Association of Digoxin With Preserved Echocardiographic Indices in the Interstage Period: A Possible Mechanism to Explain Improved Survival?

Background For patients with hypoplastic left heart syndrome, digoxin has been associated with reduced interstage mortality after the Norwood operation, but the mechanism of this benefit remains unclear. Preservation of right ventricular (RV) echocardiographic indices has been associated with better outcomes in hypoplastic left heart syndrome. Therefore, we sought to determine whether digoxin use is associated with preservation of the RV indices in the interstage period. Methods and Results We conducted a retrospective cohort study of prospectively collected data using the public use data set from the Pediatric Heart Network Single Ventricle Reconstruction trial, conducted in 15 North American centers between 2005 and 2008. We included all patients who survived the interstage period and had echocardiographic data post-Norwood and pre-Glenn operations. We used multivariable linear regression to compare changes in RV parameters, adjusting for relevant covariates. Of 289 patients, 94 received digoxin at discharge post-Norwood. There were no significant differences in baseline clinical characteristics or post-Norwood echocardiographic RV indices (RV end-diastolic volume indexed, RV end-systolic volume indexed, ejection fraction) in the digoxin versus no-digoxin groups. At the end of the interstage period and after adjustment for relevant covariates, patients on digoxin had better preserved RV indices compared with those not on digoxin for the ΔRV end-diastolic volume (11 versus 15 mL, P=0.026) and the ΔRV end-systolic volume (6 versus 9 mL, P=0.009) with the indexed ΔRV end-systolic volume (11 versus 20 mL/BSA1.3, P=0.034). The change in the RV ejection fraction during the interstage period between the 2 groups did not meet statistical significance (-2 versus -5, P=0.056); however, the trend continued to be favorable for the digoxin group. Conclusions Digoxin use during the interstage period is associated with better preservation of the RV volume and tricuspid valve measurements leading to less adverse remodeling of the single ventricle. These findings suggest a possible mechanism of action explaining digoxin's survival benefit during the interstage period.

Hypoplastic left heart syndrome (HLHS): molecular pathogenesis and emerging drug targets for cardiac repair and regeneration.

INTRODUCTION: Hypoplastic left heart syndrome (HLHS) is a severe developmental defect characterized by the underdevelopment of the left ventricle along with aortic and valvular defects. Multiple palliative surgeries are required for survival. Emerging studies have identified potential mechanisms for the disease onset, including genetic and hemodynamic causes. Genetic variants associated with HLHS include transcription factors, chromatin remodelers, structural proteins, and signaling proteins necessary for normal heart development. Nonetheless, current therapies are being tested clinically and have shown promising results at improving cardiac function in patients who have undergone palliative surgeries. AREAS COVERED: We searched PubMed and clinicaltrials.gov to review most of the mechanistic research and clinical trials involving HLHS. This review discusses the anatomy and pathology of HLHS hearts. We highlight some of the identified genetic variants that underly the molecular pathogenesis of HLHS. Additionally, we discuss some of the emerging therapies and their limitations for HLHS. EXPERT OPINION: While HLHS etiology is largely obscure, palliative therapies remain the most viable option for the patients. It is necessary to generate animal and stem cell models to understand the underlying genetic causes directly leading to HLHS and facilitate the use of gene-based therapies to improve cardiac development and regeneration.

A word on netting of angiotensin-converting enzyme inhibitor therapy in hypoplastic left heart syndrome following stage-I.

NPC-QIC Registry data showed that angiotensin-converting enzyme inhibitors were described in almost 38% for patients with single ventricle physiology after stage-I Norwood palliation. However, mortality and ventricular dysfunction or atrioventricular valve insufficiency seems to be not improved by oral application of angiotensin-converting enzyme inhibitors. The final conclusion was that despite limited evidence of benefit for patients with hypoplastic left heart syndrome, prescription of angiotensin-converting enzyme inhibitors during interstage is still common. Taking into account of the predominant cardiovascular regulation in newborns and young infants by circulating catecholamines, no real improvement is to be expected from angiotensin-converting enzyme inhibitor monotherapy. The goals of drug therapy after stage-I Norwood palliation in hypoplastic left heart syndrome are prevention of systemic right ventricle failure, balancing pulmonary and systemic blood flow, and reduction of oxygen consumption with regard to limitations of oxygen supply by the single ventricle, furthermore, avoiding harmful effects of endogenous catecholamine production in the long term on somatic and cognitive development. In this light of knowledge, we want to recommend the use of a long-acting and highly specific ß1-adrenoreceptor blocker for almost all patients after stage-I Norwood palliation and a combination with angiotensin-converting enzyme inhibitors only by indication after exclusion of potential side effects.

