Immunologically untreated fresh xenograft implantation in a pig-to-goat model

Immunologically untreated frozen-stored xenografts show controlled rejection and repair due to reduced cellularity in our previous study. To clarify the issue, we compared results obtained using fresh and frozen-stored xenografts. Porcine pulmonary valved conduits were prepared without immunologic treatment and implanted in the right ventricular outflow tract of goats under cardiopulmonary bypass immediately after harvest without frozen storage (the fresh group) or after frozen storage (-70 degrees C for 3 - 7 days) (the frozen group). Four goats were assigned to be raised for 3 (N = 1) or 6 (N = 3) months postoperatively in each group. One goat in the frozen group assigned for the 6-month observation expired at 2 months postoperatively because of thrombotic occlusion of the pulmonary valve. The other goats survived until the scheduled sacrifice. According to echocardiographic findings, one animal sacrificed at 3 months in the frozen group showed more than a moderate degree of pulmonary regurgitation, but all animals in the fresh group showed less than a mild degree. On gross examination, leaflets were slightly better preserved in the fresh group and aneurysmal dilatation of the pulmonary artery was observed at 3 months only in the frozen group. Microscopically, pulmonary arteries showed less severe degenerative changes in the fresh group. Moreover, in the fresh group, viable donor valve cells were still present until 3 months postoperatively (though it disappeared at 6 months postoperatively) and a linear endothelial lining of viable host cells was prominent on all leaflets, whereas this was not the case in the frozen group. In conclusion, fresh xenografts preserved cellular viability and showed fewer degenerative changes than frozen-stored xenografts. Thus, immunologically untreated fresh xenografts could provide a potential valve substitute with distinctive advantages in terms of self-healing potential as compared with frozen-stored xenografts.     

Valved and nonvalved right ventricular--pulmonary arterial extracardiac conduits. An experimental comparison

Extracardiac conduits are essential in operations for congenital discontinuity between the right ventricle and the pulmonary artery. The disturbing degree of obstruction reported in clinical series of extracardiac conduits containing porcine valves has been attributed in part to early valve deterioration and the development of a thick neonintimal lining within the Dacron graft. This study compares the hemodynamic differences and the thickness of the neointimal lining in right ventricular extracardiac conduits with and without a porcine valve. Woven Dacron conduits (16 mm) were implanted in 15 adult mongrel dogs, and then the proximal pulmonary artery was occluded with Dacron tape. In six dogs, the extracardiac conduit contained a porcine valve, whereas in the other nine it did not. Cardiac output, transconduit gradient, and resistance were measured at operation and 6 and 12 months postoperatively in both groups. No hemodynamic differences were noted. After 1 year, the thickness of the neointimal lining was threefold greater in valved conduits (1,370 +/- 313.1 mu versus 367 +/- 28.07 mu, p less than 0.005). The neointima along the Dacron graft was thickest proximal and distal to the porcine valve. The luminal peel in valved conduits contained fenestrations and intimal flaps, similar to those observed clinically. In our model, a porcine valve in a right ventricular extracardiac conduit is associated with intimal hyperplasia not seen in nonvalved conduits. If the pulmonary vascular resistance is normal, then the absence of a valve within the conduit does not significantly change hemodynamics and may warrant clinical application to prevent late conduit obstruction.     

牛颈静脉带瓣管道重建犬右心室流出道的血流动力学研究

目的观察自制牛颈静脉带瓣管道重建犬右心室流出道后的血流动力学性能. 方法应用经戊二醛处理的牛颈静脉带瓣管道对7只犬行肺动脉与右心室连接,重建右心室流出道前后测定肺血流动力学,行超声心动图检查牛颈静脉带瓣管道通畅情况. 结果重建术后1年7只犬均存活.重建右心室流出道前后肺动脉收缩压、舒张压和平均压均无明显改变,右心室舒张压无明显变化,收缩压和平均压显著增加(P<0.01).术后超声心动图检查瓣膜关闭良好,无明显反流,跨瓣压差小;术后1年超声心动图检测发现全部带瓣管道通畅,未见明显血栓形成,除1只犬瓣叶活动稍差合并轻度反流外,其余犬瓣叶活动良好.心导管测压显示肺动脉与右心室之间压差为3～19 mm Hg(1kPa=7.5mmHg),管道内舒张压显著高于右心室舒张压,右心室造影显示牛颈静脉带瓣管道和肺动脉无明显梗阻.结论戊二醛处理牛颈静脉带瓣管道重建右心室流出道具有良好的血流动力学性能.     

