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Experimental right ventricle to pulmonary artery discontinuity: Outcome of polyurethane valved conduits
Abstract
The ideal substitute for the treatment of ventricle-pulmonary artery discontinuity remains a topic of controversy, because of calcifications and degeneration of biologic substitutes leading to subsequent reoperations. Because polyurethane valves used in ventricular assist devices show a satisfactory biocompatibility, the aim of this study was to evaluate a valved conduit composed of a Dacron graft incorporating a trileaflet 25 mm polyurethane valve.
The conduit was implanted between the right ventricle and the main pulmonary artery in adult sheep, with ligation of the proximal pulmonary artery. The animals received no medications. Serial hemodynamic data were collected at the time of implantation and at postoperative intervals of 6 and 12 months.
The peak pressure gradient across the valve increased significantly between implantation (0.17 +/- 5.6 mm Hg) and 6 months after operation (7.3 +/- 3 mm Hg, p = 0.0007) and remained stable thereafter (6.7 +/- 3 mm Hg at 12 months), whereas the cardiac output remained unchanged (4.6 +/- 0.6 L/min at implantation, 4 +/- 0.6 L/min at 6 months, and 3.9 +/- 1.1 L/min at 12 months). At the completion of the study, valve samples were processed and vapor coated with carbon for microscopic examination. There was one instance of nonadherent thrombus formation inside a cusp but no structural failures. The other valves were free of calcium deposits and no significant amounts of phosphorus could be detected by scanning electron microscopy and energy dispersive spectrometry.
These data demonstrate the good hemodynamic performance, low thrombogenicity, and acceptable durability of the polyurethane valves implanted in the right side of the heart in a chronic sheep model.
... Polymeric heart valve prostheses have been used in both experimental [1][2][3][4][5][6] and clinical studies [7][8][9][10][11]. These constructs, which have been fabricated from polyurethane and other elastomers, have all failed due to either thrombosis or calcification or both [1][2][3][4][5][6][7][8][9][10][11]. ...
... Polymeric heart valve prostheses have been used in both experimental [1][2][3][4][5][6] and clinical studies [7][8][9][10][11]. These constructs, which have been fabricated from polyurethane and other elastomers, have all failed due to either thrombosis or calcification or both [1][2][3][4][5][6][7][8][9][10][11]. However, the attraction of the potential desirable features of a polymer heart valve remains. ...
... Calcification of trileaflet polyurethane valves and comparable prostheses fabricated from other elastomers have been reported from both experimental and clinical studies. These polymeric calcifications have pathologic features [1][2][3][4][5][6][7][8][9][10] comparable to those observed in the present study. Calcification of polyurethane is typically surface oriented with the bulk of the polymer unaffected. ...
Calcification of polyurethane cardiovascular implants is an important disease process that has the potential to compromise the long-term function of devices such as polymer heart valves and ventricular assist systems. In this study we report the successful formulation and characterization of bisphosphonate-derivatized polyurethanes, hypothesized to resist implant calcification based on the pharmacologic activity of the immobilized bisphosphonate. Fully polymerized polyurethanes (a polyurea-polyurethane and a polycarbonate polyurethane) were modified (post-polymerization) with bromoalkylation of the hard segments followed by attachment of a bisphosphonate group at the bromine site. These bisphosphonate-polyurethanes resisted calcification in rat 60 day subdermal implants compared to nonmodified control polyurethane implants, that calcify. Bisphosphonates-modified polyurethanes were also studied in circulatory implants using a pulmonary valve cusp replacement model in sheep. Polyurethane cusps modified with bisphosphonate did not calcify in 90 day implants. compared to control polyurethane cusps implants, that demonstrated nodular surface oriented calcific deposits. It is concluded that bisphosphonate modified polyurethanes resist calcification both in subdermal implants and in the circulation. This novel biomaterial approach offers great promise for long-term blood stream implantation with calcification resistance.
... The following case series has been reported from Our University Hospital which is an internationally recognized teaching hospital and a tertiary care center based in Pakistan, in accordance with the PROCESS guidelines for case series 24 . Right ventricle-pulmonary artery (RV-PA) anatomic discontinuity is present in approximately 5% of hearts with congenital defects 1 . Some of the conditions that need restoration of continuity are variants of tetralogy of Fallot (TOF), pulmonary atresia and in discordant heart morphology 2 . ...
Objectives
Right ventricular outflow tract continuity abnormalities are one of the most commonly encountered entities in the field of congenital cardiac surgery. Various strategies including homograft, valve conduit, Contegra are used to restore continuity between right ventricle and pulmonary artery. In countries like Pakistan these may not be easily available and affordable. We report the experience of our short observational study of using a handmade trileaflet valve conduit to reconstruct the right ventricular outflow tract.
Methodology
From September 2015 to December 2016, a total of 15 patients with different congenital heart diseases underwent open-heart surgery at our institute. Restoration of right ventricular to pulmonary artery continuity was achieved using handmade valve conduit utilizing bovine pericardium and thin sheet PTFE sheets (0.1 mm) as conduit and valve respectively.
Results
Patients ranged from 1 to 16 years. Seven patients had previous palliation including 4 blalock taussig (BT) Shunts and 3 pulmonary artery (PA) banding. Postoperative complications were observed in 4 patient including 2 in hospital deaths and 2 required interventions. One patient developed aneurysm at RV- conduit junction requiring surgical repair and the other underwent conduit dilatation for moderate to severe stenosis (gradient 60 mmHg). No significant regurgitation was observed in this series. Overall postoperative gradients were stable with mean gradient 25.3 mmHg (8 mmhg - 60 mmHg).
Conclusion
The use of handmade valve conduits has acceptable morbidity and mortality. These are cost effective alternatives in this part of the world, where well-established conduits have cost implications and uncertain availability.