Angiotensin-Converting Enzyme Inhibitor Prescription for Patients With Single Ventricle Physiology Enrolled in the NPC-QIC Registry.

Background The routine use of angiotensin-converting enzyme inhibitors (ACEI) during palliation of hypoplastic left heart syndrome is controversial. We sought to describe ACEI prescription in the interstage between stage 1 palliation (stage I Norwood procedure) discharge and stage 2 palliation (stage II superior cavopulmonary anastomosis procedure) admission using the NPC-QIC (National Pediatric Cardiology Quality Improvement Collaborative) registry. Methods and Results Analysis of all patients (n=2180) enrolled in NPC-QIC from 2008 to 2016 included preoperative anatomy, risk factors, and echocardiographic data. ACEI were prescribed at stage I Norwood procedure discharge in 38% of patients. ACEI prescription declined from 2011 to 2016 compared with pre-2010 (36.8% versus 45%; P=0.005) with significant variation across centers (range 7-100%; P<0.001) and decreased prescribing rates associated with increased center volume (P=0.004). There was no difference in interstage mortality (P=0.662), change in atrioventricular valve regurgitation (P=0.101), or change in ventricular dysfunction (P=0.134) between groups. In multivariable analysis of all patients, atrioventricular septal defect (odds ratio [OR], 1.84; 95% CI, 1.28-2.65) or double outlet right ventricle (OR, 1.47; CI, 1.02-2.11), and preoperative mechanical ventilation (OR, 1.37; 95% CI, 1.12-1.68) were associated with increased ACEI prescription. In multivariable analysis of patients with complete echocardiographic data (n=812), ACEI prescription was more common with at least moderate atrioventricular valve regurgitation (OR, 1.88; 95% CI, 1.22-2.31). Conclusions ACEI prescription remains common in the interstage despite limited evidence of benefit. ACEI prescription is associated with preoperative mechanical ventilation, double outlet right ventricle, and atrioventricular valve regurgitation with marked inter-center variation. ACEI prescription is not associated with reduction in mortality, ventricular dysfunction, or atrioventricular valve regurgitation during the interstage.

Changing trends in IVIG use in pediatric patients: A retrospective review of practices in a network of major USA pediatric hospitals.

The use of immunoglobulins is gradually increasing. Intravenous immunoglobulins (IVIG) are used as replacement therapy for primary and secondary immune deficiencies, and as an anti-inflammatory and immunomodulatory medication for the treatment of neurologic, dermatologic, and rheumatologic diseases. The objective of this study was to analyze trends in the IVIG use in pediatric patients hospitalized to 47 US-based children's hospitals from 2007 to 2014. IVIG was used for the treatment of >2300 primary diagnoses in 53,648 unique patients. The number of IVIG admissions increased by 30.2% during the study period, while the mean rate of IVIG admissions/100,000 admissions increased only 5.8%. Most patients receiving IVIG were children and adolescents. IVIG was frequently used off-label or for the treatment of FDA-approved indications in children under two years of age and BMT patients <20 years of age. Primary immune deficiencies represented only 1.2% of all IVIG admissions. Pediatric patients with mucocutaneous lymph node syndrome (Kawasaki disease, KD) and idiopathic thrombocytopenic purpura (ITP) were two primary consumers of the IVIG. Another top-ranked indications were acute infectious polyneuritis (Guillain-Barré syndrome, GBS) and prophylaxis of infections in patients receiving antineoplastic chemotherapy. IVIG usage is a dynamic process guided by emerging evidence and FDA approval for new indications. IVIG was mostly prescribed for treatment of diseases with pathologic immune responses to foreign of self-antigens. These indications usually, require higher amounts of IVIG per admission. More studies are needed to understand whether IVIG treatments of off-label indications are effective and cost-efficient.

Digoxin Use in Infants with Single Ventricle Physiology: Secondary Analysis of the Pediatric Heart Network Infant Single Ventricle Trial Public Use Dataset.

