Juan Carlos Chachques

Development of cardiac support bioprostheses for ventricular restoration and myocardial regeneration

OBJECTIVESnVentricular constraint devices made of polyester and nitinol have been used to treat heart failure patients. Long-term follow-up has not demonstrated significant benefits, probably due to the lack of effects on myocardial tissue and to the risk of diastolic dysfunction. The goal of this experimental study is to improve ventricular constraint therapy by associating stem cell intrainfarct implantation and a cell-seeded collagen scaffold as an interface between the constraint device and the epicardium.nnnMETHODSnIn a sheep ischaemic model, three study groups were created: Group 1: coronary occlusion without treatment (control group). Group 2: postinfarct ventricular constraint using a polyester device (Acorn CorCap). Group 3: postinfarct treatment with stem cells associated with collagen matrix and the polyester device. Autologous adipose mesenchymal stem cells cultured in hypoxic conditions were injected into the infarct and seeded into the collagen matrix.nnnRESULTSnAt 3 months, echocardiography showed the limitation of left ventricular end-diastolic volume in animals both treated with constraint devices alone and associated with stem cells/collagen. In Group 3 (stem cell + collagen treatment), significant improvements were found in ejection fraction (EF) and diastolic function evaluated by Doppler-derived mitral deceleration time. In this group, histology showed a reduction of infarct size, with focuses of angiogenesis and minimal fibrosis interface between CorCap and the epicardium due to the interposition of the collagen matrix.nnnCONCLUSIONSnMyocardial infarction treated with stem cells associated with a collagen matrix and ventricular constraint device improves systolic and diastolic function, reducing adverse remodelling and fibrosis. The application of bioactive molecules and the recent development of nanobiotechnologies should open the door for the creation of a new semi-degradable ventricular support bioprosthesis, capable of controlled stability or degradation in response to physiological conditions of the left or right heart.

An experimental model of the Ross operation: Development of resorbable reinforcements for pulmonary autografts

OBJECTIVESnTo circumvent the issue of pulmonary autograft (PA) dilation after the Ross procedure, surgical reinforcement strategies have been suggested in clinical or anecdotal series. However, no preclinical large-animal model of the Ross procedure is available, which is needed to enable full comprehension of the pathologic mechanisms and the effectiveness of reinforcement techniques during growth. Our aim was to develop a large-animal model of the Ross operation, to reproduce the clinical scenario in which this procedure might be applied, and allow for development and testing of various devices and techniques to improve PA performance. In addition, we aimed to test the effectiveness of a bioresorbable mesh for PA reinforcement.nnnMETHODSnAn experimental model of transposition of the pulmonary trunk as an autograft in the aortic position has been developed and performed under cardiopulmonary bypass in 20 growing lambs, aged 3 months. The experimental design included: a control group that underwent PA transposition; a group in which the PA was reinforced with an external, synthetic, nonresorbable, polypropylene grid; and a group that received various combinations of resorbable meshes. Animals were followed up during growth for 6 months by angiography and echocardiography and eventually killed for pathologic analysis.nnnRESULTSnAll animals survived the procedure with no complications. The model was easy and reproducible. Resorbable meshes prevented PA dilation and preserved its progressive growth process, aiding histologic remodelling.nnnCONCLUSIONSnWe developed an easy and reproducible model of the Ross procedure, allowing for a reliable simulation of the clinical scenario. Resorbable PA reinforcement may represent an interesting option in this context.

Development of bioartificial myocardium by electrostimulation of 3D collagen scaffolds seeded with stem cells.

Electrostimulation (ES) can be defined as a safe physical method to induce stem cell differentiation. The aim of this study is to evaluate the effectiveness of ES on bone marrow mesenchymal stem cells (BMSCs) seeded in collagen scaffolds in terms of proliferation and differentiation into cardiomyocytes. BMSCs were isolated from Wistar rats and seeded into 3D collagen type 1 templates measuring 25 × 25 × 6 mm. Bipolar in vitro ES was performed during 21 days. Electrical impedance and cell proliferation were measured. Expression of cardiac markers was assessed by immunocytochemistry. Viscoelasticity of collagen matrix was evaluated. Electrical impedance assessments showed a low resistance of 234±41 Ohms which indicates good electrical conductivity of collagen matrix. Cell proliferation at 570 nm as significantly increased in ES groups after seven day (ES 0.129±0.03 vs non-stimulated control matrix 0.06±0.01, P=0.002) and after 21 days, (ES 0.22±0.04 vs control 0.13±0.01, P=0.01). Immunocytoche mistry of BMSCs after 21 days ES showed positive staining of cardiac markers, troponin I, connexin 43, sarcomeric alpha-actinin, slow myosin, fast myosin and desmin. Staining for BMSCs marker CD29 after 21 days was negative. Electrostimulation of cell-seeded collagen matrix changed stem cell morphology and biochemical characteristics, increasing the expression of cardiac markers. Thus, MSC-derived differentiated cells by electrostimulation grafted in biological scaffolds might result in a convenient tissue engineering source for myocardial diseases.

