Background: Heart failure (HF) is the leading cause of mortality in United States. Animal models used to test novel HF therapeutics are inadequate as pathological features of human HF are not replicated. Available large-animal swine myocardial ischemia (MI) models mimic human HF; however, do not achieve ejection fractions (EF) less than 40%. Objective: We sought to develop a reproducible swine MI model with EF below 35%. Methods: Yucatan miniature pigs (n=18) were anesthetized, catheterized and collagen suspension (COL) of microfibrillar hemostat (INSTAT MCH, Ethicon) mixed in contrast and saline solution was injected into the left anterior descending coronary artery (LAD) under fluoroscopic guidance. COL injections started distally and filled side branches during catheter retraction. Complete transient LAD occlusion was confirmed at 2hrs by coronary angiography. Cardiac function was evaluated at 3mos using a 1.5T MRI System (Siemens Magnetom Avanto). LV volumes at end systole (LVESD) and diastole (LVEDD), EF, wall thickness (WT) in area at risk (AAR) and normal zones (NZ) were calculated. Uninjected Yucatan pigs (n=3) served as controls. Results: Twelve of 18 pigs survived COL infarction. At 3mos, EF was reduced in COL injected pigs compared to control (27.0±2.3 vs. 61.6±1.3%, respectively, P<0.001). LVESV and LVEDV were 4- and 2-fold higher and WT in AAR and NZ were reduced 6- and 2-fold, respectively in COL injected compared to controls. Conclusions: A reproducible large animal model of MI was produced by catheter based LAD collagen delivery resulting in EFs below 35% and progression to HF. By closely resembles human HF, it a highly useful for testing potential HF therapies.

AbstractReconstruction of the pulmonary valve and outflow tract is frequently needed to repair congenital defects. Current substitutes lead to graft failure and reoperation due to calcification, shrinkage, progressive insufficiency or transvalvular gradients, and relative growth of the patient compared to the valve. CorMatrix extracellular matrix (ECM), derived from decellularized, non-crosslinked small intestine submucosa (SIS) is used for general cardiac repairs and regenerates into normal cardiac tissue with growth potential. Previously, we showed that an ECM pulmonary valve leaflet remodeled into a neo-leaflet histologically similar to native valve architecture. In this study we used an ECM valved conduit for pulmonary valve replacement in an ovine model to demonstrate its potential to remodel into native tissue. A trileaflet valved conduit was produced from CorMatrix ECM sutured into a tube then intussuscepted to form a tube within a tube. At three equidistant points the inner tube was sutured to the outer tube forming three leaflets to guide unidirectional flow with physiologic opening and closing mechanics. Under cardiopulmonary bypass the ovine pulmonary valve and pulmonary artery section was removed and replaced with the ECM valved conduit. Valve function was evaluated by echocardiography post-operatively and at bi-monthly intervals until euthanasia at 3, 5, 8, and 12 months. Histological evaluation included H and E, Movat pentachrome, von Kossa, anti-CD31, and anti-eNOS. Our echocardiography results show that a pulmonary valve constructed from ECM opens and closes completely without regurgitation or stenosis for 12 months. Grossly, explanted valves appeared similar to native valves and were remodeling after 3 months with further progression to native morphology after 5, 8 and 12 months. Histological examination showed diffuse cellular infiltration by 3 months. At 5 months, collagen organization was increased and glycosaminoglycans were distributed throughout the middle of the leaflet. At 3 months, SEM and eNOS staining demonstrated a confluent and functional endothelial lining on the pulmonary artery and hinge regions of the valve. At 5 months, this lining extended to the center of the leaflet with confluent areas at the leaflet tip. At 8 and 12 months, a tri-layered structure similar to native valve architecture was demonstrated histologically by a Movat stain with a confluent endothelial lining demonstrated by eNOS and CD31 staining. The von Kossa stain showed an absence of calcific deposits at all time points except occasionally at the suture. These results demonstrate the potential of a CorMatrix ECM pulmonary valve to remodel into endothelialized tissue that is indistinguishable from the host’s native valve both grossly and histologically. Such a regenerated valve would be expected to improve patient outcomes since it remodels into native tissue with growth potential.