Digoxin has been associated with reduced interstage mortality after Norwood procedure. We sought to determine its association with survival and change in weight-for-age Z-score (WAZ) before the superior cavopulmonary connection (SCPC) surgery and at 14 months in a heterogeneous group of single ventricle infants. We performed a post-hoc analysis of the Pediatric Heart Network Infant Single Ventricle public use dataset to determine associations between digoxin and survival, transplant-free survival, and change in WAZ pre-SCPC and at 14 months. Sub-analyses of survival and transplant-free survival were performed for subjects who underwent Damus-Kaye-Stansel (DKS)/Norwood. Propensity score weighting was used in Cox hazard-proportion models. Of 229 subjects, 82 (36%) received digoxin and 147 (64%) received no digoxin. Pre-SCPC and 14-month survival and transplant-free survival were not significantly different between the digoxin and no digoxin groups for the main cohort and DKS/Norwood sub-group. However, in DKS/Norwood subjects there was a trend towards improved interstage transplant-free survival in the digoxin group (95.7 vs. 89.6%, p = 0.08). Digoxin was associated with a greater decrease in WAZ from birth to pre-SCPC (- 1.96 ± 0.19 vs. - 1.31 ± 0.18, p < 0.001) and birth to 14 months (- 0.64 ± 0.15 vs. - 0.19 ± 0.15, p = 0.03). Digoxin was not associated with improved survival during the interstage or at 14 months in a mixed single ventricle cohort, but there was a trend towards improved interstage transplant-free survival in post-Norwood infants. As digoxin was associated with poorer weight gain, further research is needed to identify the risks/benefits for anatomic subtypes of infants with single ventricles.

Variability of antithrombotics use in patients with hypoplastic left heart syndrome and its variants following first- and second-stage palliation surgery: a national report using the National Pediatric Cardiology Quality Improvement Collaborative registry.

Purpose Patients with hypoplastic left heart syndrome and its variants following palliation surgery are at risk for thrombosis. This study examines variability of antithrombotic practice, the incidence of interstage shunt thrombosis, and other adverse events following Stage I and Stage II palliation within the National Pediatric Cardiology Quality Improvement Collaborative registry. METHODS: We carried out a multicentre, retrospective review using the National Pediatric Cardiology Quality Improvement Collaborative registry including patients from 2008 to 2013 across 52 surgical sites. Antithrombotic medications used at Stage I and Stage II discharge were evaluated. Variability of antithrombotics use at the individual patient level and intersite variability, incidence of shunt thrombosis, and other adverse events such as cardiac arrest, seizure, stroke, and need for cardiac catheterisation intervention in the interstage period were identified. Antithrombotic strategies for hybrid Stage I patients were evaluated but they were excluded from the variability and outcomes analysis. RESULTS: A total of 932 Stage I and 923 Stage II patients were included in the study: 93.8% of Stage I patients were discharged on aspirin and 4% were discharged on no antithrombotics, and 77% of Stage II patients were discharged on aspirin and 17.5% were discharged on no antithrombotics. Only three patients (0.2%) presented with interstage shunt thrombosis. The majority of patients who died during interstage or required shunt dilation and/or stenting were discharged home on aspirin. CONCLUSION: Aspirin is the most commonly used antithrombotic following Stage I and Stage II palliation. There is more variability in the choice of antithrombotics following Stage II compared with Stage I. The incidence of interstage shunt thrombosis and associated adverse events was rare.

Sildenafil exposure and hemodynamic effect after stage II single-ventricle surgery.

