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1.  The Hemodynamic Response to Dexmedetomidine Loading Dose in Children With and Without Pulmonary Hypertension 
Anesthesia and analgesia  2013;117(4):10.1213/ANE.0b013e3182a15aa6.
Dexmedetomidine, an α-2 receptor agonist, is widely used in children with cardiac disease. Significant hemodynamic responses, including systemic and pulmonary vasoconstriction, have been reported after dexmedetomidine administration. Our primary goal of this prospective, observational study was to quantify the effects of dexmedetomidine initial loading doses on mean pulmonary artery pressure (PAP) in children with and without pulmonary hypertension.
Subjects were children undergoing cardiac catheterization for either routine surveillance after cardiac transplantation (n = 21) or pulmonary hypertension studies (n = 21). After anesthetic induction with sevoflurane and tracheal intubation, sevoflurane was discontinued and anesthesia was maintained with midazolam 0.1 mg/kg IV (or 0.5 mg/kg orally preoperatively) and remifentanil IV infusion 0.5 to 0.8 μg/kg/min. Ventilation was mechanically controlled to maintain Pco2 35 to 40 mm Hg. When end-tidal sevoflurane was 0% and fraction of inspired oxygen (Fio2) was 0.21, baseline heart rate, mean arterial blood pressure, PAP, right atrial pressure, pulmonary artery occlusion pressure, right ventricular end-diastolic pressure, cardiac output, and arterial blood gases were measured, and indexed systemic vascular resistance, indexed pulmonary vascular resistance, and cardiac index were calculated. Each subject then received a 10-minute infusion of dexmedetomidine of 1 μg/kg, 0.75 μg/kg, or 0.5 μg/kg. Measurements and calculations were repeated at the conclusion of the infusion.
Most hemodynamic responses were similar in children with and without pulmonary hypertension. Heart rate decreased significantly, and mean arterial blood pressure and indexed systemic vascular resistance increased significantly. Cardiac index did not change. A small, statistically significant increase in PAP was observed in transplant patients but not in subjects with pulmonary hypertension. Changes in indexed pulmonary vascular resistance were not significant.
Dexmedetomidine initial loading doses were associated with significant systemic vasoconstriction and hypertension, but a similar response was not observed in the pulmonary vasculature, even in children with pulmonary hypertension. Dexmedetomidine does not appear to be contraindicated in children with pulmonary hypertension.
PMCID: PMC3830564  PMID: 23960035
2.  CD4 T-cells Mediate Cardiac Xenograft Rejection via Host MHC class II 
Previous studies indicate that acute CD4 T-cell-mediated cardiac allograft rejection requires donor MHC class II expression and can be independent of ‘indirect’ antigen presentation. However, other studies suggest that indirect antigen presentation to CD4 T-cells may play a primary role in cellular xenograft immunity. Thus, the relative roles of direct/indirect CD4 T-cell reactivity against cardiac xenografts is unclear. We set out to determine the role for indirect CD4 T-cell reactivity in cardiac xenograft rejection.
Rat hearts were transplanted heterotopically into wild-type and immuno-deficient mice. Recipients were untreated, treated with depleting antibodies or reconstituted with wild-type cells.
Antibody depletion confirmed that rat heart xenograft rejection in C57Bl/6 mice was CD4 T-cell-dependent. Also, heart xenografts survived long-term in B6 MHC class II (C2D) deficient mice. Graft acceptance in C2D mice was not secondary to CD4 T-cell deficiency alone, because transferred B6 CD4 T-cells failed to trigger rejection in C2D hosts. Furthermore, purified CD4 T-cells were sufficient for acute rejection of rat heart xenografts in immune-deficient B6rag1−/− recipients. Importantly, CD4 T-cells did not reject rat hearts in C2Drag1−/− hosts, contrasting results using cardiac allografts. ‘Direct’ xenoreactive CD4 T-cells were not sufficient to mediate rejection despite vigorous reactivity to rat stimulator cells in vitro.
Taken together, results show that CD4 T-cells are both necessary and sufficient for acute cardiac xenograft rejection and host MHC class II is critical in this process.
PMCID: PMC3418866  PMID: 22789136
T-cell; MHC; antigen presentation/processing; transplantation
3.  Early Predictors of Survival to and After Heart Transplantation in Children with Dilated Cardiomyopathy 
Circulation  2012;126(9):1079-1086.
The importance of clinical presentation and pre-transplantation course on outcome in children with dilated cardiomyopathy (DCM) listed for heart transplantation is not well defined.
