shunt, for infants undergoing surgical palliation of hypoplastic left heart syndrome. Thirty-three consecutive infants underwent Norwood procedure between February 1998 and November 2003, using an RV-PA conduit. There were 31 hospital survivors (94%) and 25 patients have undergone a stage II bidirectional Glenn anastomosis with an additional two deaths. Nine patients have undergone completion Fontan. This technique provides reproducible results, simplifies postoperative management, and improves outcome, especially for “low volume” programs.

Successful treatment of acute dissection of the donor aorta after orthotopic heart transplantation

Acute aortic dissection is one of the rare aortic complications that occur after orthotopic heart transplantation. We report the second case of successful surgical treatment of aortic dissection confined to the donor aorta in a recipient of an orthotopic cardiac allograft. A 68-year-old patient was admitted with chest pain and shortness of breath 7 years after orthotopic heart transplantation. He previously had undergone twice coronary artery bypass grafting. Echocardiography revealed acute dissection of the donor aorta. The patient underwent urgent Bentall procedure with a prosthetic conduit. The post-operative course was uneventful. The heart donor was a 40-year-old man with known arterial hypertension and who had received long-term ergotamine tartrate therapy for migraine. This case demonstrates that heart-transplant recipients with arterial hypertension and donor-related risk factors are prone to aortic complications and require careful follow-up.

Long-term outcome of infrainguinal bypass grafting in patients with serologically proven hypercoagulability

The purpose of this study was to test the hypothesis that the long-term outcome of infrainguinal bypass grafting in patients with congenital or acquired hypercoagulability is inferior to the results in patients without documented clotting disorders. The study was a retrospective analysis of consecutive patients from January 1994 to January 2001. Five hundred eighty-two infrainguinal bypass grafts were created in 456 patients. Indication for surgery was limb-threatening ischemia in 84%; prosthetic conduits were implanted in 38%. Seventy-four grafts were created in 57 patients with one or more serologically proven hypercoagulable states, including heparin-induced platelet aggregation (n = 37), anticardiolipin antibodies (n = 11), lupus anticoagulant (n = 8), protein C or S deficiency (n = 7), antithrombin III deficiency (n = 3), and factor V Leiden mutation (n = 1). Patients with hypercoagulability were younger (63 +/- 2 years versus 69 +/- 1 years; P =.007), more likely to have undergone prior revascularization attempts (38% versus 21%; P =.003), and more likely to have chronic anticoagulation therapy after surgery (46% versus 25%; P =.001). After 5 years (median follow-up, 19 months), patients with hypercoagulability had poorer primary patency (28% +/- 7% versus 35% +/- 5%; P =.004), primary assisted patency (37% +/- 7% versus 45% +/- 6%; P =.0001), secondary patency (41% +/- 7% versus 53% +/- 6%; P =.0001), limb salvage (55% +/- 8% versus 67% +/- 6%; P =.009), and survival (61% +/- 8% versus 74% +/- 4%; P =.02) rates. Multivariate analysis identified only prosthetic conduit choice (P =.0001), hypercoagulability (P =.0003), and limb salvage indication (P =.01) as independent predictors of graft failure. Patients with serologically proven hypercoagulability have inferior long-term patency, limb salvage, and survival rates after infrainguinal bypass. The high prevalence rate (13%) of diverse hypercoagulable states in this patient population supports serologic screening, especially in referral practices.

Arteriovenous fistula using transposed basilic vein.

Patients who need long-term haemodialysis often require multiple operations to maintain their vascular access. The options for secondary or tertiary access procedures may become increasingly limited. Prosthetic conduits are commonly used in difficult cases but are associated with a high incidence of complications. The brachial artery-transposed basilic vein arteriovenous fistula has been used in preference to a prosthetic graft on 31 occasions. There were no technical failures and 28 of these fistulas matured. No major infective complications occurred. This procedure should be considered before resorting to a prosthetic graft for vascular access.

