Chronic Sheep Model Research Articles

Investigation of a chronic single-stage sheep Fontan model

ObjectivesOur goal was to conduct a hemodynamic analysis of a novel animal model of Fontan physiology. Poor late-term outcomes in Fontan patients are believed to arise from Fontan-induced hemodynamics, but the mechanisms remain poorly understood. Recent advances in surgical experimentation have resulted in the development of a chronic sheep model of Fontan physiology; however, detailed analysis of this model is lacking. MethodsWe created a single-stage Fontan model in juvenile sheep with normal biventricular circulation. The superior vena cava was anastomosed to the main pulmonary artery, and the inferior vena cava was connected to the main pulmonary artery using an expanded polytetrafluoroethylene conduit. Longitudinal hemodynamics, including catheterization and magnetic resonance imaging were evaluated. ResultsFour out of 12 animals survived, with the longest surviving animal living 3 years after single-stage Fontan. We showed a significant era effect regarding survival (1 out of 8 and subsequently 3 out of 4 animals surviving beyond 2 months) attributed in large part to the procedural learning curve. Key characteristics of Fontan hemodynamics, namely systemic venous hypertension and low normal cardiac output, were observed. However, recapitulation of passive human Fontan hemodynamics is affected by volume loading of the right ventricle given an anatomic difference in sheep azygous venous anatomy draining to the coronary sinus. ConclusionsA significant learning curve exists to ensure long-term survival and future surgical modifications, including banding of the main pulmonary artery and ligation of the azygous to coronary sinus connection are promising strategies to improve the fidelity of model hemodynamics.

On-demand heart valve manufacturing using focused rotary jet spinning

On-demand heart valve manufacturing using focused rotary jet spinning

Assessment of Nit-Occlud atrial septal defect occluder device healing process using micro-computed tomography imaging.

After percutaneous implantation of a cardiac occluder, a complex healing process leads to the device coverage within several months. An incomplete device coverage increases the risk of device related complications such as thrombosis or endocarditis. We aimed to assess the device coverage process of atrial septal defect (ASD) occluders in a chronic sheep model using micro-computed tomography (micro-CT). After percutaneous creation of an ASD, 8 ewes were implanted with a 16-mm Nit-Occlud ASD-R occluder (PFM medical, Cologne, Germany) and were followed for 1 month (N = 3) and 3 months (N = 5). After heart explant, the device coverage was assessed using micro-CT (resolution of 41.7 μm) and was compared to histological analysis. The micro-CT image reconstruction was performed in 2D and 3D allowing measurement of the coverage thickness and surface for each device. Macroscopic assessment of devices showed that the coverage was complete for the left-side disk in all cases. Yet incomplete coverage of the right-side disk was observed in 5 of the 8 cases. 2D and 3D micro-CT analysis allowed an accurate evaluation of device coverage of each disk and was overall well correlated to histology sections. Surface calculation from micro-CT images of the 8 cases showed that the median surface of coverage was 93±8% for the left-side disk and 55±31% for the right-side disk. The assessment of tissue reactions, including endothelialisation, after implantation of an ASD occluder can rely on in vitro micro-CT analysis. The translation to clinical practice is challenging but the potential for individual follow-up is shown, to avoid thrombotic or infective complications.

Non-invasive imaging of the healing process of atrial septal defect percutaneous occluders: A proof of concept study

