Use of aortic wall patches as leaflet replacement material during aortic valve repair.

Objectives: Aortic valve repair can be limited by inadequate leaflet tissue for proper coaptation. Various kinds of pericardium have been used for cusp augmentation, but most have failed because of tissue degeneration. A more durable leaflet substitute is needed. Methods: In this report, 8 consecutive cases are presented in which autologous ascending aortic tissue was used to augment inadequate native cusps during aortic valve repair. Biologically, aortic wall is a living autologous tissue that could have exceptional durability as a leaflet substitute. Techniques for insertion are described in detail, along with procedural videos. Results: Early surgical outcomes were excellent, with no operative mortalities or complications, and all valves were competent with low valve gradients. Patient follow-up and echocardiograms to a maximum of 8 months' postrepair remain excellent. Conclusions: Because of superior biologic characteristics, aortic wall has the potential to provide a better leaflet substitute during aortic valve repair and to expand patient categories amenable to autologous reconstruction. More experience and follow-up should be generated.

The kinetics of cardiopulmonary bypass: a dual-platform proteomics study of plasma biomarkers in pediatric patients undergoing cardiopulmonary bypass.

This study was designed to investigate the expression kinetics and patterns of plasma biomarkers throughout the pediatric cardiopulmonary bypass (CPB) procedure to help predict those patients most at risk for complications. This study sampled plasma from pediatric CPB patients at five time points before, during, and after CPB. A dual-platform proteomics approach was then utilized which incorporated two-dimensional difference gel electrophoresis (2D-DIGE) coupled with matrix-assisted laser desorption ionization-time-of-flight/time-of-flight tandem mass spectrometry, and multi-analyte profile (MAP) assays to identify changes in expression of plasma protein biomarkers and characterize the patterns of these changes. A combined total of 134 proteins were identified with significant changes between the two platforms, with 53 coming from 2D-DIGE, 90 from MAP, and nine proteins that were identified using both methods. The proteins were then divided into 12 major groups based on the expression patterns, and two of the most clinically relevant proteins having the greatest changes in expression were selected from each group to use as "predictor biomarkers." A potential model for prediction of patient outcome was then generated using these 24 proteins. The patterns of biomarker expression during pediatric CPB may provide insight into the prediction, prevention, or treatment of complications resulting from CPB, thereby helping to improve the outcomes of pediatric CPB patients and reduce the incidence of complications.

Improved cerebral oxygen saturation and blood flow pulsatility with pulsatile perfusion during pediatric cardiopulmonary bypass.

Brain monitoring techniques near-infrared spectroscopy (NIRS) and transcranial Doppler (TCD) ultrasound were used in pediatric patients undergoing cardiopulmonary bypass for congenital heart defect (CHD) repair to analyze the effect of pulsatile or nonpulsatile flow on brain protection. Regional cerebral oxygen saturation (rSO2) and cerebrovascular pulsatility index (PI) were measured by NIRS and TCD, respectively, in 111 pediatric patients undergoing bypass for CHD repair randomized to pulsatile (n = 77) or nonpulsatile (n = 34) perfusion. No significant differences in demographic and intraoperative data, including surgical risk stratification, existed between groups. Patients undergoing pulsatile perfusion had numerically lower decreases in rSO2 from baseline for all time points analyzed compared with the nonpulsatile group, with significant ∼12% lower decreases at 40 and 60 min after crossclamp. Patients undergoing pulsatile perfusion had numerically lower decreases in PI from baseline for the majority of time points compared with the nonpulsatile group, with significant ∼30% lower decreases between 5 and 40 min after crossclamp. Pulsatile flow has advantages over nonpulsatile flow as measured by NIRS and TCD, especially at advanced time points, which may improve postoperative neurodevelopmental outcomes.

Dual-platform proteomics study of plasma biomarkers in pediatric patients undergoing cardiopulmonary bypass.

