Right ventricular outflow tract reconstruction using a Goretex membrane monocusp valve in infant animals

Fate of Polytetrafluoroethylene Monocusp Pulmonary Valves in an Animal Model

Creation of a competent pulmonary monocusp valve facilitates transition from pressure to volume overload following right ventricular outflow tract reconstruction. To determine intermediate-term results and performance of the different types of polytetrafluoroethylene membrane used to construct monocusp valves and transannular patches, 12 infant lambs underwent excision of the native pulmonary valve and insertion of a monocusp valve and transannular patch made from one of 4 types of membrane. Echocardiography was performed after 3, 6, 9, and 12 months, and cardiac catheterization was carried out prior to animal sacrifice at 6 ( n = 4) or 12 ( n = 8) months. There was no postoperative morbidity or mortality. On echocardiography, 6 valves were mobile (50%), 4 had diminished mobility (33%), and 2 were fixed (17%) prior to sacrifice. At catheterization, mild, moderate, and severe pulmonary regurgitation was observed in 4 valves each (33%), with no stenosis. Right ventricular outflow tract reconstruction with polytetrafluoroethylene monocusp valves can be safely accomplished with good early competence, variable degrees of late insufficiency, and no stenosis. Compared to an open microstructure, the closed polytetrafluoroethylene microstructure showed a milder fibroinflammatory reaction and fewer foci of microcalcification, with sparing of the free edge of the monocusp; this correlated with better intermediate-term hemodynamic performance.

Current status of right ventricular outflow tract reconstruction: complete translation of a review article originally published in Kyobu Geka 2014;67:65-77

Right ventricular outflow tract (RVOT) reconstruction is becoming more prevalent as the number of adult patients who require repeated surgery long after definitive repair of congenital heart defects during childhood has increased. Early primary repair and annulus-preserving surgery have been the two current strategies of RVOT reconstruction from the viewpoint of timing and indications for surgical intervention; however, the long-term outcomes of both procedures remain unknown. Although various materials have been used for pulmonary valve replacement during RVOT reconstruction, deficient durability due primarily to immunological rejection frequently arises, particularly when implanted into young patients. A multicenter study in Japan showed that the clinical outcomes of expanded polytetrafluoroethylene (ePTFE) valved patches/conduits that we developed and manufactured comprised an excellent alternative material for RVOT reconstruction. Such enhanced outcomes might have partly been attributable to the biocompatibility and low antigenicity of ePTFE, and also to the fluid dynamic properties arising from the structural characteristics of a bulging sinus and a fan-shaped valve. However, numerous issues concerning RVOT reconstruction, such as indications for and the timing of definitive repair, as well as the choice of materials for pulmonary valve replacement, must be resolved to achieve better patient prognoses and quality of life. This review describes recent surgical strategies and outstanding issues associated with RVOT reconstruction.

Right ventricular outflow tract reconstructive model in adult sheep

Patients born with congenital right ventricular outflow tract lesions are faced with invasive procedures to establish hemodynamic and physiological stability. Commonly, multiple subsequent surgical procedures are required due to deterioration of a previous repair. These procedures carry additive risks of mortality and morbidity. Less aggressive procedures with accompanying lower risk is ideal. Success in percutaneously placing a transcatheter valve has previously been reported; however, continued safety and efficacy of any technique needs continual assessment. We developed a model for preclinical evaluation of a percutaneous placement of a pulmonic transcatheter valve in adult sheep, including preoperative, surgical, and postoperative techniques for long-term evaluation. Adult sheep were assessed and determined to be acceptable for study enrollment. Perioperative antibiotics and analgesics were given prior to a left thoracotomy. A Medtronic, Hancock 1 valve conduit was inserted for reconstruction of the right ventricular outflow tract. The Hancock 1 valve conduit alone represented the control group and the test animals comprised the addition of a Melodytrade mark transcatheter pulmonary valve (TPV), within the Hancock 1 valve conduit. Fifteen adult sheep survived the surgical implant procedure with no perioperative mortality. There were four early postoperative deaths, three due to infection and one due to heart failure, secondary to intraoperative heart block. The remaining 11 animals remained healthy, gained weight, and survived to termination at 5 months. An initial definite-sized valve conduit was implanted, followed by inserting a single size TPV, which allowed a more accurate physiological assessment of any chosen valve. Our developed adult sheep model for percutaneous TPV implantation for right ventricular outflow tract lesions was successful for long-term assessment by utilizing our preoperative, surgical, and postoperative techniques.

Tissue regeneration observed in a porous acellular bovine pericardium used to repair a myocardial defect in the right ventricle of a rat model

OBJECTIVE

Nonliving synthetic materials have been widely used to repair myocardial defects; however, material-related failures do occur. To overcome these problems, an acellular bovine pericardium with a porous structure fixed with genipin (the AGP patch) was developed.