A composite semiresorbable armoured scaffold stabilizes pulmonary autograft after the Ross operation: Mr Ross's dream fulfilled

OBJECTIVESnUse of resorbable external reinforcement of the pulmonary autograft during the Ross operation has been suggested, but the differential regional potential for dilation of the aorta, mainly regarding the neo-root and the neo-Valsalva sinuses, represents an unresolved issue. Auxetic materials could be useful in preventing dilation given their favorable mechanical properties. We designed a composite semiresorbable armoured bioprosthesis constituted by polydioxanone and expanded polytetrafluoroethylene and evaluated its effectiveness as a pulmonary autograft reinforcement device in an animal model of the Ross procedure.nnnMETHODSnAn experimental model of the Ross procedure was performed in 20 three-month-old growing lambs. The pulmonary autograft was alternatively nonreinforced (control group n = 10) or reinforced with composite bioprosthesis (reinforced group n = 10). Animals were followed up during growth for 6 months by angiography and echocardiography. Specific stainings for extracellular matrix and immunohistochemistry for metalloproteinase-9 were performed.nnnRESULTSnReference aortic diameter increased from 14 ± 1 mm to 19 ± 2 mm over 6 months of growth. In the control group, pulmonary autograft distension (28 ± 2 mm) was immediately noted, followed by aneurysm development at 6 months (40 ± 2 mm, P < .001 vs reference). In the reinforced group, an initial dilation to 18 ± 1 mm was detected and the final diameter was 27 ± 2 mm (42% increase). Two deaths due to pulmonary autograft rupture occurred in the control group. On histology, the control group showed medial disruption with connective fibrous replacement, whereas in the reinforced group compensatory intimal hyperplasia was present in the absence of intimal tears. The bioprosthesis promoted a positive matrix rearrangement process favoring neoarterialization and elastic remodeling as demonstrated on specific staining for elastin collagen and metalloproteinase-9.nnnCONCLUSIONSnThe device adapted and functionally compensated for the characteristics of autograft growth, guaranteeing a reasonable size of the autograft at 6 months, but more important, because the device is biocompatible, it did not disrupt the biological process of growth or cause inflammatory damage to the wall.

Mesothelial Cells vs. Skeletal Myoblasts for Myocardial Infarction

Cell transplantation for the regeneration of ischemic myocardium is limited by poor graft viability and low cell retention. Omental flaps in association with growth factors and cell sheets have recently been used to increase the vascularization of ischemic hearts. This experimental study was undertaken to evaluate the hemodynamic evolution and histological modifications of infarcted myocardium treated with mesothelial cells, and to compare the results with those of hearts treated with skeletal myoblasts. Myocardial infarction was created by surgical ligature of 2 coronary branches in 34 sheep; 6 died immediately due to ventricular fibrillation. Mesothelial cells were isolated from greater omentum, and myoblasts from skeletal muscle. After expanding the cells for 3 weeks, infarcted areas were treated with culture medium (control group), mesothelial cells, or myoblasts. After 3 months, echocardiographic studies showed significant limitation of ventricular dilatation and improved ejection fractions in both cell-treated groups compared to the controls. In the mesothelial cell group, histological studies showed significantly more angiogenesis and arteriogenesis than in the control and skeletal myoblast groups. Mesothelial cells might be useful for biological revascularization in patients with ischemic heart disease.

Compliance mismatch and compressive wall stresses drive anomalous remodelling of pulmonary trunks reinforced with Dacron grafts.

