Inhaled nitric oxide to test the vasodilator capacity of the pulmonary vascular bed in children with long-standing pulmonary hypertension and congenital heart disease

Outcomes in Patients with Pulmonary Arterial Hypertension Underwent Transcatheter Closure of an Atrial Septal Defect

Pulmonary arterial hypertension (PAH) related to an atrial septal defect (ASD) poses a challenge to transcatheter closure of an ASD (tcASD). We aimed to determine the predictors for remaining PAH (rPAH) post-tcASD. This retrospective study was conducted at a single tertiary university hospital. Adult patients with an ASD and PAH were divided into three groups according to pulmonary vascular resistance (PVR). Normalization of pulmonary atrial systolic pressure (PASP) was defined as an estimated right ventricular systolic pressure < 40 mmHg and was determined using transthoracic echocardiography. Among 119 patients, 80% showed PAH normalization post-tcASD. Normalization of PAH post-tcASD was observed in 100%, 56.2%, and 28.6% of patients in mild, moderate, and severe PVR groups, respectively. The patients’ New York Heart Association functional class improved. Multivariate logistic regression analysis showed that age and high PVR were significant risk factors for rPAH. A receiving operator curve analysis showed a PASP cutoff value > 67.5 mmHg to be predictive of rPAH post-tcASD, with an area under the curve value of 0.944 (sensitivity, 0.922; specificity 0.933). Most patients, including moderate-to-severe PAH patients, improved hemodynamically and clinically with tcASD. Since patients with severe PAH are at a risk of rPAH, tcASD should be performed by selecting the patient carefully based on pre-procedure medication, a vasoreactivity test, and a balloon occlusion test.

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.

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.

Can pulmonary vasodilator therapy expand the operative indications for congenital heart disease?

The operability of congenital heart disease with left to right shunt depends on the severity of the pulmonary vascular disease induced by the increased pulmonary blood flow. Although some recommendations exist regarding operative indications according to pathological, hemodynamic, and epidemiological factors, the evidence underlying these recommendations is not conclusive. Recently, oral pulmonary vasodilator therapy has been reported to improve outcomes in patients with idiopathic pulmonary arterial hypertension, and this therapy also appears to be effective in patients with congenital heart disease and pulmonary arterial hypertension, including those with postoperative pulmonary hypertension and Eisenmenger syndrome. It is expected that the availability of novel pulmonary vasodilator therapy will expand the operative indications in patients with congenital heart disease with left to right shunt, but there is currently insufficient evidence to definitively determine this. A multicenter double-blind study should be conducted to further examine this issue.

Saudi Guidelines on the Diagnosis and Treatment of Pulmonary Hypertension: Pulmonary hypertension in children

Pulmonary hypertension (PH) is relatively uncommon in children. Pulmonary arterial hypertension (PAH) in pediatric comprises a wide spectrum of diseases, from a transient neonatal condition to a progressive disease associated with morbidity and mortality. Most common PAH in pediatric are idiopathic (IPAH) or PAH associated with congenital heart disease (PAH-CHD), while other associated conditions, such as connective tissue disease (CTD), are less common in pediatrics. Despite better understanding of PH and the availability of new medications during recent decades; the diagnosis, investigation and choice of therapy remain a challenge in children, as evidence-based recommendations depend mainly on adult studies. In this review, we provide a detailed discussion about the distinctive features of PAH in pediatric, mainly emphacysing on classification and diagnostic algorithm.

Patients with congenital systemic-to-pulmonary shunts and increased pulmonary vascular resistance: what predicts postoperative survival?

Background

We carried out a retrospective data review of patients with systemic to pulmonary shunts that underwent surgical repair between February 1990 and February 2012 in order to assess preoperative pulmonary vascular dynamic risk factors for predicting early and late deaths due presumably to pulmonary vascular disease.

Methods and Results

A total of 1024 cases of congenital systemic-to-pulmonary shunt and advanced pulmonary vascular disease beyond infancy and early childhood were closed surgically. The mean follow up duration was 8.5±5.5 (range 0.7 to 20) years. Sixty-one in-hospital deaths (5.96%, 61/1024) occurred after the shunt closure procedure and there were 46 late deaths, yielding 107 total deaths. We analyzed preoperative pulmonary vascular resistance index (PVRI), pulmonary vascular resistance index on pure oxygen challenge (PVRIO), difference between PVRI and PVRIO (PVRID), Qp∶Qs, and Rp∶Rs as individual risk predictors. The results showed that these individual factors all predicted in-hospital death and total death with PVRIO showing better performance than other risk factors. A multivariable Cox regression model was built,and suggested that PVRID and Qp∶Qs were informative factors for predicting survival time from late death and closure of congenital septal defects was safe with a PVRIO<10.3 WU.m² and PVRID>7.3 WU.m² on 100% oxygen.