OBJECTIVES: To determine sildenafil exposure and hemodynamic effect in children after stage II single-ventricle surgery. DESIGN: Prospective, dose escalation trial. SETTING: Single-center, pediatric catheterization laboratory. PATIENTS: Twelve children poststage II single-ventricle surgical palliation and undergoing elective cardiac catheterization: median age 1.9 years (range, 0.8, 4.0), weight 11 kg (8, 13), nine females, and 10 with a single right ventricle. INTERVENTIONS: Catheterization and echocardiography performed before and immediately after single-dose IV sildenafil (0.125, 0.25, 0.35, or 0.45 mg/kg over 20 min). MEASUREMENTS: Peak sildenafil and desmethyl sildenafil concentration, change in hemodynamic parameters measured by cardiac catheterization and echocardiography including indexed pulmonary vascular resistance, and myocardial performance. MAIN RESULTS: Maximum sildenafil concentrations ranged from 92 to 775 ng/mL and were above the in vitro threshold needed for 77% phosphodiesterase type 5 (PDE-5) inhibition in 80% of subjects and 90% inhibition in 80% of subjects with doses ≥0.35 mg/kg. Sildenafil lowered pulmonary vascular resistance index in all 12 subjects (median pulmonary vascular resistance index 2.2 [range, 1.6, 7.9]; decreased to 1.7 [1.2, 5.4] WU × m; p < 0.01) with no dose-response effect. Sildenafil improved pulmonary blood flow (+8% [0, 20], p = 0.04) and saturations (+2% [0, 16], p = 0.04) in those with baseline pulmonary vascular resistance index ≥ 2 WU × m (n = 7). Change in saturations correlated inversely with change in pulmonary vascular resistance index (r = 0.74, p < 0.01). Sildenafil also lowered mean blood pressure (-12% [-20, +10]; p = 0.04). There was no change in cardiac index and no effect on myocardial performance. There were no adverse events. CONCLUSIONS: Sildenafil demonstrated nonlinear exposure with high interindividual variability but was well tolerated and effectively lowered pulmonary vascular resistance index in all subjects. Sildenafil did not acutely improve myocardial performance or increase cardiac index.

Preoperative management in patients with single-ventricle physiology.

OBJECTIVE: Advancements in the preoperative management of patients with single-ventricle physiology continue to evolve. Previous reports have questioned the benefit of using inhaled nitrogen in single-ventricle patients, suggesting that this therapeutic modality may not provide adequate systemic cardiac output. The objective of this study was to review our institutional experience managing preoperative patients with single-ventricle physiology using a combination of afterload reduction and inhaled hypoxemic therapy. DESIGN, SETTING, AND PATIENTS: This is a retrospective review of 49 consecutive single-ventricle patients admitted preoperatively between July 2004 and January 2009, to the cardiac intensive care unit at Children's Hospital of Pittsburgh who underwent single-ventricle palliation, and treated preoperatively with milrinone and inhaled nitrogen. Therapeutic interventions and indirect indicators of cardiac output were collected on day of admission (time 0) and compared with those collected on the morning of surgery (time 1); data included clinical assessment, hemodynamic measurements, and laboratory values. RESULTS: When comparing time 0 to time 1, there was a statistically significant decrease in lactate (from 2.2 to 1.8 mEq/L [P < 0.001]) and an increase in pH (from 7.36 to 7.41 [P < 0.001]), serum bicarbonate (from 24.16 to 27.55 mmol/L [P < 0.001]) and arterial PaO2 (from 38.10 to 41.82 mm Hg [P = 0.027]). Preoperatively, there were no deaths, and only two patients had an evidence of multiorgan dysfunction on day of surgery (time 1). CONCLUSION: Our results suggest that a combination of afterload reduction and hypoxemic therapy was able to maintain an appropriate distribution of the cardiac output in the majority of preoperative patients with single-ventricle physiology. An adequate balance of systemic and pulmonary blood flow was successfully achieved with an increase in arterial PaO2 values.

Impact of pharmacotherapy on interstage outcomes in single ventricle infants.

OBJECTIVE: To characterize the pharmacotherapeutic regimens used in infants with single ventricle heart disease and determine the influence of outpatient medications on interstage weight gain. DESIGN: Retrospective review. SETTING: Tertiary care pediatric hospital. PATIENTS: All patients discharged from our institution with single ventricle heart disease that underwent neonatal first stage surgical palliation between 2002 and 2009 were included. Patients who died prior to second stage palliation or underwent orthotopic heart transplantation were excluded. OUTCOME MEASURES: Outpatient medication regimens during the interstage period were reviewed. Medication regimens were compared between surgical eras and between patient groups experiencing different outcomes. A logistic regression model was developed to determine independent factors for an interstage increase in weight-for-age z-score (WAZ) and a linear regression model to determine medications significant for an increase in weight gain per day. RESULTS: The study cohort consisted of 161 patients (58% male). Most patients in this cohort had either hypoplastic left heart syndrome (51%) or unbalanced complete atrioventricular canal (29%). Patients were placed on a median of four medications (range 1-9) at discharge from first surgical palliation, with aspirin (79%), furosemide (79%), and angiotensin converting enzyme inhibitors (ACE-I) (73%) most commonly prescribed. A median of six medication doses per day (range 2-18) were prescribed at discharge. Most patients (71%) had a decrease in WAZ during the interstage period. Use of digoxin (P < 0.01) and high-dose furosemide (P = .02) were associated with a decrease in WAZ score during the interstage period. Additionally, the use of ACE-I, ranitidine, proton-pump inhibitors, or promotility agents was not associated with improved somatic growth during the interstage period. CONCLUSIONS: Infants with single ventricle heart disease have a high-medication burden during the interstage period. Despite the focused and intensified use of medications to improve feeding tolerance and somatic growth, current pharmacotherapeutic regimens appear to have little effect on interstage weight gain.