Methods and Results
The impact of age, duration of illness, gender, race, ventricular geometry and the diagnosis of myocarditis on outcome in 261 DCM children enrolled in the Pediatric Cardiomyopathy Registry and Pediatric Heart Transplant Study was studied. Endpoints included: 1) listing as UNOS Status 1, 2) death while waiting and 3) death post-transplantation. The median age at the time of diagnosis was 3.4 years, and mean time from diagnosis to listing was 0.62±1.3 years. Risk factors associated with death while waiting were ventilator use and older age at listing in patients not mechanically ventilated (p=0.0006 and p=0.03, respectively). Shorter duration of illness (p=0.04) was associated with listing as UNOS Status 1. Death post-transplantation was associated with myocarditis at presentation (p=0.009), non-white race (p<0.0001) and a lower left ventricular end-diastolic dimension z-score at presentation (p=0.04). In the myocarditis group, 17% (4/23) died of acute rejection post-transplantation.
Mechanical ventilator use and older age at listing predicted death while waiting, while non-white race, smaller left ventricular dimension and myocarditis were associated with death post-transplantation. Although 97% of children with clinically or biopsy diagnosed myocarditis at presentation survived to transplantation, they had significantly higher mortality post-transplantation compared with children without myocarditis, raising the possibility that pre-existing viral infection or inflammation adversely affects graft survival.
PMCID: PMC3510785  PMID: 22800850
dilated cardiomyopathy; heart transplantation; myocarditis; pediatrics
4.  Prolongation of Cardiac Allograft Survival by a Novel Population of Autologous CD117+ Bone Marrow-Derived Progenitor Cells1 
Autologous CD117+ progenitor cells (PC) have been successfully utilized in myocardial infarction and ischemic injury, potentially through the replacement/repair of damaged vascular endothelium. To date, such cells have not been used to enhance solid organ transplant outcome. In this study, we determined whether autologous bone marrow-derived CD117+PC could benefit cardiac allograft survival, possibly by replacing donor vascular cells. Autologous, positively selected CD117+PC were administered post-transplantation and allografts were assessed for acute rejection. Although significant generation of recipient vascular cell chimerism was not observed, transferred PC disseminated both to the allograft and to peripheral lymphoid tissues and facilitated a significant, dose-dependent prolongation of allograft survival. While CD117+PC dramatically inhibited alloreactive T-cell proliferation in vitro, this property did not differ from non-protective CD117− bone marrow populations. In vivo, CD117+ PC did not significantly inhibit T cell alloreactivity or increase peripheral regulatory T cell numbers. Thus, rather than inhibiting adaptive immunity to the allograft, CD117+ PC may play a cytoprotective role in prolonging graft survival. Importantly, autologous CD117+PC appear to be distinct from bone marrow-derived mesenchymal stem cells (MSC) previously used to prolong allograft survival. As such, autologous CD117+PC represent a novel cellular therapy for promoting allograft survival.
PMCID: PMC3059253  PMID: 21114653
stem cells; transplantation; acute allograft rejection; tolerance induction
5.  Outcome of Acute Graft Rejection Associated with Hemodynamic Compromise in Pediatric Heart Transplant Recipients 
Pediatric cardiology  2010;32(1):1-7.
We sought to analyze the outcome of hemodynamically significant acute graft rejection in pediatric heart transplant recipients from a single-center experience. Acute graft rejection remains a major cause of morbidity and mortality for patients who undergo orthotopic heart transplantation and has been associated with the severity of the rejection episode. A retrospective review of all children experiencing a hemodynamically significant rejection episode after orthotopic heart transplantation was performed. Fifty-three patients with 54 grafts had 70 rejection episodes requiring intravenous inotropic support. Forty-one percent of these patients required high-dose inotropic support, with the remaining 59% of patients requiring less inotropic support. Overall graft survival to hospital discharge was 41% for patients in the high-dose group compared to 94% in the low-dose group. Six-month graft survival in patients who required high-dose inotropes remained at 41% compared to 44% in the low-dose group. Hemodynamically significant acute graft rejection in pediatric heart transplant recipients is a devastating problem with poor short- and long-term outcomes. Survival to hospital discharge is dismal in patients who require high-dose inotropic support. In contrast, survival to discharge is quite good in patients who require only low-dose inotropic support; however, six-month graft survival in this group is low secondary to a high incidence of graft failure related to worsening or aggressive transplant coronary artery disease.
PMCID: PMC3120936  PMID: 20963408
Acute graft rejection; Pediatric heart transplant
6.  Long-Term Outcome of Palliation with Internal Pulmonary Artery Bands After Primary Heart Transplantation for Hypoplastic Left Heart Syndrome 
Pediatric cardiology  2009;30(4):419-425.
