Response to a single dose of sildenafil in single-ventricle patients: an echocardiographic evaluation.

New evidence of increased phosphodiesterase-5 (PDE-5) in hypertrophied human myocardium suggests that sildenafil, a selective PDE-5 inhibitor, may improve muscle contraction and therefore improve ventricular function. The purpose of this study was to compare ventricular function as assessed by echocardiography in 10 surgically palliated single-ventricle patients at baseline and again after a single dose of sildenafil. The velocity time integral of the ventricular outflow tract was increased 2 h after sildenafil administration (p = 0.01), thus suggesting an improvement in cardiac output.

Reduction in postoperative high-density lipoprotein cholesterol levels in children undergoing the Fontan operation.

Despite the emerging relevance of high-density lipoprotein (HDL) in the inflammatory cascade and vascular barrier integrity, HDL levels in children undergoing cardiac surgery are unexplored. As a measure of HDL levels, the HDL-cholesterol (HDL-C) in single-ventricle patients was quantified before and after the Fontan operation, and it was determined whether relationships existed between the duration and the type of postoperative pleural effusions. The study prospectively enrolled 12 children undergoing the Fontan operation. Plasma HDL-C levels were measured before and after cardiopulmonary bypass. The outcome variables of interest were the duration and type of chest tube drainage (chylous vs. nonchylous). The Kendall rank correlation coefficient and the Wilcoxon rank sum test were used. There were 11 complete observations. The median preoperative HDL-C level for all the subjects was 30 mg/dl (range, 24-53 mg/dl), and the median postcardiopulmonary bypass level was 21 mg/dl (range, 14-46 mg/dl) (p = 0.004). There was a tendency toward a moderate inverse correlation (-0.42) between the postcardiopulmonary bypass HDL-C level and the duration of chest tube drainage, but the result was not statistically significant (p = 0.07). In the chylous effusion group, the median postcardiopulmonary bypass HDL-C tended to be lower (16 vs. 23 mg/dl; p = 0.09). After the Fontan operation, the plasma HDL-C levels in children are significantly reduced. It is reasonable to conclude that the reduction in HDL-C reflects reduced plasma levels of HDL particles, which may have pertinent implications in postoperative pleural effusions given the antiinflammatory and endothelial barrier functions of HDL.

Hemodynamic patterning of the avian atrioventricular valve.

In this study, we develop an innovative approach to rigorously quantify the evolving hemodynamic environment of the atrioventricular (AV) canal of avian embryos. Ultrasound generated velocity profiles were imported into Micro-Computed Tomography generated anatomically precise cardiac geometries between Hamburger-Hamilton (HH) stages 17 and 30. Computational fluid dynamic simulations were then conducted and iterated until results mimicked in vivo observations. Blood flow in tubular hearts (HH17) was laminar with parallel streamlines, but strong vortices developed simultaneous with expansion of the cushions and septal walls. For all investigated stages, highest wall shear stresses (WSS) are localized to AV canal valve-forming regions. Peak WSS increased from 19.34 dynes/cm(2) at HH17 to 287.18 dynes/cm(2) at HH30, but spatiotemporally averaged WSS became 3.62 dynes/cm(2) for HH17 to 9.11 dynes/cm(2) for HH30. Hemodynamic changes often preceded and correlated with morphological changes. These results establish a quantitative baseline supporting future hemodynamic analyses and interpretations.

Cardiac function and circulating cytokines after endotoxin exposure in neonatal mice.

