Sildenafil therapy for neonatal and childhood pulmonary hypertensive vascular disease

Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension: Basing Care on Physiology

Bronchopulmonary dysplasia (BPD) is the heterogeneous chronic lung developmental disease of prematurity, which is often accompanied by multisystem comorbidities. Pulmonary vascular disease and pulmonary hypertension (PH) contribute significantly to the pathogenesis and pathophysiology of BPD and dramatically influence the outcomes of preterm infants with BPD. When caring for those patients, clinicians should consider the multitude of phenotypic presentations that fall under the "BPD-PH umbrella," reflecting the need for matching therapies to specific physiologies to improve short- and long-term outcomes. Individualized management based on the patient's prenatal and postnatal risk factors, clinical course, and cardiopulmonary phenotype needs to be identified and prioritized to provide optimal care for infants with BPD-PH.

A systematic review of clinical study evidence for pulmonary vasodilator therapy following surgery with cardiopulmonary bypass in children with CHD

OBJECTIVES

Complications from pulmonary hypertension are one of the leading contributors to morbidity and mortality post-cardiopulmonary bypass surgery in children with CHD. Pulmonary vasodilator therapies are commonly used post-operatively, but the optimal target patient population, therapy choice, timing of therapy initiation, and duration of therapy are not well defined.

METHODS

We used PubMed and EMBASE to identify studies from 2000 to 2020 investigating the use of pulmonary vasodilator therapy post-cardiopulmonary bypass in children aged 0-18 years. To ensure eligibility criteria, studies were systematically reviewed by two independent reviewers.

RESULTS

We identified 26 studies of 42,971 children across four medication classes; 23 were single centre, 14 were prospective, and 11 involved randomisation (four of which employed a placebo-control arm). A disproportionate number of children were from a single retrospective study of 41,872 patients. Definitions varied, but change in pulmonary haemodynamics was the most common primary outcome, used in 14 studies. Six studies had clinical endpoints, with mortality the primary endpoint for two studies. Treatment with inhaled nitric oxide, iloprost, and sildenafil all resulted in improved haemodynamics in specific cohorts of children with post-operative pulmonary hypertension, although improved outcomes were not consistently demonstrated across all treated children. Iloprost may be a cheaper alternative to inhaled nitric oxide with similar haemodynamic response.

CONCLUSION

Studies were predominantly single-centre, a control arm was rarely used in randomised studies, and haemodynamic endpoints varied significantly. Further research is needed to reduce post-operative morbidity and mortality from pulmonary hypertension in children with CHD.

Pulmonary hypertension in the child with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of prematurity resulting from complex interactions of perinatal factors that often lead to prolonged respiratory support and increased pulmonary morbidity. There is also growing appreciation for the dysmorphic pulmonary bed characterized by vascular growth arrest and remodeling, resulting in pulmonary vascular disease and its most severe form, pulmonary hypertension (PH) in children with BPD. In this review, we comprehensively discuss the pathophysiology of PH in children with BPD, evaluate the current recommendations for screening and diagnosis of PH, discern associated comorbid conditions, and outline the current treatment options.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Complementary Effect of Maternal Sildenafil and Fetal Tracheal Occlusion Improves Lung Development in the Rabbit Model of Congenital Diaphragmatic Hernia

OBJECTIVE

To evaluate the effect of combining antenatal sildenafil with fetal tracheal occlusion (TO) in fetal rabbits with surgically induced congenital diaphragmatic hernia (CDH).

BACKGROUND

Although antenatal sildenafil administration rescues vascular abnormalities in lungs of fetal rabbits with CDH, it only partially improves airway morphometry. We hypothesized that we could additionally stimulate lung growth by combining this medical treatment with fetal TO.

