Percutaneous Pulmonary Valve Replacement: 3-Month Evaluation of Self-Expanding Valved Stents

Transcatheter pulmonary valve replacement: a new polycarbonate urethane valve

OBJECTIVES

Transcatheter pulmonary valve replacement has become a valid treatment option for right ventricular outflow tract diseases. However, some limitations occur in patients with wide, compliant right ventricular outflow tracts that might be amenable to treatment with self-expanding valved protheses. An experimental ovine study was designed to evaluate a novel dip-coated, low-profile trileaflet polycarbonate urethane (PCU) heart valve mounted into a self-expandable nitinol stent.

METHODS

The PCU valves were produced by a dip-coating technique, mounted in a conical-shaped nitinol stent and provided with a leaflet thickness of 100-150 µm. The valved stents were implanted percutaneously via transfemoral access in 6 consecutive sheep divided into 2 groups. Three animals were followed up for 1 month and the remainder, for 6 months. Angiographic measurements and transthoracic echocardiography were performed before and after implantation and at the end of the 1- or 6-month observation period, respectively.

RESULTS

Orthotopic positioning of the valve was achieved in all animals. All except 1 had competent valves during the follow-up period. The peak-to-peak gradient across the PCU valved stents was 4.6 ± 1.0 mmHg after 1 month and 4.4 ± 2.3 mmHg after 6 months of follow-up. Macroscopic and microscopic post-mortem evaluation indicated good morphological and structural results. There were no stent fractures, leaflet calcification or thrombus formation.

CONCLUSIONS

This study demonstrates successful transcatheter pulmonary valve replacement with a novel dip-coated valved nitinol stent. The trileaflet PCU prostheses indicated good functional and biocompatible properties after a 6-month observation period.

Transcatheter Pulmonary Valve Replacement and Acute Increase in Diastolic Pressure are Associated with Increases in Both Systolic and Diastolic Pulmonary Artery Dimensions

Stable positioning of a transcatheter pulmonary valve (TPV) in native outflow tracts depends on a clear understanding of underlying anatomy and outflow tract dimensions. We hypothesized that restoration of pulmonary competence may acutely alter these dimensions. A retrospective single-center review of consecutive patients after TPV placement from 2007 to 2014 was performed. Patients with less than moderate pulmonary regurgitation were excluded. We reviewed acute catheterization data on 46 patients, most with tetralogy of Fallot (70%). Baseline and post-implant (7.5 ± 3 min post-deployment) measurements of central pulmonary arteries (PAs) were determined angiographically. The right PA diameter increased (20 ± 4-24 ± 6 mm systole*, 16 ± 4-21 ± 6 mm diastole*), as did the left PA (20 ± 6-24 ± 8 mm systole*, 16 ± 5-21 ± 7 mm diastole*). PA pressures increased from averages of 29.3/10.6 (17) to 29.8/15.1 (21) mmHg. We noted that pre-implant systolic PA diameter correlated with diastolic PA diameter post-implant (r = 0.9). On follow-up catheterization in seven patients [median 3 years; (1-8)], combined central PA diameter decreased an average of 20% (systole: 20% ± 12, diastole: 18% ± 11) as compared to post-implant measurements. Acute pulmonary valve competence in patients with at least moderate pulmonary regurgitation results in an immediate increase in PA diameter (20% systole and 30% diastole). The cause of this diameter change is unclear. This acute change may have implications for device and patient selection (*p < 0.001).

Transcatheter pulmonary valve replacement by hybrid approach using a novel polymeric prosthetic heart valve: proof of concept in sheep

Background

Since 2000, transcatheter pulmonary valve replacement has steadily advanced. However, the available prosthetic valves are restricted to bioprosthesis which have defects like poor durability. Polymeric heart valve is thought as a promising alternative to bioprosthesis. In this study, we introduced a novel polymeric transcatheter pulmonary valve and evaluated its feasibility and safety in sheep by a hybrid approach.