Synthetic grafts are often satisfactory employed in cardiac and vascular surgery, including expanded poly(ethylene terephthalate) or expanded poly(tetrafluoroethylene). However, accumulating evidences suggest the emergence of worrisome issues concerning the long-term fate of prosthetic grafts as large vessel replacement. Disadvantages related to the use of synthetic grafts can be traced in their inability of mimicking the elasto-mechanical characteristics of the native vascular tissue, local suture overstress leading to several prosthesis-related complications and retrograde deleterious effects on valve competence, cardiac function and perfusion. Motivated by this, in the present work it is analyzed - by means of both elemental biomechanical paradigms and more accurate in silico Finite Element simulations - the physical interaction among aorta, autograft and widely adopted synthetic (Dacron) prostheses utilized in transposition of pulmonary artery, highlighting the crucial role played by somehow unexpected stress fields kindled in the vessel walls and around suture regions, which could be traced as prodromal to the triggering of anomalous remodelling processes and alterations of needed surgical outcomes. Theoretical results are finally compared with histological and surgical data related to a significant experimental animal campaign conducted by performing pulmonary artery transpositions in 30 two-month old growing lambs, followed up during growth for six months. The in vivo observations demonstrate the effectiveness of the proposed biomechanical hypothesis and open the way for possible engineering-guided strategies to support and optimize surgical procedures.

Intrapulmonary Shear Stress Enhancement: A New Therapeutic Approach in Pulmonary Arterial Hypertension

ObjectivePulmonary arterial hypertension (PAH) is a dysfunctional endothelium disease with increased pulmonary vascular resistance (PVR) and poor prognosis. Current therapies are still insufficient. Here we propose a new pulsatile device as a more effective tool for PAH management compared with traditional treatments.Materials and MethodsTwelve piglets (10.3xa0±xa03.8xa0kg) were given either intrapulmonary pulsatile [P (nxa0=xa06)] or nonpulsatile [NP (nxa0=xa06)] tadalafil treatment. After median sternotomy and heparin injection (250xa0IU/kg), both groups underwent aorto-pulmonary surgical shunt for 1xa0h. During a second 1xa0h period in group P, a catheter prototype, driven by a small ventilator, was introduced into the pulmonary trunk and pulsated intermittently at 110xa0bpm irrespective of heart rate (90.6xa0±xa010.74 bpm). In group NP, tadalafil was given orally (1xa0mg/kg).ResultsHemodynamics and cardiac output (CO) were significantly (pxa0<xa00.05) improved in group P compared with group NP: CO was 0.56xa0±xa00.0.26 versus 0.54xa0±xa00.11 (L/min), respectively. Mean pulmonary artery pressure (PAP) was decreased in group P compared with group NP: PAP was 9.6xa0±xa02.97 versus 32.2xa0±xa05.07, respectively. Vascular resistances (dynes.s.cm−5/kg) were significantly lower in group P versus group NP: pulmonary resistance was 85xa0±xa042.12 versus 478xa0±xa0192.91 and systemic resistance was 298.8xa0±xa0172.85 versus 1301xa0±xa0615.79, respectively. Using Western blot analysis, endogenous NO synthase expression in PA segments was nonsignificantly (pxa0>xa00.05) greater in group P (0.81xa0±xa00.78) versus (0.62xa0±xa00.35) group NP.ConclusionInduced with an appropriate device, intrapulmonary shear stress–mediated endothelial function enhancement provides a more effective nearly physiological therapy for PAH.

Intrapulmonary shear stress enhancement: A new therapeutic approach in acute myocardial ischemia

OBJECTIVEnIschemic heart disease (IHD) is a leading cause of mortality with insufficient results of current therapies, most probably due to maintained endothelial dysfunction conditions. Alternatively, we propose a new treatment that promotes endothelial shear stress (ESS) enhancement using an intrapulmonary pulsatile catheter.nnnMETHODSnTwelve piglets, divided in equal groups of 6: pulsatile (P) and non-pulsatile (NP), underwent permanent left anterior descending coronary artery ligation through sternotomy. After 1 h of ischemia and heparin injection (150 IU/kg): in P group, a pulsatile catheter was introduced into the pulmonary trunk and pulsated intermittently over 1 h, and irrespective of heart rate (110 bpm). In NP group, nitrates were given (7 ± 2 mg/kg/min) for 1 h.nnnRESULTSnIn P group all 6 animals survived ischemia for 120 min, but in NP group only 2 animals survived. The 4 animals that died during the experiment in NP group survived for 93 ± 14 min. Hemodynamics and cardiac output (CO) were significantly improved in P group compared with NP group: CO was 0.92 ± 0.15 vs. 0.52 ± 0.08 in NP group (L/min; p < 0.05), respectively. Vascular resistances (dynes.s.cm(-5)/kg) were significantly (p < 0.05) lower in P group versus NP group: pulmonary resistance was 119 ± 13 vs. 400 ± 42 and systemic resistance was 319 ± 43 vs. 1857 ± 326, respectively. Myocardial apoptosis was significantly (p < 0.01) lower in P group (0.66 ± 0.07) vs. (4.18 ± 0.27) in NP group. Myocardial endothelial NO synthase mRNA expression was significantly (p < 0.01) greater in P group (0.90 ± 0.09) vs. (0.25 ± 0.04) in NP group.nnnCONCLUSIONSnIntrapulmonary pulsatile catheter could improve hemodynamics and myocardial contractility in acute myocardial ischemia. This represents a cost-effective method, suitable for emergency setting as a first priority, regardless of classical coronary reperfusion.