METHODS

CDH was created on gestational day (GD)23 (n=54). Does were randomized to receive either sildenafil 10 mg/kg/d or placebo by subcutaneous injection from GD24 to GD30. On GD28, fetuses were randomly assigned to TO or sham neck dissection. At term (GD30) fetuses were delivered, ventilated, and finally harvested for histological and molecular analyses. Unoperated littermates served as controls.

RESULTS

The lung-to-body-weight ratio was significantly reduced in sham-CDH fetuses either (1.2 ± 0.3% vs 2.3 ± 0.3% in controls, P=0.0003). Sildenafil had no effect on this parameter, while CDH fetuses undergoing TO had a lung-to-body-weight ratio comparable to that of controls (2.5 ± 0.8%, P<0.0001). Sildenafil alone induced an improvement in the mean terminal bronchiolar density (2.5 ± 0.8 br/mm vs 3.5 ± 0.9 br/mm, P=0.043) and lung mechanics (static elastance 61 ± 36 cmH2O /mL vs 113 ± 40 cmH2O/mL, P=0.008), but both effects were more pronounced in fetuses undergoing additional TO (2.1 ± 0.8 br/mm, P=0.001 and 31 ± 9 cmH2O/mL, P<0.0001 respectively). Both CDH-sham and CDH-TO fetuses treated with placebo had an increased medial wall thickness of peripheral pulmonary vessels (41.9 ± 2.9% and 41.8 ± 3.2%, vs 24.0 ± 2.9% in controls, P<0.0001). CDH fetuses treated with sildenafil, either with or without TO, had a medial thickness in the normal range (29.4% ± 2.6%). Finally, TO reduced gene expression of vascular endothelial growth factor and surfactant protein A and B, but this effect was counteracted by sildenafil.

CONCLUSION

In the rabbit model for CDH, the combination of maternal sildenafil and TO has a complementary effect on vascular and parenchymal lung development.

Safety of enteral sildenafil in hemodynamically unstable children

BACKGROUND

Enteral sildenafil may be used in the intensive care unit for treatment of pulmonary arterial hypertension. We aimed to determine if initial enteral sildenafil dosing is safe in children receiving concurrent vasoactive infusions.

METHODS

We performed a single-centre retrospective chart review that included patients less than 2 years of age in paediatric and cardiovascular intensive care units at an academic medical centre from 1 January, 2010 to 30 November, 2016. Included patients received concomitant enteral sildenafil and a continuously infused vasoactive agent. Exclusion criteria consisted of mechanical circulatory support, any form of dialysis, or a suspicion of septic shock at the time of sildenafil initiation. We sought to identify patients who developed worsening hemodynamic instability after initiation of enteral sildenafil defined as one or more of the following observations within 24 hours of sildenafil initiation: sildenafil discontinuation, total fluid bolus receipt &gt;10 ml/kg, increased vasoactive support, epinephrine intravenous push administration, and/or the initiation of mechanical circulatory support.

RESULTS

Worsening hemodynamic instability was identified in 35% of the 130-patient cohort. Patients younger than 4 months were at increased risk of further hemodynamic instability compared with older patients (56% versus 44%, p = 0.0003) despite receiving lower median doses (1.28 mg/kg/day versus 1.78 mg/kg/day, p = 0.01).

CONCLUSIONS

Critically ill children receiving vasoactive infusions may be at increased risk for further hemodynamic instability after initiation of enteral sildenafil, particularly in younger patients. This population may benefit from lower starting enteral sildenafil doses of 0.25 mg/kg/dose or less every 8 hours to avoid further hemodynamic compromise.