After percutaneous implantation of an atrial septal defect (ASD) occluder, a complex healing process leads to the device coverage within several months. However, an unexplained incomplete device coverage increases the risk of device related complications such as thrombosis or infectious endocarditis. The aim of the study was to non-invasively assess the device coverage process of ASD occluders in a chronic sheep model using micro-CT technology. After percutaneous creation of an ASD, 8 ewes were implanted with a 16-mm Nit-Occlud ASD-R occluder (PFM medical, Germany) and were followed for 1 month ( n = 3) and 3 months ( n = 5) before sacrifice. The device coverage was then assessed using micro-CT and was compared to histological analysis (gold standard). The micro-CT image resolution was 41.7 μm, reconstruction was performed in 2D and 3D with Amira® software allowing measurement of the coverage thickness and surface for each disk of the analyzed devices, using a code. Histological study was performed following resin embedding and Richardson blue staining. ASD creation and device closure was successful in 100% animals without complications. Following sacrifice, macroscopic assessment of devices showed that the coverage was complete for the left-side disk regardless of the duration of the follow-up and variable for the right-side disk, depending of the protrusion of this disk. 2D and 3D micro-CT analysis allowed an accurate evaluation of device coverage of each disk and was overall well correlated to histology slices ( Fig. 1 ). Surface calculation from micro-CT images showed that the median surface of coverage was 93 ± 8% for the left-side disk and 55 ± 31% for the right-side disk. This preliminary study made the proof of concept that micro-CT is a reliable tool to assess the coverage of intra-cardiac occluders in vitro. The translation to clinical practice is challenging but would allow an individual follow-up.

Nifedipine disturbs fetal cardiac function during hypoxemia in a chronic sheep model at near term gestation

Nifedipine is a widely used drug in pregnancies complicated by maternal hypertensive disorders that can be associated with placental insufficiency and fetal hypoxemia. The evidence regarding fetal myocardial responses to nifedipine in hypoxemia is limited. We hypothesized that nifedipine would not impair fetal sheep cardiac function under hypoxemic environment. In particular, we investigated the effects of nifedipine on fetal ventricular functional parameters and cardiac output. A total of 21 chronically instrumented fetal sheep at 122 to 134 gestational days (term, 145 days) were included in this study. Fetal cardiac function was evaluated by measuring global longitudinal strain, indices describing ventricular systolic and diastolic function, and cardiac outputs using two-dimensional speckle tracking and tissue and spectral pulsed-wave Doppler echocardiography. Fetal carotid artery blood pressure and blood gas values were invasively monitored. After baseline data collection, fetal hypoxemia was induced by maternal hyperoxygenation. After hypoxemia phase data collection, 9 fetuses received nifedipine infusion, and 12 fetuses received saline infusion. Data were collected 30 and 120 minutes after the infusion was started. After 120 minutes of data collection, maternal and fetal oxygenation were normalized, and normoxemia phase data were collected, while infusion was continued. Hypoxemia decreased fetal carotid artery mean arterial pressure from 40 (8) mm Hg to 35 (8) mm Hg (P<.007), and left ventricular global longitudinal strain showed less deformation than at baseline (P=.001). Under hypoxemia, nifedipine caused a reduction in right ventricular global longitudinal strain (P<.05), a decrease in right ventricular isovolumic relaxation velocity and its deceleration (P<.01) indicating diastolic dysfunction, and a drop in right ventricular cardiac output (P<.05). Nifedipine did not alter fetal left ventricular functional parameters or cardiac output. When normoxemia was restored, fetal right ventricular functional parameters and cardiac output returned to baseline level. In hypoxemic fetus, nifedipine impaired right ventricular function and reduced its cardiac output. The detrimental effects of nifedipine on fetal right ventricular function were abolished, when normoxemia was restored. Our findings suggest that in a hypoxemic environment nifedipine triggers detrimental effects on fetal right ventricular function.

In-vivo Evaluation of a Novel Surgical Heart Valve Prosthesis Designed to Be Durable, Anticoagulant-free and Silent

Objective: Heart valves prostheses still face limitations: reoperations with tissue valves or lifelong anticoagulation with mechanical valves. The Triflo valve, a tri-leaflet valve made of high-resistant bio-inert materials, aimed at overcoming these limitations. We studied safety and performance in a chronic sheep model. Methods: The Triflo valve (size 21mm) was implanted in two models: 90 days in aortic position (n=7) and 70 days in pulmonary position (n=4). In the pulmonary model, On-X valves (n=2) were used as control. After 7 days of low-molecular-weight heparin, no further anticoagulant was administered. Serial blood testing, echocardiography, acoustic measurements, fluoroscopy and autopsy were done. Results: The Triflo valve demonstrated excellent surgical handling. There were one aborted procedure and one early death in the aortic study, both unrelated to the prosthesis. All other sheep (n=9) recovered fast and remained in excellent clinical condition until the scheduled sacrifice. In aortic position, we observed low peak and mean gradients (8.1+/-2.7 and 4.8+/-1.9 mmHg), high effective orifice area (2.3+/-0.2 cm2), no valvular regurgitation, and perfect left ventricular function. At explantation, the surface of all Triflo valves was clean, without any valve thrombosis. All major organs were free from thrombo-embolic (TE) damage. In pulmonary position, leaflet mobility of all valves remained also normal and no TE-damage was found in the lungs. Hematological parameters were stable without any sign of hemolysis. On-X valves in pulmonary position functioned well, but generated significantly louder acoustic signals (p < 0.05). Conclusions: The Triflo valve showed safety and effectiveness in both aortic and pulmonary position. These favorable in-vivo results, with excellent hemodynamic behavior and stable long-term function even in the absence of anticoagulants, demonstrate that this valve can proceed to first-in-human studies.

