Adolfo A. Leirner

Natural and prosthetic heart valve calcification: morphology and chemical composition characterization.

Calcification is the most common cause of damage and subsequent failure of heart valves. Although it is a common phenomenon, little is known about it, and less about the inorganic phase obtained from this type of calcification. This article describes the scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy and Ca K-edge X-ray absorption near edge structure (XANES) characterization performed in natural and bioprosthetic heart valves calcified in vivo (in comparison to in vitro-calcified valves). SEM micrographs indicated the presence of deposits of similar morphology, and XANES results indicate, at a molecular level, that the calcification mechanism of both types of valves are probably similar, resulting in formation of poorly crystalline hydroxyapatite deposits, with Ca/P ratios that increase with time, depending on the maturation state. These findings may contribute to the search for long-term efficient anticalcification treatments.

Perspectivas da evolucão clínica de pacientes com cardiomiopatia chagásica listados em prioridade para o transplante cardíaco

INTRODUCTION: Heart failure is responsible for high mortality rates of patients on heart transplantation waiting lists. In Chagas cardiomyopathy, the presence of biventricular dysfunction increases the severity of this situation. METHOD: One hundred and forty-one patients suffering from cardiogenic shock, listed as high priority for heart transplantation, were studied. Forty-six patients presented with Chagas cardiomyopathy and 95 with other cardiomyopathies. Heart failure was treated using intravenous inotropic drugs and intra-aortic balloon pump implantation. Five patients with Chagas disease underwent paracorporeal left ventricular assist device implantation. RESULTS: During a mean follow-up of 2.8 months, 58 (41.1%) of the 141 patients were transplanted, while 73 (53.7%) died and 10 were removed from the waiting list. The mortality rates in chagasic and non-chagasic patients were 45.6% and 54.7%, respectively. The mean expected survival of patients with Chagas disease, who did not undergo heart transplantation, was only 1.5 months, with these patients presenting a relative risk for death of 1.6 compared to patients with other heart diseases (p<0.05). The five chagasic patients submitted to left ventricular assist device implantation were maintained on support for a mean of 22 days, with two of them undergoing transplantation, two died due to multiple organ failure and one remains on circulatory support. None of these patients presented right ventricular dysfunction and there were no device related complications. CONCLUSION: The evolution of heart failure seems to be rapid in patients with Chagas cardiomyopathy. Therefore, an early indication of mechanical circulatory support is important as a bridge to heart transplantation in these patients.

Dynamic non-linear behavior and stability of a ventricular assist device

This paper investigates the non-linear dynamic behavior and stability of the internal membrane of a ventricular assist device (VAD). This membrane separates the blood chamber from the pneumatic chamber, transmitting the driving cyclic pneumatic loading to blood flowing from the left ventricle into the aorta. The membrane is a thin, nearly spherical axi-symmetric shallow cap made of polyurethane and reinforced with a cotton mesh. Experimental evidence shows that the reinforced membrane behaves as an isotropic elastic material and exhibits both membrane and flexural stiffness. So, the membrane is modeled as an isotropic pressure loaded shallow spherical shell and its dynamic behavior and snap-through buckling considering different types of dynamic excitation relevant to the understanding of the VAD behavior is investigated. Based on Marguerre kinematical assumptions, the governing partial differential equations of motion are presented in the form of a compatibility equation and a transverse motion equation. The results show that the shell, when subjected to compressive pressure loading, may loose its stability at a limit point, jumping to an inverted position. If the compressive load is removed, the shell jumps back to its original configuration. This non-linear behavior is the key feature in the VAD behavior.

Prospects in lyophilization of bovine pericardium.

Almost 30 years after the introduction of heart valve prostheses patients worldwide are benefiting from the implant of these devices. Among the various types of heart valves, the ones made of treated bovine pericardium have become a frequently used replacement of the hearts native valve. Lyophilization, also known as freeze-drying, is an extremely useful technique for tissue storage for surgical applications. This article gives a brief overview on the current bovine pericardium lyophilization development, including the chemical modification to improve physical-chemical characteristics and the advanced technologies used to guarantee a high-quality product. It was shown that lyophilization process can be successfully applied as a method of bovine pericardium preservation and also as a technological tool to prepare new materials obtained by chemical modification of native tissues.