Nitric Oxide Reverses the Position of the Heart during Embryonic Development

Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) plays crucial roles in cardiac homeostasis. Adult cardiomyocyte specific overexpression of eNOS confers protection against myocardial-reperfusion injury. However, the global effects of NO overexpression in developing cardiovascular system is still unclear. We hypothesized that nitric oxide overexpression affects the early migration of cardiac progenitor cells, vasculogenesis and function in a chick embryo. Vehicle or nitric oxide donor DEAN (500 mM) were loaded exogenously through a small window on the broad side of freshly laid egg and embryonic development tracked by live video-microscopy. At Hamburg Hamilton (HH) stage 8, the cardiac progenitor cells (CPC) were isolated and cell migration analysed by Boyden Chamber. The vascular bed structure and heart beats were compared between vehicle and DEAN treated embryos. Finally, expression of developmental markers such as BMP4, Shh, Pitx2, Noggin were measured using reverse transcriptase PCR and in-situ hybridization. The results unexpectedly showed that exogenous addition of pharmacological NO between HH stage 7⁻8 resulted in embryos with situs inversus in 28 out of 100 embryos tested. Embryos treated with NO inhibitor cPTIO did not have situs inversus, however 10 embryos treated with L-arginine showed a situs inversus phenotype. N-acetyl cysteine addition in the presence of NO failed to rescue situs inversus phenotype. The heart beat is normal (120 beats/min) although the vascular bed pattern is altered. Migration of CPCs in DEAN treated embryos is reduced by 60% compared to vehicle. BMP4 protein expression increases on the left side of the embryo compared to vehicle control. The data suggests that the NO levels in the yolk are important in turning of the heart during embryonic development. High levels of NO may lead to situs inversus condition in avian embryo by impairing cardiac progenitor cell migration through the NO-BMP4-cGMP axis.

Paediatric pulmonary arterial hypertension: updates on definition, classification, diagnostics and management

Paediatric pulmonary arterial hypertension (PAH) shares common features of adult disease, but is associated with several additional disorders and challenges that require unique approaches. This article discusses recent advances, ongoing challenges and distinct approaches for the care of children with PAH, as presented by the Paediatric Task Force of the 6th World Symposium on Pulmonary Hypertension. We provide updates of the current definition, epidemiology, classification, diagnostics and treatment of paediatric PAH, and identify critical knowledge gaps. Several features of paediatric PAH including the prominence of neonatal PAH, especially in pre-term infants with developmental lung diseases, and novel genetic causes of paediatric PAH are highlighted. The use of cardiac catheterisation as a diagnostic modality and haemodynamic definitions of PAH, including acute vasoreactivity, are addressed. Updates are provided on issues related to utility of the previous classification system to reflect paediatric-specific aetiologies and approaches to medical and interventional management of PAH, including the Potts shunt. Although a lack of clinical trial data for the use of PAH-targeted therapy persists, emerging data are improving the identification of appropriate targets for goal-oriented therapy in children. Such data will likely improve future clinical trial design to enhance outcomes in paediatric PAH.

Cardiopulmonary Resuscitation in Infants and Children With Cardiac Disease: A Scientific Statement From the American Heart Association

Cardiac arrest occurs at a higher rate in children with heart disease than in healthy children. Pediatric basic life support and advanced life support guidelines focus on delivering high-quality resuscitation in children with normal hearts. The complexity and variability in pediatric heart disease pose unique challenges during resuscitation. A writing group appointed by the American Heart Association reviewed the literature addressing resuscitation in children with heart disease. MEDLINE and Google Scholar databases were searched from 1966 to 2015, cross-referencing pediatric heart disease with pertinent resuscitation search terms. The American College of Cardiology/American Heart Association classification of recommendations and levels of evidence for practice guidelines were used. The recommendations in this statement concur with the critical components of the 2015 American Heart Association pediatric basic life support and pediatric advanced life support guidelines and are meant to serve as a resuscitation supplement. This statement is meant for caregivers of children with heart disease in the prehospital and in-hospital settings. Understanding the anatomy and physiology of the high-risk pediatric cardiac population will promote early recognition and treatment of decompensation to prevent cardiac arrest, increase survival from cardiac arrest by providing high-quality resuscitations, and improve outcomes with postresuscitation care.