Non-invasive assessment of cardiac percutaneous occluders healing process using computed tomography imaging: a proof of concept study

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): National Research Agency (ANR) French Federation of Cardiology : “Aide à la recherche par équipe 2018, Cardiopathies de l’enfant” Introduction After percutaneous implantation of an atrial septal defect (ASD) occluder device, a complex healing process leads to the device coverage within several months. However, an unexplained incomplete device coverage is at risk of complications such as thrombosis or infectious endocarditis. Purpose The aim of the study was to assess the device coverage process of ASD occluder devices in a chronic sheep model using micro-CT technology. Methods After percutaneous creation of an ASD by catheterization, 8 ewes (mean age 5.4 ± 0.7 yo and mean weight 55.6 ± 7.9 kg) were implanted with a 16-mm Nit-Occlud ASD-R occluder (PFM medical, Cologne, Germany) and were followed for 1 month (N = 3) and 3 months (N =5). After heart explantation, a iodine contrast agent was used to enhance the tissue signal. The device coverage was then assessed by micro-CT and the results were compared to histology, used as the gold standard for healing evaluation. The micro-CT image resolution was 41.7 µm. Reconstruction was performed in 2D and 3D with Amira® software, allowing to obtain images that were exploited by a code to measure the surface for each disk of the analyzed devices. Histological study was performed after resin embedding and Richardson blue staining was used. The pathologist was blinded to the duration of animals’ follow-up and micro-CT results. Results ASD creation and device closure was successful in 100% animals without complications. Following heart explantation, macroscopic assessment of devices showed that the coverage was complete for the left-side disk regardless of the duration of the follow-up and variable for the right-side disk, depending of the protrusion of this disk. 2D and 3D micro-CT analysis allowed an accurate evaluation of device coverage of each disk and was overall well correlated to histology slices (cf Figure). Surface calculation from micro-CT images showed that the median surface of coverage was 93 ± 8% for the left-side disk and 55 ± 31% for the right-side disk. Conclusion This preliminary study made the proof of concept that micro-CT is a reliable tool to assess the coverage of intra-cardiac occluders in vitro. The translation to clinical practice is challenging but would allow an individual follow-up, to avoid thrombotic or infective complications. Abstract Figure.

Non-invasive imaging of the healing process of atrial septal defect percutaneous occluders: A proof of concept study

After percutaneous implantation of an atrial septal defect (ASD) occluder, a complex healing process leads to the device coverage within several months. However, an unexplained incomplete device coverage increases the risk of device related complications such as thrombosis or infectious endocarditis. The aim of the study was to non-invasively assess the device coverage process of ASD occluders in a chronic sheep model using micro-CT technology. After percutaneous creation of an ASD, 8 ewes were implanted with a 16-mm Nit-Occlud ASD-R occluder (PFM medical, Germany) and were followed for 1 month ( N = 3) and 3 months ( N = 5) before sacrifice. The device coverage was then assessed using micro-CT and was compared to histological analysis (gold standard). The micro-CT image resolution was 41.7 μm, reconstruction was performed in 2D and 3D with Amira® software allowing measurement of the coverage thickness and surface for each disk of the analyzed devices, using a code. Histological study was performed following resin embedding and Richardson blue staining. ASD creation and device closure was successful in 100% animals without complications. Following sacrifice, macroscopic assessment of devices showed that the coverage was complete for the left-side disk regardless of the duration of the follow-up and variable for the right-side disk, depending of the protrusion of this disk. 2D and 3D micro-CT analysis allowed an accurate evaluation of device coverage of each disk and was overall well correlated to histology slices ( Fig. 1 ). Surface calculation from micro-CT images showed that the median surface of coverage was 93 ± 8% for the left-side disk and 55 ± 31% for the right-side disk. This preliminary study made the proof of concept that micro-CT is a reliable tool to assess the coverage of intra-cardiac occluders in vitro. The translation to clinical practice is challenging but would allow an individual follow-up.