Early results of bilateral pulmonary artery banding for hypoplastic left heart syndrome.

OBJECTIVE: To compare the haemodynamics and perioperative course of initial palliation with bilateral pulmonary artery banding (PAB) and the Norwood procedure. METHODS: Between April 2004 and December 2007, 43 consecutive children with hypoplastic left heart syndrome (HLHS) or a variant underwent initial palliation (PAB, n=18; Norwood, n=25). Clinical perioperative data were analysed. In the PAB group, lipo-prostaglandin E1 administration was continued with hospitalisation until stage 2 palliation with a bi-directional Glenn shunt and the Norwood procedure. RESULTS: There were no significant differences in the age and operative weight of patients who received stage 1 palliation (PAB, 12+/-9 days, 2.7+/-0.6 kg; Norwood, 12+/-8 days, 2.8+/-0.4 kg). The PAB group had more high-risk patients than the Norwood group (PAB, 83%; Norwood, 48%, p=0.04). Increased early and inter-stage mortality were observed in patients who underwent the Norwood procedure (early mortality with PAB, 6% vs Norwood, 12%; inter-stage mortality, 6% vs 27%, respectively). Mortality between stages 1 and 2 was 11% for the PAB group and 36% for the Norwood group. The Kaplan-Meier survival estimate at 1 year did not differ between groups (77% for the PAB group, 64% for the Norwood group). Ductal stenosis was found in one patient in the PAB group during the follow-up period. Twenty-eight patients underwent stage 2 reconstruction, and the patients in the PAB group were younger at the time of surgery (PAB, 116 days; Norwood, 224 days). There were no significant differences between groups in pulmonary artery index regarding body surface area (BSA) (PAB, 179 mm(2)BSA(-1); Norwood, 194 mm(2)BSA(-1)) and the incidence of ventricular dysfunction after stage 2 construction (PAB, 21%; Norwood, 21%). CONCLUSIONS: Bilateral PAB with continuous lipo-prostaglandin E1 administration may improve early and intermediate mortality in infants with HLHS. Intimate care with hospitalisation may contribute to the results.

Fibroblast Growth Factor-2 regulates proliferation of cardiac myocytes in normal and hypoplastic left ventricles in the developing chick.

The developing heart increases its mass predominantly by increasing the number of contained cells through proliferation. We hypothesized that addition of fibroblast growth factor-2, a factor previously shown to stimulate division of the embryonic myocytes, to the left ventricular myocardium in an experimental model of left heart hypoplasia created in the chicken would attenuate phenotypic severity by increasing cellular proliferation. We have established an effective mode of delivery of fibroblast growth factor-2 to the chick embryonic left ventricular myocardium by using adenovirus vectors, which was more efficient and better tolerated than direct injection of recombinant fibroblast growth factor-2 protein. Injection of control adenovirus expressing green fluorescent protein did not result in significant alterations in myocytic proliferation or cell death compared with intact, uninjected, controls. Co-injection of adenoviruses expressing green fluorescent protein and fibroblast growth factor-2 was used for verification of positive injection, and induction of proliferation, respectively. Treatment of both normal and hypoplastic left ventricles with fibroblast growth factor-2 expressing adenovirus resulted in to 2 to 3-fold overexpression of fibroblast growth factor-2, as verified by immunostaining. An increase by 45% in myocytic proliferation was observed following injection of normal hearts, and an increase of 39% was observed in hypoplastic hearts. There was a significant increase in anti-myosin immunostaining in the hypoplastic, but not the normal hearts. We have shown, therefore, that expression of exogenous fibroblast growth factor-2 in the late embryonic heart can exert direct effects on cardiac myocytes, inducing both their proliferation and differentiation. These data suggest potential for a novel therapeutic option in selected cases of congenital cardiac disease, such as hypoplastic left heart syndrome.