Successful Surgical Repair and Perioperative Management of 6-Month-Old With Total Anomalous Pulmonary Venous Return in a Developing Country: Considerations for the Treatment of Pulmonary Hypertension

Total anomalous pulmonary venous return (TAPVR) is a rare congenital cardiac defect, accounting for 1.5-3% of cases of congenital heart disease. With prenatal ultrasonography, the majority of these patients are diagnosed in utero with definitive surgery performed during the neonatal period. However, as prenatal screening may not be available in developing countries, patients may present in later infancy. We present successful surgical repair of a 6-month-old infant with TAPVR who presented for medical care at 5 months of age in Lima, Peru. The late presentation of such infants and the limited resources available for the treatment of elevated pulmonary vascular resistance may impact successful surgical correction of such defects. The perioperative care of such infants in developing countries is discussed and strategies for managing postoperative pulmonary hypertension is reviewed.

Pulmonary Hypertension Therapy and a Systematic Review of Efficacy and Safety of PDE-5 Inhibitors

Pulmonary hypertension (PH) is a syndrome that is of growing concern to pediatricians worldwide. Recent data led to concerns about the safety of phosphodiesterase type 5 (PDE5) inhibitors in children and a US Food and Drug Administration safety advisory. Our objective is to provide insight into therapies for PH in children and to systematically review the comparative effectiveness and safety of PDE5 inhibitors in the management of pediatric patients with PH. We searched the following databases through February 2015: Medline, Embase, SCOPUS, and the Cochrane Central Register of Controlled Trials. We included studies that examined PDE5 inhibitor use in children with PH. Allowed comparators were either no medication or other classes of medication for management of PH. Study inclusion was via a 2-stage process with 2 reviewers and a predesigned form. Of 1270 papers identified by the literature search, 21 were included: 8 randomized controlled trials and 13 observational studies (9 retrospective, 4 prospective). There is strong evidence that PDE5 inhibitor use improves echocardiography measurements, cardiac catheterization parameters, and oxygenation compared with baseline or placebo in pediatric patients with PH. Evidence suggests that low- and moderate-dose sildenafil are safe regimens for children. There are a relatively small number of randomized controlled trials that address use of PDE5 inhibitors in pediatric patients with PH. PDE5 inhibitors are effective agents for cardiovascular and oxygenation end points in pediatric PH and important components of a multimodal pharmacotherapeutic approach to this growing challenge. Additional studies are needed to define optimal PH therapy in childhood.

Pulmonary Hypertension and Pulmonary Vasodilators

Pulmonary hypertension in the perinatal period can present acutely (persistent pulmonary hypertension of the newborn) or chronically. Clinical and echocardiographic diagnosis of acute pulmonary hypertension is well accepted but there are no broadly validated criteria for echocardiographic diagnosis of pulmonary hypertension later in the clinical course, although there are significant populations of infants with lung disease at risk for this diagnosis. Contributing cardiovascular comorbidities are common in infants with pulmonary hypertension and lung disease. It is not clear who should be treated without confirmation of pulmonary vascular disease by cardiac catheterization, with concurrent evaluation of any contributing cardiovascular comorbidities.

Sildenafil in pediatric pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease of varied etiologies. Although PAH has no curative treatment, a greater understanding of pathophysiology, technological advances resulting in early diagnosis, and the availability of several newer drugs have improved the outlook for patients with PAH. Sildenafil is one of the therapeutic agents used extensively in the treatment of PAH in children, as an off-label drug. In 2012, the United States Food and Drug Administration (USFDA) issued a warning regarding the of use high-dose sildenafil in children with PAH. This has led to a peculiar situation where there is a paucity of approved therapies for the management of PAH in children and the use of the most extensively used drug being discouraged by the regulator. This article provides a review of the use of sildenafil in the treatment of PAH in children.