Unraveling the Mechanisms of Endogenous Tissue Restoration after Bioresorbable Pulmonary Valve Implantation in Sheep

Objective: Endogenous Tissue Restoration (ETR) utilizes the regenerative response of the human body to transform an off-the-shelf available, synthetic, absorbable graft into a living functional valve. Recent preclinical studies have shown the principle of ETR for heart valve grafts to be promising1Bennink G Torri S Brugmans M et al.A novel restorative pulmonary valved conduit in a chronic sheep model: Mid-term hemodynamic function and histologic assessment.J Thorac Cardiovasc Surg. 2018; 155 (doi:10.1016/j.jtcvs.2017.12.046.): 2591-2601Google Scholar,2Kluin J Talacua H Smits AIPM et al.In situ heart valve tissue engineering using a bioresorbable elastomeric implant – From material design to 12 months follow-up in sheep.Biomater. 2017; 125 (doi:10.1016/j.biomaterials.2017.02.007.): 101-117Google Scholar. However, further detailed knowledge on the underlying mechanisms of the material-driven regenerative response remains elusive. The goal of the present study was to gain a mechanistic understanding of these processes by histopathological analysis of ETR heart valves. Methods: In this study, Xeltis Pulmonary Valved Conduits (XPV, Xeltis B.V., Eindhoven, The Netherlands) implanted in an ovine model were analyzed. Explanted valves (follow-up time: 2, 6, 12 (N=5 per timepoint) and 24 months (N=2)) were embedded in paraffin and sectioned longitudinally. Spatiotemporal analysis was performed using a comprehensive sheep-specific antibody panel3Dekker S van Geeman D van den Bogaerdt AJ et al.Sheep-specific immunohistochemical panel for the evaluation of regenerative and inflammatory processes in tissue-engineered heart valves.Front. Cardiovasc. Med. 2018; 5 (doi:10.3389/fcvm.2018.00105.): 105Google Scholar. Results: Detailed knowledge on graft absorption as well as neo-tissue formation and a better understanding of cellular influences was obtained. Interestingly, foreign body giant cells were located within the graft material at iNOS-rich degradation and tissue remodeling sites in the hinge region of the leaflet, starting as early as 2 months after implantation. In the conduit material, on the other hand, foreign body giant cells remained on the outer layers with only limited infiltration into the scaffold material. Interestingly, at the same time point vascularization was observed throughout the conduit material. Extracellular matrix components, such as collagens and elastin were formed in a highly heterogeneous fashion, suggesting an important role for hemodynamic loads on the inflammatory and regenerative processes. Conclusions: Our results enhance the mechanistic understanding of material-driven endogenous tissue restoration. These findings also highlight, the importance of the micro-environment imposed by the graft material on the regenerative response towards a biomaterial. KEYWORD: ICTEHV-O-02 The authors do not declare any conflict of interest.

Effects of nifedipine and sildenafil on placental hemodynamics and gas exchange during fetal hypoxemia in a chronic sheep model

