Valved Conduits for Right Ventricular Outflow Tract Reconstruction: A Review of Current Technologies and Future Directions

The need for right ventricular outflow tract reconstruction is common and growing in congenital heart surgery given expanding indications for the repair of congenital as well as acquired heart disease. Various valved conduit options currently exist including homografts, xenograft pulmonary valved conduits (Contegra™), and porcine valved conduits. The major limitation for all conduits is implant durability, which requires reoperation. Currently, cryopreserved homografts are often used given their superiority shown in long-term data. Significant limitations remain in the cost and availability of the graft, particularly for smaller sizes. Contegra conduits are available in a variety of sizes. Nonetheless, the data regarding long-term durability are less robust and studies comparing durability with homografts have been conflicting. Additionally, there is concern for increased rates of late endocarditis in this conduit. Porcine valved conduits offer a reliable option but are limited by structural valve degeneration associated with all types of bioprosthetic heart valve replacements. New developments in the field of tissue engineering have produced promising bio-restorative valved conduits that may overcome many of the limitations of previous conduit technologies. These remain in the early stages of clinical testing. This review summarizes the clinical data surrounding the conduits used most commonly in clinical practice today and explores emerging technologies that may bring us closer to developing the ideal conduit.

Ross Procedure in the era of Handmade-Valved Conduits for Right Ventricular Outflow Tract Reconstruction in Children: Short-Term Surgical Outcomes

Objective

Ross procedure is considered as the “gold standard” for aortic valve replacement, but the conduits used for right ventricular outflow tract (RVOT) reconstruction, such as homografts and bovine jugular vein (BJV) conduits, are of limited availability in China. Handmade expanded polytetrafluoroethylene-valved conduits (HVCs) have been used recently as the alternative for RVOT reconstruction, but their specific experience in Ross procedure is limited in the literature.

Methods

This was a retrospective review of 27 children who underwent Ross procedure in our center from January 2018 to January 2022.

Results

Mean age at surgery was 8.0 ± 3.8 years. During the study period, BJV conduits were used for RVOT reconstruction in 6 patients (22%), and HVCs were used in 21 patients (78%). Median conduit size was 20 mm (range, 16–24 mm), and mean conduit Z-score was +0.8 ± 0.9. Median time for cardiopulmonary bypass was 158 min (range, 109–275 min), and mean time for aortic crossclamping was 110 ± 21 min. There was no early mortality. During a median follow-up time of 1.4 years (range, 0.1–3.7 years), 3 patients (11%) with BJV conduits had peak conduit velocity of > 3.5 m/s; 3 patients (11%) with HVCs developed moderate conduit insufficiency; no patients had more than moderate conduit insufficiency. Three patients with BJV conduits had 5 reinterventions, and all received conduit replacement with HVCs.

Conclusion

HVC is an appealing alternative to BJV conduit for RVOT construction for children undergoing Ross procedure, with favorable short-term outcomes.

Application of Homograft Valved Conduit in Cardiac Surgery

Valved conduits often correct the blood flow of congenital heart disease by connecting the right ventricle to the pulmonary artery (RV-PA). The homograft valved conduit was invented in the 1960s, but its wide application is limited due to the lack of effective sterilization and preservation methods. Modern cryopreservation prolongs the preservation time of homograft valved conduit, which makes it become the most important treatment at present, and is widely used in Ross and other operations. However, homograft valved conduit has limited biocompatibility and durability and lacks any additional growth capacity. Therefore, decellularized valved conduit has been proposed as an effective improved method, which can reduce immune response and calcification, and has potential growth ability. In addition, as a possible substitute, commercial xenograft valved conduit has certain advantages in clinical application, and tissue engineering artificial valved conduit needs to be further studied.

Mid-term Outcomes for Polytetrafluoroethylene Valved Conduits

BACKGROUND

Various conduits for right ventricular outflow tract reconstruction (RVOTR) have been reported but most of them are not available in China. We developed a simple handsewn valved conduit using expanded polytetrafluoroethylene (ePTFE). This study evaluated the mid-term outcomes for this conduit.

METHODS

This retrospective study included a total of 72 patients who underwent RVOTR with ePTFE valved conduits between January 2014 and June 2020. During follow-up, echocardiograms were performed for all patients and magnetic resonance imaging for patients with repaired Fallot.

RESULTS

Patients had a median age of 69 (interquartile range, 28-127) months and a median follow-up period of 33 (interquartile range, 9-51) months . There was no early death , but two late deaths (2.78%) occurred. The median conduit size was 18 mm (interquartile range, 18-20) and Z score was +1.3 (interquartile range, +0.6-+2). Peak velocity across the ePTFE valve was 2.38 m/s (95% confidence interval, 2.11 - 2.63 m/s). Pulmonary valve regurgitation was none or trivial in 27 (38.5%) patients, mild in 42 (60.0%) patients and moderate in one (1.4%) patient. Conduit dysfunction occurred in five patients: four developed moderate conduit stenosis and one moderate regurgitation. The right ventricular end diastolic volume index in repaired Fallot was significantly decreased after surgery(171 ml/m² vs 130 ml/m², P<0.001).No reintervention or conduit replacement was needed.