Background. We evaluated the in vitro strength and in vivo arterial-wall response to an extracellular-matrix-based patch material in a sheep model of carotid artery repair.Materials and Methods. A six-ply sheet of acellular, porcine extracellular matrix (ECM) was subjected to in vitro material strength testing and implanted in 15 sheep for 30, 90, and 180 d. Bovine pericardium was used as a control in some animals. In vivo graft patency was assessed by angiography. Explanted grafts were evaluated by histopathology and burst-strength testing.Results. Mean (SD) in vitro suture retention force of the ECM sheet was 14.5 (3.06) N; tensile strength was 29.7 (6.11) N; and probe burst strength was 185 (22.6) N. In vivo, mild stenosis was observed at 30 d for all patches; stenosis was absent at 90 d in the ECM-repaired arteries but not bovine pericardium controls. Pseudoaneurysm was not observed in any animal. Histopathology showed progressive graft degradation, collagen deposition, formation of neocapillaries and fibrocellular neointima, and endothelialization, but no calcification. Mean (SD) burst pressure for unrepaired arteries was 2608 (858) mmHg and 1473 (694) mmHg for ECM-repaired vessels. Mean change in diameter from unloaded state to burst pressure was 29% (9.7) for unrepaired vessels and 24% (13.4) for ECM-repaired vessels.Conclusions. The six-ply ECM sheet can withstand the forces encountered after carotid artery repair. In sheep, it shows evidence of progressive, constructive remodeling as early as 30 d post-implantation with rapid deposition of endothelium. ECM shows promise as a patch material for CEA repair. (C) 2012 Elsevier Inc. All rights reserved.

Thromboembolic complications in Bileaflet mechanical heart valves (BMHVs) are believed to be due to the combination of high shear stresses and large recirculation regions. Relating blood damage to design geometry is therefore essential to ultimately optimize the design of BMHVs. The aim of this research is to quantitatively study the effect of 3D channel geometry on shear-induced platelet activation and aggregation, and to choose an appropriate blood damage index (BDI) model for future numerical simulations. The simulations in this study use a recently developed lattice-Boltzmann with external boundary force (LBM-EBF) method [Wu, J., and C. K. Aidun. Int. J. Numer. Method Fluids 62(7):765–783, 2010; Wu, J., and C. K. Aidun. Int. J. Multiphase flow 36:202–209, 2010]. The channel geometries and flow conditions are re-constructed from recent experiments by Fallon [The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets in School of Chemical and Biomolecular Engineering. Atlanta: Georgia Institute of Technology] and Fallon et al. [Ann. Biomed. Eng. 36(1):1]. The fluid flow is computed on a fixed regular 'lattice' using the LBM, and each platelet is mapped onto a Lagrangian frame moving continuously throughout the fluid domain. The two-way fluid–solid interactions are determined by the EBF method by enforcing a no-slip condition on the platelet surface. The motion and orientation of the platelet are obtained from Newtonian dynamics equations. The numerical results show that sharp corners or sudden shape transitions will increase blood damage. Fallon's experimental results were used as a basis for choosing the appropriate BDI model for use in future computational simulations of flow through BMHVs.

Bileaflet mechanical heart valves (BMHVs) have been widely used to replace native valves. Unfortunately, the design of bileaflet MHVs produces flow fields that may cause damage to blood elements, especially at the hinge area. The objectives of this study are to analyze the flow properties around the hinge area and through the valve, to further understand the cause of blood damage and provide improved designs to reduce the adverse hemodynamic effects of valves that cause platelet activation and damage blood elements. An important part of this improvement is to understand the hemodynamic effects produced by different valve designs, and how the surrounding flow fields affect thromboembolic formation. The hemodynamics of the valve flow is characterized by complex spatial and temporal three-dimensional structures that arise from the pulsatility of the flow, the complexity of the geometry and the flow-dependent motion of the valve leaflets. High fidelity simulations of the valve flow fields throughout the cardiac cycle is required to improve and refine existing valve designs so as to ultimately develop bileaflet MHVs with minimal thromboembolic complications.