METHODS

The AGP patch was used to repair a surgically created myocardial defect in the right ventricle of a rat model. A commercially available expanded polytetrafluoroethylene (e-PTFE) patch was used as a control. At retrieval, a computerized mapping system was used to acquire local epicardial electrograms of each implanted sample, and the appearance of each retrieved sample was grossly examined. The retrieved samples were then processed for histologic examination.

RESULTS

The amplitude of local electrograms on the AGP patch increased significantly with increasing implantation duration, whereas only low-amplitude electrograms were observed on the e-PTFE patch throughout the entire course of the study. No aneurysmal dilation of the implanted patches was seen for either studied group. Additionally, no tissue adhesion was observed on the outer (epicardial) surface of the AGP patch, whereas a moderate tissue adhesion was observed on the e-PTFE patch. On the inner (endocardial) surface, intimal thickening was observed for both studied groups; however, no thrombus formation was found. Intact layers of endothelial and mesothelial cells were identified on the inner and outer surfaces of the AGP patch, respectively. At 4 weeks postoperatively, smooth muscle cells, together with neomuscle fibers (with a few neocollagen fibrils), neoglycosaminoglycans, and neocapillaries, were observed to fill the pores in the AGP patch, an indication of tissue regeneration. These observations were more pronounced at 12 weeks postoperatively. In contrast, no apparent tissue regeneration was observed in the e-PTFE patch.

CONCLUSION

The present study indicated that the AGP patch holds promise to become a suitable patch for surgical repair of myocardial defects.

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.

Annular and leaflet augmentation in Noonan's syndrome with dysplastic pulmonary valve

Two patients with dysplastic pulmonary valves associated with Noonan's syndrome successfully underwent leaflet augmentation with pericardial membrane and annular enlargement with preservation of valve competence. Both patients are doing well at 36 and 37 months, respectively, postoperatively. Echocardiography and clinical assessment showed gradients of 12 and 16 mmHg, respectively, and negligible pulmonary valve insufficiency. The surgical technique is simple and provides an attractive alternative in patients with dysplastic pulmonary valve and small pulmonary orifice and annulus.

Histologic changes of nonbiodegradable and biodegradable biomaterials used to repair right ventricular heart defects in rats

OBJECTIVES

Nonbiodegradable synthetic materials have been widely used to repair cardiac defects. Material-related failures, however, such as lack of growth, thrombosis, and infection, do occur. Because a biodegradable scaffold can be replaced by the patient's own cells and will be treated as a foreign body for a limited period, we compared four biodegradable materials (gelatin, polyglycolic acid (PGA), and copolymer made of epsilon-caprolactone and l-lactic acid reinforced with a poly-l-lactide knitted [KN-PCLA] or woven fabric [WV-PCLA]) with a nonbiodegradable polytetrafluoroethylene (PTFE) material. An animal heart model was tested that simulates the in vivo clinical condition to which a synthetic material would be used.

METHODS

The five patches were used to repair transmural defects surgically created in the right ventricular outflow tracts of adult rat hearts (n = 5, each patch group). The PTFE patch group served as a control group. At 8 weeks after implantation, the biomaterials were excised. Patch size, patch thickness, infiltrated cell number, extracellular matrix composition, and patch degradation were evaluated.

RESULTS

The PTFE patch itself did not change in size except for increasing in thickness because of fibroblast and collagen coverage of both its surfaces. Host cells did not migrate into the PTFE biomaterial. In contrast, cells migrated into the biodegrading gelatin, PGA, and KN-PCLA and WV-PCLA scaffolds. Cellular ingrowth per unit patch area was highest in the KN-PCLA patch. The KN-PCLA patch increased modestly in size and thinness. The WV-PCNA patch did not change in size or thickness. Fibroblasts and collagen were the dominant cellular infiltrate and extracellular matrix formed in the biodegrading scaffolds. The in vivo rates of biomaterial degradation, thinning, and expansion were material specific. All the subendocardial patch surfaces were covered with endothelial cells. No thrombi were seen.

CONCLUSIONS

The unique, spongy matrix structure of the PCLA patch favored cell colonization relative to the other patches. The strong, durable outer poly-l-lactide fabric layers in these patches offered physical, biocompatible, and bioresorbable advantages relative to the other biodegradable materials studied. Host cells migrated into all the biomaterials. The cells secreted matrix and formed tissue, which was endothelialized on the endocardial surface. The biomaterial degradation rates and the tissue formation rates were material related. The PCLA grafts hold promise to become a suitable patch for surgical repair.