... pp.245-253 plications are gradually receiving much attention. For example, the biodegradable SMPs are useful in medicine including wound sutures, filling and sealing cranial aneurysms [2][3][4]. continuous-fiber-reinforced shape memory composites have developed substantial interest in future deployable space-structure industry [5][6][7]. Several investigators have exploited the SMP-based MEMS with functions such as gripping or releasing therapeutic medical devices within blood vessels [8][9]. ...
... Therefore, the search for new and more effective occlusive materials continues789. Polyurethanes (PU), because of their low thrombogenicity , are polymers widely used in the construction of hematology related products and devices101112. Shape memory polyurethanes (SMPu) are being intensely investigated as biomaterials. ...
Cold hibernated elastic memory (CHEM) polyurethane-based foam is a new shape memory polymeric self-deployable structure. Standard cytotoxicity and mutagenicity tests were conducted on CHEM in vitro, to ensure biocompatibility before studying potential medical applications. In vivo, lateral wall aneurysms were constructed on both carotid arteries of eight dogs. Aneurysms were occluded per-operatively with CHEM blocks. In two dogs, CHEM embolization was compared with gelatin sponge fragment embolization. Internal maxillary arteries (Imax) were also occluded with CHEM using a 6F transcatheter technique. Angiography and pathology were used to study the evolution of aneurysms and Imax at 3 and 12 weeks. Imax embolized with CHEM foam remained occluded at 3 weeks. Most aneurysms embolized with CHEM showed a small residual crescent of opacification at initial angiography, but angiographic scores were significantly better at 3 weeks. Thick neointima formation over the CHEM at the neck of aneurysms was demonstrated at pathology. The foamy nature of CHEM favours the ingrowth of cells involved in neointima formation. New devices for endovascular interventions could be designed using CHEM's unique physical properties.
... There was even a report of successful percutaneous placement of this valve in 7 children and 1 adult [29]. Other potential valve replacements on the horizon are synthetic polyurethane valves [30] and decellularized homograft valves (Synergraft; CryoLife, Inc, Kennesaw, GA) [31]. Clearly, as time goes on, we will be able to determine if the Freestyle porcine valve (or any of the previously mentioned valves) will have satisfactory durability and hemodynamic performance to supplant homograft valves in reconstruction of the right ventricular outflow tract in children. ...
The ideal choice for valved reconstruction of the right ventricular outflow tract (RVOT) in children is undetermined. This study explores the Freestyle porcine aortic root for these patients.
From January 1998 to December 2002, 56 patients ages 1.6 to 29.9 years old (mean 11.8 years old) underwent RVOT reconstruction using a Freestyle porcine aortic root. The patients averaged 1.9 prior operations (range 0 to 5) for tetralogy of Fallot +/- pulmonary atresia (28 patients), critical pulmonary stenosis (10 patients), Ross procedure (5 patients), pulmonary atresia/intact ventricular septum (4 patients), complete atrioventricular septal defect +/- tetralogy of Fallot (4 patients), and others (5 patients). At time of RVOT reconstruction, 42 patients (75%) had additional procedures including the following: tricuspid or mitral repair (24 patients), pulmonary arterioplasty +/- Glenn (12 patients), ventricular septal defect closure (5 patients), aortic valve replacement (3 patients), placement of a cardioverter/defibrillator or pacemaker (3 patients), and others (8 patients).
One patient developed mediastinitis; another was treated for Candida endocarditis (his excised homograft unexpectedly grew Candida). All patients are well on follow-up from 2 to 60 months (mean 30 +/- 20 months) with no deaths. The patient with endocarditis underwent conduit replacement for recurrent pulmonary stenosis 3.5 years postoperatively. Echocardiography revealed mild or no pulmonary insufficiency in 93%. The calculated mean peak systolic RVOT gradient by echocardiography was 19.7 +/- 15.4 mm Hg.
These data demonstrate excellent results with the Freestyle bioprosthesis for RVOT reconstruction in children. This valve may serve as a readily available alternative to homograft valves in RVOT reconstruction, particularly since early insufficiency seems to be less problematic. Questions of long-term durability and significance of echocardiographic stenosis remain unanswered.
... In addition, polyurethanes are known to be non-thrombogenic, so these catheters will not activate the coagulation cascade. Because of their low thrombogenicity, polyurethanes are widely used in the construction of hematology related products and devices789. SMP materials are considered to be used for orthopedic braces and splints that can be custom fitted. ...
Shape memory polymers (SMP) are lightweight, have a high strain/shape recovery ability, are easy to process, and required properties can be tailored for variety of applications. Recently a number of medical applications have been considered and investigated, especially for polyurethane-based SMP. SMP materials were found to be biocompatible, non-toxic and non-mutagenic. The glass transition temperature (T(g)) can be tailored for shape restoration/self-deployment of clinical devices when inserted in the human body. Newly developed SMP foams, together with cold hibernated elastic memory (CHEM) processing, further broaden their potential biomedical applications. Polyurethane-based SMP are described here and major advantages are identified over other medical materials. Some SMP applications are already used in a clinical setting, whereas others are still in development. Lately, several important applications are being considered for CHEM foams as self-deployable vascular and coronary devices. One example is the endovascular treatment of aneurysms.
This chapter reviews clinical indications for valve replacement, with emphasis on the aortic, mitral, and tricuspid valves, as well as the physiology associated with valve replacements. Another section describes valve biomaterial and the effects of these materials on thrombogenicity, resistance or susceptibility to infection. Finally, an introduction to newer biomaterial and valve designs will further pique the reader, with the intent of spawning new approaches in the ongoing refinement of cardiac valves.
