Modification of pulmonary hypertension secondary to congenital heart disease by prostacyclin therapy

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.

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.

Intravenous sildenafil lowers pulmonary vascular resistance in a model of neonatal pulmonary hypertension

Persistent pulmonary hypertension secondary to meconium aspiration syndrome is an important cause of morbidity and mortality in the neonatal population. We investigated the use of the phosphodiesterase-5 inhibitor sildenafil, in its intravenous form, as a pulmonary vasodilator in a model of meconium aspiration syndrome. Pulmonary hypertension was induced in 18 piglets, by endotracheal instillation of human meconium, 6 piglets subsequently received an infusion of intravenous sildenafil for 2 hours, 6 received inhaled nitric oxide for 2 hours, and 6 control animals received no additional intervention. Meconium aspiration increased pulmonary vascular resistance by 70%, and increased oxygenation index by over 100%. Pulmonary vascular resistance remained elevated for the remainder of the study period in control animals. Inhaled nitric oxide reduced the pulmonary vascular resistance by 40% after 2 hours of treatment; intravenous sildenafil completely reversed the increase in pulmonary vascular resistance within 1 hour of commencing the infusion. Neither agent had an effect on systemic hemodynamics. Sildenafil also increased cardiac output by 30%, but while doing so did not adversely influence oxygenation. Intravenous sildenafil is a selective and highly effective pulmonary vasodilator, which is at least as effective as inhaled nitric oxide, in this model of neonatal persistent pulmonary hypertension.

Eisenmenger's Syndrome

In general, most authors advocate nonintervention in Eisenmenger's syndrome, but an awareness of potential palliative measures to avoid destabilizing a delicately balanced physiology is needed as well. This approach has failed to alter long-term outcome, however. Survival for patients with Eisenmenger's syndrome has not improved substantially in the past several decades. Quality of life is universally altered by the presence of cyanosis, exercise intolerance, and the comorbid conditions associated with erythrocytosis. We therefore believe that the use of novel alternatives, as they become available, is warranted and that these alternatives are likely to be best evaluated in multicenter collaborative trials. The approach to the patient with pulmonary vascular obstructive disease (PVOD) should begin with maximization of palliative therapy and should, as compliance and teaching are ensured, proceed to the use of therapies designed to reverse the underlying proliferative changes in the pulmonary vasculature. Frequent checking of potential supplemental oxygen responsiveness and use of inhaled oxygen as needed to maximize systemic arterial saturation should be considered, although evidence of the value of home oxygen use is currently lacking. We favor systemic anticoagulation to a target international normalized ratio of 2.0 to 2.5. There are currently no published data supporting this practice in patients with PVOD, but we believe that as in patients with primary pulmonary hypertension, benefit is likely to outweigh risk. In the setting of a meticulous outpatient anticoagulation service, we have witnessed acceptably low bleeding event rates. A controlled clinical trial is warranted. Selective pulmonary vasodilators and antiproliferative agents hold significant promise in altering the natural history of PVOD associated with intracardiac shunting. The risk of paradoxic embolism and the theoretical worsening of right- to-left shunting compound the already high risk of systemically administered therapies; neither, to date, has been limiting in our patients. Studies of infused or newer subcutaneous and inhaled formulations are under way, and preliminary experience suggests real benefit--improved hemodynamics, improved exercise tolerance, and increased systemic arterial saturation--in this group of patients. Lung transplantation still trades a disease for another set of problems associated with long-term immunosuppression and chronic graft rejection in patients with previous sternotomy and thoracotomy and with a high acute surgical risk. Population studies of mortality and morbidity in patients with PVOD associated with congenital heart disease who receive transplants do not seem to suggest significant improvement with this therapy. In the future, the management of Eisenmenger's syndrome will probably include a multipharmacologic approach that targets several factors in the inflammatory cascade leading to vascular proliferation, perhaps offered in concert with novel surgical or transcatheter strategies designed to limit intracardiac shunting and, if desired, provide complete repair of intracardiac defects.