CONCLUSIONS

The handsewn ePTFE valved conduit we developed has appreciable hemodynamic outcomes during the mid-term follow-up period. Long-term follow-up studies are needed to corroborate our findings.

Conduits for Right Ventricular Outflow Tract Reconstruction in Infants and Young Children

Purpose of Review: Right ventricular outflow tract (RVOT) reconstruction remains a challenge due to the lack of an ideal conduit. Data and experience are accumulating with each passing day. Therefore, it is necessary to review this topic from time to time. This is a 2021 update review focused on the history, evolution, and current situation of small-sized conduits (≤ 16 mm) for RVOT reconstruction in infants and young children.

Recent Findings: Currently, the available small-sized (≤16 mm) conduits can meet most clinical needs. Homograft is still a reliable choice for infants and young children validated by a half-century clinical experience. As an alternative material, bovine jugular vein conduit (BJVC) has at least comparable durability with that of homograft. The performance of expanded polytetrafluoroethylene (ePTFE) is amazing in RVOT position according to limited published data. The past century has witnessed much progress in the materials for RVOT reconstruction. However, lack of growth potential is the dilemma for small-sized conduits. Tissue-engineering based on cell-free scaffolds is the most promising technology to obtain the ideal conduit.

Summary: No conduit has proved to have lifelong durability in RVOT position. We are far from the ideal, but we are not in a state of emergency. In-depth clinical research as well as innovation in material science are needed to help improve the durability of the conduits used in infants and young children.

Evolution of pulmonary valve reconstruction with focused review of expanded polytetrafluoroethylene handmade valves

OBJECTIVES

Many surgeons develop unique techniques for unmet needs for right ventricular outflow reconstruction to resolve pulmonary regurgitation after corrective surgery for congenital heart diseases. Expanded polytetrafluoroethylene (ePTFE) stands out as a reliable synthetic material, and clinical results with handmade ePTFE valves have been promising. This review focuses on the historical evolution of the use of ePTFE in pulmonary valve replacement and in the techniques for pioneering the translation of the handmade ePTFE trileaflet design for the transcatheter approach.

METHODS

We searched for and reviewed publications from 1990 to 2020 in the Pubmed database. Nineteen clinical studies from 2005 to 2019 that focused on ePTFE-based valves were summarized. The evolution of the ePTFE-based valve over 3 decades and recent relevant in vitro studies were investigated.

RESULTS

The average freedom from reintervention or surgery in the recorded ePTFE-based valve population was 90.2% at 5 years, and the survival rate was 96.7% at 3 years.

CONCLUSIONS

Non-inferior clinical results of this ePTFE handmade valve were revealed compared to allograft or xenograft options for pulmonary valve replacement. Future investigations on transferring ePTFE trileaflet design to transcatheter devices should be considered.

Anisotropic Polytetrafluoroethylene Cardiovascular Conduits Spontaneously Expand in a Growing Lamb Model

BACKGROUND

Insertion of conduits from the right ventricle (RV) to the pulmonary artery (PA) is a commonly used technique for repair of congenital heart defects. The vast majority of infants and children will require reoperation and/or re-intervention to replace the conduit. Some children may require multiple reoperations, with the risk of death and morbidity increasing significantly with each subsequent operation. We evaluated the feasibility and performance of a relatively novel anisotropic conduit for cardiovascular repair in the growing lamb model.

MATERIALS AND METHODS

Lambs were allocated into a control (n = 3) or test (n = 4, anisotropic) conduit group. Control conventional polytetrafluoroethylene (PTFE) conduits or test anisotropic expanded PTFE (ePTFE) based test conduits measuring 10-11 mm in diameter were sewn as interpositional grafts in the main pulmonary artery (MPA) and followed up to 6 months. Clinical and echocardiographic evaluations were performed monthly with hemodynamic and angiographic assessment at 3 and 6 months.

RESULTS

Control conduits did not expand, all 3 animals developed one or more adverse events including tachypnea, ascites, inappetence, lethargy, and mortality due to severe right heart failure and significantly higher peak trans-conduit gradients (48.5 ± 5.1 p = 0.02). The test conduits spontaneously expanded up to 14.8 ± 0.8 mm in diameter, no adverse events were observed in any animals and trans-conduit gradients were significantly lower (27.0 ± 8.3, p = 0.02).

CONCLUSIONS

Anisotropic ePTFE conduits can be safely implanted in growing lambs with stable hemodynamics. This spontaneously expanding anisotropic conduit may represent a novel approach to congenital heart repairs that would avoid the need for reoperation or multiple operations.

Feasibility Study of Catheter-Based Interventions for Anisotropic Expanded Polytetrafluoroethylene Cardiovascular Conduits in a Growing Lamb Model

BACKGROUND

Cardiovascular repair in children often requires implant of conduits which do not have growth potential and will require reoperation. In the current study we sought to determine the feasibility of catheter-based interventions of anisotropic conduits inserted as interposition grafts in the main pulmonary artery (MPA) of growing lambs.