Prostaglandin therapy for ductal patency: how long is too long?

UNLABELLED: The management of neonates born with duct-dependent congenital heart defects in association with prematurity or low birth weight is challenging. We describe two preterm and low birth weight infants with duct-dependent congenital heart disease where cardiac surgery was successfully delayed by maintaining ductal patency using a prolonged prostaglandin infusion. This allowed time for growth and maturation and therefore reduced the risks associated with surgery and cardiopulmonary bypass. CONCLUSION: Maintenance of ductal patency by a prolonged prostaglandin infusion in low birth weight or preterm infants with duct-dependent congenital heart disease is a viable option that allows cardiac surgery to be delayed whilst awaiting further growth and development.

Population pharmacokinetics of milrinone in neonates with hypoplastic left heart syndrome undergoing stage I reconstruction.

We performed a blinded, randomized pharmacokinetic study of milrinone in 16 neonates with hypoplastic left heart undergoing stage I reconstruction to determine the impact of cardiopulmonary bypass and modified ultrafiltration on drug disposition and to define the drug exposure during a continuous IV infusion of drug postoperatively. Neonates received an initial dose of either a 100 or 250 microg/kg of milrinone into the cardiopulmonary bypass circuit at the start of rewarming. Postoperatively, milrinone was infused to clinical needs. A mixed-effect modeling approach was used to characterize milrinone pharmacokinetics during cardiopulmonary bypass, modified ultrafiltration, and postoperatively using the NONMEM algorithm. All patients in this study demonstrated a modified ultrafiltration concentrating effect that occurred despite a modified ultrafiltration drug clearance of 3.3 mL x kg(-1) x min(-1). The infants in this study demonstrated an impaired renal clearance during the immediate postoperative period. A constant infusion of 0.5 microg x kg(-1) x min(-1) resulted in drug accumulation during the initial 12 h of drug administration. Postoperatively, milrinone clearance was significantly impaired (0.4 mL x kg(-1) x min(-1)), improved by the 12th postoperative hour, and approached steady-state clearance (2.6 mL x kg(-1) x min(-1)) by postoperative day 4. In the postoperative setting of markedly impaired renal function, an infusion rate of 0.2 microg x kg(-1) x min(-1) should be considered.

Practical use of alpha blockade strategy in the management of hypoplastic left heart syndrome following stage one palliation with a Blalock-Taussig shunt.

Alpha blockade with phenoxybenzamine has been used in the postoperative management after the Norwood operation. The principle of this approach is the increase in systemic cardiac output by maximal dilation of the systemic circulation. This effect results in a more stable parallel circulation through prevention of fluctuations in systemic vascular resistance in the early postoperative period. We have incorporated this approach in our postoperative management protocol and have observed a decrease in sudden cardiac collapse. This article describes the practical use of alpha blockade strategy, its clinical application, and the most common clinical scenarios observed during the initial hours following stage one palliation with a Blalock-Taussig shunt for hypoplastic left heart syndrome in our cardiac surgery unit.

Pulmonary vascular resistance of children treated with nitrogen during early infancy.

BACKGROUND: We have empirically used supplemental nitrogen in newborns with a functional single ventricle and ductal-dependent systemic perfusion to prevent pulmonary vasodilation and deliver a greater proportion of flow to the systemic circulation. Thus, we reviewed patient outcome to determine whether adverse pulmonary vascular effects may be associated with this therapy. METHODS: From December 1991 to December 1995, the fraction of inspired oxygen was adjusted, with supplemental nitrogen if necessary, to maintain an oxygen saturation near 75% in 20 newborns awaiting heart transplantation. Medical records were reviewed to evaluate (1) the duration of nitrogen therapy, (2) pulmonary vascular histology, (3) postoperative pulmonary hemodynamics, and (4) survival. RESULTS: Thirteen patients underwent heart transplantation, 4 patients died without surgical intervention, and 3 patients underwent late aortic reconstruction. Supplemental nitrogen was used without exceeding a fraction of inspired oxygen of 0.21 for 38 +/- 6 days. One patient had evidence of changes of potentially irreversible pulmonary vascular disease. Pulmonary vascular resistance was not increased long-term in surviving patients. CONCLUSIONS: Supplemental nitrogen can be used to maintain a systemic oxygen saturation near 75% for an extended period in newborns with ductal-dependent systemic perfusion with no long-term adverse effect on pulmonary vascular resistance.