Do valved stents compromise coronary flow?

OBJECTIVE: The aim of the present study is to evaluate a new self-expanding valved stent design for minimal invasive aortic valve implantation and its interference with coronary flow. METHODS: An equine pericardial valve mounted onto a self-expanding nitinol stent (3F Therapeutics trade mark, CA, USA), outer diameter 23 mm, was evaluated (A) in vitro in a dynamic pulsatile mock loop and (B) in vivo in six calves (75+/-2.5 kg). In four animals valve stents were implanted on-pump and in two animals off-pump after induction of ventricular fibrillation. Target site for deployment was the orthotopic aorta, over the native valves. In vivo assessment was performed with intracardiac (AcuNav) and intravascular ultrasound including leaflet motion, planimetric valve orifice and residual-coronary\sinus-stent-index (RCSSI, distance stent to aortic wall/coronary diameter) calculations, coronary blood flow characteristics, transvalvular gradient, regurgitation and paravalvular leaking, in combination with continuous cardiac output measures. Macroscopic analysis was performed at necropsy. RESULTS: Two-dimensional intracardiac ultrasound showed good leaflet motion, with full valvular opening and closing in five of six valves. Planimetric valve orifice was 1.75+/-0.4 cm(2). There were no signs of coronary flow impairment with an RCSSI of 1.8+/-1.2. The implanted valved stents showed a low transvalvular gradient of 5.3+/-3.9 mmHg (mean, peak-to-peak) on invasive measurements and 4.7+/-2.5 mmHg in two-dimensional intracardiac sonography. One of six valves showed mild to moderate regurgitation and one of six valves a minor to moderate paravalvular leak due to size mismatch. CONCLUSIONS: This new self-expanding valved stent design allows for on- and off-pump aortic valve implantation in the orthotopic aorta, over the native valves without interference of the coronary blood flow and excellent acute valve function in properly sized devices.     

Percutaneous aortic valve replacement: an experimental study. I. Studies on implantation

OBJECTIVE: The purpose of this preliminary study was to devise a new surgical procedure for minimally invasive aortic valve implantation with a transluminal technique. METHODS: The new collapsible heart valve was prepared by mounting a porcine aortic valve, taken from a freshly slaughtered pig, into a self-expandable nitinol stent by means of a suture technique. The outer diameter of the valved stent ranged from 15 to 23 mm, and the length ranged from 21 to 28 mm. Before implantation in vivo, these valved stents were tested in an in vitro circulatory system. Only in vitro-tested valved stents with a pressure gradient of less than 7 mm Hg and regurgitation of I degrees or less were used for transluminal aortic valve implantation in vivo. Six of these valved stents were implanted in the descending aorta and 8 in the ascending aorta of anesthetized pigs. The catheter delivery system (22F) was extraperitoneally inserted through the left iliac artery or the infrarenal aorta. Measurements for transvalvular gradient, valvular opening and closure, blood-flow characteristics, regurgitation, and macroscopic analysis were performed at baseline and after the observation period (164 +/- 48 minutes). RESULTS: This preliminary study contained 14 animals. One animal died of ventricular fibrillation. Technical failure occurred in 2 pigs as a result of stent twisting. At the end of the observation period, the 11 successfully implanted valved stents demonstrated low transvalvular gradients (mean end-systolic Deltarho(max) of 5.4 +/- 3.3 mm Hg for the descending aorta group, 5.4 +/- 1.2 mm Hg for the supracoronary group, and 5.4 +/- 1.1 mm Hg for the subcoronary group), which did not differ from their in vitro gradients. Two-dimensional echocardiography demonstrated complete valvular closure and opening in 5 of 5 cases. Angiography indicated only a physiologic jet of regurgitation (0 degrees ) in 8 animals and mild (I degrees ) regurgitation in 3 animals. Color Doppler ultrasonography indicated no regurgitation in 5 of 5 cases and minor paravalvular leakage in 1 case. CONCLUSION: Aortic valved stents can be successfully implanted without thoracotomy by using a transluminal catheter technique. Long-term function of the valves remains to be established.     