Plasma samples from pediatric cardiac patients undergoing cardiopulmonary bypass (CPB) procedures were used to identify and characterize patterns of changes in potential biomarkers related to tissue damage and inflammation. These included proteins associated with systemic inflammatory response syndrome. Potential biomarkers were identified using a dual-platform proteomics approach requiring approximately 150 microL of plasma, which included two-dimensional difference gel electrophoresis (2D-DIGE) and a multiplexed immunoassay. Methods used in the dual approach measured levels of 129 proteins in plasma from pediatric CPB patients. Of these, 70 proteins changed significantly (p<0.05) between time points, and 36 of these retained significance after the highly stringent Bonferroni correction [p<0.001 for 2D-DIGE and p<0.00056 for multianalyte profile (MAP) assays]. Many of the changing proteins were associated with tissue damage, inflammation, and oxidative stress. This study uses a novel approach that combines two discovery proteomics techniques to identify a pattern of potential biomarkers changing after CPB. This approach required only 150 microL of plasma per time point and provided quantitative information on 129 proteins. The changes in levels of expression of these proteins may provide insight into the understanding, treatment, and prevention of systemic inflammation, thereby helping to improve the outcomes of pediatric CPB patients.

Inflammatory and hemostatic response to cardiopulmonary bypass in pediatric population: feasibility of seriological testing of multiple biomarkers.

Perioperative myocardial and cerebral damages are the major determinants of postoperative morbidity and mortality in pediatric cardiac surgery. Cardiopulmonary bypass (CPB) causes alterations in the levels of biomarkers related to inflammation, tissue damage, and other tissue pathologies. Early and accurate evaluation of inflammation and tissue damage would therefore be clinically useful. Our objective is to assess the suitability of using Multi-Analyte Profiling (MAP) (Rules Based Medicine, Austin, TX, USA) in pediatric cardiac surgery as a potential surrogate marker of clinical outcome. MAP technology platform allowed us to analyze 90 different biomarkers using only 100µL of plasma to detect any changes in the levels of 90 biomarkers. Plasma samples (100µL) were collected at five different time points: 1. before midline incision; 2. on CPB for 3-5min; 3. at the end of CPB; 4. 1h after CPB; and 5. 24h after CPB. After removing the outliers, the average and standard deviation of the values obtained from the 10 patients were calculated for each time point. The average values of each biomarker at each time point were then compared to each other and to the baseline. The pilot protocol included 10 patients (ages from 3 months to 4 years old) with similar Jenkins risks stratifications who underwent nonpulsatile CPB. We detected changes in the levels of 90 biomarkers. Biomarkers were assessed in groups. Myeloperoxidase (MPO) and pregnancy-associated plasma protein A (PAPP-A) were the earliest markers to rise with 49- and 18-fold increases 3-5min after the onset of CPB, respectively. The most striking increase was noted in the heart-type fatty acid-binding protein (FABP) levels. FABP increased 25, 193, 151, and 4-fold at time points 2, 3, 4, and 5, respectively. Surges in the novel markers of injury were followed by the markers of inflammation (i.e., C-reactive protein, interleukins) peaking at 24h after CPB. This pilot study shows that it is possible to measure 90 different biomarkers using only a very small sample of plasma to evaluate the effects of CPB. Novel markers of tissue injury (FABP, PAPP-A, or MPO) are the earliest markers to rise. Serial monitoring of multiple biomarkers may help to predict and improve outcomes after pediatric cardiac surgery.

Impact of tubing length on hemodynamics in a simulated neonatal extracorporeal life support circuit.

During extracorporeal life support (ECLS), a large portion of the hemodynamic energy is lost to various components of the circuit. Minimization of this loss in the circuit leads to better vital organ perfusion and decreases the risk of systemic inflammation. In this study, we evaluated the hemodynamic properties of differing lengths of tubing in a simulated neonatal ECLS circuit. The neonatal ECLS circuit used in this study included a Capiox Baby RX05 oxygenator (Terumo Corporation, Tokyo, Japan), a Rotaflow centrifugal pump (MAQUET Cardiopulmonary AG, Hirrlingen, Germany), and a heater and cooler unit. An 8Fr Biomedicus arterial and a 10Fr Biomedicus venous cannula were connected to the pseudopatient. One-fourth inch tubing was used for both the arterial and the venous line. A Hoffman clamp was located upstream from the pseudopatient to maintain a certain patient pressure. Three pressure transducers were placed at different sites: postoxygenator, prearterial cannula, and postarterial cannula. The system was primed with Lactated Ringer's solution; human blood was then added to maintain a hematocrit of 40%. The volume of the pseudopatient was 500mL. We hemodynamically evaluated three circuits with different lengths of tubing: 6, 4, and 2 feet (182.88, 121.92, and 60.96 cm, respectively) for both arterial and venous lines; the priming volumes including all of the components of the circuits were 195, 155, and 115mL, respectively. In each circuit, we measured the pressure drops of the arterial tubing and the arterial cannula, as well as the flow rates at different rpm (1750-3000, 250 intervals) under three patient pressures (40, 60, and 80mm Hg). All the experiments were conducted at 37°C. The pressure drop across the arterial cannula is much larger than that of arterial tubing in all set-ups, especially under high flow rates. Upon cutting the tubing from 6 to 2 feet, the pressure drop of the arterial tubing decreased by half, while the pressure drop of the arterial cannula increased due to the slightly higher flow rates. These results suggest that compared to the arterial tubing, the arterial cannula has a larger impact on the hemodynamics of the circuit. There is a little influence of tubing length on the circuit flow rate.