Conclusions

All 4 variables, PVRI, PVRIO, PVRID and Qp∶Qs, should be considered in deciding surgical closure of congenital septal defects and a PVRIO<10.3 WU.m² and PVRID>7.3 WU.m² on 100% oxygen are associated with a favorable risk benefit profile for the procedure.

Assessment of operability of patients with pulmonary arterial hypertension associated with congenital heart disease

Pulmonary arterial hypertension (PAH) is a common complication of congenital heart disease, and is now predominantly among patients with uncorrected left-to-right shunts. A growing population is characterized by persistent or recurrent PAH after surgical or interventional correction of left-to-right shunts; the latter having a worse prognosis than other forms of PAH associated with congenital heart disease. New treatments for PAH have been shown to be effective in improving PAH exercise capacity and hemodynamics, raising the hope for making previously inoperable congenital heart defects operable and shifting the framework for the assessment of operability. This review focuses on current methods for assessing operability in PAH associated with congenital heart disease, and the possibility of "treat-and-repair" vs. "repair-and-treat" strategies for patients with inoperable or borderline PAH.

Pulmonary hypertension in congenital shunts

Pulmonary arterial hypertension frequently arises in patients with congenital heart disease. The vast majority present with congenital cardiac shunts. Initially these may manifest as left-to-right (i.e. systemic-to-pulmonary) shunts. The natural history of disease progression involves vascular remodeling and dysfunction that lead to increased pulmonary vascular resistance and, finally, to the development of Eisenmenger's syndrome, which is the most advanced form. The anatomical, pathological and structural abnormalities occurring in the pulmonary circulation of these patients are, to some extent, similar to those observed in other forms of pulmonary arterial hypertension. This understanding has recently led to significant changes in the management of Eisenmenger's syndrome, with the introduction of treatment specifically targeting pulmonary vascular disease. Early closure of the cardiac shunt remains the best way of preventing pulmonary vascular lesions. However, it is still not clear which preoperative parameters predict safe and successful repair, though hemodynamic evaluation is still routinely used for assessment. Postoperative pulmonary hypertension, both in the immediate period after surgical repair and during long-term follow-up, remains a real therapeutic challenge. The clinical situation of a single ventricle with Fontan circulation also presents difficulties when pulmonary vascular lesions are present. This article reviews pulmonary hypertension associated with congenital shunts and discusses a number of the specific problems encountered.

Advances in therapies for pediatric pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive obliteration of the pulmonary vasculature, leading to right heart failure and death if left untreated. Prior to the current treatment era, pulmonary hypertension carried a poor prognosis with a high mortality rate, but its prognosis has changed over the past decades in relation to new therapeutic agents. Nevertheless, pulmonary hypertension continues to be a serious condition, which is extremely challenging to manage. The data in children are often limited owing to the small number of patients, and extrapolation from adults to children is not straightforward. While none of these new therapeutic agents have been specifically approved for children, there is evidence that each can appropriately benefit the PAH child. We review the current understanding of pediatric pulmonary hypertension, classification, diagnostic evaluation and available treatment. A description of targeted pharmacological therapy and new treatments in children is outlined.

Preoperative pulmonary hemodynamics and assessment of operability: is there a pulmonary vascular resistance that precludes cardiac operation?

Preoperative pulmonary vascular disease remains an important risk factor for death or right-heart failure in selected children undergoing two-ventricle repair, single-ventricle palliation, or heart transplantation. Preoperative criteria for poor outcome after operation remain unclear. The purpose of this review is to critically assess both the historic and current data and make recommendations where appropriate. An extensive literature search was undertaken in October 2009. Data were analyzed by an expert multidisciplinary team and recommendations were made by consensus. PubMed was searched in October 2009. Data were analyzed and recommendations were made by consensus of a multidisciplinary team. In patients with suspected pulmonary vascular disease anticipating a two-ventricle repair, although preoperative testing via cardiac catheterization with vasodilators is reasonable, the preoperative parameters and the precise values of these parameters that best correlate with early and late outcome remain unclear. Further investigation is warranted in selected populations, such as the growing group of children with congenital heart disease complicated by chronic lung disease of prematurity, and in the developing world where patients may be more likely to present late with advanced pulmonary vascular disease. In patients with a functional single ventricle, there is growing evidence that mean pulmonary artery pressure of >15 mm Hg may be associated with both early and late mortality after the Fontan operation. The relationship of preoperative pulmonary hemodynamics to early and late morbidity remains to be defined. There most likely is a level of preoperative pulmonary vascular disease that puts an individual patient at increased risk for death or severe cyanosis after a bidirectional cavopulmonary anastomosis. It remains unclear, however, how to best assess this risk preoperatively. The limitations in obtaining an accurate assessment of pulmonary vascular disease in the complex single ventricle are discussed. In children awaiting cardiac transplantation with elevated pulmonary vascular disease of >6 U.m and/or transpulmonary gradient of >15 mm Hg, heart transplantation is deemed feasible in most transplant centers if the administration of inotropes or vasodilators can decrease the pulmonary vascular disease to <6 U.m or transpulmonary gradient to <15 mm Hg. In patients with preoperative pulmonary vascular disease, there may be contributing factors to the pulmonary vascular disease, such as the specifics of the cardiac lesion (atrioventricular valve regurgitation, low cardiac output), parenchymal and/or airway issues, and/or individual genetic predisposition. Amelioration of any reversible factors before operation and optimization of their management in the preoperative and postoperative period are recommended.