A series of shape memory epoxy composites reinforced by varied carbon-black (CB) contents were prepared. Stress relaxation tests were preformed to characterize the viscoelastic behavior of the specimens at different temperatures. An empirical rheological model was used to simulate the impacts of the temperature and CB content on the viscoelastic behavior of the materials. The results show that the additive of CB particles can significantly improve the stiffness and decrease viscoelastic properties of shape memory epoxy. In addition, parameter analyses in the theoretical simulation present a further understanding about the impact of the additives on the properties of SMPs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Viscoelastic behavior has a remarkable impact on the functional realization of shape memory polymers and their composites. Our previous work reported that a series of shape memory epoxies with varied curing agents and contents were synthesized and exhibited higher shape fixture and recovery rates. The viscoelastic behavior of the materials at different temperatures is experimentally investigated in this study. Stress–strain hysteresis under uniaxial tension, stress relaxation, and creep tests are performed. The energy dissipation factor and residual strain factor as functions of temperatures are presented in the basis of stress–strain hysteresis tests. Moreover, the effects of test temperature, curing‐agent type, and content on the viscoelastic behavior of these materials are discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
The purpose of this study was to characterize the partial strain recovery of a thermoset shape‐memory polymer under a constraining stress. Three polymer networks were synthesized from tert‐butyl acrylate and poly(ethylene glycol) dimethacrylate (PEGDMA) solutions. The molecular weight and the weight fraction of the PEGDMA crosslinking monomer was altered systematically to maintain a constant glass transition temperature (T g = 54°C) but tailorable rubbery moduli, which varied by almost an order of magnitude for the three polymer networks (E r′ = 1.8–11.3°MPa). The shape‐recovery behavior of the polymers under a constraining stress was characterized for programming temperature below (20°C) and above (70°C) the T g . The experiments revealed a peak in the recovered strain for samples programmed at 20°C. Recovered strain scaled linearly with the constraining stress by the rubbery modulus. The work performed by the shape‐memory polymer networks was observed to be primarily a function of constraining stress and crosslinking density, while programming temperature had a relatively mild influence; however, the efficiency of the shape‐memory effect was shown to be a function of constraining stress and programming temperature, but was independent of crosslinking density. Maximum work efficiencies (up to 45%) were observed for programming temperature of 70°C. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Shape memory polymers (SMPs) and their composites are a class of novel smart materials. In order to achieve adjustable thermomechanical and shape memory properties, a series of shape memory epoxy systems were synthesized by varying the types of curing agents and their contents. Thermal frozen/recovery tests, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were performed to investigate shape memory behaviors and thermomechanical properties of fabricated specimens. The results show that thermomechanical properties and critical shape transition temperature of shape memory epoxy systems can be adjusted by changing types and contents of curing agents, but all specimens fabricated in this study exhibit ideal shape memory effects.
Shape memory polymers own many advantages compared with traditional shape memory alloys or ceramics. In order to improve their shape recovery stress and realize a stable recovery response during the deployable process, the structure of SMP sandwich beam composed of two metallic skin and one SMP core is considered. The recovery behaviors of pure SMP and SMP beams reinforced by one-layer metallic skin are also discussed for comparison. The results confirm that the deployable properties of SMP matrix can be significantly improved by using sandwich structure.
Shape memory polymers (SMPs) can have a large frozen strain but providing much lower recovery stresses. To overcome such disadvantage, sandwich structures consisted of a SMP core and two thin metallic skins was considered. Due to much compliance of the SMP core, SMP sandwich beam is buckled at a lower packaging strain. Buckling is the fundamental character of SMP sandwich beam under bending. The critical buckling parameters about two types of SMP sandwich beams were theoretically derived.
Shape memory polymers (SMPs) can keep a temporary state and subsequently recover to the original shape through a prescribed thermomechanical process. Although different theoretical models have been presented, the viscous effects were seldom considered. This article aims to provide an insight into the viscoelastic property of SMPs and its effect on the functional realization. Systematic thermomechanical experiments were performed. Special considerations were focused on the viscoelastic response of SMPs in the vicinity of the glass transition temperature Tg. The relations between shape switching transition temperature Ttran and Tg were also discussed. The results confirm that Ttran departs from Tg due to the viscoelastic effect and does not keep a constant value during heating and cooling processes. The viscoelastic effect reaches to maximum value at Tg, then decreases slowly at cooling and quickly at heating. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
The thermomechanical constitutive equations are critical for shape memory polymers (SMPs) in analyzing their shape, memory, and recovery responses under different constraints. In this study, a new physical-based, temperature and time-dependent constitutive model was proposed. The deformation mechanisms of this class of functional materials were explained, and the theoretical predicting values by different models were compared with available experimental results. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Present prosthetic heart valves, while hemodynamically effective, remain limited by progressive structural deterioration of tissue valves or the burden of chronic anticoagulation for mechanical valves. An idealized valve prosthesis would eliminate these limitations. Polymeric heart valves (PHVs), fabricated from advanced polymeric materials, offer the potential of durability and hemocompatibility. Unfortunately, the clinical realization of PHVs to date has been hampered by findings of in vivo calcification, degradation and thrombosis. Here, the authors review the evolution of PHVs, evaluate the state of the art of this technology and propose a pathway towards clinical reality. In particular, the authors discuss the development of a novel aortic PHV that may be deployed via transcatheter implantation, as well as its optimization via device thrombogenicity emulation.
Shape memory polymers (SMPs) can have a large frozen strain but with a very small recovery stiffness in comparison with shape
memory metals or ceramics. To provide more deployable stresses for the application of actuators, sandwich beams consisting
of a SMP core and two thin metallic skins were considered. The packaging behaviors of two types of SMP sandwich beams, aluminum/SMP/aluminum
and steel/SMP/steel, were discussed. Due to the high compliance of SMP core on packaging condition that the testing temperature
is above the activation temperature of the material, buckling and post-buckling are the essential deformation mechanisms of
SMP sandwich beams under bending. Theoretical solutions were derived in studying such non-linear behaviors, including the
initiation of critical buckling, post-buckling response, and final failure modes. Systematic parameter’s analyses, e.g., buckling
half-wavelength, amplitude, location of the neutral-strain surface in different packaging curvatures, were also presented.