The purpose of this study was to describe the long-term outcome of infants with hypoplastic left heart syndrome (HLHS) who underwent placement of internal pulmonary artery bands as part of a transcatheter palliation procedure followed by primary heart transplantation. Transcatheter palliation included stenting of the ductus arteriosus, decompression of the left atrium by atrial septostomy, and internal pulmonary artery band placement. Cardiac hemodynamics, pulmonary artery architecture, and pulmonary artery growth since transplantation are described. Nine infants with HLHS had internal pulmonary artery bands placed and underwent successful heart transplant. No infant required reconstruction of the pulmonary arteries at the time of transplant. At 1 year after transplant, all of the recipients had normal mean pulmonary artery pressure, pulmonary vascular resistance, and transpulmonary gradient. Pulmonary angiography performed at 1 year after transplant demonstrated no distortion of pulmonary artery anatomy with significant interval growth of the branch pulmonary arteries. There was 100% survival to hospital discharge after transplant in this cohort of infants. Transcatheter placement of internal pulmonary artery bands for HLHS offers protection of the pulmonary vascular bed while preserving pulmonary artery architecture and growth with good long-term outcome.
PMCID: PMC3117302  PMID: 19365660
Congenital heart disease; Heart catheterization; Heart transplant; Infant
7.  Acute Cardiac Rejection Requires Directly Cytotoxic CD4 T cells: A Parallel Pathway between Fas and Perforin1 
Transplantation  2010;89(1):33-39.
CD4 T cells can suffice as effector cells to mediate primary acute cardiac allograft rejection. While CD4 T cells can readily kill appropriate target cells in vitro, the corresponding role of such cytolytic activity for mediating allograft rejection in vivo is unknown. Therefore, we determined whether the cytolytic effector molecules perforin and/or FasL (CD95L) were necessary for CD4 T cell-mediated rejection in vivo.
Wild type C3H(H-2k) or Fas (CD95)-deficient C3Hlpr (H-2k) hearts were transplanted into immune-deficient C57B6rag−/− (H-2b) mice. Recipients then were reconstituted with naïve purified CD4 T cells from either wild-type, perforin (pfp)-deficient, or FasL (gld)-deficient T cell donors.
In vitro, alloreactive CD4 T cells were competent to lyse donor MHC class II+ target cells, largely by a Fas-dependent mechanism. In vivo, the individual disruption of either donor Fas expression (lpr) or CD4 T cell-derived perforin had no signifcant impact on acute rejection. However, FasL-deficient (gld) CD4 T cells demonstrated delayed allograft rejection. Importantly, the simultaneous removal of both donor Fas expression and CD4 T cell perforin completely abrograted acute rejection, despite the persistence of CD4 T cells within the graft.
Results demonstrate that the direct rejection of cardiac allografts by CD4 effector T cells requires the alternative contribution of graft Fas expression and T cell perforin expression. To our knowledge, this is the first demonstration that cytolytic activity by CD4 T cells can play an obligate role for primary acute allograft rejection in vivo.
PMCID: PMC2939493  PMID: 20061916
Cytotoxicity; Cytotoxic CD4 T cells; Transplantation; Acute Rejection
8.  CD4 T cell–mediated cardiac allograft rejection requires donor but not host MHC class II 
Journal of Clinical Investigation  2000;106(8):1003-1010.
Numerous studies indicate that CD4 T cells are required for acute cardiac allograft rejection. However, the precise role for CD4 T cells in this response has remained ambiguous owing to the multipotential properties of this T-cell subpopulation. In the current study, we demonstrate the capacity of CD4 T cells to serve as direct effector cells of cardiac allograft rejection. We show that CD4 T cells are both necessary and sufficient for acute graft rejection, as indicated by adoptive transfer experiments in immune-deficient SCID and rag1–/– recipients. We have analyzed the contribution of direct (donor MHC class II restricted) and indirect (host MHC class II restricted) antigen recognition in CD4-mediated rejection. Acute CD4 T cell–mediated rejection required MHC class II expression by the allograft, indicating the importance of direct graft recognition. In contrast, reciprocal experiments indicate that CD4 T cells can acutely reject allogeneic cardiac allografts established in rag1–/– hosts that were also MHC class II deficient. This latter result indicates that indirect presentation of donor antigens by host MHC class II is not required for acute CD4-mediated rejection. Taken together, these results indicate that CD4 T cells can serve as effector cells for primary acute cardiac allograft rejection, predominantly via direct donor antigen recognition and independent of indirect reactivity.
PMCID: PMC314344  PMID: 11032860

Results 1-8 (8)