Pediatric Pulmonary Hypertension: Guidelines From the American Heart Association and American Thoracic Society

Pulmonary hypertension is associated with diverse cardiac, pulmonary, and systemic diseases in neonates, infants, and older children and contributes to significant morbidity and mortality. However, current approaches to caring for pediatric patients with pulmonary hypertension have been limited by the lack of consensus guidelines from experts in the field. In a joint effort from the American Heart Association and American Thoracic Society, a panel of experienced clinicians and clinician-scientists was assembled to review the current literature and to make recommendations on the diagnosis, evaluation, and treatment of pediatric pulmonary hypertension. This publication presents the results of extensive literature reviews, discussions, and formal scoring of recommendations for the care of children with pulmonary hypertension.

Risk-benefit considerations when prescribing phosphodiesterase-5 inhibitors in children

INTRODUCTION

Sildenafil (Revatio®) and tadalafil (Adcirca®) are specific inhibitors of the phosphodiesterase-5 enzyme and produce pulmonary vasodilation by inhibiting the breakdown of cyclic guanosine monophosphate (cGMP) in the walls of pulmonary arterioles.

AREAS COVERED

We focus on the efficacy and safety of sildenafil and tadalafil in the treatment of pulmonary hypertension (PH) in children through a PubMed literature search.

EXPERT OPINION

Although used since 1999 in the treatment of PH in children, it is only in the past few years that robust evidence for the use of sildenafil has emerged principally in the pivotal STARTS-1 study. The open-label extension of this study, STARTS-2, has revealed safety concerns substantiated by FDA post marketing surveillance leading to recommendations to use lower doses. More recently, tadalafil has been introduced allowing once daily dosing with apparently similar efficacy to sildenafil in children. Recently there have been suggestions that sildenafil and tadalafil may have a place in treating muscular dystrophy.

Safety of sildenafil in infants*

OBJECTIVE

In view of the recent U.S. Food and Drug Administration's warning against the use of sildenafil in pediatric patients, we aimed to provide an updated overview of the dosing and safety of sildenafil in infants and to explore the relevance of the present safety concerns to the infant population.

DATA SOURCE

The National Library of Medicine PubMed and Cochrane Database of Systematic Reviews were searched using the following terms: Sildenafil AND (infant OR infants OR newborn OR newborns OR child OR children OR childhood OR pediatric OR pediatrics OR paediatric OR paediatrics).

STUDY SELECTION

Studies presenting original clinical data regarding the dosing, use, or safety of sildenafil in infants with pulmonary hypertension would be included.

DATA EXTRACTION

Of the 49 included studies, case reports and case series were the most common type of publications (n = 25). The identified trials included 625 children, with more than 140 infants. Persistent pulmonary hypertension of the newborn and pulmonary hypertension associated with other conditions were the most common underlying diagnoses.

CONCLUSION

There is currently no evidence of serious adverse event in infants exposed to sildenafil. Present safety concerns regarding the use of sildenafil in pediatric patients should be further explored before being applied to infant population. Sildenafil remains a valuable option for the treatment of pulmonary hypertension in young infants. Prospective studies should be designed in such a way that they include a safety assessment to evaluate potential adverse outcomes of sildenafil therapy in this population.

Pulmonary vein stenosis and the pathophysiology of "upstream" pulmonary veins

BACKGROUND

Surgical and catheter-based interventions on pulmonary veins are associated with pulmonary vein stenosis (PVS), which can progress diffusely through the "upstream" pulmonary veins. The mechanism has been rarely studied. We used a porcine model of PVS to assess disease progression with emphasis on the potential role of endothelial-mesenchymal transition (EndMT).

METHODS

Neonatal piglets underwent bilateral pulmonary vein banding (banded, n = 6) or sham operations (sham, n = 6). Additional piglets underwent identical banding and stent implantation in a single-banded pulmonary vein 3 weeks postbanding (stented, n = 6). At 7 weeks postbanding, hemodynamics and upstream PV pathology were assessed.