Histological Evaluation of Biocompatibility of Lyophilized Bovine Pericardium Implanted Subcutaneously in Rats

This article aims at investigating in vivo evaluation of lyophilization procedure on the biocompatibility of bovine pericardium treated with glutaraldehyde (GA). The bovine pericardium was fixed with 0.5% glutaraldehyde during 10 days and preserved in 4% formaldehyde (FA). Two groups of samples were prepared from treated membranes: Group 1, nonlyophilized samples and Group 2, lyophilized samples. Male Sprague-Dawley rats (4 weeks after birth) were anesthetized (pentobarbital sodium 25 mg/kg of body weight) and in each one were implanted subcutaneously in the dorsal region a sample from Group 1 and another from Group 2. These samples were explanted after 30 days for histological analysis. No intercurrences took place after the surgery. No differences (P > 0.05) in the calcification, granulomatous reaction, mononuclear infiltration, and granulation tissue development was observed between both groups. The implanted lyophilized samples presented a trend for a reduced inflammatory reaction. Lyophilization of the bovine pericardium does not seem to increase the above listed tissue reaction.

The influence of freezing rates on bovine pericardium tissue Freeze-drying

The bovine pericardium has been used as biomaterial in developing bioprostheses. Freeze-drying is a drying process that could be used for heart valves preservation. The maintenance of the characteristics of the biomaterial is important for a good heart valve performance. This paper describes the initial step in the development of a bovine pericardium tissue freeze-drying to be used in heart valves. Freeze-drying involves three steps: freezing, primary drying and secondary drying. The freezing step influences the ice crystal size and, consequently, the primary and secondary drying stages. The aim of this work was to investigate the influence of freezing rates on the bovine pericardium tissue freeze-drying parameters. The glass transition temperature and the structural behaviour of the lyophilized tissues were determined as also primary and secondary drying time. The slow freezing with thermal treatment presented better results than the other freeze-drying protocols.

Cytotoxicity and Genotoxicity of Bovine Pericardium Preserved in Glycerol

Bovine pericardium is a widely utilized biomaterial. Usually, after harvesting, it is advantageous that the pericardium be immersed in glycerol to improve its shelf life. This can induce some degree of toxicity in the material. The studies were performed in compliance with the rules of ISO 10993 and OECD 487, in the biological evaluation of medical devices. The material was prepared without previous washing. After sterilization by gamma radiation the pericardium was immersed in RPMI 1640 culture medium to fulfill the extraction condition. The same extract was employed in the cytotoxic and genotoxic tests. The procedures were carried out with Chinese hamster ovary cell line and to determine the cytotoxicity, a colorimetric method with the tetrazolium compound MTS was used. For the genotoxicity, following the in vitro micronucleus assay, the test was developed with and without metabolic activation. The Cytotoxicity Index was graphically estimated at the extract concentration of 78%. In the genotoxicity test, the average value of cell proliferation index was found to be 1.62 +/- 0.02 with S9 metabolic activator and 1.91 +/- 0.01 without S9 metabolic activator. Both values are similar to the negative control value in the micronucleus assay. We observed that although the pericardium preserved in glycerol shows a certain level of cytotoxicity, it does not show any genotoxicity.

Influence of biopump with and without intraaortic balloon on the coronary and carotid flow

BACKGROUND The objective of this study was to evaluate the influence of biopump used for left ventricular assistance on the coronary and carotid flows in dogs with normal heart. The efficacy of the simultaneous use of an intraaortic balloon pump to compensate the possible deleterious effects of the circulatory assistance with continuous flow was also analyzed. METHODS Fifteen dogs were studied. The hemodynamic evaluation included serial measurements of the classic parameters. Carotid and coronary blood flows were obtained by electromagnetic transducers. RESULTS The hemodynamic evaluation did not show significant statistical changes. The use of circulatory-isolated assistance with biopump shows reduction (24.6% +/- 6.1%) in coronary flow, in relation to the control situation and the concomitant use of biopump and intraaortic balloon pump showed similar coronary flow. Regarding carotid flow, a similar trend was observed in relation to the positive influence of the pulsatile flow with an intraaortic balloon pump without statistical significance (p = 0.0582). CONCLUSIONS The biopump reduces the coronary flow in dogs. The use of intraaortic balloon pump with the biopump increases the coronary flow significantly, reaching similar values to those observed without the circulatory assistance.