KeywordsShape memory polymer–Sandwich structure–Shape recovery–Buckling
The reduced availability of homografts and investigations into the ideal valved conduit have prompted a search for alternative options. This prospective study evaluated the Contegra, a new biological valved conduit consisting of a glutaraldehyde-preserved heterologous bovine jugular vein having a trileaflet venous valve.
Between April 1999 and May 2001, 26 patients (mean age 13.5+/-12.5 years; range: 4 months to 43 years), of mean body weight 33.9+/-26.7 kg (range: 4.0-91.0 kg), underwent implantation of a Contegra valved conduit for the following diagnoses: pulmonary valve replacement during Ross operation (n = 11), pulmonary atresia with ventricular septal defect (n = 6), tetralogy of Fallot (n = 3), truncus arteriosus (n = 3), Taussig-Bing syndrome (n = 2), and pulmonary valve regurgitation (n = 1). Conduit size was 14 mm in two patients, 16 mm in four, 18 mm in three, 20 mm in three, and 22 mm in 14. Mean cardiopulmonary bypass time was 156+/-33 min (range: 105-233 min), and mean aortic cross-clamp time 79+/-29 min (range: 0-128 min).
There were no hospital deaths. During a mean follow up of 14.7+/-6.9 months (range: 1-26 months) there was one late death (4% mortality) that was unrelated to the valved conduit. Three children underwent reoperation; in all cases this was nonconduit-related. All 25 late survivors are currently free from reoperation and complications due to presence of the conduit. Echocardiographically monitored valve regurgitation was absent in 12 cases, trivial in nine and mild in four. The discharge situation was maintained during systematic follow up. No difference was found between the pressure gradient at discharge and at the last follow up.
The new conduit provided consistently good results during its first two years of use. The main advantages were: (i) excellent off-the-shelf availability; (ii) large variety of available sizes (12 to 22 mm internal diameter); (iii) easy tailoring and suturing; (iv) adequate hemodynamics; (v) no need for proximal or distal extension; and (vi) reduced cost (half that of a conventional homograft).
Hydrodynamic performance of a decellularized pulmonary porcine valve was evaluated with a computer versatile pulse duplicator and compared to glutaraldehyde fixated stentless porcine bioprosthesis and a polyurethane heart valve.
Decellularized pulmonary porcine matrices (Group I, n = 5) were treated chemically to become cell-free collagen matrices. The findings of this heart valve were compared with aortic glutaraldehyde treated porcine prostheses (Group II, n = 5) and polyurethane three leaflet valve prostheses (Group III, n = 1). Measurements were performed in 0.9% saline test fluid at room temperature. Measurements compared were closing time, closing volume, systemic pressure difference and energy losses. Each valve was measured 6 times with 70 beats/minute, a stroke volume of 70 ml corresponds to a cardiac output of 4.9 L/minute.
Group I and group III showed no significant differences between parameters. The measured closing time was significantly different (p < 0.001) between group I and II, respectively 24.333 and 53.600 ms and group II and III respectively 53.600 and 24.000. Difference in closing volume was significant (p < 0.05) between groups II and I respectively 3.67 and 0.68 ms and group II and III respectively 3.67 and 0.71. Systolic mean pressure gradient was 18.25 +/- 1.04 mm Hg in group II which was significantly different (p < 0.001) from groups I and III, respectively 10.65 +/- 0.29 mm Hg and 7.70 +/- 0.30 mm Hg.
Decellularized pulmonary porcine valves showed the same excellent performance as polyurethane valve prosthesis, which are superior to the investigated glutaraldehyde fixed xenograft.
As the specialties of pediatrics and pediatric cardiology continue to forge ahead with better diagnoses, medical care, and surgical results, an expanding population of patients with congenital heart disease (CHD) outgrows the pediatric age group, yet does not quite graduate to routine adult cardiology or general medicine. The adult with congenital heart disease (ACHD) faces medical, surgical, and psychosocial issues that are unique to this population and must be addressed as such. This review attempts to discuss and highlight some of the important advances and controversies brought up in the past year, in the care and management of these patients.
The past five to 10 years have seen dynamic interest in understanding sequelae of corrected, uncorrected, or palliated congenital heart disease. The search for the ideal surgery, optimal prosthesis, and a smooth transition to adult care continues and is reflected in the vast amount of academic work and publications in this field. Of particular interest, conduit reoperations and single ventricle pathway modifications are still an art and a science in evolution.
While all are agreed that there is a pressing need to focus on the delivery of care to the adult with congenital heart disease, this essentially requires a clearer understanding of late sequelae of CHD. The sheer heterogeneity of anatomy, age, surgery, and institutional management protocols can make it difficult to develop clear guidelines. This review attempts to give an up-to-date perspective on some of the new findings related to the more common lesions and problems faced in this group.
This study was designed to evaluate the outcome of Contegra xenograft valved conduit (Contegra, Medtronic Inc, Minneapolis, MN).
From April 1999 to December 2003, 67 patients with a mean age of 16.1 +/-15.0 years (2 months to 53 years) and a mean weight of 39.7 +/- 27.1 kg (4 to 95 kg) were discharged after implantation of a Contegra conduit. The diagnosis contained the following: pulmonary valve replacement during Ross operation (n = 27), pulmonary valve regurgitation (n = 9), tetralogy of Fallot (n = 7), pulmonary atresia with ventricular septal defect (n = 7), double outlet right ventricle (n = 7), truncus arteriosus (n = 5), Taussig-Bing (n = 2), obstructed conduit (n = 2), and double discordance (n = 1). Conduit size was 14 mm in 2, 16 mm in 7, 18 mm in 12, 20 mm in 13, and 22 mm in 33 patients. Mean cardiopulmonary bypass was 155 +/- 48 min (65 to 337 min) and mean aortic cross clamping was 69 +/- 38 min (0 to 146 min). All patients underwent echocardiography, 23 of 67 (34%) patients had cardiac catheterization, and 23 of 67 (34%) patients had electrocardiograph-gated multislice computer tomography.