Infrapopliteal-Lower Extremity Revascularization with Prosthetic Conduit: A 20-Year Experience

The use of prosthetic conduits for lower extremity revascularization in the infrapopliteal location remains controversial. The objective of this report is to describe the immediate and long-term results in a series collected over two decades. Of the approximately 1,500 lower extremity revascularizations performed between 1978 and 1998, 81 infrapopliteal bypass cases using polytetrafluoroethylene (PTFE) as conduit in 77 patients were identified. Autogenous conduit was unavailable (86%) due to prior surgery: coronary artery bypass graft (25%), femoro-popliteal bypass (60%), or femoro-distal bypass (23%). All cases were done for critical ischemia using PTFE (6 mm, 95%; ring reinforced, 54%) under general (75%) or regional (25%) anesthesia. The distal anastomosis was to the anterior tibial artery (43%), posterior tibial artery (28%), tibioperoneal trunk (16%), or peroneal artery (12%), and vein patch was used in 25% of cases. Postoperative features included acute graft thrombosis in 11 cases (14%), all done under general anesthesia, perioperative death in 3 (4%), and a mean in-hospital stay of 17 days. Long-term follow-up has ranged from 1 to 144 months (mean, 22 months). At 36 months, primary patency was 20%, secondary patency 42%, and limb salvage 55% calculated by the Kaplan-Meier method. Univariate analyses revealed regional anesthesia was associated with prolonged primary patency (35% vs 15%, p=0.026) while the use of ring-reinforced PTFE conduit was associated with prolonged limb salvage (65% vs 40%, p=0.042). All other variables including gender, smoking, diabetes mellitus, renal failure, decade of operation, use of vein patch or postoperative warfarin were not significantly associated with either prolonged patency or limb salvage. Despite poor primary patency, distal prosthetic bypass can lead to long-term limb salvage. These data suggest distal anastomotic vein patches and postoperative anticoagulation may not be beneficial adjuncts. However, the use of regional anesthesia may decrease the incidence of perioperative thrombosis and the use of ring reinforced conduit may prolong limb salvage.

Endovascular Repair of Recurrent Thoracoabdominal Aortic Aneurysm

To report the endovascular repair of a complicated, recurrent thoracoabdominal aortic aneurysm (TAAA) using stacked, customized stent-grafts. A 75-year-old man was evaluated for an enlarging 7-cm suprarenal abdominal aortic aneurysm. The patient had repair of a distal TAAA in the past, as well as multiple visceral revascularizations from the infrarenal aorta. A 3-segment aortic endograft with proximal and distal extensions was delivered with the aid of a prosthetic conduit from the right common iliac artery to the end of the right renal artery; spinal fluid drainage was performed to mitigate paraplegia. The stent-graft components were serially deployed from the level of the left common carotid artery and ended with the bare springs of the distal extension covering the renal arteries. The patient was discharged but returned within a month for drainage of a purulent retroperitoneal hematoma. He has since resumed his preoperative activities and remains well with documented exclusion of the aneurysm and satisfactory visceral and distal perfusion at 21 months. This case illustrates that aortic endografting can be a viable option for the treatment of recurrent thoracoabdominal aortic aneurysms.

Percutaneous insertion of the pulmonary valve

ObjectivesWe report our experience of percutaneous valve insertion in pulmonary position in humans. BackgroundOver the past 40 years, prosthetic conduits have been developed to surgically establish continuity between the right ventricle and the pulmonary artery. However, stenosis and insufficiency of the conduit due to valvular degeneration or panus ingrowth frequently occur, limiting patients’ lifespan. Percutaneous stenting of conduits has recently emerged as a technique for delaying surgical replacement, but it creates a pulmonary regurgitation when crossing the valve. MethodsSeven children and one adult with stenosis and/or insufficiency of the pulmonary graft underwent percutaneous implantation of a bovine jugular valve in pulmonary position. ResultsPercutaneous pulmonary valve (PV) replacement was successful in all patients. No complications occurred in early follow-up. Angiography, hemodynamic studies and echocardiography after the procedure showed no significant regurgitation of the implanted valve. Implantation was effective in relieving the obstruction in five patients. All patients showed improvement in their clinical status at the latest follow-up (mean 10.1 months). ConclusionsNon-surgical insertion of the PV is possible without any major complications. This new technique may have an important role in the management of conduit obstructions and pulmonary regurgitation.