Complications after cardiac surgery in neonates can occur because of activation of the inflammatory system. This study used lipopolysaccharide (LPS) endotoxin exposure to cause cytokine activation in neonatal mice and examine left ventricular (LV) function and the effects of antioxidant treatment on cytokine levels. Neonatal mice (6 d old) were injected with either 25 mg/kg LPS (n = 13) or PBS (n = 14), and LV function (echocardiography) was measured at 4 h. Plasma levels of TNF-α, IL-4, IL-6, and IL-10 were measured at 30 min, 1, 2, and 4 h after injection (n = 5 mice per group). Effects of pretreatment with N-acetylcysteine (NAC, 50 mg/kg) on cytokine levels were examined at 2 and 4 h after PBS or LPS (n = 5 mice per group). Four hours after LPS, heart rate was increased (434 ± 14 versus 405 ± 14 bpm, p < 0.05). LV end-diastolic dimension and ejection time were reduced with LPS (both p < 0.05). LPS exposure increased plasma TNF-α, IL-6, and IL-10 levels. NAC pretreatment attenuated the increases in TNF-α and IL-6 levels, but augmented IL-10 levels at 2 h post-LPS. LPS exposure altered cardiac performance and activated cytokines in neonatal mice, which may be ameliorated using antioxidants.

Fibulin-1 is required for morphogenesis of neural crest-derived structures.

Here we report that mouse embryos homozygous for a gene trap insertion in the fibulin-1 (Fbln1) gene are deficient in Fbln1 and exhibit cardiac ventricular wall thinning and ventricular septal defects with double outlet right ventricle or overriding aorta. Fbln1 nulls also display anomalies of aortic arch arteries, hypoplasia of the thymus and thyroid, underdeveloped skull bones, malformations of cranial nerves and hemorrhagic blood vessels in the head and neck. The spectrum of malformations is consistent with Fbln1 influencing neural crest cell (NCC)-dependent development of these tissues. This is supported by evidence that Fbln1 expression is associated with streams of cranial NCCs migrating adjacent to rhombomeres 2-7 and that Fbln1-deficient embryos display patterning anomalies of NCCs forming cranial nerves IX and X, which derive from rhombomeres 6 and 7. Additionally, Fbln1-deficient embryos show increased apoptosis in areas populated by NCCs derived from rhombomeres 4, 6 and 7. Based on these findings, it is concluded that Fbln1 is required for the directed migration and survival of cranial NCCs contributing to the development of pharyngeal glands, craniofacial skeleton, cranial nerves, aortic arch arteries, cardiac outflow tract and cephalic blood vessels.

Increased ventricular preload is compensated by myocyte proliferation in normal and hypoplastic fetal chick left ventricle.

Hemodynamics influence cardiac development, and alterations in blood flow may lead to impaired cardiac growth and malformations. The developing myocardium adapts to augmented workload by increasing cell number (hyperplasia). The aim of this study was to determine the influence of alterations in ventricular preload on fetal myocyte proliferation by manipulation of intracardiac shunting at the atrial level. We hypothesized that partial clipping of the right atrial appendage would increase the blood flow to the left ventricle and, in turn, lead to an increase in chamber volume and myocardial mass based on myocyte proliferation. Using an ex ovo culture setup, we performed partial right atrial clipping on embryonic day 8 chick embryos. Ultrasound imaging was performed before and after the surgery to assess the changes in left ventricular volume. Sampling after 24 hours was preceded by 2 hour of pulse-labeling with 5-bromodeoxyuridine. Ultrasound imaging showed that partial right atrial clipping led to a significant increase in left ventricular end-diastolic volume, demonstrating increased blood flow and preload. Anti-5-bromodeoxyuridine immunolabeling revealed a significant increase in myocyte proliferation in the left ventricle and atrium. No significant changes were found in the right heart structures. Increased left ventricular myocyte proliferation and myocardial mass after right atrial clipping was also observed in embryos with experimental left ventricular hypoplasia. These results demonstrate the ability of fetal myocardium to respond to increased preload by myocyte hyperplasia and support the rationale for prenatal surgical interventions in certain cases of congenital heart disease such as hypoplastic left heart syndrome.

Transitions in early embryonic atrioventricular valvular function correspond with changes in cushion biomechanics that are predictable by tissue composition.