In a mean follow-up of 26.4 months (1 to 56 months) there was one late death (1 of 67 patients; 1.5% mortality) unrelated to the conduit. Five patients underwent reoperation; four were nonconduit-related and one was to replace a twisted conduit. Five patients underwent interventional cardiology; three were nonconduit-related and two were to stent a twisted or stenotic conduit. Echocardiography showed absent valve regurgitation in 30 of 67 (45%) patients, trivial in 21 of 67 (31%) patients, mild in 16 of 67 (24%) patients. The transconduit pressure gradient remained stable during follow-up, with peak pressure gradient 17 +/- 11 mm Hg and mean gradient 8 +/- 6 mm Hg. Internal diameters corresponded to 110% +/- 20% of the implanted diameter at level of proximal anastomosis, 112% +/- 18% at valve level, and 110% +/- 14% at distal anastomosis. Calcifications were not found, with the exception of a minimal (2.3 mm) parietal calcification.
The Contegra valved conduit provided excellent morphology and hemodynamics, and freedom from calcification in a medium-term follow-up.
The limited lifespan of all currently available conduits leads to repeat operations and interventional procedures in many children. Each reoperation entails considerable risk to life, expenditure and compromised quality of life as the conduit degenerates. The ideal conduit should be available freely, inexpensive, require no anticoagulation, be resistant to infection, free from thromboembolism, have no gradients or regurgitation and have unlimited durability. This review explores various options as surgeons and researchers endeavor to develop the ideal conduit--which will fulfill all of the above-mentioned criteria. Various currently available conduits are analyzed. Special emphasis is given to tissue-engineered valves and percutaneous valve implantations.
Bulk, surface and bioactivity of newly synthesized hydroxy telechelic polyisoprene-based (H-HTPI) polyurethane were investigated by means of ATR-FT-IR, contact-angle measurements, cell viability, calcification, and platelet and fibrinogen quantification. The influence of isophorone diisocyanates isocyanurate (I-IPDI) content on these properties was determined. Results generally showed a non-significant difference in these properties when they were compared with a commercially available biomedical polyurethane (PU), such as Tecoflex. Unexpectedly, where the increase of isocyanate content for commercial diisocyanate-based biocompatible PU significantly increases the surface contact angle, the new hydroxy telechelic polyisoprene-based PU showed a decrease of water contact angle with increasing I-IPDI content in the polymer. Nevertheless, the overall surface exhibited hydrophobic properties, i.e., theta > 85. Polymer cytotoxicity, assessed with L929 cell line in direct contact with the surface of the samples, showed no toxic effects on the cells. Interestingly, regardless of the I-IPDI content, platelet adhesion and fibrinogen adsorption, as well as the mineral deposition were fairly similar for all synthesized PUs. Our findings revealed that replacing diisocyanates by their isocyanurate homologues is a very relevant approach for preparation of polyurethanes with different mechanical properties while maintaining similar surface properties.
Fundamental distinctions exist between systems designed for temporary (<15 days) and long-term (>2 years) ventricular support. These are illustrated with a description of two ABIOMED systems: an extracorporeal system (“the BVS”) designed for short-term in-hospital use and an implantable system (“the VAS”) designed for longterm ambulatory use. In the last decade, temporary support to either or both ventricles has moved from the research laboratory to the clinical arena. During this same period, devices designed for permanent assist or total replacement have entered an intensive reliability testing phase with some limited clinical trials. Temporary systems are indicated for postcardiotomy ventricular dysfunction, post-MI cardiogenic shock, and as a bridge to cardiac transplantation. Indications for permanent support are essentially identical to those for cardiac transplantation, namely: end-stage cardiomyopathies of ischemic, viral, or unknown etiology. The BVS system, currently undergoing clinical trials, was developed for in-hospital temporary use following technical considerations designed to expand clinical applicability of cardiac support beyond research and teaching hospitals. The VAS system, currently undergoing reliability tests, was developed following technical criteria designed to minimize the risks of thromboembolism, infection, and other potential complications in permanently implanted ambulatory recipients.
From 1985 to 1990, 89 patients underwent placement of 41 aortic and 54 pulmonic cryopreserved allograft valved conduits between the right ventricle and the pulmonary arteries. Six patients underwent replacement with a second allograft conduit. Median age at operation was 4.3 years, and 20 patients were infants less than 1 year of age. Conduit sizes averaged 11 mm in the conduits placed in 20 infants and 20 mm in the 75 placed in patients more than 1 year of age. There were 7 early deaths in 89 patients (7.8%, 70% confidence levels 5.4% to 11.3%) and 9 late deaths in 82 hospital survivors (11%, 70% confidence levels 8% to 15%). Actuarial survival was 81% (70% confidence levels 75% to 86%) at 33 months, and no deaths were due to conduit problems. Late reoperation was required in 13 patients (7 for conduit obstruction, 1 for conduit valve insufficiency, and 5 for nonconduit-related problems). Six of the eight reoperations were done in patients who had small (< or = 13 mm) conduits placed during infancy. Conduit failure was similar between pulmonic and aortic allografts. There were no deaths in the eight patients who required conduit reoperation. Actuarial freedom from reoperation for conduit dysfunction was 80.5% (70% confidence levels 72% to 86%) at 53 months for the entire group and 94% (confidence levels 88% to 97%) at 44 months for patients more than 1 year of age. Cryopreserved allograft conduits have good early and midterm results and are comparable to porcine xenograft conduits. Despite a likely need for replacement within 3 years, we continue to favor the use in infants of an allograft valved conduit over a xenograft Dacron conduit. The need to replace a cryopreserved allograft conduit appears similar for conduits of aortic or pulmonic origin.