In vivo repopulation of xenogeneic and allogeneic acellular valve matrix conduits in the pulmonary circulation

BACKGROUND: Approaches to in vivo repopulation of acellularized valve matrix constructs have been described recently. However, early calcification of acellularized matrices repopulated in vivo remains a major obstacle. We hypothesised that the matrix composition has a significant influence on the onset of early calcification. Therefore, we evaluated the calcification of acellularized allogenic ovine (AVMC) and xenogenic porcine (XVMC) valve matrix conduits in the pulmonary circulation in a sheep model. METHODS: Porcine (n = 3) and sheep (n = 3) pulmonary valve conduits were acellularized by trypsin/EDTA digestion and then implanted into healthy sheep in pulmonary valve position using extracorporeal bypass support. Transthoracic echocardiography (TTE) was performed at 12 and 24 weeks after the implantation. The animals were sacrificed at week 24 or earlier when severe calcification of the valve conduit became evident by TTE. The valves were examined histologically and biochemically. RESULTS: All AVMC revealed severe calcification after 12 weeks with focal endothelial cell clustering and no interstitial valve tissue reconstitution. In contrast, after 24 weeks XVMC indicated mild calcification on histologic examination (von Kossa staining) with histologic reconstitution of valve tissue and confluent endothelial surface coverage. Furthermore, immunohistologic analysis revealed reconstitution of surface endothelial cell monolayer (von Willebrand factor), and interstitial myofibroblasts (Vimentin/Desmin). CONCLUSIONS: Porcine acellularized XVMC are resistant to early calcification during in vivo reseeding. Furthermore, XVMC are repopulated in vivo with valve-specific cell types within 24 weeks resembling native valve tissue.     

Valved jugular vein segments for right ventricular outflow tract reconstruction in young sheep

OBJECTIVE: This study was undertaken to investigate the degeneration and calcification of valved bovine jugular vein segments for right ventricular outflow tract reconstruction in juvenile sheep. METHODS: Seven valved bovine jugular vein conduits (Contegra model 220; VenPro Corporation, Irvine, Calif) and 3 control conduits (MH100; Medtronic, Inc, Minneapolis, Minn) were implanted in the pulmonary artery in young sheep. After 20 weeks the conduits were explanted and qualitatively analyzed by epicardial echocardiography, gross examination, x-ray analysis, light microscopy, and transmission electron microscopy. Calcification was determined quantitatively by flame atomic absorption spectrometry. RESULTS: Two Contegra conduits could not be analyzed because of endocarditis. All other Contegra conduits functioned well, with preserved structure and minimal calcification. The control MH100 conduits exhibited extensive fibrous sheathing, with calcification of the aortic wall portion and the commissural part of the Hancock valve. CONCLUSIONS: The Contegra conduit's performance was clearly superior to that of the control MH100 conduit when implanted in the pulmonary artery position in juvenile sheep for 5 months.     

Evaluation of kangaroo aortic valved conduits in a juvenile sheep model: preliminary findings

BACKGROUND: Biological heart valve substitutes, manufactured from either porcine or bovine tissue, have been in use for more than 30 years. Despite low thrombogenicity and excellent performance, bioprosthetic heart valves tend to degenerate and calcify early in young patients because of patient and valve related factors. The aim of this study was to examine the calcification behavior of glutaraldehyde-preserved kangaroo heart valves in a juvenile sheep model. METHODS: Porcine (n = 10) and kangaroo (n = 10) valved conduits were implanted in the descending aortic position of juvenile sheep and retrieved after 6, 8, and 12 months. Retrieved valved conduits were examined for morphological changes and calcification of the valve tissue, using Von Kossa's stain technique and atomic absorption spectrophotometry. RESULTS: Structural valve deterioration, characterized by increased stiffness and severe calcification, occurred in 100% of the porcine conduits within 4 months. Kangaroo valve leaflets were significantly (p < 0.001) less calcified at 6 months (3.39+/-1.80 microg/mg), 8 months (5.86+/-4.57 microg/mg), and at 12 months (14.38+/-6.72 microg/mg), compared to porcine valves at 3 months (176.45+/-42.88 microg/mg ) and at 4 months (154.67+/-52.67 microg/mg ). Porcine aortic wall tissue was more calcified (118.24+/-42.86 microg/mg) than kangaroo aortic wall tissue (79.55+/-26.40 microg/mg). CONCLUSIONS: Kangaroo heart valves calcify less than porcine heart valves. These findings suggest that a different donor valve tissue has a lower calcification potential probably due to a difference in the morphological ultrastructure. This could result in improved long-term durability of kangaroo heart valves.     