Effect of Harvesting and Sorting on β-1 Integrin in Canine Microvascular Cells

Background. The goal of seeding prosthetic conduits with endothelial cells (ECs) has focused attention on the role of EC adhesion molecules. Cell preparation techniques may affect adhesion molecule expression and graft seeding.Methods. Using fluorescent antibody labeling and flow cytometric analysis, this study examined the effectsof monolayer detachment (scraping vs trypsinization), timing of immunolabeling (pre- vs postdetachment), gene transfection (transfected vs nontransfected), and cell selection (antibiotic vs fluorescence sorting) techniques on β-1 integrin expression in canine microvascular EC (K9MVEC).Results. Cell scraping resulted in a significantly higher β-1 integrin mean fluorescence intensity than did cell trypsinization (P < 0.05). No difference was observed with immunolabeling prior to versus following monolayer harvesting. Gene transfection had no significant effect on β-1 integrin expression. No advantage was observed between cell selection methods (P > 0.05).Conclusion. This study suggests that the monolayer harvesting technique employed has a significant impact on β-1 integrin quantification by flow cytometric analysis. Furthermore, microvascular EC expression of β-1 integrin was not adversely affected by gene transfection.

Is prosthetic renal artery reconstruction a durable procedure? An analysis of 489 bypass grafts

Objective: Renal artery stenosis has been classically addressed with saphenous vein bypass graft or transaortic endarterectomy performed either primarily or in combination with an aortic procedure. In this series, we report the outcome of our 12-year experience with renal artery reconstruction using prosthetic conduit. Methods: Patients undergoing renal artery bypass grafting from 1987 to 1999 were identified. Demographics, indications, concurrent operations, complications, and patency were analyzed. Patients underwent postoperative duplex scan with subsequent ultrasound scans at 6-month intervals. Results: There were 489 procedures performed in 414 patients with indications: high-grade renal artery stenosis in combination with abdominal aortic aneurysm repair or symptomatic aortoiliac occlusive disease (309 [63%]), renovascular hypertension (118 [24%]), and renal salvage (20 [4%]). Indications for the remainder included trauma, renal artery aneurysm, or an infected aortic graft. Inflow was aorta or aortic graft in 95% of patients with the remainder taken from the iliac or visceral vessels. The retroperitoneal approach was used in 97.8%. Nonfatal complications occurred in 11.4% with a 1.4% early and 4.8% late occlusion rate. Renal function worsened in 3.1% of all patients. Secondary patency at 1 and 5 years was 98% and 96%, respectively. Conclusion: Renal artery reconstruction with prosthetic conduit has an acceptable and durable result whether used for primary renal artery reconstruction or concomitant reconstruction with aortic procedures. (J Vasc Surg 2001;34:127-32.)

Invited commentary

Techniques for reconstruction of the right ventricular outflow tract that will result in long-term freedom from reoperation remain an elusive goal for surgeons treating right ventricle-pulmonary artery discontinuity. Prosthetic conduits and allografts impose the subsequent certainty of reoperation, especially in growing infants, and there are occasional problems of finding space for them under the sternum in the mediastinum. This has led to a search for better ways to bridge the gap by utilizing autologous tissue. In 1981, LeCompte described mobilizing the pulmonary arteries and translocating them anterior to the aorta to permit direct anastomosis to the right ventricle. Barbero-Marcial in 1990 described several patients with truncus in whom he utilized flaps of pulmonary artery to create the floor of an RV-PA connection, the roof consisting of a pericardial patch containing a monocusp valve. Others have borrowed this concept for correcting conditions such as tetralogy with an absent main pulmonary artery as well as for bridging over an anomalous coronary artery crossing the RV outflow tract.