RESULTS

Banded piglets developed pulmonary hypertension. The upstream pulmonary veins exhibited intimal thickening associated with features of EndMT, including increased transforming growth factor (TGF)-β1 and Smad expression, loss of endothelial and gain of mesenchymal marker expression, and coexpression of endothelial and mesenchymal markers in banded pulmonary vein intimal cells. These immunopathologic changes and a prominent myofibroblast phenotype in the remodeled pulmonary veins were consistently identified in specimens from patients with PVS, in vitro TGF-β1-stimulated cells isolated from piglet and human pulmonary veins, and human umbilical vein endothelial cells. After stent implantation, decompression of a pulmonary vein was associated with reappearance of endothelial marker expression, suggesting the potential for plasticity in the observed pathologic changes, followed by rapid in-stent restenosis.

CONCLUSIONS

Neonatal pulmonary vein banding in piglets recapitulates critical aspects of clinical PVS and highlights a pathologic profile consistent with EndMT, supporting the rationale for evaluating therapeutic strategies designed to exploit reversibility of upstream pulmonary vein pathology.

Clinical trials in neonates and children: Report of the pulmonary hypertension academic research consortium pediatric advisory committee

Drug trials in neonates and children with pulmonary hypertensive vascular disease pose unique but not insurmountable challenges. Childhood is defined by growth and development. Both may influence disease and outcomes of drug trials. The developing pulmonary vascular bed and airways may be subjected to maldevelopment, maladaptation, growth arrest, or dysregulation that influence the disease phenotype. Drug therapy is influenced by developmental changes in renal and hepatic blood flow, as well as in metabolic systems such as cytochrome P450. Drugs may affect children differently from adults, with different clearance, therapeutic levels and toxicities. Toxicity may not be manifested until the child reaches physical, endocrine and neurodevelopmental maturity. Adverse effects may be revealed in the next generation, should the development of ova or spermatozoa be affected. Consideration of safe, age-appropriate tablets and liquid formulations is an obvious but often neglected prerequisite to any pediatric drug trial. In designing a clinical trial, precise phenotyping and genotyping of disease is required to ensure appropriate and accurate inclusion and exclusion criteria. We need to explore physiologically based pharmacokinetic modeling and simulations together with statistical techniques to reduce sample size requirements. Clinical endpoints such as exercise capacity, using traditional classifications and testing cannot be applied routinely to children. Many lack the necessary neurodevelopmental skills and equipment may not be appropriate for use in children. Selection of endpoints appropriate to encompass the developmental spectrum from neonate to adolescent is particularly challenging. One possible solution is the development of composite outcome scores that include age and a developmentally specific functional classification, growth and development scores, exercise data, biomarkers and hemodynamics with repeated evaluation throughout the period of growth and development. In addition, although potentially costly, we recommend long-term continuation of blinded dose ranging after completion of the short-term, double-blind, placebo-controlled trial for side-effect surveillance, which should include neurodevelopmental and peripubertal monitoring. The search for robust evidence to guide safe therapy of children and neonates with pulmonary hypertensive vascular disease is a crucial and necessary goal.

Advances in pediatric pulmonary arterial hypertension

PURPOSE OF REVIEW

Pulmonary arterial hypertension (PAH) is an important cause of morbidity and mortality in children. Approved medications for the treatment of adult PAH have been used to treat children, but evidence-based treatment algorithms for children are lacking.

RECENT FINDINGS

Pediatric PAH registries have begun to define the incidence and prevalence of idiopathic PAH and PAH associated with congenital heart disease. A pediatric-specific classification of pulmonary hypertensive vascular disease has been proposed. Furthermore, the first randomized placebo-controlled trial of type-5 phosphodiesterase therapy in treatment-naïve children with PAH has been completed and reported. This trial highlights the importance of the difficulties of performing clinical trials in children with targeted PAH therapy as well as the importance of long-term follow-up of adverse events.

SUMMARY

Classification, clinical trials, and therapy for children with PAH must take into account the unique aspects of PAH in children.