Results of homograft aortic valve replacement for active endocarditis

Since July 1985, cryopreserved homograft prostheses have been used for aortic valve replacement in 10 patients, aged 2 to 77 years, with active endocarditis. Five patients had positive bacterial cultures from excised valves, and all had clinical findings of uncontrolled infection while receiving appropriate antibiotics. Homograft valves (four) or valved conduits (six) were implanted for treatment of sepsis (6 patients), congestive heart failure (3) or recurrent emboli (1 patient), and complicating native (5 patients) or prosthetic valve (5) endocarditis. Staphylococci (6 patients), streptococci (3), and Candida (1) were infecting organisms. Preoperatively, Doppler echocardiography showed aortic regurgitation in all patients. At operation, 9 patients had gross vegetations, 9 had single or multiple abscess cavities, and 5 had pericarditis. Complex reconstruction of the aortic valve and annulus with homograft conduits was necessary in 6 patients (3 with previous aortoventriculoplasty). Two early deaths (ventricular failure, perioperative stroke) occurred. Mean follow-up of all operative survivors was 2.1 years (range, 0.6 to 3.6 years), and one late death resulted from arrhythmia. Homograft valve regurgitation increased in 1 patient, and 7 late survivors are asymptomatic. No patient has had recurrence of endocarditis. We conclude that cryopreserved homograft aortic valve/root replacement is an effective method for management of active endocarditis complicated by annular destruction.     

Externally stented polytetrafluoroethylene valved conduits for right heart reconstruction. An experimental comparison with Dacron valved conduits

Valve-containing conduits have made possible the repair of many congenital anomalies that involve right ventricular-pulmonary arterial discontinuity. The distressing problem of neointimal peel formation with eventual conduit obstruction in patients with Dacron valved conduits has led to the need for premature replacement in many patients. Externally stented polytetrafluorethylene has demonstrated superior patency in the venous system experimentally and clinically and was believed to have potential advantages over Dacron for conduit construction. This study compares the transconduit resistance and the thickness of the neointimal peel in right ventricular-pulmonary arterial conduits constructed of externally stented polytetrafluoroethylene with those of woven Dacron. The 19 mm externally stented polytetrafluoroethylene conduits (Impra, Inc.) containing a Hancock porcine valve (Extracorporeal Inc.) were implanted in six adult mongrel dogs followed by proximal occlusion of the pulmonary artery. In six additional animals, a Dacron valved conduit of similar size and length was inserted. Cardiac output, transconduit gradient, and resistance were measured at operation and at 3 months. All conduits were subsequently explanted, opened longitudinally, and the thickness of the neointimal peel (excluding suture lines) measured. No hemodynamic differences were noted during the 3 month follow-up. However, the thickness of the neointimal peel was fourfold greater in Dacron conduits (609 +/- 144 mu) than in the conduits constructed of externally stented polytetrafluoroethylene (156 +/- 50 mu) (p less than 0.01). The thick peel in Dacron conduits extended into the outflow portion of the porcine valve cusps and prevented their full excision. The neointima in externally stented polytetrafluoroethylene conduits was thin and uniform and did not extend onto the leaflets or limit their mobility. This study demonstrated that the early hemodynamic performance of externally stented polytetrafluoroethylene conduits was comparable to that of Dacron conduits; Dacron conduits were subject to an accelerated rate of peel formation that affected leaflet mobility and may be a factor in early valve degeneration; a thin neointima formed in externally stented polytetrafluoroethylene conduits and valve leaflet motion was preserved. This study showed that externally stented polytetrafluoroethylene conduits offer advantages over Dacron valved conduits and warrant clinical application.     

