Diagnosis and treatment of severe pediatric pulmonary hypertension

Pediatric lung transplantation: promise being realized

PURPOSE OF REVIEW

Lung transplantation for infants and children is an accepted but rarely exercised option for the treatment of end-stage lung disease, with outcomes equivalent to those for adults. However, widespread misconceptions regarding pediatric outcomes often confound timely and appropriate referral to specialty centers. We present the updated information for primary pediatricians to utilize when counseling families with children confronted by progressive end-stage pulmonary or cardiovascular disease.

RECENT FINDINGS

We provide general guidelines to consider for referral, and discuss allocation of organs in children, information regarding standard treatment protocols, and survival outcomes.

SUMMARY

Lung transplantation is a worthwhile treatment option to consider in children with end-stage lung disease. The treatment is complex, but lung transplant provides substantial survival benefit and markedly improved quality of life for children and their families. This timely review provides comprehensive information for pediatricians who are considering options for treatment of children with end-stage lung disease.

Assessment of pulmonary arterial hypertension and vascular resistance by measurements of the pulmonary arterial flow velocity curve in the absence of a measurable tricuspid regurgitant velocity in childhood congenital heart disease

This study aimed to determine mean pulmonary arterial pressure (PAPmean) and pulmonary vascular resistance (PVR) using transthoracic echocardiography (TTE) measurements of the pulmonary artery flow velocity curve in children with pulmonary arterial hypertension (PAH) and congenital heart disease when the tricuspid regurgitant velocity (TRV) is not sufficient. This study enrolled 29 congenital heart disease cases with pulmonary arterial hypertension and 40 healthy subjects followed at our center. The mean age was 66.9 ± 77.9 months in the patient group and 76.3 ± 62.1 months in the control group. A positive correlation was found between TRV and systolic pulmonary arterial pressure (r = 0.394, p = 0.035, 95% confidence interval [CI] = 0.032-0.665), whereas a negative correlation was found between corrected acceleration time (AcTc) and PAPmean (r = -0.559, p = 0.002, 95% CI = -0.768 to -0.242). Furthermore, a negative correlation was found between parameters TRV and AcTc (r = -0.383, p = 0.001, 95% CI = -0.657 to -0.019). Based on the cutoff criterion of 124 ms for AcTc, sensitivity was found to be 79.3% and specificity to be 77.5% in distinguishing between the PAH patients and the healthy control patients (receiver operating characteristic [ROC] area under the curve [AUC] = 0.804, 95% CI = 0.691-0.890, p < 0.0001). The sensitivity and specificity of the concomitant use of AcTc and/or TRV were found to be 90 and 73%, respectively, in distinguishing between the PAH patients and the the healthy control patients. The data obtained by TTE also can be appropriate for measuring PAPmean, PVR, and the vasoreactivity test and for determining the priority of implementing cardiac catheterization even if there is no measurable TRV value.

Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children.

METHODS

The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C).

CONCLUSIONS

The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.

Long-term effect of bosentan in adults versus children with pulmonary arterial hypertension associated with systemic-to-pulmonary shunt: does the beneficial effect persist?

BACKGROUND

Data on long-term response to bosentan in adults and especially children with pulmonary arterial hypertension (PAH) associated with systemic-to-pulmonary shunt are scarce.

METHODS

We studied bosentan efficacy in 30 patients (20 adults, 10 children) with the disease at short- (4 months), and long-term follow-up (through 2.7 years). World Health Organization functional class (WHO class), transcutaneous oxygen saturation, and 6-minute walk distance were assessed at baseline, 4 months, 1 year, 1.5 years, and at latest follow-up (median 2.7 years).

RESULTS

At baseline, children tended to have more severe disease compared with adults with regard to WHO class and congenital heart defects. At 4 months' follow-up, WHO class and 6-minute walk distance significantly improved in both adults and children. During long-term follow-up, this improvement persisted through 1 year but declined thereafter in the total group. In the children, a progressive decline in exercise capacity was observed from 1-year follow-up, whereas in the adults, improvement lasted longer. No change from baseline was seen in transcutaneous oxygen saturation. Three (10%) patients died, 2 (7%) discontinued bosentan, and 5 (17%) required additional PAH therapy (of whom 1 eventually died). One- and 2-year persistence of beneficial bosentan effect was 68% and 43% (total group), 78% and 57% (adults), and 50% and 20% (children), respectively.