Four types of valved conduits used to correct venous ventricle to pulmonary artery (V-PA) discontinuity were compared.
Four hundred fifty-seven patients with congenital heart defects requiring a V-PA connection during the past 25 years were reviewed. Age at implant varied from 1 day to 64 years (mean, 9.1 years). Four types of valved prostheses were used: 1) homograft conduit (HC, n = 178), 2) valved Dacron conduit (VDC, n = 126), 3) polystan conduit (PC, n = 47), and 4) orthotopic pulmonary valve implant (PVI, n = 106). There were 83 early deaths (18.2%) and 34 late deaths (8.5%). Follow-up ranged from 1 month to 22 years (mean, 3.5 years). One hundred eight conduit replacements were performed in 93 patients (21%). The overall patient survival was 73 +/- 2.3%, 67 +/- 3.2%, and 56 +/- 6.8% at 5, 10, and 15 years, respectively. Factors predictive of patient survival were diagnosis (p < 0.001) and valve size (p < 0.001). Age at operation (p < 0.001) and type of valve (p < 0.001) were the only risk factors for valve survival. At 5 years, survival of PVI (89 +/- 5%) and VDC (89 +/- 4%) was significantly better than survival of HC (46 +/- 13%) or PC (57 +/- 9%).
Patients who survived the initial construction of a V-PA conduit had a reasonable long-term survival. A PVI was the most durable prosthesis. A Dacron porcine-valved conduit had significantly better durability than either a cryopreserved homograft or a PC.
This study evaluates our experience with the cryopreserved homograft valved conduit used for reconstruction of the pulmonary circulation in patients with congenital heart disease.
Between July 1, 1985, and December 31, 1990, 219 patients had cryopreserved homograft extracardiac valved conduits placed in the pulmonary circuit. Average age at operation was 7.2 years. Of these, 132 patients had a pulmonary homograft, and 87 had an aortic homograft. Twenty-four patients (11%) died in hospital. Hospital survivors (n = 195) have been followed an average of 29.8 months (SD, +/- 18.4 months). Fourteen patients died during follow-up, almost all related to the complexity of their original cardiac malformation. Thirty-two patients (15%) have required reoperation for conduit-related problems. Actuarial freedom from conduit reoperation is 55 +/- 12% at 5 years. The most common indication for reoperation was calcific stenosis (n = 27). Other indications for reoperation were pseudoaneurysm (n = 2), conduit infection (n = 2), and pulmonary insufficiency (n = 1). Reoperation rate for patients with aortic homografts (16 of 87) compared with that for pulmonary homografts (16 of 132) was not significantly different by the actuarial method.
Long-term function of cryopreserved homograft valved conduits in the pulmonary circulation is disappointing.
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)
The Abiomed BVS System 5000 (Abiomed Cardiovascular, Inc., Danvers, Mass.) is a gravity-filled, pneumatically driven external prosthetic ventricle that has been implanted as a circulatory support device in six patients 9 to 58 years of age, presenting with a refractory heart failure nonamenable to any type of corrective operation. Three (including a 9-year-old girl) had an end-stage nonobstructive myocardiopathy, and two (including one patient who had had a massive recent myocardial infarction) had an ischemic heart disease. When first seen, the 58-year-old patient had an acute rejection and graft failure occurring 2 months after a first transplantation. All patients showed evidence of a low-output state (cardiac index less than 1.5 L/min/m2), with renal failure (mean urinary output, less than 27 ml/min) and hypoxia (mean arterial oxygen pressure = 56 torr under 80% forced inspiratory oxygen), despite maximum pharmacologic support (dobutamine, 16 to 18 gamma/kg/min; dopamine, 3 to 18 gamma/kg/min; adrenaline, 0.2 to 0.7 gamma/kg/min; furosemide, 7 to 17 gamma/kg/min). The device was implanted through a midline sternotomy and under peripheral normothermic bypass. Five patients received a biventricular support, and one a single left prosthetic ventricle. The cannulation included a right-angled cannula in both the left and right atrium and a suture of the arterial Dacron tubes onto the ascending aorta and main pulmonary artery. After careful deairing of the tubing and ventricles, the console was activated and the bypass progressively discontinued. Heparin infusion was begun 3 hours after chest closure and was continued for the duration of assist pumping, which was 2 to 11 days (mean duration, 7.43 days). The system could provide a complete support of the circulation with both right and left ventricular index remaining stable at 2.4 to 3 L/min/m2. After a dramatic improvement at the time of the system activation, the urinary output remained adequate, thus allowing for a decreasing need for diuretic therapy. In two cases, including one of isolated left ventricular assist pumping, the circulation could be totally supported during 11 hours and 23 hours, respectively, of refractory ventricular tachycardia. Four of six patients were shortly weaned from inotropic agents. Hematologic studies showed a moderate decrease of the coagulation factors level during the first 6 hours of circulatory support, and this remained stable and within normal limits thereafter. There have been three cases of bleeding complications necessitating surgical revision on the sixth hour, the twelfth hour, and the sixth day, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
This paper concerns the heart valves to be used mainly in artificial hearts. Most of our tricusp semilunar valves are made of polyurethane. These valves have functioned in artificial hearts for up to 62 days, and have been implanted in sheep for 1 year without evidence of thromboembolism. Our valves have a wide opening, using redundant leaflets that are "bistable." Accelerated testing by air jet provides 1,000 closures per second. Regurgitation is measured in an apparatus with the help of a competent valve. All polyurethanes change with age, but Silastic does not.