Pediatric extracorporeal life support systems: education and training at Penn State Hershey Children's Hospital.

The following is a description of the training offered to extracorporeal life support (ECLS)-trained staff at the Penn State Hershey Children's Hospital. Changes with the ECLS circuit prompted the need for an initiative to train staff in the care of patients requiring ECLS support. In addition to didactic material, we incorporated a "hands-on" approach in designing the education. During the didactic portion, the circuit was demonstrated as a wet lab. The final step offered a voluntary visit to the animal research facility utilizing clinical case scenarios which allowed participants to articulate and demonstrate proper circuit management.The effort throughout this process was to build a competent ECLS team which will ultimately provide our patients with the greatest chance for a full recovery.

Segmental differences of impaired diastolic relaxation following cardiopulmonary bypass surgery in children: a tissue Doppler study.

Impaired myocardial relaxation is an important aftereffect of cardiopulmonary bypass (CPB). Infants with their immature calcium metabolism may be particularly vulnerable. However, it has been difficult to quantitate diastolic dysfunction clinically. This study used tissue Doppler to measure regional diastolic myocardial velocities in 31 pediatric patients undergoing open heart surgery. Color tissue Doppler images were acquired in the operating room before and 8 and 24 h post CPB surgery. Early (E) and atrial (A) diastolic velocities were determined. Long axis motion was assessed from apical views near the mitral and tricuspid rings and radial wall motion from the parasternal view. The study included 31 children aged 3.6 +/- 4.4 years (6 days to 16 years), with a mean weight of 14.7 +/- 13.7 kg and body surface area of 0.59 +/- 0.35 m(2). Tissue Doppler analysis of regional wall motion revealed abnormal left ventricle (LV) and right ventricle (RV) diastolic relaxation in the early postoperative phase after CPB. Initially, all segments were significantly altered, but by 24 h, regional differences became apparent: LV radial wall motion was recovered, while longitudinal fibers in LV and RV appeared to be less resilient. RV myocardial mechanics were most abnormal. Tissue Doppler analysis may deepen our understanding of myocardial recovery and offers a sensitive tool to compare different cardioprotective strategies.

Clinical real-time monitoring of gaseous microemboli in pediatric cardiopulmonary bypass.

We describe the occurrence and distribution of gaseous microemboli with real-time monitoring in a pediatric cardiopulmonary bypass (CPB) circuit and in the cerebral circulation of patients using the Emboli Detection and Classification (EDAC) system and transcranial Doppler (TCD). Four patients (weights 3.2-13.8 kg) were studied. EDAC monitors were located on the venous line and on the postfilter arterial line to measure gaseous microemboli in the CPB circuit. TCD was used to measure high-intensity transient signals (HITS) in the middle cerebral artery. Before the initiation of CPB, EDAC detected gaseous microemboli in two cases when giving volume through the arterial line. At the initiation of CPB, gross air appeared in the venous line and gaseous microemboli were detected in the arterial line in all patients. EDAC detected a total of 3192-14 699 gaseous microemboli in the arterial line during the whole CPB period, more than 99% of which were smaller than 40 microns. After cessation of CPB, EDAC detected gaseous microemboli in the arterial line in all cases. The TCD detected HITS in two cases (25 and 315), and detected no HITS in two cases. We observed that the venous line acted as a principal source of gaseous microemboli, particularly when using vacuum-assisted venous drainage, and that a significant number of these gaseous microemboli smaller than 40 microns were subsequently transferred to the patient. Using EDAC and TCD together could strengthen the monitoring of gaseous microemboli in the extracorporeal circuit and cerebral circulation.