Glutaraldehyde-Fixed Bovine Iliac Veins Used as Bioprosthetic Conduits: An Experimental Animal Study

The ideal prosthetic conduit for surgical repair of complex congenital heart disease has yet to be found. Twenty conduits were implanted between the right ventricle and pulmonary artery in growing sheep as follows: four Dacron porcine valve conduits (mean time in place, 142 days); four avalved glutaraldehyde-fixed bovine iliac veins (mean 132 days); and 12 glutaraldehyde-fixed bovine iliac veins containing a porcine valve (mean 180 days). Fifteen conduits were left in place from 167 to 244 days (mean 204 days), and five were explanted earlier (mean 54 days). Pathological study included gross, x-ray, histological, and ultrastructural investigation. Five conduits failed because of infective endocarditis. The valved Dacron conduits showed significant tissue ingrowth and calcification of the valve graft. The valved bovine iliac veins presented calcification at the valve level and vein wall, as well as a valvelike calcific fibrous ridge at the proximal anastomosis with the right ventricle. The avalved bovine iliac veins also presented calcific deposits along the wall and a valvelike calcific ridge at the ventricular anastomosis. Histological and ultrastructural studies of the vein tunica media revealed the phenomena of inflammatory rejection and foreign body reaction with loss of smooth muscle cells (medionecrosis) and fibrotic replacement. In conclusion, bovine iliac veins undergo inflammation with medionecrosis indicating that smooth muscle cell antigenicity is not attenuated by glutaraldehyde fixation.     

Total repair for truncus arteriosus]

Total repair for truncus arteriosus using an external conduit was performed in 12 patients from 1978 through 1989. Six cases were infants (mean age: 3.4 months) and 6 were children (mean age; 1 years 9 months). Two cases had Collet-Edwards type II truncus and the other 10 cases had type I truncus. One of the infants was associated with an interruption of the aorta and another had a severe regurgitation of the truncal valve (TrV). For external conduits, we used a non-valved conduit in one infant, a composite valved conduit of Dacron containing a heterograft valve in 4 children and a valved pericardial roll made of an autologous or porcine pericardium in 5 infants and 2 children. One infant with a severe regurgitation of the TrV needed valve replacement along with enlargement of the annulus of the TrV. One infant who had replacement of the TrV died early postoperatively. Another infant died 10 months after total repair due to an infection of an external conduit. Cardiac catheterization was performed in all 10 survivors. The mean value for the systolic pulmonary/systemic pressure ratio decreased from 0.98 +/- 0.09 preoperatively to 0.36 +/- 0.09 postoperatively. Replacement of an external conduit was performed due to a conduit stenosis in 2 children and 1 infant, 10 years and 2 months, 7 years and 9 months, and 1 year and 8 months after the total repair, respectively. In one of these 2 children, replacement of the aortic valve was performed due to a severe aortic regurgitation. We conclude that our results of total repair for truncus arteriosus were satisfactory. However, it remains to be solved how to manage an infant with truncus arteriosus associated with a severe regurgitation of the TrV.     

Aortic root and right ventricular outflow tract reconstruction using composite biological valved conduits after failed Ross procedure

The Ross procedure or pulmonary autograft has been frequently used for surgical treatment of aortic valve disease. One considerable disadvantage of the Ross procedure is the involvement of two valves (aortic and pulmonary) in treatment of single (aortic) valve disease. Both the aortic and pulmonary valves are at risk for future degeneration. Concurrent failure of both valves after a Ross procedure is rare but presents a significant technical challenge when reoperation is necessary. We describe a novel approach to this complication using composite biological valved conduits comprised of stentless bioprosthetic valves and polyester grafts.     

Size-Reduced Cryopreserved Pulmonary Valve Allograft for an RV-PA Conduit: Technical Modification and Functional Evaluation

Cryopreserved pulmonary allografts harvested from adults at the time of kidney donation were size reduced and used in two children with pulmonary atresia and ventricular septal defect. A technical modification for the creation of size-reduced pulmonary allograft conduits is described. Postoperative ultrasonic and cineangiographic assessments revealed excellent function of the pulmonary bicuspid valved conduit with a minimal pressure gradient and essentially no regurgitation. Although the long-term fate of cryopreserved bicuspid pulmonary valve and conduit is unknown, this conduit provides excellent handling characteristics that render allograft conduits preferable to synthetic conduits. In addition, the remodeled bicuspid pulmonary allograft conduits have exhibited excellent hemodynamic characteristics and are a reasonable alternative to other types of conduits when an appropriate size allograft is not available.     