METHODS

Lambs underwent interpositional implant of either an anisotropic expanded polytetrafluoroethylene (ePTFE) (Test) conduit or conventional PTFE (Control) conduit. In the postoperative period, lambs were anesthetized and underwent catheter-based interventions consisting of hemodynamic and angiographic data collection, balloon dilation and/or stenting of the conduit at 3, 6 or 9 month postoperative time point.

RESULTS

At 3 months, control lambs showed significant increases in right ventricular pressures and trans-conduit gradients in comparison to test lambs. Test conduit diameters were significantly larger compared to controls due to spontaneous radial expansion of the anisotropic conduit. Balloon dilation of test conduits at 3 and 6 months showed a reduction in RV pressure and statistically significant improvement in the RV outflow tract gradient as well as significant increase in graft diameter, compared to both control and pre-dilation conditions. Furthermore, the test conduit diameter increased significantly compared to the pre-balloon and control conditions at each time point. Necropsy of test conduits showed no evidence of tears, perforations, or clot and smooth interiors with well-healed anastomoses.

CONCLUSIONS

Anisotropic conduits implanted as interposition grafts in the MPA show spontaneous expansion, and can safely and effectively undergo catheter-based interventions, with significant increases in graft diameter occurring after balloon dilation.

In vitro Assessment of the Impacts of Leaflet Design on the Hemodynamic Characteristics of ePTFE Pulmonary Prosthetic Valves

Prosthetic pulmonary valves are widely used in the management procedures of various congenital heart diseases, including the surgical pulmonary valve replacement (PVR) and right ventricular outflow tract reconstruction (RVOT). The discouraging long-term outcomes of standard prostheses, including homografts and bioprosthetic, constrained their indications. Recent developments in the expanded-polytetrafluoroethylene (ePTFE) pulmonary prosthetic valves provide promising alternatives. In this study, the hemodynamic characteristics of bileaflet and trileaflet ePTFE valve designs were experimentally evaluated. The in vitro tests were performed under the right ventricle (RV) flow conditions by using an in vitro RV circulatory system and particle image velocimetry (PIV). The leaflet kinetics, trans-valvular pressure gradients, effective orifice areas, regurgitant fractions, energy losses, velocity fields, and Reynolds shear stress (RSS) in both prostheses were evaluated. The opening of the bileaflet and trileaflet valve takes 0.060 and 0.088 s, respectively. The closing of the former takes 0.140 s, in contrast to 0.176 s of the latter. The trans-valvular pressure is 6.8 mmHg in the bileaflet valve vs. 7.9 mmHg in the trileaflet valve. The effective orifice area is 1.83 cm2 in the bileaflet valve and 1.72 cm2 in the trileaflet valve. The regurgitant fraction and energy loss of bileaflet are 7.13% and 82 mJ, which are 7.84% and 101.64 mJ in its bileaflet counterpart. The maximum RSS of 48.0 and 49.2 Pa occur at the systole peak in the bileaflet and trileaflet valve, respectively. A higher average RSS level is found in the bileaflet valve. The results from this preliminary study indicate that the current bileaflet prosthetic valve design is capable of providing a better overall hemodynamic performance than the trileaflet design.

Outcome of 40 consecutive cases of modified Ross procedure using novel Dacron valved conduit

OBJECTIVE

The Ross procedure is an established option for aortic valve disease in children. Due to limited availability of pulmonary homograft, we devised a novel technique for right ventricular outflow tract (RVOT) reconstruction by preparing indigenous Dacron valved conduit.

METHODS

Forty consecutive cases of modified Ross procedure done at our center (2013-2018) were analyzed. Thirty-seven patients (95%) were followed up with median duration of 2.5 (0.08-5.5) years. Median age was 12 (5-39) years. Nineteen (47.5%) patients had rheumatic aortic valve disease, while 19 (47.5%) had congenital aortic valve disease. Aortic root replacement with pulmonary autograft was performed in all patients. Dacron conduit for RVOT reconstruction was used with on table sewn bileaflet valve using Dacron patch (n = 22), expanded polytetrafluoroethylene (ePTFE) membrane (n = 10), bioprosthetic valve (n = 4), and pericardium (n = 4). Additional surgical procedures included mitral valve repair (n = 10), septal myectomy (n = 2), ascending aorta replacement (n = 1), ruptured sinus of valsalva (RSOV) repair (n = 1), and ventricular septal defect (VSD) closure (n = 1).

RESULTS

There was one in-hospital mortality while one late death occurred at 3.5 years postoperatively. The neo-aortic valve regurgitation on echocardiographic evaluation at last follow-up was trivial (n = 28), mild (n = 7), and moderate (n = 2). Mild RVOT obstruction was present in 8 patients while 18 patients had mild pulmonary regurgitation. No patient required reintervention during follow-up.

CONCLUSION

Our early results of modified Ross procedure are encouraging, however, long-term follow-up is required.