Recent advances in the treatment of pediatric pulmonary artery hypertension

As our understanding of the pathogenesis of PAH evolves, newer strategies for its treatment are being developed and implemented. Based on studies with adult PPH patients, anticoagulation is now regarded as a mainstay of therapy and is associated with prolonged survival. Before the era of vasodilator therapy, which began in the late 1970s, most children with PPH died within 1 year of diagnosis. Now with chronic calcium channel blockade, survival and QOL are improved in children who acutely respond to vasodilator drug testing. In the author's experience, the 5-year survival rate for patients treated with chronic oral calcium channel blockade who respond acutely to vasodilator testing is 97% versus 35% for those who do not respond acutely. Continuous i.v. prostacyclin has also been used successfully, with a 5-year survival rate of 92% in children in whom oral calcium channel blockade failed (although in some patients the prostacyclin therapy was used as a bridge to transplantation) versus 29% in children in whom oral calcium channel blockade also failed and for whom chronic prostacyclin was unavailable. Before the availability of long-term prostacyclin therapy, 30% to 40% of patients with PPH died while waiting for transplantation. Prostacyclin has virtually eliminated this situation. The results of lung transplantation for adult patients with PPH at 3 years are similar to the results of those on continuous i.v. prostacyclin. Ultimately, the best therapy for an individual child depends on the results of longer follow-up studies. Inhaled nitric oxide has also been used to treat PAH in newborns and other forms of acute and chronic PAH. Although less experience exists with long-term inhaled nitric oxide than with long-term prostacyclin, the preliminary results of long-term inhaled nitric oxide are promising and await further study. The "optimal" vasodilator for long-term therapy, (e.g., calcium channel blockade), prostacyclin, nitric oxide, or potential future therapies, such as prostacyclin analogs, endothelin receptor blockers and thromboxane synthase inhibitors or receptor blockers, must be based on a thorough evaluation with acute vasodilator testing and overall risk-benefit considerations for the various therapeutic regimens. Further clarification of the mechanisms of the development and perpetuation of the PAH process will undoubtedly lead to a refinement in treatment strategies for patients with PAH, which not too long ago was often considered untreatable and fatal. By increasing our understanding of the pathogenesis and pathophysiology of primary and secondary PAH disorders, one day we may be able to prevent or cure these diseases as opposed to providing only palliative therapy. Despite this, therapeutic advances have significantly improved the outcome for children with PAH.

Combined effects of nitric oxide and oxygen during acute pulmonary vasodilator testing

OBJECTIVES

We compared the ability of inhaled nitric oxide (NO), oxygen (O2) and nitric oxide in oxygen (NO+O2) to identify reactive pulmonary vasculature in pulmonary hypertensive patients during acute vasodilator testing at cardiac catheterization.

BACKGROUND

In patients with pulmonary hypertension, decisions regarding suitability for corrective surgery, transplantation and assessment of long-term prognosis are based on results obtained during acute pulmonary vasodilator testing.

METHODS

In group 1, 46 patients had hemodynamic measurements in room air (RA), 100% O2, return to RA and NO (80 parts per million [ppm] in RA). In group 2, 25 additional patients were studied in RA, 100% O2 and 80 ppm NO in oxygen (NO+O2).

RESULTS

In group 1, O2 decreased pulmonary vascular resistance (PVR) (mean+/-SEM) from 17.2+/-2.1 U.m2 to 11.1+/-1.5 U.m2 (p < 0.05). Nitric oxide caused a comparable decrease from 17.8+/-2.2 U.m2 to 11.7+/-1.7 U.m2 (p < 0.05). In group 2, PVR decreased from 20.1+/-2.6 U.m2 to 14.3+/-1.9 U.m2 in O2 (p < 0.05) and further to 10.5+/-1.7 U.m2 in NO+O2 (p < 0.05). A response of 20% or more reduction in PVR was seen in 22/25 patients with NO+O2 compared with 16/25 in O2 alone (p = 0.01).