Endocardial cushions are critical to maintain unidirectional blood flow under constantly increasing hemodynamic forces, but the interrelationship between endocardial cushion structure and the mechanics of atrioventricular junction function is poorly understood. Atrioventricular (AV) canal motions and blood velocities of embryonic chicks at Hamburger and Hamilton (HH) stages 17, 21, and 25 were quantified using ultrasonography. Similar to the embryonic zebrafish heart, the HH17 AV segment functions like a suction pump, with the cushions expanding in a wave during peak myocardial contraction and becoming undetectable during the relaxation phase. By HH25, the AV canal contributes almost nothing to the piston-like propulsion of blood, but the cushions function as stoppers apposing blood flow with near constant thickness. Using a custom built mesomechanical testing system, we quantified the nonlinear pseudoelastic biomechanics of developing AV cushions, and found that both AV cushions increased in effective modulus between HH17 and HH25. Enzymatic digestion of major structural constituent collagens or glycosaminoglycans resulted in distinctly different stress-strain curves suggestive of their individual contributions. Mixture theory using histologically determined volume fractions of cells, collagen, and glycosaminoglycans showed good prediction of cushion material properties regardless of stage and cushion position. These results have important implications in valvular development, as biomechanics may play a larger role in stimulating valvulogenic events than previously thought.

Evidence for Hox-specified positional identities in adult vasculature.

BACKGROUND: The concept of specifying positional information in the adult cardiovascular system is largely unexplored. While the Hox transcriptional regulators have to be viewed as excellent candidates for assuming such a role, little is known about their presumptive cardiovascular control functions and in vivo expression patterns. RESULTS: We demonstrate that conventional reporter gene analysis in transgenic mice is a useful approach for defining highly complex Hox expression patterns in the adult vascular network as exemplified by our lacZ reporter gene models for Hoxa3 and Hoxc11. These mice revealed expression in subsets of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) located in distinct regions of the vasculature that roughly correspond to the embryonic expression domains of the two genes. These reporter gene patterns were validated as authentic indicators of endogenous gene expression by immunolabeling and PCR analysis. Furthermore, we show that persistent reporter gene expression in cultured cells derived from vessel explants facilitates in vitro characterization of phenotypic properties as exemplified by the differential response of Hoxc11-lacZ-positive versus-negative cells in migration assays and to serum. CONCLUSION: The data support a conceptual model of Hox-specified positional identities in adult blood vessels, which is of likely relevance for understanding the mechanisms underlying regional physiological diversities in the cardiovascular system. The data also demonstrate that conventional Hox reporter gene mice are useful tools for visualizing complex Hox expression patterns in the vascular network that might be unattainable otherwise. Finally, these mice are a resource for the isolation and phenotypic characterization of specific subpopulations of vascular cells marked by distinct Hox expression profiles.

An in vivo analysis of hematopoietic stem cell potential: hematopoietic origin of cardiac valve interstitial cells.

Recent studies evaluating hematopoietic stem cell (HSC) potential raise the possibility that, in addition to embryonic sources, adult valve fibroblasts may be derived from HSCs. To test this hypothesis, we used methods that allow the potential of a single HSC to be evaluated in vivo. This was achieved by isolation and clonal expansion of single lineage-negative (Lin-), c-kit(+), Sca-1(+), CD34- cells from the bone marrow of mice that ubiquitously express enhanced green fluorescent protein (EGFP) combined with transplantation of individual clonal populations derived from these candidate HSCs into a lethally irradiated congenic non-EGFP mouse. Histological analyses of valve tissue from clonally engrafted recipient mice revealed the presence of numerous EGFP+ cells within host valves. A subpopulation of these cells exhibited synthetic properties characteristic of fibroblasts, as evidenced by their expression of mRNA for procollagen 1alpha1. Further, we show by Y-chromosome-specific fluorescence in situ hybridization analysis of female-to-male transplanted mice that the EGFP+ valve cells are the result of HSC-derived cell differentiation and not the fusion of EGFP+ donor cells with host somatic cells. Together, these findings demonstrate HSC contribution to the adult valve fibroblast population.