Cavopulmonary anastomosis improves left ventricular assist device support in acute biventricular failure

OBJECTIVE Right ventricular failure during left ventricular assist device (LVAD) support can result in severe hemodynamic compromise with high mortality. This study investigated the acute effects of cavopulmonary anastomosis on right ventricular loading and LVAD performance in a model of severe biventricular failure. METHODS LVAD support was performed by means of centrifugal pump implantation in 14 anesthetized dogs (20-30 kg) with severe biventricular failure obtained by ventricular fibrillation induction. Animals were randomized to be submitted to classical cavopulmonary anastomosis (Glenn shunt) or to control group and were maintained under LVAD support for 2h. Left and right atrial, right ventricular and systemic pressures were monitored, while total pulmonary flow was simultaneously recorded by transonic flowmeters located on the superior vena cava and pulmonary trunk. Blood gas and venous lactate determinations were also obtained. RESULTS Ventricular fibrillation maintenance resulted in acute LVAD performance impairment after 90 min in the control group, while animals with Glenn circuit maintained normal LVAD pump flow (55+/-13 ml kg(-1)min(-1) vs 21+/-4 ml kg(-1)min(-1), p<0.001) and better peripheral perfusion (blood lactate of 29+/-10 pg/ml vs 46+/-9 pg/ml, p<0.001). Left and right atrial pressures did not change significantly, while right ventricular pressure was lower in animals with Glenn circuit (13+/-3 mm Hg vs 22+/-8 mm Hg, p=0.005). Right ventricular unloading with Glenn shunt also resulted in superior total pulmonary flow (59+/-13 ml kg(-1)min(-1) vs 17+/-3 ml kg(-1)min(-1), p<0.001). CONCLUSION The concomitant use of cavopulmonary anastomosis during LVAD support in a model of severe biventricular failure limited right ventricular overloading and resulted in better hemodynamic performance.

A new approach to heart valve tissue engineering: mimicking the heart ventricle with a ventricular assist device in a novel bioreactor.

The ‘biomimetic’ approach to tissue engineering usually involves the use of a bioreactor mimicking physiological parameters whilst supplying nutrients to the developing tissue. Here we present a new heart valve bioreactor, having as its centrepiece a ventricular assist device (VAD), which exposes the cell–scaffold constructs to a wider array of mechanical forces. The pump of the VAD has two chambers: a blood and a pneumatic chamber, separated by an elastic membrane. Pulsatile air‐pressure is generated by a piston‐type actuator and delivered to the pneumatic chamber, ejecting the fluid in the blood chamber. Subsequently, applied vacuum to the pneumatic chamber causes the blood chamber to fill. A mechanical heart valve was placed in the VADs inflow position. The tissue engineered (TE) valve was placed in the outflow position. The VAD was coupled in series with a Windkessel compliance chamber, variable throttle and reservoir, connected by silicone tubings. The reservoir sat on an elevated platform, allowing adjustment of ventricular preload between 0 and 11 mmHg. To allow for sterile gaseous exchange between the circuit interior and exterior, a 0.2 µm filter was placed at the reservoir. Pressure and flow were registered downstream of the TE valve. The circuit was filled with culture medium and fitted in a standard 5% CO2 incubator set at 37 °C. Pressure and flow waveforms were similar to those obtained under physiological conditions for the pulmonary circulation. The ‘cardiomimetic’ approach presented here represents a new perspective to conventional biomimetic approaches in TE, with potential advantages. Copyright