Early and late results of fresh autologous pericardial valved conduits

The objective of this study was to evaluate the early and late results of an autologous pericardial valved conduit in the pulmonary circulation. Between 1983 and 1997, 86 autologous pericardial valved conduits were used to achieve venous ventricle-pulmonary artery continuity. The mean patient age at the time of implantation was 4.16 ± 4.10 years (15 days to 24 years). All patients had two-dimensional postoperative and yearly Doppler echocardiograms in which the valve function and the presence of distal, valvar, and proximal stenosis were evaluated. There were 13 early deaths (15%). Twenty-one patients (24.4%) showed trivial, 54 (62.8%) mild, nine (10.4%) moderate, and two (2.3%) severe pulmonary regurgitation in the early postoperative period. The 73 survivors were monitored from 1 to 15 years (mean, 6.5 years; median, 7.1 years). There were five late deaths. The mean conduit diameter at the time of implantation was 15.8 mm, increasing to 18.21 mm at last evaluation (P < .0001). There were nine reoperations, with only one conduit replacement. Freedom from reintervention at 5 and 10 years was 89% and 80%, respectively. In conclusion, autologous pericardial valved conduits provide good early and excellent long-term results that compare favorably with those of other conduits. Copyright © 1999 by W.B. Saunders Company     

Tricuspid Atresia: Corrective Operation without a Bioprosthetic Valve

A case of successful correction of type IB tricuspid atresia is described in which the patient's own normal pulmonary valve was used in its natural location. Morphological features of tricuspid atresia suggest that use of the in situ pulmonary valve is possible in most patients with normally related great arteries. Elimination of the requirement for valved conduits and bioprosthetic valves may eventually permit corrective operation in the very young child.     

A Novel Technique in a Sheep Model for Evaluating Prosthetic Heart Valve Performance

There have been many various animal studies to evaluate the structural integrity and antithrombogenicity of prosthetic heart valves. We were interested in developing a novel sheep model to study the thrombogenicity of mechanical heart valves placed into the systemic circulation but without the need for cardiac bypass. Also, we wanted to minimize the risk of paraplegia from complete thoracic aortic clamping. Six sheep underwent left lateral thoracotomy for placement of a mechanical heart valve in parallel with the descending thoracic aorta. A valved conduit with a dacron tube graft sutured to the back end was fashioned. Employing partial aortic occlusion with a side-biting clamp, the proximal and distal ends were anastomosed in an end-to-side fashion. Once flow was confirmed through the graft, the native aorta was occulded with umbilical tape. The sheep received no postoperative anticoagulation. The median operative time and estimated blood loss (EBL) was 170 min and 250 cc, respectively. Patency of the valved conduits was confirmed during the initial procedure, and there was no incidence of paraplegia postoperatively. Two animals expired shortly after extubation and at necropsy the valved conduits were patent with preserved valve function. The four survivors were sacrificed a median of 37 days postoperatively. Prior to euthanasia, the valved conduits were evaluated in situ with ultrasound. In all cases, the valves had clot formation at the hinges, which prevented active movement of the leaflets. This novel in vivo technique provides an alternative in testing the thrombogenicity of prosthetic heart valves without cardiac bypass or the risk of paraplegia in an animal that is extremely sensitive to complete aortic cross-clamp.     