Animal model development for the Penn State pediatric ventricular assist device.

In March 2004, the National Heart, Lung, and Blood Institute awarded five contracts to develop devices providing circulatory support for infants and small children with congenital and acquired cardiac disease. Since 2004, the team at Penn State College of Medicine has developed a pneumatically actuated ventricular assist device (VAD) with mechanical tilting disk valves. To date, hemodynamic performance, thrombogenesis, and hemolysis have been chronically evaluated in 16 animals, including 4 pygmy goats and 12 sheep. Major complications, mainly respiratory failure, have been encountered and resolved by a multi-disciplinary team. Multi-modal analgesia, appropriate antibiotic therapy, and attentive animal care have contributed to successful outcomes. Time after implant has ranged from 0 to 40 days. Most recently, a sheep implanted with Version 3 Infant VAD was electively terminated at 35 days postimplant, with no major adverse events. This report describes a successful in vivo model for evaluating a pediatric VAD.

Chronic Ovine Studies Demonstrate Low Thromboembolic Risk in the Penn State Infant Ventricular Assist Device.

Mechanical circulatory support for children under 6 years of age remains a challenge. This article describes the preclinical status and the results of recent animal testing with the Penn State Infant Left Ventricular Assist Device (VAD). The objectives have been to 1) demonstrate acceptably low thromboembolic risk to support Food and Drug Administration approval, 2) challenge the device by using minimal to no anticoagulation in order to identify any design or manufacturing weaknesses, and 3) improve our understanding of device thrombogenicity in the ovine animal model, using multicomponent measurements of the coagulation system and renal ischemia quantification, in order to better correlate animal results with human results.The Infant VAD was implanted as a left VAD (LVAD) in 18-29 kg lambs. Twelve LVAD and five surgical sham animals were electively terminated after approximately 30 or 60 days. Anticoagulation was by unfractionated heparin targeting thromboelastography R times of 2x normal (n = 6) or 1x normal (n = 6) resulting in negligible heparin activity as measured by anti-Xa assay (<0.1 IU/ml). Platelet inhibitors were not used.There were no clinically evident strokes or evidence of end organ dysfunction in any of the 12 electively terminated LVAD studies. The degree of renal ischemic lesions in device animals was not significantly different than that found in five surgical sham studies, demonstrating minimal device thromboembolism.In summary, these results in a challenging animal test protocol support the conclusion that the Penn State Infant VAD has a low thromboembolic risk and may allow lower levels of anticoagulation.

Semi-degradable poly(ß-amino ester) networks with temporally controlled enhancement of mechanical properties.

Biodegradable polymers are clinically used in numerous biomedical applications, and classically show a loss of mechanical properties within weeks of implantation. This work demonstrates a new class of semi-degradable polymers that show an increase in mechanical properties through degradation via a controlled shift in a thermal transition. Semi-degradable polymer networks, poly(ß-amino ester)-co-methyl methacrylate, were formed from a low glass transition temperature crosslinker, poly(ß-amino ester), and high glass transition temperature monomer, methyl methacrylate, which degraded in a manner dependent upon the crosslinker chemical structure. In vitro and in vivo degradation revealed changes in mechanical behavior due to the degradation of the crosslinker from the polymer network. This novel polymer system demonstrates a strategy to temporally control the mechanical behavior of polymers and to enhance the initial performance of smart biomedical devices.

Chronic in vivo testing of the Penn State infant ventricular assist device.

The Penn State Infant Ventricular Assist Device (VAD) is a 12-14 ml stroke volume pneumatically actuated pump, with custom Björk-Shiley monostrut valves, developed under the National Heart, Lung, and Blood Institute Pediatric Circulatory Support program. In this report, we describe the seven most recent chronic animal studies of the Infant VAD in the juvenile ovine model, with a mean body weight of 23.5 ± 4.1 kg. The goal of 4-6 weeks survival was achieved in five of seven studies, with support duration ranging from 5 to 41 days; mean 26.1 days. Anticoagulation was accomplished using unfractionated heparin, and study animals were divided into two protocol groups: the first based on a target activated partial thromboplastin time of 1.5-2 times normal, and a second group using a target thromboelastography R-time of two times normal. The second group required significantly less heparin, which was verified by barely detectable heparin activity (anti-Xa). In both groups, there was no evidence of thromboembolism except in one animal with a chronic infection and fever. Device thrombi were minimal and were further reduced by introduction of the custom valve. These results are consistent with results of adult VAD testing in animals and are encouraging given the extremely low levels of anticoagulation in the second group.