Forgotten driving forces in right heart failure (Part II): experimental study.

Background: Cardiac-assist devices for right ventricular failure remain controversial with poor results. This study evaluated a pulsatile cardiac-assist device in an acute right ventricular failure model vs. current therapies. Materials and methods: Pulmonary regurgitation was created in 12 piglets by valve avulsion and external transfixation of 2 pulmonary artery cusps suspended to the pulmonary arterial wall. The piglets were divided into 2 treatment groups: a pulsatile group P and a non-pulsatile group NP. Management started when severe right ventricular failure was observed (48.1u2009±u200924.5u2009min). In group P, pulsatile trousers driven by a pneumatic generator were pulsated intermittently at 40 beats·min−1. Group NP was treated with oral tadalafil 1u2009mg·kg−1, intravenous fluids, and adrenaline 0.3u2009µg·kg−1. After 1u2009h of therapy, cardiac output was significantly better in group P than group NP (1u2009±u20090.2 vs. 0.7u2009±u20090.2u2009L·min−1). Mean right ventricular pressure (16u2009±u20096 vs. 24u2009±u20092u2009mm Hg) and pulmonary arterial pressure (22u2009±u20091 vs. 31u2009±u20092u2009mm Hg) were lower in group P. Vascular resistances indices were lower in group P than group NP: pulmonary resistance index was 174u2009±u200960 vs. 352u2009±u2009118 dyne·sec·cm−5·kg−1; systemic resistance index was 611u2009±u200970 vs. 1215u2009±u2009315u2009dyne·sec·cm−5·kg−1. Western-blot analysis showed higher endogenous NO synthase expression in group P pulmonary arteries. Conclusions: The pulsatile suit can be used safely as a noninvasive cardiac-assist device in acute right ventricular failure. This represents a cost-effective nearly physiological method, suitable for adults and children.

Biomechanics drive histological wall remodeling of neoaortic root: A mathematical model to study the expression levels of ki 67, metalloprotease, and apoptosis transition

The pulmonary artery autograft (PA) is the ideal substitute for aortic valve disease in children and young adult. However, it is harnessed by the issue of long-term dilation and regurgitation, often requiring surgery. PA implanted in aortic position during the growth phase in children undergoes a process of mechanical remodeling. We previously developed a semiresorbable armored prosthesis able to mechanically sustain the neoaorta preventing dilation and to gradually integrate with the PA wall inducing a progressive arterial-like tissue positive remodeling. We also described the mechanisms of growth, remodeling and stress shielding of the reinforced PA through a mathematical model. We sought to demonstrate the biological counterpart and the potential molecular mechanisms underlying this histological and mechanical remodeling. A specific mathematical model was developed to describe mechanical behavior of the PA. Mallory trichrome red staining and immunohistochemistry for MMP-9 were performed to elucidate extracellular matrix remodeling phenomena. Apoptosis and cell proliferation were determined by TUNEL assay and immunohistochemistry for Ki67, respectively. An histological remodeling phenomenon sustained by increased level of MMP-9, augmented cell proliferation and reduced apoptosis in the reinforced PA was demonstrated. The mathematical model predicted the biomechanical behavior subtended by the histological changes of the PA in these settings. Changes in metalloproteinases (MMP-9), cell proliferation and apoptosis are the main actors in the remodeling process occurring after transposition of the PA into systemic regimens. Use of semiresorbable reinforcements might induce a positive remodeling of the PA in the context of Ross operation.