Advances in diagnosis and treatment of pulmonary arterial hypertension in neonates and children with congenital heart disease

BACKGROUND

This article aims to review recent advances in the diagnosis and treatment of pulmonary arterial hypertension in neonates and children with congenital heart disease.

DATA SOURCES

Articles on pulmonary arterial hypertension in congenital heart disease were retrieved from PubMed and MEDLINE published after 1958.

RESULTS

A diagnosis of primary (or idiopathic) pulmonary arterial hypertension is made when no known risk factor is identified. Pulmonary arterial hypertension associated with congenital heart disease constitutes a heterogenous group of conditions and has been characterized by congenital systemic-to-pulmonary shunts. Despite the similarities in histologic appearance of pulmonary vascular disease, there are differences between pulmonary arterial hypertension secondary to congenital systemic-to-pulmonary shunts and those with other conditions with respect to pathophysiology, therapeutic strategies, and prognosis. Revision and subclassification within the category of secondary pulmonary arterial hypertension based on pathophysiology were conducted to improve specific treatments. The timing of surgical repair is crucial to prevent and minimize risk of postoperative pulmonary arterial hypertension. Drug therapies including prostacyclin, endothelin-receptor antagonist, phosphodiesterase inhibitor, and nitric oxide have been evolved with promising results in neonates and children.

CONCLUSIONS

Among the different forms of congenital heart diseases, an early correction generally prevents subsequent development of pulmonary arterial hypertension. Emerging therapies for treatment of patients with idiopathic pulmonary arterial hypertension also improve quality of life and survival in neonates and children with congenital heart disease associated with pulmonary arterial hypertension. Heart and lung transplantation or lung transplantation in combination with repair of the underlying cardiac defect is a therapeutic option in a minority of patients. Partial repair options are also beneficial in some selected cases. Randomized controlled trials are needed to evaluate the safety and efficacy of these therapies including survival and long-term outcome.

Adenosine for vasoreactivity testing in pulmonary hypertension: a head-to-head comparison with inhaled nitric oxide

BACKGROUND

APVT is an invasive method recommended for symptomatic patients with PAH that permits the identification of the minority of patients (<20%) that may benefit from long-term calcium channel blockers. Adenosine has been indicated in guidelines as a vasodilator agent of choice for APVT, although it has not been directly compared with iNO, the gold standard for this test. The objective of the study was to compare adenosine with inhaled nitric oxide (iNO) for acute pulmonary vasoreactivity testing (APVT) in pulmonary arterial hypertension (PAH), in order to determine the efficacy and safety of the first in the clinical setting.

METHODS

The measurements of cardiac output, pulmonary and systemic resistance were done in the basal state and with a stepwise increase of the dose of each drug until either maximum dosage (adenosine: 500 microg/kg/min or iNO: 80 ppm) or side effects observed or a positive response were reached, according to current guidelines. The order of drugs used in each test was consecutively alternated during the study.

RESULTS

Six of the 39 studied patients (15%) presented a positive response to iNO; none to adenosine (p = 0.047, McNemar's test). Twenty-three patients (59%) did not reach the maximum dose of adenosine due to side effects, including bronchospasm, thoracic pain and bradycardia.

CONCLUSIONS

APVT testing with adenosine was not able to detect PAH patients responsive to iNo and provoked frequent adverse effects. Adenosine should not be used as a vasodilator drug in APVT.