Embryogenesis of the heart muscle.

This article concerns the development of myocardial architecture--crucial for contractile performance of the heart and its conduction system, essential for generation and coordinated spread of electrical activity. Topics discussed include molecular determination of cardiac phenotype (contractile and conducting), remodeling of ventricular wall architecture and its blood supply, and relation of trabecular compaction to noncompaction cardiomyopathy. Illustrated are the structure and function of the tubular heart, time course of trabecular compaction, and development of multilayered spiral systems of the compact layer.

Can preeclampsia be considered a renal compartment syndrome? A hypothesis and analysis of the literature.

The morbidity and mortality associated with preeclampsia is staggering. The physiology of the Page kidney, a condition in which increased intrarenal pressure causes hypertension, appears to provide a unifying framework to explain the complex pathophysiology. Page kidney hypertension is renin-mediated acutely and ischemia-mediated chronically. Renal venous outflow obstruction also causes a Page kidney phenomenon, providing a hypothesis for the increased vulnerability of a subset of women who have what we are hypothesizing is a "renal compartment syndrome" due to inadequate ipsilateral collateral renal venous circulation consistent with well-known variation in normal venous anatomy. Dynamic changes in renal venous anatomy and physiology in pregnancy appear to correlate with disease onset, severity, and recurrence. Since maternal recumbent position is well known to affect renal perfusion and since chronic outflow obstruction makes women vulnerable to the ischemic/inflammatory sequelae, heightened awareness of renal compartment syndrome physiology is critical. The anatomic and physiologic insights provide immediate strategies to predict and prevent preeclampsia with straightforward, low-cost interventions that make renewed global advocacy for pregnant women a realistic goal.

Cardiac fibroma in an infant: single ventricle palliation as a bridge to heart transplantation.

A prenatal echocardiogram revealed a large right ventricular mass. Following birth, there was obstruction to pulmonary blood flow and cyanosis. The tumor's size and location prevented resection. The patient underwent "single ventricle palliation," including placement of a systemic-to-pulmonary shunt as a newborn. This palliation served as a successful bridge to heart transplantation at 7 months of age. Pathologic examination revealed cardiac fibroma.

Tricuspid valve replacement with a melody stented bovine jugular vein conduit.

Atrioventricular valve replacement options are limited in infants and small children. The Melody stented bovine jugular vein conduit is being used with increasing frequency for percutaneous pulmonary valve replacement. The Melody valve can be serially dilated over time to accommodate the somatic growth of pediatric patients. We report the initial experience of using the Melody valve as a surgical tricuspid valve replacement in an infant.

Effects of aprotinin or tranexamic acid on proteolytic/cytokine profiles in infants after cardiac surgery.

BACKGROUND: After cardiopulmonary bypass (CPB), elaboration of cytokines, and subsequent induction of interstitial proteases, such as matrix metalloproteinases (MMPs), can result in a complex postoperative course. The serine protease inhibitor, aprotinin, which has been used in congenital heart surgery putatively for modulating fibrinolysis is now unavailable, necessitating the use of lysine analogues such as tranexamic acid (TXA). The present study tested the hypothesis that distinctly different plasma profiles of signaling molecules and proteases would be differentially affected after the administration of aprotinin or TXA in the context of congenital cardiac surgery and CPB. METHODS: Thirty-seven patients (age, 4.8 +/- 0.3 months) undergoing corrective surgery for ventricular septal defect and tetralogy of Fallot received either aprotinin (n = 22) or TXA (n = 15). Using a high throughput multiplex suspension immunoassay, plasma was serially quantified for cytokines and MMPs: before aprotinin or TXA (baseline), after separation from CPB, and 4, 12, 24, and 48 hours post-CPB. RESULTS: Tumor necrosis factor-alpha increased initially after CPB in both the aprotinin and TXA groups, but at 24 and 48 hours post-CPB was approximately 50% lower in the aprotinin group (p < 0.05). The IL-10 levels were threefold higher in the TXA group compared with the aprotinin group immediately post-CBP (p < 0.05). Plasma levels of MMP types associated with inflammation, MMP-8, and MMP-9, were twofold higher in the late post-CPB period in the TXA group when compared with the aprotinin group. CONCLUSIONS: After ventricular septal defect or tetralogy of Fallot repair in children, cytokine induction occurs, which is temporally related to the emergence of a specific MMP profile. Moreover, these unique findings demonstrated differential effects between the serine protease inhibitor aprotinin and the lysine analogue TXA with respect to cytokine and MMP induction in the early postoperative period. The different cytokine-proteolytic profile between these antifibrinolytics may in turn influence biologic processes in the postoperative period.