The 12 mm Dacron conduit containing a porcine valve is the smallest valved conduit manufactured and is used in the youngest infants with the most diminutive pulmonary arterial system. The outcome of patients with such a conduit is unknown. Between 1975 and 1985 there were 49 hospital survivors after placement of a 12 mm extracardiac valved conduit from the right ventricle to the pulmonary artery. Follow-up is available in 42 patients, aged 1 to 16 months (mean 3.5) and weighing 2.5 to 8.7 kg (mean 3.8). Twenty-eight patients (67%) have undergone subsequent conduit replacement, and 11 (26%) are alive and asymptomatic with a mean follow-up of 56 months. There were three late deaths. The interval between implantation and conduit change was 4.5 to 101 months (mean 44), allowing a weight gain of 2.7 to 23 kg (mean 10.4) before reoperation at age 12 to 117 months (mean 49). Despite elevated right ventricular pressures equaling systemic values, 37% of these patients were clinically asymptomatic. The gradient across the 12 mm valved conduit before explantation ranged from 30 to 173 torr (mean 83) with an almost equal predilection for stenosis at the proximal anastomosis, valve, conduit, distal anastomosis, and main pulmonary artery. The intervening pulmonary artery growth determined the size of the replacement conduit, 14 to 25 mm (mean 16), and was the main factor influencing the results of reoperation. This study demonstrates that the 12 mm porcine valve-containing conduit affords palliation in this difficult subset of patients with the smallest pulmonary arterial tree.
Between 1971 and 1983, 201 patients received synthetic right heart conduits, predominantly porcine-valved Dacron conduits, at The Children's Hospital, Boston. There were 45 hospital deaths (22%). Follow-up has been achieved in 148 of 156 survivors (95%). Thirty-four conduits have been replaced, all because of conduit obstruction. The actuarial freedom from conduit replacement was 81% at 5 years, 61% at 7 years, and 0% at 10 years for valved conduits. There was no significant difference to 5 years in reoperation rate between patients with Carpentier-Edwards and those with Hancock conduits. Patients older than 18 years at the time of conduit insertion were 92% free of conduit replacement at 5 years. Those with nonvalved conduits were 100% reoperation free at 4 years. The actuarial survival of patients with valved conduits was 91% at 5 years and 83% at 10 years. The poor performance of porcine-valved tightly woven Dacron conduits warrants a change to use of an alternative conduit, particularly in smaller children. Possible alternatives include antibiotic-sterilized homografts and valved or nonvalved high-porosity knitted Dacron conduits appropriately pretreated with collagen impregnation or fibrin glue.
The main disadvantages of today's heart valve prostheses are the need for lifelong anticoagulation for mechanical valves and problems with biodegradation for tissue valves. Therefore, a new valve type devoid of these problems would be a major step forward. In order to evaluate a new valve design made by dipmolding with different PU materials, an animal test series was carried out in which two valves from each material were implanted into the mitral position of growing Jersey calves. The surgical procedure and postoperative catheterization data are presented. The survival times ranged between 127 and 291 days. Organs and explanted valves were examined post mortem according to general pathology standards. Specifically, the valves were histologically examined for calcium deposits and investigated by light microscopy, REM and EDAX. All explanted valves showed calcification and immobilization, but the results suggest that at least two PU materials attain survival times which are far beyond the lifetime of bioprostheses under the same implant conditions, justifying further in vivo studies in adult animals.
Morphologic, chemical, and hemodynamic studies were made of eight prototype polyurethane trileaflet cardiac valve prostheses that had been implanted in juvenile sheep for 17 to 21 weeks in the mitral position. Calcification of the polyurethane leaflet surfaces was the principal finding. Quantitative chemical analyses revealed calcium values with a mean of 42.7 +/- 21 mg/gm dry weight of leaflet. Morphologically, two distinct types of calcification were observed: One was associated with the polyurethane surface or the interface between the leaflet surface and microthrombi or fibrous sheaths; the other was characterized by calcification associated with degenerated cells within thrombotic material and the fibrous sheath. These morphologic findings were in accord with the results of hemodynamic performance studies indicating that these heart valve prostheses had become both stenotic and regurgitant.
Actuarial freedom from reoperation for obstruction in 147 patients receiving cryopreserved or fresh allograft valved conduits between a ventricle and the pulmonary arteries was 94% at 3.5 years. The 2 patients undergoing reoperation were 6 and 36 months of age at the time of insertion of the allograft. Among 24 patients in whom cardiac catheterization was performed on indication late postoperatively, 5 had gradients of more than 40 mm Hg across the conduit. For comparison, among 78 patients receiving xenograft or irradiated allograft valved conduits, the percentages of freedom from conduit reoperation at 3.5, 5, 10, and 15 years were 99%, 95%, 59%, and 11%, respectively. The diameters of the allograft and xenograft valves inserted varied directly with the age and size of the patients, but in patients 3 to 5 years of age, allografts with a diameter of at least 21 mm could usually be used.
Total surgical repair of congenital heart lesions with pulmonary artery right ventricular discontinuity has required a valve containing conduit for optimum results. Excellent results have been attained by constructing a new pulmonary valve and artery using human aortic homografts. Certain disadvantages have been noted: difficulty in procurement, limited tissue for tailoring of the prosthesis, difficulty in prevention of distortion, and early calcification of the conduit. A dacron conduit containing a porcine heterograft aortic valve that does not possess these disadvantages has now been used in five patients for construction of pulmonary artery right ventricular continuity. This conduit is a uniform product, available in multiple sizes. Follow up data of up to two years including postoperative catheterization studies demonstrate this prosthesis to be a satisfactory and perhaps a superior alternative to the aortic homograft for restoring pulmonary artery right ventricular continuity.
Valved conduits made by incorporating Björk-Shiley tilting disc valve prostheses in woven dacron' arterial grafts have been used to bridge discontinuity between the right ventricle and the distal pulmonary arteries in 9 patients. Age at operation varied between I2 days and I2 years. Five patients had persistent truncus arteriosus, 3 had pulmonary atresia, and I had d-transposition of the great arteries with ventricular septal defect and subpulmonary stenosis. The only deaths have been in 2 desperately ill infants under 3 months of age. Survivors include a 2-monthold infant with truncus arteriosus. Clinically the reconstructions continue to function satisfactorily after follow-up periods of up to i8 months, without identifiable evidence of valve dysfunction or pulmonary embolism.