Assessment of pulmonary vasoreactivity in children with pulmonary hypertension

PURPOSE OF REVIEW

With the current advance in understanding and treatment of pulmonary arterial hypertension in children, pulmonary vasoreactivity testing would navigate the treatment option. An inclusive review of the milestone studies and also recent literature over the last few years on the pulmonary vasoreactivity testing in children will provide the update on various available pulmonary vasodilator agents, markers related to vasoreactivity response, the implication of the testing result on child management and outlook for the long-term outcome.

RECENT FINDINGS

There continue to be emerging data regarding pulmonary vasodilators for vasoreactivity testing in children and the genetic predictor of pulmonary vasoreactivity response, particularly in children with idiopathic and familial pulmonary hypertension. Despite a recent advance in pulmonary hypertension therapy leading to improved prognosis in children, the novel knowledge on standardized pulmonary vasoreactivity testing in children and its interpretation remain limited and controversial.

SUMMARY

The precise definition of pulmonary vasoreactivity testing remains debatable, particularly in children with pulmonary hypertension related to congenital heart defect. Defining the responder, in order to navigate the treatment option, is frequently dictated by institutional experience and facilities. Meanwhile, the criteria for responder in children with idiopathic pulmonary artery hypertension are reasonably consistent. In general, responders seem to have less severe disease and better prognosis.

Review of inhaled iloprost for the control of pulmonary artery hypertension in children

In the pediatric population, pulmonary hypertension may present as an acute event in the setting of lung or cardiac pathology or as a chronic disease, mainly as idiopathic pulmonary hypertension or associated with congenital heart disease. Recently, new pharmacologic approaches have demonstrated significant efficacy in the management of adults with pulmonary arterial hypertension; these include intravenous epoprostenol, prostacyclin analogs, endothelin receptor antagonists and phosphodiesterase type 5 inhibitors. The same treatment strategies are currently used in children. There are only few reports of the use of inhaled iloprost in pediatrics, only one of which reported the use of chronic inhaled iloprost in a significant number of children. This report showed that 1) the acute pulmonary vasodilator response to inhaled iloprost is equivalent to that of inhaled nitric oxide; 2) acute inhalation of iloprost can induce bronchoconstriction 3) the addition of inhaled iloprost can reduce the need for intravenous prostanoid therapy in some patients; 4) most children tolerated the combination of inhaled iloprost and endothelin receptor antagonist or phosphodiesterase inhibitors; 5) Several patients had clinical deterioration during chronic inhaled iloprost therapy and required rescue therapy with intravenous prostanoids. In this review we will discuss the role of inhaled iloprost in acute and chronic pulmonary hypertension in children.

Aerosolized iloprost for pulmonary vasoreactivity testing in children with long-standing pulmonary hypertension related to congenital heart disease

BACKGROUND

In congenital heart disease with increased pulmonary blood flow and pressure, progressive changes in the vascular structure can lead to irreversible pulmonary hypertension (PH). Pulmonary hemodynamic parameters are used to determine whether surgical correction is no longer indicated. In this study, aerosolized iloprost was used to assess pulmonary vasoreactivity in children with long-standing PH related to congenital heart disease.

METHODS

Children with long-standing and severe PH secondary to congenital heart disease were included in this study. Various hemodynamic parameters were measured before and after iloprost inhalation (0.5 microg/kg), and vascular resistance was determined. Responders to the iloprost test were defined as those with a decrease in both pulmonary vascular resistance (PVR) and pulmonary-to-systemic vascular resistance ratio (R(p)/R(s)) of >10%.

RESULTS

Eighteen children aged between 7 months and 13 years with long-standing and severe PH secondary to congenital heart disease were studied. Thirteen children had a positive response, resulting in a mean (+/- SD) decrease of PVR from 9.3 +/- 4.6 to 4.6 +/- 2.7 Wood U x m(2) (P < 0.001), and a mean decrease of R(p)/R(s) from 0.54 +/- 0.37 to 0.24 +/- 0.14 (P = 0.005).

CONCLUSIONS

Iloprost-induced pulmonary vasodilator responses vary among children with PH related to congenital heart disease. The use of inhaled iloprost in the cardiac catheterization laboratory results in pulmonary vasoreactivity for some of these children particularly a reduction in PVR and the pulmonary-to-systemic vascular resistance ratio.