Circulating matrix metalloproteinase levels after ventricular septal defect repair in infants.

BACKGROUND: Surgery for congenital heart disease initiates a complex inflammatory response that can influence the postoperative course. However, broad integration of the cytokine and proteolytic cascades (matrix metalloproteinases: MMPs), which may contribute to postoperative outcomes, has not been performed. METHODS AND RESULTS: Using a low-volume (50-60 µL), high-sensitivity, multiplex approach, we serially measured a panel of cytokines (interleukins 2, 4, 6, 8, and 10, tumor necrosis factor alpha, interleukin 1ß, and granulocyte-macrophage colony stimulating factor) and matrix metalloproteinases (matrix metalloproteinases 2, 3, 7, 8, 9, 12, and 13) in patients (n = 9) preoperatively and after repair of ventricular septal defect. Results were correlated with outcomes such as inotropic requirement, oxygenation, and fluid balance. Serial changes in perioperative plasma levels of the cytokines and matrix metalloproteinases exhibited distinct temporal profiles. Plasma levels of interleukins 2, 8, and 10 and matrix metalloproteinase 9 peaked within 4 hours, whereas levels of matrix metalloproteinase 3 and 8 remained elevated at 24 and 48 hours after crossclamp removal. Area-under-the-curve analysis of early cytokine levels were associated with major clinical variables, including inverse correlations between early interleukin 10 levels and cumulative inotrope requirement at 48 hours (r: -0.85; P < .005) and late matrix metalloproteinase 7 levels and cumulative fluid balance (r: -0.90; P < .001). CONCLUSIONS: The unique findings of this study were that serial profiling a large array of cytokines and proteolytic enzymes after surgery for congenital heart disease can provide insight into relationships between changes in bioactive molecules to early postoperative outcomes. Specific patterns of cytokine and matrix metalloproteinase release may hold significance as biomarkers for predicting and managing the postoperative course after surgery for congenital heart disease.

High-frequency ultrasonographic imaging of avian cardiovascular development.

The chick embryo has long been a favorite model system for morphologic and physiologic studies of the developing heart, largely because of its easy visualization and amenability to experimental manipulations. However, this advantage is diminished after 5 days of incubation, when rapidly growing chorioallantoic membranes reduce visibility of the embryo. Using high-frequency ultrasound, we show that chick embryonic cardiovascular structures can be readily visualized throughout the period of Stages 9-39. At most stages of development, a simple ex ovo culture technique provided the best imaging opportunities. We have measured cardiac and vascular structures, blood flow velocities, and calculated ventricular volumes as early as Stage 11 with values comparable to those previously obtained using video microscopy. The endocardial and myocardial layers of the pre-septated heart are readily seen as well as the acellular layer of the cardiac jelly. Ventricular inflow in the pre-septated heart is biphasic, just as in the mature heart, and is converted to a monophasic (outflow) wave by ventricular contraction. Although blood has soft-tissue density at the ultrasound resolutions and developmental stages examined, its movement allowed easy discrimination of perfused vascular structures throughout the embryo. The utility of such imaging was demonstrated by documenting changes in blood flow patterns after experimental conotruncal banding.