Methods

We designed a novel polymeric trileaflet transcatheter pulmonary valve with a balloon-expandable stent, and the valve leaflets were made of 0.1-mm expanded polytetrafluoroethylene (ePTFE) coated with phosphorylcholine. We chose glutaraldehyde-treated bovine pericardium valves as control. Pulmonary valve stents were implanted in situ by a hybrid transapical approach in 10 healthy sheep (8 for polymeric valve and 2 for bovine pericardium valve), weighing an average of 22.5±2.0 kg. Angiography and cardiac catheter examination were performed after implantation to assess immediate valvular functionality. After 4-week follow-up, angiography, echocardiography, computed tomography, and cardiac catheter examination were used to assess early valvular function. One randomly selected sheep with polymeric valve was euthanized and the explanted valved stent was analyzed macroscopically and microscopically.

Findings

Implantation was successful in 9 sheep. Angiography at implantation showed all 9 prosthetic valves demonstrated orthotopic position and normal functionality. All 9 sheep survived at 4-week follow-up. Four-week follow-up revealed no evidence of valve stent dislocation or deformation and normal valvular and cardiac functionality. The cardiac catheter examination showed the peak-peak transvalvular pressure gradient of the polymeric valves was 11.9±5.0 mmHg, while that of two bovine pericardium valves were 11 and 17 mmHg. Gross morphology demonstrated good opening and closure characteristics. No thrombus or calcification was seen macroscopically.

Conclusions

This design of the novel ePTFE transcatheter pulmonary valve is safe and effective to deploy in sheep by hybrid approach, and the early valvular functionality is good.

Percutaneous options for heart failure in adults with congenital heart disease

In the context of congenital heart disease (CHD), the complex biochemical and physiologic response to the pressure- or volume-loaded ventricle can be induced by stenotic and shunt/regurgitant lesions, respectively. A range of transcatheter therapies have recently emerged to expand the therapeutic potential of the more traditional surgical and medical interventions for heart failure in patients with CHD. Together, these complementary interventions aim to treat the growing patient population with adult CHD (ACHD). In this article, the most commonly used transcatheter interventions for heart failure in patients with ACHD are reviewed.

Fluid Structure Interaction With Contact Surface Methodology for Evaluation of Endovascular Carotid Implants for Drug-Resistant Hypertension Treatment

Drug-resistant hypertensive patients may be treated by mechanical stimulation of stretch-sensitive baroreceptors located in the sinus of carotid arteries. To evaluate the efficacy of endovascular devices to stretch the carotid sinus such that the induced strain might trigger baroreceptors to increase action potential firing rate and thereby reduce systemic blood pressure, numerical simulations were conducted of devices deployed in subject-specific carotid models. Two models were chosen—a typical physiologic carotid and a diminutive atypical physiologic model representing a clinically worst case scenario—to evaluate the effects of device deployment in normal and extreme cases, respectively. Based on the anatomical dimensions of the carotids, two different device sizes were chosen out of five total device sizes available. A fluid structure interaction (FSI) simulation methodology with contact surface between the device and the arterial wall was implemented for resolving the stresses and strains induced by device deployment. Results indicate that device deployment in the carotid sinus of the physiologic model induces an increase of 2.5% and 7.5% in circumferential and longitudinal wall stretch, respectively, and a maximum of 54% increase in von Mises arterial stress at the sinus wall baroreceptor region. The second device, deployed in the diminutive carotid model, induces an increase of 6% in both circumferential and longitudinal stretch and a 50% maximum increase in von Mises stress at the sinus wall baroreceptor region. Device deployment has a minimal effect on blood-flow patterns, indicating that it does not adversely affect carotid bifurcation hemodynamics in the physiologic model. In the smaller carotid model, deployment of the device lowers wall shear stress at sinus by 16% while accelerating flow entering the external carotid artery branch. Our FSI simulations of carotid arteries with deployed device show that the device induces localized increase in wall stretch at the sinus, suggesting that this will activate baroreceptors and subsequently may control hypertension in drug-resistant hypertensive patients, with no consequential deleterious effects on the carotid sinus hemodynamics.

Eighteen-month outcome of pulmonary valve stent implantation by direct right ventricle puncture: an animal study

OBJECTIVE

The purpose of this study was to investigate the feasibility and safety of pulmonary valve implantation via direct right ventricle puncture.