IntroductionWe hypothesized that nifedipine and sildenafil would have no detrimental effects on placental hemodynamics and gas exchange under fetal hypoxemia. MethodsIn 33 chronically instrumented fetal sheep, placental volume blood flow (QPlac) and umbilical artery (UA) vascular impedance were measured by Doppler ultrasonography. Fetal carotid artery blood pressure and blood gas values were monitored. After baseline data collection, maternal and fetal hypoxemia were induced. Following hypoxemia phase data collection, 12 fetuses received sildenafil and 9 fetuses nifedipine infusion, and 12 fetuses served as controls receiving saline infusion. Data were collected 30 and 120 min after infusion was started. Then maternal oxygenation was normalized and normoxemia phase data were collected, while infusion was continued. ResultsHypoxemia significantly decreased fetal pO2 and blood pressure. In the sildenafil group at 30- and 120-min hypoxemia + infusion phases, fetal blood pressure and QPlac were significantly lower and pCO2 higher than at baseline without returning to baseline level at normoxemia + infusion phase. In hypoxemia, nifedipine did not affect fetal blood pressure or placental hemodynamics. Both in the sildenafil and nifedipine groups, fetal pO2 remained significantly lower at normoxemia + infusion phase than in the control group. Umbilical artery vascular impedance did not change during the experiment. DiscussionIn fetal hypoxemia, sildenafil had detrimental effects on placental hemodynamics that disturbed placental gas exchange. Nifedipine did not alter placental hemodynamics in hypoxemia but disturbed placental gas exchange upon returning to normoxemia. Umbilical artery vascular impedance did not reflect alterations in placental hemodynamics.

P1234Weight fluctuation demonstrates residual atrial arrhythmogenic substrate despite final weight loss in a chronic sheep model: implications for epicardial fat and fibrofatty infiltrates

Abstract Background Obesity-mediated epicardial adipose tissue (EAT) expansion drives fat cell infiltration which forms the unique substrate for atrial fibrillation (AF). The LEGACY study showed the benefits of weight loss but an attenuated response with weight fluctuation. How fluxes in weight impacts the atrial substrate in not known. Objective To investigate EAT and the atrial substrates due to weight fluctuation, with comparison to stable obesity. Methods We studied 24 sheep in 3 equal groups over 80 weeks: 1. Obesity induced by high calorie diet fed ad libitum; 2. Weight fluctuation induced by 20-week cycle of weight gain/loss (20:20:20:20); and 3. Lean controls fed quality hay to maintain baseline weight. All sheep underwent: daily weight measurement; haemodynamic and imaging assessments (cardiac MRI; dual-energy X-ray absorptiometry; and matrix assisted laser desorption infrared lipid imaging); electrophysiological studies and electroanatomic mapping; histological and structural analysis. Evaluations included: atrial voltage, conduction velocity, and refractoriness (7 sites, 2 cycle lengths), electrogram fractionation, EAT volume, fibro-fatty infiltration, myolysis of myocytes, and spatial distribution of intra-atrial lipids. Results The Table shows the group differences. Compared to reference controls, obesity demonstrated: Increased atrial volume and pressure, abnormal atrial electrical properties, expanded EAT and ensuing fibro-fatty infiltrations, and myolysis of myocytes. Despite comparable weight and EAT with controls, weight fluctuation resulted in extensive and severe fibro-fatty infiltrations, and twofold greater myolysis that persisted. Moreover, characteristic profiles and abundance of lipid species in the atrial myocardium were noted on further evaluation. More importantly, EAT and fibro-fatty infiltrates strongly correlated with increased atrial volume and pressure; with only fibro-fatty infiltrates correlating with fractionated electrograms (r=0.71, p&lt;0.001) and conduction slowing (r=−0.59, p=0.006). Similarly, atrial myolysis exhibited significant correlations with atrial enlargement and haemodynamics, and electrical substrates (p&lt;0.05 for all). Conclusions Obesity induces fibro-fatty replacement of atrial myocytes and deterioration of contractile units, which may drive impaired electrical remodeling. Despite final weight loss, weight fluctuation demonstrates residual electro-structural, fibro-fatty and contractile substrates.