The effectiveness of the T6 process (surfactant treatment) to decrease calcification of porcine aortic valvular (PAV) and bovine pericardial (BPV) bioprostheses was investigated. Morphologic and biochemical studies were made of standard and T6-treated PAVs and BPVs that had been implanted for a mean of 20 weeks in the tricuspid position in young sheep. Gross, radiographic, histologic and ultrastructural observations showed that the calcific deposits were less severe in T6-treated (n = 9) than in standard PAVs (n = 7), but were similar in severity in T6-treated (n = 6) and standard BPVs (n = 7). This was confirmed by results of quantitative analyses for calcium in half of each cusp of each explanted valve. Because these results showed large differences in standard deviations in the 4 groups of sheep, natural logarithmic and square-root transformations were used for statistical comparisons. The mean calcium content (milligrams of calcium per gram of dry tissue) of standard PAVs (111 +/- 53) was greater than that of T6-treated PAVs (11 +/- 3) (p = 0.0037). The calcium content of T6-treated PAVs was lower than that of T6-treated BPVs (96 +/- 26) (p = 0.031). However, the calcium content of standard BPVs (35 +/- 13) was not different from that of T6-treated BPVs or standard PAVs. Thus, under conditions of relatively short-term implantation in the sheep model, the T6 process is useful for decreasing the extent of calcification in PAVs, but not in BPVs.
Analysis of the late results in 352 patients surviving insertion of an extracardiac conduit before mid 1977 has provided a mean follow-up interval of 65 months. Three fourths of the patients remain in improved condition after operation. Serial measurements of transconduit gradient are available in 90. The median change was +7 mm Hg and the mean +21 mm Hg. Reoperation was required in 16 percent of patients (mortality rate 9 percent), most commonly (77 percent) because of progressive conduit stenosis, more commonly for transposition of the great arteries than for other types of anomalies, and more commonly after use of a homograft aortic conduit than a Hancock conduit. The side of the aorta on which the conduit was placed exerted no significant influence. The postrepair transconduit gradient did not affect the need for reoperation. Late survival was 95 percent at 1 year, 85 percent at 5 years, and 73 percent at 10 years and was significantly better (probability [p] less than 0.006) for patients with pulmonary atresia than for the others. The hospital mortality rate was highest, and the late mortality rate lowest, for children less than 5 years of age; the overall survival rate in this age group was lower. The postrepair right ventricular to left ventricular pressure ratio, together with age, was a principal prognostic indicator of late survival, being less good when more than 0.73. THe most frequent causes of late death were progressive congestive heart failure and sudden death.
The development of the extracardiac conduit has been one of the greatest advances in cardiac surgery. Conduits have decreased the mortality rate of several standard operations and have made possible the correction of numerous complex congenital cardiac anomalies that previously were uncorrectable. However, the ideal conduit has not yet been developed. We have reviewed the long-term (16 to 29 years) results of our early experience with this technique.
The prosthetic heart valves were fabricated from a polyurethane containing a 4,4'-diphenylmethane diisocyanate hard segment, chain-extended with butanediol and with a polyether soft segment. The rate of calcification of these polyurethane heart valves was much slower in a dynamic in vitro test system than similar bioprosthetic heart valves. The calcified deposits were located exclusively at regions of material failure. Fourier transform infrared (FTIR) spectroscopy indicated the involvement of the polyether soft segments of the polymer directly in the calcification process. Calcification of polymer fractions also suggested that small molecular weight extractable components are accelerating factors in the calcification process.
The ABIOMED total artificial heart (TAH) is designed for long-term tether-free use in patients with end-stage heart disease. Blood pumping is achieved through hydraulic fluid motion across flexing diaphragms. The hydraulic power is derived from a miniature centrifugal pump (50% efficiency). Flow directional change needed for alternate left and right filling and ejection is achieved with a rotary valve. With no mechanical contact with the flexing membrane, the wedge angle between the two pumps sandwiching the energy convertor can be easily optimized for anatomic fit. The blood pumps (80 ml strokes) are fitted with trileaflet polyetherurethane valves (24 mm). The TAH is implanted using twist-lock stepless quick connectors to the inflow cuffs and outflow grafts. Left-right flow balance is achieved with an atrial hydraulic shunt placed between the left cuff and inflow valve. Animal studies show that the TAH fits very well in Long Horn calves weighing 90 to 100 kg and can provide cardiac output in excess of 10 L/min. A cadaver (85 kg) study showed the TAH fits within the pericardial region.
Hydrodynamic testing of the Abiomed polyurethane trileaflet valve has been carried out to establish performance data of valve function. A Medtronic Hall tilting disk, a Carbomedics bileaflet, a Hancock II bioprosthesis and an Abiomed polyurethane trileaflet valve, all size 27 mm, underwent both pulsatile and steady-flow hydrodynamic testing. Results of the variation of pressure difference with RMS pulsatile flow and steady flow, and effective orifice area, showed that the Abiomed valve had significantly poorer opening characteristics than the tissue valve and the two mechanical valves. The Abiomed valve's performance was seen to be related to its construction and manufacture. This study highlights some of the problems associated with the design and development of synthetic trileaflet heart valve prostheses.
Effects of two types of preimplantation processes on calcifi-cation of bioprosthetic valves
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Jones M, Eidbo EE, Walters SM, Ferrans VJ, Clark RE. Effects of two types of preimplantation processes on calcifi-cation of bioprosthetic valves. In: Bodnar E, Yacoub M, editors. Biologic and bioprosthetic valves. New York: Yorke Medical Books; 1986. p. 451-9.
A compact and noise free electrohydraulic total artificial heart
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