CONCLUSIONS

Our experience with bosentan suggests short-term improvement in both adults and children with PAH associated with systemic-to-pulmonary shunt. At long-term follow-up, a progressive decline in beneficial bosentan effect was observed. The decline appeared most pronounced in the pediatric patients, who, in this study, tended to have more severe disease at baseline.

Cardiac Effects of Pulmonary Disease

Pulmonary hypertension (PHT) is the primary cardiac consequence of pulmonary disease. It develops as alveolar hypoxia of pulmonary disease, coupled with vasoactive and mitogenic substances released from pulmonary endothelial and vascular smooth muscle cells damaged by the primary disease process, mediates arterial vasoconstriction and vascular remodeling to raise pulmonary vascular resistance. Independent of the underlying pulmonary disease, PHT produces clinical signs of respiratory distress, exercise intolerance, syncope, and right heart failure. Diagnosis of PHT is made by estimation of pulmonary artery pressures by means of continuous-wave Doppler echocardiographic assessment of tricuspid or pulmonic regurgitant flow velocity. Treatment of PHT is directed at the underlying pulmonary disease but may also aim to attenuate pulmonary artery pressure and limit the clinical sequelae of PHT. No treatments are of proven benefit in veterinary patients; irrespective of the nature of the inciting pulmonary disease, the prognosis is often grave.

Therapeutic Applications of Sildenafil Citrate in the Management of Paediatric Pulmonary Hypertension

Pulmonary hypertension is characterised by a progressive increase in pulmonary vascular resistance and a poor prognosis. The exact underlying mechanisms are still poorly understood; however, it is hypothesised that pulmonary medial hypertrophy and endothelial dysfunction lead to impaired production of vasodilators such as nitric oxide (NO) and prostacyclin, and increased expression of vasoconstrictors such as endothelin-1. The current treatment modalities for pulmonary hypertension include conventional supportive therapies and more specific pharmacological therapies that are targeted at abnormalities of endothelial function. NO and phosphodiesterase type 5 (PDE5) inhibitors induce pulmonary vasodilation by increasing intracellular cyclic guanosine monophosphate (cGMP) concentrations. Sildenafil citrate is a highly selective inhibitor of PDE5. Investigations in animal models and recent clinical case reports with some studies in the paediatric population suggest that sildenafil may be a promising agent in treating pulmonary hypertension. The effect of sildenafil on pulmonary vasculature appears to be independent of the underlying cause, thereby providing a role in idiopathic pulmonary arterial hypertension (PAH), PAH associated with congenital heart disease, pulmonary hypertension secondary to lung disease or persistent pulmonary hypertension of the newborn. It may also be beneficial in postoperative pulmonary hypertension and in neonates who are difficult to wean from inhaled NO. It is easily administered and effective, and has minimal systemic adverse effects. Although the reported results in children with pulmonary hypertension are promising, it is an experimental drug and large-scale randomised controlled studies are required to validate the safety, efficacy and dosage in the paediatric population.

A microstructural hyperelastic model of pulmonary arteries under normo- and hypertensive conditions

This work represents the first application of a statistical mechanics based microstructural orthotropic hyperelastic model to pulmonary artery mechanics under normotensive and hypertensive conditions. The model provides an analogy between the entangled network of long molecular chains and the structural protein framework seen in the medial layer, and relates the mechanical response at macro-level to the deformation (entropy change) of individual molecular chains at the micro-level. A finite element approach was adopted to implement the model. Material parameters were determined via comparing model output to measured pressure-stretch results from normotensive and hypertensive trunks and branches obtained from a rat model of pulmonary arterial hypertension. Results from this initial study show that this model appears reasonable for the study of hyperelastic and anisotropic pulmonary artery mechanics. Typical tangent modulus values ranged from 200 to 800 kPa for normotensive arteries-this increased to beyond 1 MPa for hypertensive vessels. Our study also provokes the hypothesis that increase of cross-linking density may be one mechanism by which the pulmonary artery stiffens in hypertension.

Effect of the oral endothelin antagonist bosentan on the clinical, exercise, and haemodynamic status of patients with pulmonary arterial hypertension related to congenital heart disease

OBJECTIVE

To evaluate the clinical, exercise, and haemodynamic effects of chronic oral administration of the non-selective endothelin receptor antagonist bosentan on patients with pulmonary arterial hypertension (PAH) related to congenital heart disease (CHD).