Current treatment options in children with pulmonary arterial hypertension and experiences with oral bosentan

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by vasoconstriction and progressive remodelling of the pulmonary arterial wall leading to right ventricular failure and death. Idiopathic PAH (IPAH) and PAH associated with congenital heart defects account for the majority of paediatric patients with PAH. During the last few decades, several pharmacological approaches have been introduced, including calcium channel-blockers (CCBs), prostacyclin analogues, endothelin receptor antagonists and, most recently, phosphodiesterase inhibitors. This paper reviews the treatment options available to children with a special focus on the initial experience with bosentan. Although CCBs have been shown to increase survival in IPAH, the beneficial effect appears to be limited to a small number of patients, defined as 'responders' to the vasoreactivity testing. With the availability of prostacyclin (intravenous epoprostenol) and then prostacyclin analogues, the treatment options have increased markedly and particularly in patients who have not responded to conventional therapy. Although epoprostenol has been shown to be efficacious in PAH, the drug is not ideal owing to serious complications arising from the invasive mode of application, particularly in children. Phosphodiesterase-5 inhibitors have also shown beneficial effects. Targeting the endothelin (ET) system with the oral, dual ET(A)/ET(B) receptor antagonist, bosentan has been demonstrated to improve the cardiopulmonary haemodynamics, exercise capacity, quality-of-life and survival in adult patients with PAH. Specific ET(A) antagonists may also present the same beneficial profile. Recent experience with bosentan in paediatric patients with PAH indicates that the results obtained in adult patients may be extrapolated to children, thus offering a safe and effective therapy that is easy to administer.

Noninvasive Doppler tissue measurement of pulmonary artery compliance in children with pulmonary hypertension

BACKGROUND

We have shown previously that input impedance of the pulmonary vasculature provides a comprehensive characterization of right ventricular afterload by including compliance. However, impedance-based compliance assessment requires invasive measurements. Here, we develop and validate a noninvasive method to measure pulmonary artery (PA) compliance using ultrasound color M-mode (CMM) Doppler tissue imaging (DTI).

METHODS

Dynamic compliance (C(dyn)) of the PA was obtained from CMM DTI and continuous wave Doppler measurement of the tricuspid regurgitant velocity. C(dyn) was calculated as: [(D(s) - D(d))/(D(d) x P(s))] x 10(4); where D(s) = systolic diameter, D(d) = diastolic diameter, and P(s) = systolic pressure. The method was validated both in vitro and in 13 patients in the catheterization laboratory, and then tested on 27 pediatric patients with pulmonary hypertension, with comparison with 10 age-matched control subjects. C(dyn) was also measured in an additional 13 patients undergoing reactivity studies.

RESULTS

Instantaneous diameter measured using CMM DTI agreed well with intravascular ultrasound measurements in the in vitro models. Clinically, C(dyn) calculated by CMM DTI agreed with C(dyn) calculated using invasive techniques (23.4 +/- 16.8 vs 29.1 +/- 20.6%/100 mm Hg; P = not significant). Patients with pulmonary hypertension had significantly lower peak wall velocity values and lower C(dyn) values than control subjects (P < .01). C(dyn) values followed an exponentially decaying relationship with PA pressure, indicating the nonlinear stress-strain behavior of these arteries. Reactivity in C(dyn) agreed with reactivity measured using impedance techniques.

CONCLUSION

The C(dyn) method provides a noninvasive means of assessing PA compliance and should be useful as an additional measure of vascular reactivity subsequent to pulmonary vascular resistance in patients with pulmonary hypertension.

EXPERIMENTAL THERAPIES FOR HYPOXIA-INDUCED PULMONARY HYPERTENSION DURING ACUTE LUNG INJURY

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing thoracic, transplant, and trauma surgeons. The recent discovery of efficacious drugs that are selective for the pulmonary vasculature has brought about the potential for very powerful therapeutic agents. Inhaled nitric oxide (NO) therapy has already found broad clinical utility, yet its use is limited by potential toxicities. Rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. Finally, phosphodiesterase-5 inhibitors have been found to selectively vasodilate the pulmonary vasculature in the midst of HPV. The purposes of this review are to: 1) discuss the advantages and disadvantages of inhaled preparations of NO; 2) address experimental alternatives to inhaled preparations of NO to treat HPV; 3) explore potential therapeutic avenues associated with inhibition of Rho-kinase; and, 4) examine the use of phosphodiesterase-5 (PDE-5) inhibitors and combination therapy in the treatment of HPV.

Severe paediatric pulmonary hypertension: new management strategies

Pulmonary hypertension is a significant complication in many paediatric disease states. This article discusses current understanding of pulmonary hypertension and includes definition, diagnosis, and management. A description of the latest advances in targeted pharmacological therapy in children is also provided as well as impact on morbidity and mortality.