Inotropes in the hypoplastic left heart syndrome: effects in an animal model.

BACKGROUND: Despite substantial changes in the surgical treatment of children born with the hypoplastic left heart syndrome, overall mortality remains high. Although further improvements in outcomes appear to depend on more effective perioperative care, few experimental data exist to guide appropriate pharmacologic therapy in these infants. Because different inotropic agents may have different effects on the ratio of pulmonary to systemic flow (Qp/Qs), we hypothesize that they may not be equally effective at increasing oxygen delivery. METHODS: In neonatal piglets (n = 6; 3.5 to 6.5 kg), we placed an innominate artery-to-pulmonary artery shunt, created an atrial septal defect, and then occluded right ventricular outflow. We examined the effects of a number of commonly used inotropic agents, administering high and low concentrations of dopamine (5 and 15 micrograms.kg-1 .min-1), dobutamine (5 and 15 micrograms.kg-1.min-1), and epinephrine (0.05 and 0.1 microgram /min). RESULTS: Dobutamine at 15 micrograms.kg-1.min-1 increased the Qp/Qs ratio from 1.03 +/- 0.6 at baseline to 2.52 +/- 0.55 (p < 0.05) and decreased oxygen delivery from 50 +/- 4.3 to 36 +/- 1.7 mL/min (p < 0.1). The arterial-venous oxygen difference increased as oxygen delivery went down, going from 44% +/- 1% to 48% +/- 2% (p < 0.1). Epinephrine at 0.1 microgram.kg-1.min-1 decreased the Qp/Qs ratio from 1.23 +/- 0.21 to 0.82 +/- 0.08 (p < 0.05) and increased oxygen delivery from 40 +/- 9.7 to 56 +/- 1.7 mL/min (p < 0.05). Systemic venous oxygen saturation increased from 36% +/- 4.8% to 50% +/- 8.6% (p < 0.05). Although dopamine decreased the Qp/Qs ratio and increased oxygen delivery, these changes were not statistically significant. CONCLUSIONS: Dopamine, dobutamine, and epinephrine all increased cardiac output but had substantially different effects on the Qp/Qs ratio and on oxygen delivery, possibly due to differential effects on systemic and pulmonary vascular resistances. This suggests that inotropic agents may not be equally beneficial in the clinical setting. Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery.

The pharmacokinetics of injectable allopurinol in newborns with the hypoplastic left heart syndrome.

OBJECTIVE: The purpose of this investigation was to determine the pharmacokinetic disposition of intravenous allopurinol and its metabolite oxypurinol in neonates with the hypoplastic left heart syndrome (HLHS) and to evaluate the subsequent degree of xanthine oxidase inhibition using serum uric acid as a marker. METHODS: Pharmacokinetic data were evaluated in 12 stable preoperative neonates with HLHS after a single intravenous allopurinol administration of 5 mg/kg or 10 mg/kg. Pharmacokinetic parameters were determined for elimination half-life, clearance, volume of distribution, and mean residence time. Xanthine oxidase inhibition, measured by serum uric acid reduction, was also measured. RESULTS: Pharmacokinetic parameters revealed no statistically significant differences between a 5-mg/kg and 10-mg/kg dose of intravenous allopurinol on elimination half-life, clearance, volume of distribution, and mean residence time. Mean serum uric acid levels were significantly reduced from baseline by 39.99 and 42.94%, respectively, in the 5- and 10-mg/kg treatment groups. DISCUSSION: The enzyme xanthine oxidase plays a key biochemical role in the generation of toxic oxygen-derived free radicals during ischemia-reperfusion conditions. Allopurinol and its active metabolite oxypurinol inhibit xanthine oxidase, and significantly reduce the conversion of hypoxanthine to xanthine and xanthine to uric acid. Cell injury may be caused by toxic oxygen free radicals produced by ischemia-reperfusion injury such as could occur during the repair of HLHS under hypothermic total circulatory arrest. We hypothesize that allopurinol may provide protection from cellular injury in this clinical context.