Effect of poly(ethylene glycol) diacrylate concentration on network properties and in vivo response of poly(ß-amino ester) networks.

Poly(ß-amino ester) networks have shown promise as tissue scaffolds. The objective of this work was to examine the effect of changing poly(ethylene glycol) diacrylate concentration on poly(ß-amino ester) network properties and to assess the degradable polymers' in vivo response, using magnetic resonance imaging (MRI) and immunohistochemistry. The networks were synthesized from hexanediol diacrylate (HDDA), poly(ethylene glycol) diacrylate (PEGDA), and a primary amine, 3-methoxypropylamine (3-MOPA), with a fixed overall molar ratio of diacrylate to amine. Network properties were verified to insure that the networks possessed equivalent initial properties and structure other than chemistry. The effect of varying PEGDA concentration on water content, mass loss, and modulus was determined, where increasing the concentration of PEGDA increases both water content, mass loss rate, and decreases modulus. We also show that manipulating the network composition at ratios of 0:100, 10:90 and 25:75 (PEGDA:HDDA) does not elicit a major inflammatory response to subcutaneous implantation of the networks in mice. This work provides a foundation for tailoring poly(ß-amino ester) networks, based on degradation rate and modulus, as a means to tune the polymer properties for various biomedical applications.

Translational research in pediatric extracorporeal life support systems and cardiopulmonary bypass procedures: 2011 update.

Over the past 6 years at Penn State Hershey, we have established the pediatric cardiovascular research center with a multidisciplinary research team with the goal to improve the outcomes for children undergoing cardiac surgery with cardiopulmonary bypass (CPB) and extracorporeal life support (ECLS). Due to the variety of commercially available pediatric CPB and ECLS devices, both in vitro and in vivo translational research have been conducted to achieve the optimal choice for our patients. By now, every component being used in our clinical settings in Penn State Hershey has been selected based on the results of our translational research. The objective of this review is to summarize our translational research in Penn State Hershey Pediatric Cardiovascular Research Center and to share the latest results with all the interested centers.

Hepatic progenitor cell resistance to TGF-beta1's proliferative and apoptotic effects.

The success of hepatocellular therapies using stem or progenitor cell populations is dependent upon multiple factors including the donor cell, microenvironment, and etiology of the liver injury. The following experiments investigated the impact of TGF-beta1 on a previously described population of hepatic progenitor cells (HPC). The majority of the hepatic progenitor cells were resistant to endogenously produced TGF-beta1's proapoptotic and anti-proliferative effects unlike more well-differentiated cellular populations (e.g., mature hepatocytes). Surprisingly, in vitro TGF-beta1 supplementation significantly inhibited de novo hepatic progenitor cell colony formation possibly via an indirect mechanism(s). Therefore despite the HPC's direct resistance to supplemental TGF-beta1, this cytokine's inhibitory effect on colony formation could have a potential negative impact on the use of these cells as a therapy for patients with liver disease.

Proliferation and hepatic differentiation of adult-derived progenitor cells.

Hepatic progenitor cells, capable of maturing into hepatocytes and biliary cells, are hypothesized to be involved in all forms of liver regeneration and may prove clinically useful at reconstituting damaged livers. A murine hepatic progenitor cell population from young adult liver tissue has been isolated and characterized to establish a model for the development of liver cell therapies and for analysis of immune responses after transplantation. Hepatic progenitor cells were isolated from 3- to 6-week-old C57BL/6 mice using modifications of a two-stage liver perfusion technique followed by low speed centrifugation. Cellular analysis by phase contrast, fluorescent and confocal microscopy demonstrated that the hepatic progenitors (1) formed ex vivo colonies with a morphological appearance similar to committed hepatocytic progenitors isolated from embryonic mice and rats; (2) they are smaller than mature hepatocytes; (3) in culture they demonstrated peak expression of an oval cell marker at day 14, whereas albumin expression continued to increase beyond day 21 of culture, and (4) a subset of the progenitors phenotypically differentiated into mature hepatocytes or biliary cells. The unique antigenic profile of these hepatic progenitor cells and their ability to differentiate suggests that purification of the cells should allow for their potential use in transplantation.