METHODS

A standard thoracotomy and direct right ventricle puncture were performed in 8 healthy sheep to implant the pulmonary valve stents. Animals were followed up for 18 months.

RESULTS

Three sheep died within the first 4 months after stent placement. The remaining 5 animals survived. After 18 months, examinations by color echocardiography, 64-slice computed tomography scan, and cardiac catheter showed an ideal position of each stent. The function of the pulmonary valves and hearts was not different compared with the preoperative conditions of the sheep. Anatomic examination revealed that the stent was covered by a layer of endothelial tissue with no stent fracture or valvular calcification. The histologic evaluation of the stent and surrounding tissue showed that the surface of the stent was smooth and covered by a complete layer of endothelial cells without obvious infiltration of inflammatory cells. The vascular wall was integrative without tear phenomenon in each layer of tissue.

CONCLUSIONS

These results show that pulmonary valve stents can be implanted via direct right ventricle puncture. Further studies evaluating xenograft valve material and the effect of implantation in vivo are needed.

Percutaneous tissue-engineered pulmonary valved stent implantation

PURPOSE

The purpose of this study was to evaluate the feasibility of percutaneously implanted tissue-engineered valved stents in the ovine pulmonary valve position.

DESCRIPTION

Porcine pulmonary heart valves and small intestinal submucosa were obtained from a slaughterhouse, and the intestinal submucosa used to cover the inside of the porcine pulmonary valved stents. Endothelial cells and autologous myofibroblasts were obtained from carotid artery segments of juvenile sheep. After myofibroblast seeding, constructs were placed in a dynamic bioreactor system and were cultured for 16 days. After Endothelial cell seeding, the tissue-engineered valved stents were deployed into the pulmonary valve annular site. Angiography was performed at implantation and explantation (4 weeks). Constructs were analyzed macroscopically and microscopically.

EVALUATION

Orthotopic positioning of the stents (n = 3) at the time of implantation and explantation, as well as normal valve function, was observed through angiography. Gross morphology confirmed excellent opening and closing of all leaflets. Strong expression of alpha-smooth muscle actin in neointerstitial cells and of von-Willebrand-Factor in endothelial cells was revealed by immunocytochemistry.

CONCLUSIONS

This study demonstrates successful merging of two novel technologies: (1) percutaneous valved stent implantation and (2) tissue engineering of autologous heart valves.

Percutaneous heart valve replacement: histology and calcification characteristics of biological valved stents in juvenile sheep

INTRODUCTION

Percutaneous techniques to replace the pulmonary valve are emerging as an alternative to congenital cardiac surgical procedures. Promising experimental and early clinical results have been reported so far, focusing on technical feasibility and valved stent function. The present study aimed to describe the micropathology after experimental percutaneous valve replacement.

METHODS

Self-expanding nitinol stents carrying a valved bovine jugular vein were transfemorally implanted into the pulmonary position of nine sheep. After 3 months of survival, macro- and micropathological examinations were carried out using standard staining techniques and immunohistochemistry. Additionally, calcification characteristics were determined by X-ray examinations and von Kossa stainings.

RESULTS

Six of nine animals survived the 3-month study time with good angiographic and echocardiographic function. All valves were grossly functional at the time of explantation. Slight fibrous overgrowth was seen at the inflow portions of two valved stents. No cuspal perforations or intracuspal hematomas were observed. Light microscopy proved the absence of cellular inflammatory infiltrates in any tissue samples. The myocardium directly proximal to the stent appeared structurally normal without calcification. The overall structure of the native pulmonary artery was well preserved with few mineral deposits spread diffusely throughout the wall distal to the stent. Massive calcification appeared in the bovine jugular-vein wall together with increased numbers of T lymphocytes. Neither calcific deposits in the cusps nor extrinsic mineralization was noted.

CONCLUSION

For the first time, micropathologic evaluation of percutaneously implanted heart valves is described. The results demonstrate that calcification of valved stents occurs in the wall portions without affecting the cusps. The cardiac structures in the vicinity had normal histology without inflammation.