Comparative in vitro study of bileaflet and tilting disk valve behavior in the pulmonary position.

A study of mechanical heart valve behavior in the pulmonary position as a function of pulmonary vascular resistance is reported for the St. Jude Medical bileaflet (SJMB) valve and the MedicalCV Omnicarbon (OTD) tilting disk valve. Tests were conducted in a pulmonic mock circulatory system and impedance was varied in terms of system pulmonary vascular resistance (PVR). An impedance spectrum was found using instantaneous pulmonary artery pressure and flow rate curves. Both valves fully opened and closed at and above a nominal PVR of 3.0 mmHg/L/min. The SJMB valve was prone to leaflet bounce at closure, but otherwise completely closed, at settings above and below this nominal setting. At PVR values at and below 2.0 mmHg/L/min, the SJMB valve exhibited two types of leaflet aberrant behavior: single leaflet only closure while the other leaflet fluttered, and incomplete closure where both leaflets flutter but neither remain fully closed. The OTD valve fully opened and closed to a PVR value of 1.6 mmHg/L/min. At lower values, the valve did not close. Valves designed for the left heart can show aberrant behavior under normal conditions as pulmonary valves.

Current issues and perspectives in hypoplasia of the left heart.

Hypoplastic left heart syndrome is a rare but serious form of congenital cardiac disease, characterized by underdevelopment of the components of the left heart, rendering the left ventricle non-functional. Its aetiology is largely unknown, but there is certainly a genetic component. Prenatal diagnosis nowadays uncovers about half of cases. Postnatal options for treatment include comfort care, 3-stage palliative surgery, or cardiac transplantation. In this review, we discuss the morphology, possible pathogenetic mechanisms, clinical management, and perspectives of prenatal intervention based on work in animal models.

Hemodynamic status after the Norwood procedure: a comparison of right ventricle-to-pulmonary artery connection versus modified Blalock-Taussig shunt.

BACKGROUND: The aim of this study is to compare hemodynamic status, in particular systemic oxygen delivery, in patients undergoing a Norwood procedure with a right ventricle-to-pulmonary artery (RV-PA) versus a modified Blalock-Taussig (mBT) shunt. METHODS: From June 2000 to November 2003, 44 consecutive neonates with hypoplastic left heart syndrome underwent a Norwood procedure. The first 25 patients received an mBT shunt; the subsequent 19 an RV-PA shunt. Hemodynamic data, including mixed venous oxygen saturation, was determined during the first 48 hours after surgery. RESULTS: The mBT and RV-PA shunt patients had no significant differences in systemic oxygen saturation, mixed venous oxygen saturation, arteriovenous oxygen saturation difference, or oxygen excess factor during the first 48 hours. Mixed venous saturation declined to a nadir in both groups at 6 to 12 hours. The RV-PA patients had significantly higher diastolic and mean blood pressures, and lower systolic blood pressure. Mean heart rate, common atrial pressure, and inotrope score did not differ between the two groups. The RV-PA patients received higher fraction of inspired oxygen and minute ventilation to achieve partial pressures of arterial oxygen and carbon dioxide, and pH, similar to mBT patients. Durations of mechanical ventilation, intensive care unit stay, and hospital stay did not differ between mBT and RV-PA patients. Operative survival in the mBT versus RV-PA group was 20 of 25 (80%) versus 17 of 19 (89%; p = 0.7). CONCLUSIONS: Indicators of postoperative systemic oxygen delivery are equivalent in neonates who have undergone a Norwood procedure with an mBT or RV-PA shunt. Both mBT and RV-PA patients undergo similar declines in hemodynamic status 6 to 12 hours after surgery. Any advantages of one approach over the other lie in areas other than systemic oxygen delivery, such as resistance to physiologic insults, or preservation of ventricular function.