Pulmonary Vascular Effects of Inhaled Nitric Oxide and Oxygen Tension in Bronchopulmonary Dysplasia

Pulmonary hypertension contributes significantly to morbidity and mortality in bronchopulmonary dysplasia (BPD), but little is known about the relative contribution of arterial tone, structural remodeling, and vessel density to pulmonary hypertension, especially in older patients. To determine the role of high pulmonary vascular tone in pulmonary hypertension, we studied the acute effects of oxygen tension, inhaled nitric oxide (iNO), and calcium channel blockers (CCB) in 10 patients with BPD who underwent cardiac catheterization for evaluation of pulmonary hypertension. During normoxic conditions, mean pulmonary arterial pressure (PAP) and pulmonary to systemic vascular resistance ratio (PVR/SVR) were 34 +/- 3 mm Hg and 0.42 +/- 0.07, respectively. In response to hypoxia, PAP and PVR/SVR increased by 50 +/- 8% and 82 +/- 14%, respectively (p < 0.01). Hyperoxia decreased PVR/SVR by 28 +/- 9% (p = 0.05). The addition of iNO treatment (20-40 ppm) to hyperoxia decreased PAP and PVR/SVR by 29 +/- 5% (p < 0.01) and 45 +/- 6% (p < 0.05) from baseline values, respectively, achieving near normal values. CCB did not alter PAP or PVR/SVR from baseline values. We conclude that hyperoxia plus iNO causes marked pulmonary vasodilatation in older patients with BPD, suggesting that heightened pulmonary vascular tone contributes to pulmonary vascular disease in BPD.

Sildenafil: Emerging Cardiovascular Indications

The discovery in 1989 of sildenafil, a highly selective inhibitor of phosphodiesterase-5 (PDE-5), was the result of extensive research on chemical agents targeting PDE-5 that might potentially be useful in the treatment of coronary heart disease. Initial clinical studies on sildenafil in the early 1990s were not promising with respect to its antianginal potential. However, the incidental discovery of its antiimpotence effect led to its approval of for the treatment of erectile dysfunction. Thereafter, several reports of adverse cardiac events in patients on sildenafil raised concerns about its safety in cardiovascular disorders. Novel therapeutic indications are emerging for sildenafil with the recent discovery that PDE-5 is expressed in various other tissues such as the arterial vasculature, including pulmonary and coronary arteries, venous vasculature, skeletal muscles, platelets, and visceral and tracheobronchial muscles. In this review we briefly summarize the pharmacology of sildenafil and the current available evidence on its potential therapeutic applications in cardiovascular disorders.

Hypoxic pulmonary vasoconstriction in cardiothoracic surgery: basic mechanisms to potential therapies

Hypoxic pulmonary vasoconstriction is postulated to be an adaptive mechanism to match lung perfusion with ventilation; however, the consequences of the maladaptive effects of pulmonary vasoconstriction represent formidable therapeutic challenges. Understanding the basic mechanisms of hypoxic pulmonary vasoconstriction will enhance the assimilation of translational research into clinical practice. The purposes of this review are to (1) define basic mechanisms of pulmonary vasoconstriction and vasorelaxation; (2) delineate the biphasic contractile response to hypoxia; (3) critically examine data that support the mediator hypothesis versus the ion channel hypothesis; and (4) explore potential mechanistic-based therapies for hypoxic pulmonary vasoconstriction.

Pulmonary arterial hypertension in children

Pulmonary arterial hypertension is a serious progressive condition with a poor prognosis if not identified and treated early. Because the symptoms are nonspecific and the physical findings can be subtle, the disease is often diagnosed in its later stages. Remarkable progress has been made in the field of pulmonary arterial hypertension over the past several decades. The pathology is now better defined, and significant advances have occurred in understanding the pathobiologic mechanisms. Risk factors have been identified, and the genetics have been characterized. Advances in technology allow earlier diagnosis as well as better assessment of disease severity. Therapeutic modalities such as new drugs, e.g., epoprostenol, treprostinil, and bosentan, and surgical/interventional options, e.g., transplantation and atrial septostomy, which were unavailable several decades ago, have had a significant impact on prognosis and outcome. Thus, despite our inability to cure pulmonary arterial hypertension, advances in medical treatments over the past two decades have resulted in significant improvement in outcomes for children with various forms of pulmonary arterial hypertension. This report is a review the current state of the art for pulmonary arterial hypertension in 2004, with an emphasis on childhood pulmonary arterial hypertension and specific recommendations for current practice and future directions.

Acute hemodynamic effects and home therapy using a novel pulsed nasal nitric oxide delivery system in children and young adults with pulmonary hypertension

In 26 patients, we evaluated a novel pulsed nasal delivery system for nitric oxide (NO) that, in the short term, was as effective as continuous delivery for decreasing pulmonary artery pressure and pulmonary vascular resistance. In 2 patients, NO delivered in the home using this pulsing system was well tolerated for up to 2 years. The long-term safety, efficacy, and acceptability of NO delivered in the home remains to be studied.