Use of bovine jugular vein to reconstruct the right ventricular outflow tract: early results

OBJECTIVE: We evaluate early results of bovine jugular vein conduits in the pulmonary outflow. METHODS: Between April 2000 and September 2001, 31 conduits were placed in the outflow of the right ventricle. Patients who received a conduit as a staged surgical procedure were excluded (n = 3). Implantation age ranged from 0 to 21 years (median, 3.4 years). Conduit diameter ranged from 12 to 20 mm (median, 14 mm). Transthoracic echocardiography was performed at discharge and 3 months after surgery. Patients with significant pulmonary regurgitation and/or stenosis underwent cardiac catheterization. RESULTS: Four patients died during the follow-up period. Three deaths were unrelated to the conduit. One death was related to the complete thrombosis of the conduit. At 3 months evaluation, pulmonary valve regurgitation was absent or trivial in 19, mild in 2 and severe in 3 of 24 survivors. Four patients had nonfatal conduit-related complications. A transient thrombus formation within 1 leaflet was noted postoperatively in a patient with a moderate pulmonary regurgitation. Three patients required reoperation 3 to 5.8 months after the implantation for conduit failure (mean, 4.3 months). Cardiac catheterization before replacement revealed an aneurysmal dilation of the conduit below a severe stenosis of the pulmonary bifurcation due to important neointimal proliferation. CONCLUSIONS: Early failure of bovine jugular vein valved conduits can occur because of exaggerated intimal proliferation or thrombotic process within the conduit. Because of these complications, close echocardiographic follow-up is mandatory during the first weeks after implantation.     

A novel technique in a sheep model for evaluating prosthetic heart valve performance.

There have been many various animal studies to evaluate the structural integrity and antithrombogenicity of prosthetic heart valves. We were interested in developing a novel sheep model to study the thrombogenicity of mechanical heart valves placed into the systemic circulation but without the need for cardiac bypass. Also, we wanted to minimize the risk ofparaplegia from complete thoracic aortic clamping. Six sheep underwent left lateral thoracotomy for placement of a mechanical heart valve in parallel with the descending thoracic aorta. A valved conduit with a dacron tube graft sutured to the back end was fashioned. Employing partial aortic occlusion with a side-biting clamp, the proximal and distal ends were anastomosed in an end-to-side fashion. Once flow was confirmed through the graft, the native aorta was occulded with umbilical tape. The sheep received no postoperative anticoagulation. The median operative time and estimated blood loss (EBL) was 170 min and 250 cc, respectively. Patency of the valved conduits was confirmed during the initial procedure, and there was no incidence of paraplegia postoperatively. Two animals expired shortly after extubation and at necropsy the valved conduits were patent with preserved valve function. The four survivors were sacrificed a median of 37 days postoperatively. Prior to euthanasia, the valved conduits were evaluated in situ with ultrasound. In all cases, the valves had clot formation at the hinges, which prevented active movement of the leaflets. This novel in vivo technique provides an alternative in testing the thrombogenicity of prosthetic heart valves without cardiac bypass or the risk of paraplegia in an animal that is extremely sensitive to complete aortic cross-clamp.     

Extracardiac valved conduits in the pulmonary circuit

Extracardiac valved conduits represent one of the weakest facets of reconstructive surgery for congenital heart disease in that they invariably need to be replaced because of growth of the patient or because of valve or conduit failure. Between 1979 and 1989, 141 patients had 169 valved conduits placed between the heart and the pulmonary artery circuit. There were 81 male and 60 female patients, aged 2 days to 35 years (mean age, 5.9 years), with 46 patients less than 1 year of age. We performed primary repair in 117 patients; in this group, there have been 28 conduit replacements in 27 patients. In 17 patients initial repair with a conduit was performed elsewhere and we replaced these conduits in 15 and removed them in 2. A further group of 9 patients were seen after repair of tetralogy of Fallot or double-outlet right ventricle, with severe pulmonary incompetence or right ventricular outflow tract aneurysm. All had valved conduits inserted as secondary procedures. The types of valved conduits used were xenograft (n = 126) and homograft (n = 43). There were six hospital deaths (3.6%; 70% confidence limits [CL], 2% to 6%) and seven late deaths (4.1%; CL, 2.5% to 6.5%) in a total of 169 conduit insertions. Forty-five conduits have been removed and 43 reinserted without early or late mortality (0%; CL, 0% to 4%). Actuarial survival after conduit insertion was 87% at 5 years (CL, 80% to 92%), including operative mortality. Actuarial freedom from conduit replacement was 37% at 5 years (CL, 20% to 56%). Conduit insertion in infants and small children ensures subsequent replacement, but this can be done at low risk.(ABSTRACT TRUNCATED AT 250 WORDS)