CONCLUSIONS

Inhaled NO and O2 produced a similar degree of selective pulmonary vasodilation. Our data suggest that combination testing with NO + O2 provides additional pulmonary vasodilation in patients with a reactive pulmonary vascular bed in a selective, safe and expeditious fashion during cardiac catheterization. The combination of NO+O2 identifies patients with significant pulmonary vasoreactivity who might not be recognized if O2 or NO were used separately.

Chronic pulmonary hypertension--the monocrotaline model and involvement of the hemostatic system

Monocrotaline (MCT) is a toxic pyrrolizidine alkaloid of plant origin. Administration of small doses of MCT or its active metabolite, monocrotaline pyrrole (MCTP), to rats causes delayed and progressive lung injury characterized by pulmonary vascular remodeling, pulmonary hypertension, and compensatory right heart hypertrophy. The lesions induced by MCT(P) administration in rats are similar to those observed in certain chronic pulmonary vascular diseases of people. This review begins with a synopsis of the hemostatic system, emphasizing the role of endothelium since endothelial cell dysfunction likely underlies the pathogenesis of MCT(P)-induced pneumotoxicity. MCT toxicology is discussed, focusing on morphologic, pulmonary mechanical, hemodynamic, and biochemical and molecular alterations that occur after toxicant exposure. Fibrin and platelet thrombosis of the pulmonary microvasculature occurs after administration of MCT(P) to rats, and several investigators have hypothesized that thrombi contribute to the lung injury and pulmonary hypertension. The evidence for involvement of the various components of the hemostatic system in MCT(P)-induced vascular injury and remodeling is reviewed. Current evidence is consistent with involvement of platelets and an altered fibrinolytic system, yet much remains to be learned about specific events and signals in the vascular pathogenesis.

Additive effect of beraprost on pulmonary vasodilation by inhaled nitric oxide in children with pulmonary hypertension

Combined administration of inhaled nitric oxide and beraprost sodium resulted in a more intense decrease in pulmonary vascular resistance than nitric oxide given alone (mean -33% vs -45%, p <0.05), without serious systemic hypotension. Combined therapy with nitric oxide and beraprost sodium is highly desirable in treating primary and secondary pulmonary hypertension in children.

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

Nitric oxide-induced vasodilator capacity greatly varies among children with pulmonary hypertension and elevated vascular resistance. The decline of this selective response seems to parallel the progression of established vascular disease and thus may be helpful for the selection of patients for operation.

Persistent pulmonary hypertension in high-risk congenital diaphragmatic hernia patients: incidence and vasodilator therapy

Survival of congenital diaphragmatic hernia patients depends on the gravity of pulmonary hypoplasia and persistent pulmonary hypertension (PPH). Many vasoactive drugs have been used in the treatment of PPH, but often they also lower peripheral resistance, leading to a significant drop in arterial blood pressure. The incidence of PPH in 52 high-risk diaphragmatic hernia patients and the results of treatment with tolazoline and prostacyclin were evaluated in a study lasting 52 months and involving 52 patients. High-risk patients require ventilatory support within 6 hours after birth. Study parameters were alveolar-arterial oxygenation difference (AaDO2), oxygenation index (OI), and mean arterial blood pressure (MABP), measured at set times before and after administration of tolazoline or prostacyclin. Twenty-one patients had documented episodes of PPH (46%), and 18 of them died. Tolazoline did not lower AaDO2 and OI values, but MABP dropped significantly. Prostacyclin caused a significant decrease of AaDO2 and OI values without an effect on MABP. We concluded: (1) PPH presented in 46% of our patients, associated with a high mortality rate; (2) tolazoline is not an effective dilator of the pulmonary vascular bed and lowers MABP; and (3) prostacyclin is an effective pulmonary vasodilator as reflected by ventilation parameters without systemic side effects; it does not affect overall outcome but can used as a "bridge" to extracorporeal membrane oxygenation.