A novel restorative pulmonary valved conduit in a chronic sheep model: Mid-term hemodynamic function and histologic assessment

ObjectiveTo evaluate the safety and the short-term function of a novel pulmonary valved conduit (Xeltis Pulmonary Valved Conduit; XPV) up to 12 months in a sheep model. MethodsXPV and Hancock bioprosthetic valved conduits (H, used as control) were implanted in adult sheep in the pulmonary artery position. Animals were killed at 2 months (n = 6 XPV), 6 months (n = 6 XPV and n = 3 H), and 12 months (n = 6 XPV) and examined histologically. During follow-up, function of the device as well as diameter of both XPV and H were assessed by transthoracic echocardiography. ResultsOf 18 animals that received an XPV, 15 survived until they were killed; 3 animals that received H survived the planned observational interval. XPV showed mild neointimal thickening and degradation beginning at 2 months with an ongoing process until 12 months. Only 1 of the 18 animals with XPV had significant calcification at 6 months. Pathologic specimen did not show any significant narrowing of the conduit whereas neointimal thickness showed a peak at 6 months. Inflammatory process reached a maximum at 6 months and the degradation process at 12 months. Gel permeation chromatography analysis showed molecular weight loss beginning at 2 months with a peak at 12 months for the conduit with slower absorption for the leaflets. The wall of the H conduits showed more neointimal thickening, narrowing, and calcification compared with XPV, but the leaflets demonstrated minimal changes. ConclusionsBoth conduits demonstrated an acceptable safety and functionality. Significant calcification was rarely observed in the XPV, whereas the H developed more neointimal thickness with calcification of the porcine aortic root portion of the wall.

Flexible mechanoprosthesis made from woven ultra-high-molecular-weight polyethylene fibres: proof of concept in a chronic sheep model.

Ultra-high-molecular-weight polyethylene (UHMWPE) fibres are flexible, have high tensile strength, and platelet and bacterial adhesion is low. Therefore, UHMWPE may overcome limitations of current mechanical valves and bioprostheses. In this study, the biocompatibility and functionality of prototype handmade stented valves from woven UHMWPE (U-valve) was assessed in a chronic sheep model with acetylsalicylic acid monotherapy. Native pulmonary valves of 23 sheep were replaced by U-valves (n = 18) or Perimount bovine bioprostheses (reference group, n = 5). Sheep received 80 mg of acetylsalicylic acid daily. Follow-up was conducted at 1 week (n = 4), 1 month (n = 5), 3 months (n = 5) and 6 months (n = 4) in the U-valve group and at 3 months (n = 2) and 6 months (n = 3) in the reference group. Epicardial echocardiography and histology were used to assess valve function and tissue deposition, respectively. Seventeen U-valve sheep (94%) and 3 reference sheep (60%) survived the perioperative period. One reference valve sheep was sacrificed after 4 months because of congestive heart failure. At explantation, all U-valves were intact without leaflet tearing. Up to 3 months, U-valves were flexible and free of stenosis. Regurgitation was mostly mild though gradually increasing; histology showed minimal connective tissue near the leaflet base and sparse calcification. At 6 months, connective tissue was diffusely observed on the leaflets with retraction and consecutive regurgitation and leaflet thickening. Valves made from UHMWPE fibres demonstrated early feasibility in the pulmonary valve position with reasonably good haemodynamics and intact valve materials up to 6 months. Gradual leaflet thickening and retraction were observed after 3 months due to connective tissue overgrowth.

The miniaturized pediatric continuous-flow device: Preclinical assessment in the chronic sheep model

BackgroundThe Infant Jarvik 2015 is an implantable axial-flow ventricular assist device (VAD) that has undergone the major evolutionary design modifications to improve hemocompatibility. This study was conducted in anticipation of data submission to the US Food and Drug Administration to obtain Investigational Device Exemption approval. MethodsThe VAD was implanted via a left thoracotomy in Barbado sheep (n = 10, 26 (19-34] kg). Anticoagulation was maintained with coumadin, with a target international normalized ratio of greater than the individual sheep's baseline values. The VAD was managed at the highest possible speed as clinically tolerable. Complete necropsy was performed at the end of the study. ResultsThere were 2 early mortalities: tension pneumothorax (n = 1) and shower emboli of the fragmented myocardium (n = 1). The remaining 8 sheep (2 with 30-day and 6 with 60-day protocols) completed the anticipated study duration in excellent condition, with the 6 completing 60-day sheep showing appropriate weight gain during support. There were no signs of clinically significant hemolysis, with the final plasma-free hemoglobin of 2 (1-17) mg/dL. Necropsy showed old renal infarction in 7 sheep. Although thromboembolism can be the potential etiology, given the mild anticoagulation regimen, other sources of emboli were identified in 2 sheep (graft coating material and fragmented myocardium). Flow study demonstrated favorable increase in flow (up to 3.0 L/min) in proportion to change in pump speed. ConclusionsThis study has demonstrated that the Infant Jarvik 2015 VAD is capable of maintaining its functionality for an extended period of time with minimal hemolysis.