Intravenous sildenafil is a potent pulmonary vasodilator in children with congenital heart disease

BACKGROUND

Increased pulmonary vascular resistance (PVR) because of congenital heart disease (CHD) may be caused by a dysfunction in endogenous pulmonary endothelial nitric oxide (NO) production. In other forms of pulmonary vascular disease with increased PVR, an elevated activity of a phosphodiesterase type 5 (PDE-5), responsible for the degradation of cyclic guanidine monophosphate (cGMP), the second messenger of endothelially produced NO, has been demonstrated. This study compares the effects of inhaled NO before and after the specific inhibition of the PDE-5 by intravenous sildenafil (Viagra) in pre- and postoperative children with increased PVR because of CHD.

METHODS AND RESULTS

12 children with congenital heart disease (age 0.2 to 15.7 years, median 2.4 years) and increased mean pulmonary arterial pressure, and 12 postoperative children (age 0.11 to 0.65 years, median 0.32 years) with increased PVR (8.3+/-1.0 Wood Units*m2) were studied during cardiac catheterization ("cath laboratory"), or within 2 hours after return from cardiac surgery ("post op"), respectively. All were sedated, tracheally intubated and paralyzed. During alveolar hyperoxygenation (FiO2=0.65), the effects of inhaled NO (20 ppm) were compared before and after the stepwise infusion of sildenafil ("cath laboratory", 1 mg/kg; post op, 0.25 mg/kg). Intravenous sildenafil more effectively reduced PVR than NO (11.5% versus 4.3% in the "cath laboratory" patient group, P<0.05, and 25.8% versus 14.6% in the post op patient group, P=0.09. The increase in cGMP in response to NO was potentiated (2- to 2.4-fold) by PDE-5 inhibition. While the vasodilating effects of sildenafil showed pulmonary selectivity, its infusion was associated with increased intrapulmonary shunting in the postoperative patients (Qs/Qt=16.5+/-4.7% to 25.5+/-18.2% P=0.04).

CONCLUSIONS

Intravenous sildenafil is as effective as inhaled NO as a pulmonary vasodilator in children with congenital heart disease. Although clinically insignificant in this study, increased intrapulmonary shunting with sildenafil may be disadvantageous in some patients after CHD surgery.

Pulmonary arterial wall distensibility assessed by intravascular ultrasound in children with congenital heart disease: an indicator for pulmonary vascular disease?

BACKGROUND

Both pulmonary hypertension and pulmonary overflow are associated with functional and structural changes of the pulmonary arterial wall. Current techniques to evaluate the pulmonary vasculature neglect the pulsatile nature of pulmonary flow.

STUDY OBJECTIVES

To determine whether the dynamic properties of the pulmonary arterial wall are altered in patients with abnormal pulmonary hemodynamics due to congenital heart defects, and whether these changes are associated with the progression of pulmonary vascular disease (PVD).

PATIENTS AND METHODS

In 43 children with PVD due to congenital heart defects and 12 control subjects, pulmonary arterial pulsatility (the relative increase in vessel area during the cardiac cycle) and distensibility (the inverse of the stress/strain elastic modulus) were determined with intravascular ultrasound. Results were correlated with clinical and hemodynamic parameters.

RESULTS

Pulsatility correlated with pulmonary pulse pressure (p < 0.001), pulmonary-to-systemic vascular resistance ratio (PVR/SVR) [p = 0.001], and hemoglobin concentration (p = 0.01). However, when corrected for these variables, pulsatility did not differ between patients and control subjects. In contrast, arterial wall distensibility decreased with the severity of PVD and correlated independently with pulmonary-to-systemic arterial pressure ratio (p < 0.001) and PVR/SVR (p = 0.03), and with hemoglobin concentration (p < 0.01). Adjusted for hemodynamic variables, distensibility was still decreased in patients with PVD compared to control subjects.

CONCLUSIONS

These results demonstrate that pulmonary arterial wall distensibility is progressively decreased in PVD; moreover, this decreased distensibility is, in part, related to increased distending pressure as a result of pulmonary hypertension but also, in part, to stiffening of the arterial wall during the disease process. Arterial wall distensibility may be of additional value in the evaluation of pulmonary vasculature and ventricular workload.