The clinical features, management and outcome of persistence of the arterial duct presenting in adult life

We have reviewed the 25 patients who, between 1973 and 1988, presented to the Brompton Hospital in adulthood with persistence of the arterial duct (ductus arteriosus). As pulmonary arteriolar resistance is the main determinant of management and prognosis in this condition, the patients were divided into groups with either normal or mild elevation of resistance (less than 10 units/m2: 19 patients) or with severe elevation (greater than 10 units/m2: 6 patients). Patients with normal pressures or mild elevation tended to be older (mean age 45 years). Many (70%) were asymptomatic, but dyspnoea with signs of left heart failure was the commonest presenting complaint. Surgical closure of the duct was performed in 16 with good result in all. Survival for the entire group, however, was long. There was a symptomatic indication for surgery (due to hyperdynamic circulation) in 5. In those with severely elevated pulmonary arteriolar resistance, the mean age of presentation was 31 years and the survival short. The commonest presenting symptom was dyspnoea. Surgical closure of the duct was attempted in two patients but with a poor outcome in both. All patients with an elevated resistance had developed this complication by the third decade of life. Significant elevation was not a feature of older patients, suggesting that, in this age group, the risk of elevation is slight. Surgery, nonetheless, may be indicated for relief of symptoms due to a large systemic to pulmonary shunt.

Effects of prostacyclin on bronchoconstriction and neutropenia induced by inhaled platelet-activating factor in man

We studied the effects of prostacyclin (PGI2) on the airway responses to platelet-activating factor (PAF) in a randomized and crossover study in eight normal subjects. PGI2 or diluent (glycine buffer) was continuously infused on 2 separate days. Two breaths of PAF (21 micrograms) were inhaled three times every 15 minutes and airflow at 30% of vital capacity from partial flow-volume curves (Vp30) was measured. PGI2 (4 ng/kg/min) had no effect on Vp30 or blood pressure, whereas heart rate increased from 70.3 +/- 3.9 to 73.7 +/- 4.0 beats/min (mean +/- SEM; p less than 0.01). Two subjects did not complete the study because of transient hypotension. PGI2 had no effect on PAF-induced bronchoconstriction with maximal decreases in Vp30 of 42.0 +/- 8.0% (p less than 0.01) during PGI2 and 49.8 +/- 14.2% (p less than 0.02) during diluent infusion. Ex vivo platelet aggregation to PAF (10(-9) to 10(-7) mol/L) was significantly inhibited by PGI2. Circulating neutrophils decreased from 4.7 +/- 0.9 x 10(9)/L to 1.5 +/- 0.3 x 10(9)/L (p less than 0.05) 5 minutes after the first PAF inhalation during diluent infusion, whereas there was no significant change with PGI2. Thus, PGI2 does not influence PAF-induced bronchoconstriction in man despite causing marked inhibition of ex vivo PAF-induced platelet aggregation and preventing the fall of neutrophils.

Indomethacin enhances histamine-induced pulmonary hemodynamic changes

To determine the role of prostaglandins in porcine pulmonary hemodynamic changes caused by histamine, we compared responses to intravenous histamine with and without pre-treatment with the cyclo-oxygenase inhibitor, indomethacin. In anesthetized pigs, pulmonary artery pressure (Ppa), pulmonary arterial wedge pressure (Ppaw), left ventricular end diastolic pressure (Plved) and cardiac output (Q) were measured repeatedly for 30 minutes, following a 1 ml intrajugular injection of histamine 0.6 microM/kg (n = 6), the identical histamine dose after pre-treatment with indomethacin 5 mg/kg (n = 7), or normal saline (n = 5). Pulmonary arterial resistance (Ra) and pulmonary venous resistance (Rv) were calculated as (Ppa-Ppaw)/Q and (Ppaw-Plved)/Q respectively. Indomethacin pre-treatment caused 2-fold greater increases in Ra and Rv with histamine and more prolonged changes. We conclude that inhibition of a vasodilatory prostaglandin released from pulmonary endothelial cells results in unopposed pulmonary vasoconstriction, thereby augmenting pulmonary resistance changes due to histamine.