25: Effect of sildenafil citrate on fetal central hemodynamics and placental volume blood flow during hypoxemia in a chronic sheep model

25: Effect of sildenafil citrate on fetal central hemodynamics and placental volume blood flow during hypoxemia in a chronic sheep model

Abstract 19831: Pre-clinical in vivo Evaluation of Cormatrix as Right-sided Valved Conduit

Introduction: Although not FDA approved for heart valve repair, decellularized porcine small intestinal submucosa (Cormatrix) is currently used in quite a lot of institutes to reconstruct heart valves in patients. Recently, surgeons experienced clinical failures using Cormatrix as a patch in heart valve repair and words of caution were raised. The aim of this study was to pre-clinically evaluate CorMatrix as right-sided heart valved conduit in a xenogeneic animal model. Methods: CorMatrix was used as valved conduit in the right ventricular outflow tract in sheep (n=10) and lambs (n=10). Valved conduits were home-made and explanted after 1 month, 3 months or 6 months. Valve function was assessed by echocardiography directly after implantation and prior to termination. Explants were analyzed using histology, scanning electron microscopy, mechanical testing, biochemical analysis and immunohistochemistry. Results: All valved conduits were successfully implanted. 5 sheep and 2 lambs did not survive until planned follow-up. Diseased animals died due to valve failure after 1 or 2 months. Valve leaflets where thickened with signs of a massive inflammatory response. 5 sheep (1 month n=3, 3 months n=1 and 6 months n=1) and 8 lambs (1 month n=3, 3 months n=3, 6 months n=2) survived until planned follow up. In these animals, on echocardiography a well functioning valve with no signs of stenosis or insufficiency was seen. However all explants showed only limited signs of cellular infiltration or neotissue formation. Conclusions: In the chronic sheep and lamb model, 13 out of 20 CorMatrix pulmonary valved conduits were intact and showed good functionality, although only limited signs of tissue remodeling. However, 7 out of 20 valves failed owing to a massive inflammatory response. Further analysis is needed to understand the disturbing dichotomous outcome before clinical application can be advised

A randomized assessment of an advanced tissue preservation technology in the juvenile sheep model

Despite improved anticalcification technology, bioprosthetic heart valves still cannot be used in younger patients because of progressive structural valve degeneration. A novel advanced tissue preservation technology was developed that uses stable functional group capping and preservation by glycerolization. Valves incorporating this novel technology can be stored in a dry condition and do not require rinsing before use. The aim of the study was to assess the effects of this new technology in terms of valve function and durability in a chronic sheep model of orthotopic implantation. Forty-five juvenile sheep were randomized and either a Perimount mitral valve (6900P, control group) or the same valve design incorporating the novel tissue preservation technology (test group) was implanted in the mitral position. All valves were 25 mm. A transthoracic echocardiography was performed at 1 week and at 8 months postoperatively. The animals were then killed, an autopsy was performed, and the valves were examined radiographically (soft tissue radiograph), histologically (hematoxylin and eosin and Von Kossa staining), and chemically (calcium content). Exclusion criteria for analysis included surgical or procedural death, bacterial endocarditis or other diseases leading to premature death. Thirty-one animals (14 controls and 17 test animals) remained in perfect condition during the 8-month follow-up period. Echocardiography at 1 week showed normal valve function in both groups. At 8 months, cardiac output increased significantly to the same extent in both groups (vs baseline; P<.01). The mean transvalvular pressure gradient also increased but significantly more in the control group compared with the test group (P=.03). Flow turbulence across the prosthesis was increased in the control valves compared with the test valves. The test valves had significantly less calcium content than the controls (1.9 ± 0.3 vs 6.8± 1.6 μg/mg; P=.002). This was confirmed by radiographic analysis and histology. This study demonstrates that the novel tissue preservation technology, when applied to the Perimount mitral valve, significantly improves hemodynamic and anticalcification properties compared with the standard Perimount, a valve currently considered the standard of care.