In the United States, over 125,000 mechanical heart valves (MHVs) are implanted each year. Flow through the MHV hinge can cause thromboemboli formation. The purpose of this study was to examine various orifice geometries representing the MHV hinge region and how these geometries may contribute to platelet activation and thrombin generation. We also characterized these flow fields with digital particle image velocimetry (DPIV). Citrated human blood at room temperature was forced through the orifices (400 and 800 μm ID) with a centrifugal bypass pump, continuously infusing calcium chloride to partially reverse the citrate anticoagulant. Blood samples were tested for the presence of thrombin–antithrombin complex (TAT) and platelet factor 4 (PF4). Velocity and shear stress were measured with DPIV using a blood analog fluid seeded with fluorescent microbeads. The results indicate that small changes in geometry, although they do not affect the bulk flow, change the coagulation propensity as blood flows through the orifices. A more abrupt geometry allows more stagnation to occur resulting in more thrombin generation. PF4 measurements indicated similar levels of platelet activation for all orifices. DPIV showed differences in the jets with respect to entrainment of stagnant fluid. These results help to pinpoint the important parameters that lead to flow stasis and subsequent thrombus formation.

Introduction: Thromboembolic events caused by implanted vascular devices present serious medical challenges. In particular bileaflet mechanical heart valves (MHVs) are prone to thrombus formation in the hinge region due to a combination of high shear stress and stagnation regions. Most studies of shear-induced platelet activation and aggregation have been performed using viscometers, parallel plate flow, and other non-physiologic in vitro configurations. The present study investigated these events in a physiogically relevant environment in which thrombin formation in response to shear stress activation of platelets plays a more predominant role.Materials and methods: Anticoagulated (citrated) human blood was placed in a steady flow loop containing a 400 mu m round orifice or various MHVs in the leakage position. Simultaneous blood recalcification enhanced the thrombus forming potential of the blood. Aggrastat and AN51 were used to block binding to the platelet GPIIb/IIIa and GPIb receptors, respectively, and aspirin was used to block thromboxane production. Thrombin generation was measured indirectly by the thrombin-antithrombin III assay. Results and conclusions: Aggrastat, AN51, and aspirin all suppressed thrombin formation. Furthermore, histological results suggested important roles for vWF and fibrinogen in a two-step model of thrombus formation. Thus, thrombin is reproducibly formed in this in vitro system, a process that can be suppressed by blocking platelet activation. This system has the potential to investigate mechanisms and interventions for medical devices that contact with blood under varying shear stress conditions. (c) 2007 Elsevier Ltd. All rights reserved.

BACKGROUND:While it is established that mechanical heart valves (MHVs) damage blood elements during leakage and forward flow, the role in thrombus formation of platelet activation by high shear flow geometries remains unclear. In this study, continuously recalcified blood was used to measure the effects of blood flow through orifices, which model MHVs, on the generation of procoagulant thrombin and the resulting formation of thrombus. The contribution of platelets to this process was also assessed.METHOD OF APPROACH:200, 400, 800, and 1200 microm orifices simulated the hinge region of bileaflet MHVs, and 200, 400, and 800 microm wide slits modeled the centerline where the two leaflets meet when the MHV is closed. To assess activation of coagulation during blood recirculation, samples were withdrawn over 0-47 min and the plasmas assayed for thrombin-antithrombin-llI (TAT) levels. Model geometries were also inspected visually.RESULTS:The 200 and 400 microm round orifices induced significant TAT generation and thrombosis over the study interval. In contrast, thrombin generation by the slit orifices, and by the 800 and 1200 microm round orifices, was negligible. In additional experiments with nonrecalcified or platelet-depleted blood, TAT levels were markedly reduced versus the studies with fully anticoagulated whole blood (p < 0.05).CONCLUSIONS:Using the present method, a significant increase in TAT concentration was found for 200 and 400 microm orifices, but not 800 and 1200 microm orifices, indicating that these flow geometries exhibit a critical threshold for activation of coagulation and resulting formation of thrombus. Markedly lower TAT levels were produced in studies with platelet-depleted blood, documenting a key role for platelets in the thrombotic process.