Distal emboli as an unusual late complication of a thrombosed arteriovenous hemodialysis graft

The creation of an arteriovenous fistula for long-term hemodialysis access is one of the most commonly performed procedures in vascular and transplantation surgery. Prosthetic conduits are frequently prone to failure within their first year of construction, and after one or two revisions, they are left in their thrombosed state as permanent subcutaneous foreign bodies in the extremities. Conventional teaching has regarded these chronically thrombosed grafts to have a benign natural history, and their removal has been considered unnecessary. We describe an unusual late complication of distal thromboemboli from a chronically occluded arteriovenous graft that was implanted 10 years before and appeared as acute hand ischemia. (J Vasc Surg 2000;32:1229-31.)

Model of complete separation of the hepatic veins from the systemic venous system

Background. In patients undergoing a Fontan operation, partial diversion of the hepatic veins to the pulmonary venous atrium has been tried with various techniques. They failed because of the development of intrahepatic collaterals leading to an unacceptable right-to-left shunting. We postulate that to avoid the formation of intrahepatic collaterals, the totality of the liver has to be drained into the same pressure compartment. We have designed a model of cavopulmonary anastomosis in which a prosthetic conduit reproduces an azygos continuation, associated with the diversion of the totality of the hepatic venous return. This article reports on the early hemodynamics and the fate of the separation of the two venous compartments in long-term survivors. Methods. Eighteen goats were operated on; the pulmonary artery and hepatic vein pressures were recorded. During month 2, an opacification of the inferior vena cava and the cavopulmonary connection was performed. Between months 6 and 14, another opacification was performed, together with pressure recording at both ends of the conduit. Results. Postoperatively the pulmonary artery pressure was pulsatile with a mean of 10 mm Hg and the hepatic vein pressure was 0 mm Hg. The first angiogram showed patent tubes with fast progression of the contrast. Throughout the inferior vena cava injection, there was no opacification of the portal or hepatic veins. The late study showed a narrowed conduit in all animals. During the injection, a collateral was injected, feeding into the inferior mesenteric vein. No collateral circulation could be seen draining directly into the liver. The median gradient between the two ends of the conduit was 11 mm Hg. Conclusions. The isolation of the entire hepatic venous drainage is feasible and efficient for the separation of two pressure compartments. No intrahepatic collaterals are observed with this model at short- or long-term follow-up. The separation of the hepatic venous drainage should persist without collateral circulation as long as the inferior vena cava pressure stays at the levels observed in Fontan circulation.

Percutaneous replacement of pulmonary valve in a right-ventricle to pulmonary-artery prosthetic conduit with valve dysfunction

Valved conduits from the right ventricle to the pulmonary artery are frequently used in paediatric cardiac surgery. However, stenosis and insufficiency of the conduit usually occur in the follow-up and lead to reoperations. Conduit stenting can delay surgical replacement, but it aggravates pulmonary insufficiency. We developed an innovative system for percutaneous stent implantation combined with valve replacement. A 12-year-old boy with stenosis and insufficiency of a prosthetic conduit from the right ventricle to the pulmonary artery underwent percutaneous implantation of a bovine jugular valve in the conduit. Angiography, haemodynamic assessment, and echocardiography after the procedure showed no insufficiency of the implanted valve, and partial relief of the conduit stenosis. There were no complications after 1 month of follow-up, and the patient is presently in good physical condition. We have shown that percutaneous valve replacement in the pulmonary position is possible. With further technical improvements, this new technique might also be used for valve replacement in other cardiac and non-cardiac positions.