Extended in vivo evaluation of a miniaturized axial flow pump with a novel inflow cannula for a minimal invasive implantation procedure

Minimally invasive techniques are desirable to minimize surgical trauma during left ventricular assist device (LVAD) implantation. This is particularly challenging for full-flow support. In this study, a minimally invasive implantation technique was developed for a microaxial rotary pump. The system was evaluated in a chronic sheep model. A HeartWare MVAD (HeartWare, Miami Lakes, FL) pump (length, 50 mm; diameter, 21 mm; maximum flow, 7-8 liters/min) was combined with a novel inflow cannula, including a new flow-optimized tip. The device was implanted into sheep (range, 60-80 kg, mean, 71.6 ± 6.8 kg) through a right-sided minithoracotomy. The inflow cannula was inserted through the superior pulmonary vein, passing through the left atrium into the left ventricle. Scheduled implant period was 30 days for 8 sheep and 100 days for 3 sheep. Mean support flow was set to half of the nominal cardiac output. Six of 8 sheep finished the scheduled 30-day investigation period (one failed due to early non-pump-related post-operative bleeding and one due to prototype controller failure). The 3 sheep scheduled for 100 days reached the study end point. Peak pump flows of up to 6.9 liters/min were achieved. At necropsy, no signs of mitral valve lesions or thrombus formation around the cannula, the tip, or the insertion site were observed, except for valve leaflet erosion in 1 animal, where the cannula had been entangled in the sub-valvular chords due to lack of ultrasound monitoring. The minimally invasive implantation technique using the HeartWare MVAD pump, together with a new cannula, provided excellent results in a chronic animal model.

Fetal cardiac function after labetalol or pindolol for maternal hypertension in a sheep model of increased placental vascular resistance

We hypothesized that labetalol and pindolol have no detrimental effects on fetal cardiac function and pulmonary hemodynamics when administered for norepinephrine-induced maternal hypertension in a chronic sheep model of increased placental vascular resistance. Specifically, we investigated the effects of labetalol and pindolol on fetal cardiopulmonary responses to acute hypoxemia. Twenty chronically instrumented near-term ewes with increased placental vascular resistance after placental embolization were anesthetized and randomized to receive labetalol or pindolol for norepinephrine-induced hypertension. Thereafter, maternal inspiratory oxygen fraction was decreased to induce fetal hypoxemia. At the end of each phase, fetal hemodynamics were assessed by Doppler ultrasonography. The data were analyzed using repeated measures ANOVA. Maternal administration of norepinephrine had no effect on fetal hemodynamics. Pindolol decreased fetal heart rate and weight-indexed left ventricular cardiac output and increased pulmonary vascular impedances, while labetalol had no effect on these parameters. During hypoxemia, fetal heart rate increased to baseline in the pindolol group and pulmonary vascular impedances increased in the labetalol group, with no changes in fetal cardiac outputs. Pindolol decreased fetal left ventricular cardiac output and induced vasoconstriction in the pulmonary vasculature, but neither pindolol nor labetalol significantly modified fetal cardiopulmonary responses to acute hypoxemia.

OC09.01: Effect of increased placental vascular resistance on the aortic isthmus blood flow: an experimental study in a chronic fetal sheep model

pressure of saline solution during SGH-CP (120 mmHg) was used. Statistical analysis: Chi2 Pearsons and tau-b Kendall tests. Results: The group appurtenance of myomas by ESH classification and assessment by STEP-W system was completely consistent with intraoperative results of assessment if to diagnostics the SHG was used (tau-b = 1). High conformity was obtained by using traditional SHG (tau-b = 0.96 and 0.94) and DH (tau-b = 0.84 i 0.85). USG TV showed the lowest conformity (tau-b = 0.71 i 0.7). Conclusions: SHG-CP should be the method of choice in preoperative assessment of myomas qualified to hysteroscopic myomectomy. This especially concerns the myomas with deep penetration of myomectrium.