Diagnosis and treatment of severe pediatric pulmonary hypertension

Advances in the treatment of pulmonary hypertension during the past decade have dramatically improved patient survival. Many of these advances are based on improved understanding of the vascular biology of the normal and hypertensive pulmonary circulations. Pulmonary hypertension is an important determinant of morbidity and mortality in patients with many pediatric diseases, including congenital heart disease. This article describes current diagnostic strategies and treatments for patients with primary and secondary pulmonary hypertension.

Essentials of Nitric Oxide for the Pediatric (Cardiac) Anesthesiologist

Short- and long-term survival rates for the operative treat ment of congenital heart disease (CHD) have improved significantly in the past 2 decades. The increasing sophisti cation of the pediatric cardiologist's diagnostic armamen tarium has led to more pervasive use of fetal screening with echocardiography. Early diagnosis and pre-emptive care of the neonate with complex CHD have allowed interventional strategies in the catheterization suite or the operating room to be optimized in both the timing and the quality of pallia tive or corrective procedures. Medications such as prosta glandin E and ventilator strategies using hypoxic and hyper carbic inspired gases exemplify therapies benefitting the contemporary neonate with CHD, often allowing stabiliza tion of the patient before surgery. Surgical care of neonates, infants, and children with CHD has also improved. Insights into maturational differences in myocardial and autonomic function have led to more appropriate myocardial protection strategies and pharmacologic support of the circulation. Recognition of those anomalies in which total correction in the neonate is desirable has stimulated improvements in the technical and cognitive skills of pediatric cardiovascular sur geons and pediatric cardiac anesthesiologists to meet these challenges. The goal of this article is to provide the pediatric anesthesiologist with an overview of inhaled nitric oxide and its relevance to clinical practice.

Inhaled nitric oxide versus aerosolized iloprost in secondary pulmonary hypertension in children with congenital heart disease: vasodilator capacity and cellular mechanisms

BACKGROUND

Inhaled nitric oxide (iNO) has been used to assess the vasodilator capacity of the pulmonary vascular bed in children with congenital heart disease and elevated pulmonary vascular resistance. Inhaled iloprost is a pulmonary vasodilator for the long-term treatment of pulmonary hypertension (PHT). Because these 2 vasodilators act through different pathways (release of cGMP or cAMP, respectively), we compared the pulmonary vasodilator capacity of each.

METHODS AND RESULTS

A total of 15 children with congenital heart disease and PHT who had elevated pulmonary vascular resistance (preoperative, n=10; immediately postoperative, n=5) were first given 20 ppm of iNO for 10 minutes; then, after baseline values were reached again, they were given aerosolized iloprost at 25 ng. kg(-1). min(-1) for another 10 minutes. Finally, iNO and iloprost were given simultaneously for 10 minutes. With iNO, the pulmonary vascular resistance and systemic vascular resistance ratio decreased from 0.48+/-0.38 to 0.27+/-0.16 (P:<0.001). Similarly, iloprost decreased the ratio from 0.49+/-0.38 to 0.26+/-0.11 (P:<0.05). The combination had no additional effect on the resistance ratio. Plasma cGMP increased from 17.6+/-11.9 to 34.7+/-21.4 nmol/L during iNO (P:<0.01), and plasma cAMP increased from 55.7+/-22.9 to 65.1+/-21.2 nmol/L during iloprost inhalation (P:<0.05).

CONCLUSIONS

In children with PHT and congenital heart disease, both iNO and aerosolized iloprost are equally effective in selectively lowering pulmonary vascular resistance through an increase in cGMP or cAMP, respectively. However, the combination of both vasodilators failed to prove more potent than either substance alone. Aerosolized iloprost might be an alternative to iNO for early testing of vascular reactivity and for the postoperative treatment of acute PHT.

Ventricular Septal Defect

Ventricular septal defects (VSDs) are the most common congenital heart malformations seen in children. Because spontaneous closure occurs frequently, patients with small VSDs should be followed clinically with no limitations except endocarditis prophylaxis. Surgical closure is recommended for only small defects with significant associated lesions such as aortic regurgitation, aortic valve prolapse, right or left ventricular outflow obstruction, tricuspid regurgitation, left ventricle to right atrial shunt, or recurrent endocarditis. Enlarging left ventricular size or deteriorating left ventricular function would also be an indication for surgical repair. Moderate and large VSDs in infancy often require treatment of congestive heart failure with diuretics, digitalis, and afterload reduction. Surgical closure before 9 months of age is indicated for large VSDs and by 2 years of age for moderate shunts to prevent pulmonary vascular obstructive disease and the consequences of long-standing volume overload. Device closure of VSD is still in the investigational stage but holds promise for treatment of apical or multiple muscular VSDs.