DESIGN

Prospective non-randomised open clinical study.

SETTING

Cardiology tertiary referral centre.

PATIENTS

21 patients with a mean (SEM) age of 22 (3) years with chronic PAH related to CHD (15 with Eisenmenger's syndrome). Patients were in World Health Organization (WHO) class II to IV with oxygen saturation 87 (2)%.

INTERVENTION

Patients underwent clinical, exercise, and haemodynamic evaluations at baseline and after 16 weeks of treatment.

RESULTS

Bosentan improved (p < 0.01) WHO class, peak oxygen consumption from 16.8 (1.4) to 18.3 (1.4) ml/kg/min, exercise duration from 9.0 (0.8) to 10.7 (0.6) minutes during the treadmill test, walking distance from 416 (23) to 459 (22) m, and Borg dyspnoea index from 2.8 (0.2) to 2.0 (0.1) during the six minute walk test. Bosentan treatment improved (p < 0.05) mean pulmonary artery pressure from 87 (4) to 81 (4) mm Hg, pulmonary blood flow index from 3.2 (0.4) to 3.7 (0.5) l/min/m2, pulmonary to systemic blood flow ratio from 1.2 (0.2) to 1.4 (0.2), and pulmonary vascular resistance index from 2232 (283) to 1768 (248) dyn.s.cm(-5). Two patients died, presumably of arrhythmic causes, who were in WHO class IV at baseline and who had improved during treatment.

CONCLUSIONS

Bosentan induces short and mid term clinical, exercise, and haemodynamic improvements in patients with PAH related to CHD. Larger studies with long term endothelin receptor antagonism are needed to assess the safety and possible treatment role of bosentan in this population.

Pulmonary hypertension--a new manifestation of mitochondrial disease

Mitochondrial respiratory chain (RC) abnormalities in children can present as multiorgan disease, including liver failure, usually within the first year of life. Cardiorespiratory complications have previously been described in association with RC defects; however, to our knowledge no cases of pulmonary hypertension have been described. We discuss two patients with proven mitochondrial RC liver disease who developed severe pulmonary hypertension, one subsequent to cadaveric orthotopic liver transplantation, the second in the neonatal period. It is our contention that pulmonary hypertension should now be included as another potential manifestation of paediatric mitochondrial disease.

Extraction of Pulmonary Vascular Compliance, Pulmonary Vascular Resistance, and Right Ventricular Work From Single-Pressure and Doppler Flow Measurements in Children With Pulmonary Hypertension: a New Method for Evaluating Reactivity

Background— Current evaluation of pulmonary hypertension (PH) in children involves measurement of pulmonary vascular resistance (PVR); however, PVR neglects important pulsatile components. Pulmonary artery (PA) input impedance and ventricular power (VP) include mean and pulsatile effects and have shown promise as alternative measures of vascular function. Here we report the utility of pulsed-wave (PW) Doppler-measured instantaneous flow and pressure measurements for estimation of input impedance and VP and use this method to develop a novel parameter: reactivity in compliance.

Methods and Results— An in vitro model of the general pulmonary vasculature was used to obtain impedance and VP, measured by PW Doppler and a reference flow meter. The method was then tested in a preliminary clinical study in subjects with normal PA hemodynamics (n=4) and patients with PH undergoing reactivity evaluation (8 patients; 23 data points). In vitro results showed good agreement between the impedance spectra computed from both flow-measurement methods. Excellent correlation was seen in vitro between actual resistance and the zero-frequency (Z o ) impedance value ( r 2 =0.984). Excellent agreement was also found between Z o and PVR in the clinical measurements ( y =1.075 x +0.73; r =0.993). Furthermore, total VP and VP/cardiac output increased significantly with hypertension (128.73 to 365.91 mW and 2.42 to 6.69 mW · mL −1 · s −1 , respectively). The first-harmonic value of impedance (Z 1 ) was used as a measure of compliance reactivity; older patients exhibited markedly less compliance reactivity than did younger patients.

Conclusions— Input impedance and VP calculated from Doppler measurements and a single-catheter pressure measurement provide comprehensive characterization of PH and reactivity.

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.