Métaplasie de tissu aortique en tissu trachéal. Perspectives chirurgicales

Tracheal reconstruction after extensive resection remains an unsolved surgical problem. Numerous attempts have been made using tracheal grafts or prosthetic conduits with disappointing results. In this study, we propose a new alternative using an aortic autograft as tracheal substitute. In a first series of experiments, a half circumference of two rings was replaced with an autologous carotid artery patch. In a second series, a complete segment of trachea was replaced with an autologous aortic graft supported by an endoluminal tracheal stent. No dehiscence or stenosis was observed. Microscopic examinations at 3 and 6 months showed the replacement of the aortic tissue by tracheal tissue comprising neoformation of cartilage and mucociliary or non-keratinizing metaplastic polystratified squamous epithelium. Although these results need to be confirmed by a larger series of experiments, they showed that a vascular tissue placed in a different environment with a different function can be submitted to a metaplastic transformation which tends to restore a normal structure adapted to its new function. These remarkable findings offer new perspectives in tracheal reconstruction in human.

Direct neonatal ventriculo-arterial connections (REV): early results and future implications

Background. Is the time-honored supposition correct that insertion of a competent prosthetic conduit or homograft is necessary to achieve right ventricular (RV) to pulmonary artery continuity in neonates? A direct ventriculo-arterial connection, or réparation à l’étage ventriculaire (REV), has been successfully used to achieve RV to pulmonary artery continuity in neonates without mortality or major morbidity. Acute RV function is preserved even in the face of free pulmonary insufficiency, but scrupulous preservation of pulmonary artery patency (unobstructed pathway) must be achieved.Methods. We retrospectively reviewed the cases of 6 neonates who underwent direct ventriculo-arterial connection to achieve RV to pulmonary artery continuity during open heart procedures in the last 3 years.Results. The 6 neonates had a mean age of 12.3 days (range, 2 days to 6 weeks) and a mean weight of 3.2 kg (range, 2.7 to 3.6 kg) at operation. Two of them had a diagnosis of aortic atresia + ventricular septal defect and successfully achieved an in-series circulation. Two had pulmonary atresia + ventricular septal defect and 2, double-outlet right ventricle + transposition of the great arteries + ventricular septal defect + pulmonary atresia. Follow-up is a mean of 16 months (range, 6 to 22 months). Surgical reintervention was required in 3 neonates and resulted in excellent hemodynamics in 2 of them. In the other patient, who had bilateral long-segment branch pulmonary artery hypoplasia, stents were placed without hemodynamic benefit. All children are currently alive with preserved RV function even in the presence of free pulmonary insufficiency.Conclusions. Although the creation of a direct ventriculo-arterial connection has routinely been used for children older than 1 year with satisfactory initial results, its application in neonate is very limited. Why have neonates been denied this viable alternative? Perhaps the answer involves legitimate concerns about the consequent free pulmonary insufficiency and the presumed acute RV diastolic dysfunction.

Aortic atresia with a ventricular septal defect: modified single-stage neonatal biventricular repair

Background. The spectrum of hypoplastic left heart disease is diverse but the surgical repair is strictly dichotomous, culminating in either a univentricular or a biventricular surgical repair. Although aortic atresia with a ventricular septal defect historically has been managed by conversion to a univentricular physiology, a biventricular repair occasionally has been attempted in stages or in conjunction with the implantation of multiple allografts or prosthetic conduits. Our repair strategy recently has evolved to the use of a modified single-stage biventricular repair using only autologous tissues without conduits. Methods. Retrospective analysis (1989 to 1997) of neonates with aortic atresia with a ventricular septal defect. Results. Five neonates underwent repair of aortic atresia with a ventricular septal defect. One died in the hospital. The mean age and weight of the neonates who underwent repair were 7.8 days (range, 2 to 17 days) and 3.2 kg (range, 3 to 3.6 kg), respectively. Three neonates had a univentricular repair and 2 had a modified biventricular repair. The latter two procedures were successful and the patients were discharged from the hospital. Conclusions. Long-term results are lacking to attest to this surgical modification’s superiority over either the standard multistage univentricular operation or the single-stage biventricular repair using multiple conduits. However, we are optimistic that routine use of this modification will enable a greater percentage of neonates to undergo a biventricular repair without the need for serial conduit revisions or future aortoplasty.