ATRIAL SEPTAL DEFECT WITH PULMONARY HYPERTENSION

Application of a modified clinical classification for pulmonary arterial hypertension associated with congenital heart disease in children: emphasis on atrial septal defects and transposition of the great arteries. An analysis from the TOPP registry

Aims

A proportion of patients with pulmonary arterial hypertension associated with congenital heart disease (PAH-CHD) do not fit in the current classification. We aimed to analyse the applicability of an adapted clinical classification of PAH-CHD to pediatric patients using the TOPP-1 registry (Tracking Outcomes and Practice in Pediatric Pulmonary Hypertension) and focus on atrial septal defects (ASD) and transposition of the great arteries (TGA).

Methods and results

Hemodynamic and clinical data of all patients with PAH-CHD in the TOPP cohort were reviewed. Patients were classified according to predefined ABCDE categories (A: Eisenmenger syndrome, B: left-to-right shunt, C: coincidental defects, including all ASDs, D: corrected CHD, E: TGA), or as complex CHD (group 5), by 2 independent investigators. In case of disagreement, a third reviewer could either settle a final decision, or the patient was deemed not classifiable. Survival curves were calculated for each group and compared to idiopathic PAH patients of the registry. A total of 223 out of 531 patients in the registry had PAH-CHD, and 193 were categorized to the following groups: A 39(20%), B 27(14%), C 62(32%) including 43 ASDs, D 58(30%), E 7(4%), whereas 6 patients were categorized as group 5, and 10 patients were unable to be classified. No survival difference could be demonstrated between the groups.

Conclusions

This modified classification seems to be more applicable to pediatric PAH-CHD patients than the previous classification, but some patients with PAH-CHD who never had a shunt remain unclassifiable. The role of ASD in pediatric PH should be reconsidered.

Hemodynamic assessment of atrial septal defects

Atrial septal defect (ASD) is one of the most common congenital cardiac anomalies. ASD can present as an isolated lesion in an otherwise normal heart or in association with other congenital heart conditions. Regardless of the type of ASD, the direction and degree of shunting across the communication is mainly determined by the difference in compliance between the right and left ventricle. Hemodynamics in children is characterized by left-to-right shunting, dilated right heart structures and normal pulmonary artery pressures (PAP). Patients diagnosed at adult age often present with complications related to long-standing volume overload such as pulmonary artery hypertension and right and left ventricular dysfunction. Diagnostic catheterization is usually not indicated unless there is suggestion of pulmonary hypertension on echocardiography. In older patients and/or in those with ventricular dysfunction, measurement of left heart pressures during temporary balloon occlusion is recommended prior to device closure as it may not be tolerated. In ASD associated with other congenital malformations, shunting degree and direction will depend upon underlying condition. Restrictive ASD can result in significant hemodynamic compromise in neonates with conditions such as hypoplastic left heart syndrome (HLHS) and transposition of the great arteries (TGA). In most cases, hemodynamics can be estimated with echocardiography only.

Device closure of a large atrial septal defect in a patient with severe pulmonary arterial hypertension after 1 year use of an oral endothelin receptor antagonist

The presence of severe pulmonary arterial hypertension (PAH) in patients with atrial septal defect (ASD) is still thought to preclude shunt closure, although there are several reports of good clinical outcomes after vasodilator therapy. We report the case of a young woman with ASD and severe PAH who was able to successfully undergo percutaneous shunt closure following 1 year use of the oral endothelin receptor antagonist, bosentan.

Pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease leading to right heart failure and ultimately death if untreated. The first classification of PH was proposed in 1973. In 2008, the fourth World Symposium on PH held in Dana Point (California, USA) revised previous classifications. Currently, PH is devided into five subgroups. Group 1 includes patients suffering from idiopathic or familial PAH with or without germline mutations. Patients with a diagnosis of PAH should systematically been screened regarding to underlying mutations of BMPR2 gene (bone morphogenetic protein receptor type 2) or more rarely of ACVRL1 (activine receptor-like kinase type 1), ENG (endogline) or Smad8 genes. Pulmonary veno occusive disease and pulmonary capillary hemagiomatosis are individualized and designated as clinical group 1'. Group 2 'Pulmonary hypertension due to left heart diseases' is divided into three sub-groups: systolic dysfonction, diastolic dysfonction and valvular dysfonction. Group 3 'Pulmonary hypertension due to respiratory diseases' includes a heterogenous subgroup of respiratory diseases like PH due to pulmonary fibrosis, COPD, lung emphysema or interstitial lung disease for exemple. Group 4 includes chronic thromboembolic pulmonary hypertension without any distinction of proximal or distal forms. Group 5 regroup PH patients with unclear multifactorial mechanisms. Invasive hemodynamic assessment with right heart catheterization is requested to confirm the definite diagnosis of PH showing a resting mean pulmonary artery pressure (mPAP) of ≥ 25 mmHg and a normal pulmonary capillary wedge pressure (PCWP) of ≤ 15 mmHg. The assessment of PCWP may allow the distinction between pre-capillary and post-capillary PH (PCWP > 15 mmHg). Echocardiography is an important tool in the management of patients with underlying suspicion of PH. The European Society of Cardiology and the European Respiratory Society (ESC-ERS) guidelines specify its role, essentially in the screening proposing criteria for estimating the presence of PH mainly based on tricuspid regurgitation peak velocity and systolic artery pressure (sPAP). The therapy of PAH consists of non-specific drugs including oral anticoagulation and diuretics as well as PAH specific therapy. Diuretics are one of the most important treatment in the setting of PH because right heart failure leads to fluid retention, hepatic congestion, ascites and peripheral edema. Current recommendations propose oral anticoagulation aiming for targeting an International Normalized Ratio (INR) between 1.5-2.5. Target INR for patients displaying chronic thromboembolic PH is between 2–3. Better understanding in pathophysiological mechanisms of PH over the past quarter of a century has led to the development of medical therapeutics, even though no cure for PAH exists. Several specific therapeutic agents were developed for the medical management of PAH including prostanoids (epoprostenol, trepoprostenil, iloprost), endothelin receptor antagonists (bosentan, ambrisentan) and phosphodiesterase type 5 inhibitors (sildenafil, tadalafil). This review discusses the current state of art regarding to epidemiologic aspects of PH, diagnostic approaches and the current classification of PH. In addition, currently available specific PAH therapy is discussed as well as future treatments.

Pulmonary blood flow and pulmonary hypertension: Is the pulmonary circulation flowophobic or flowophilic?

Increased pulmonary blood flow (PBF) is widely thought to provoke pulmonary vascular obstructive disease (PVO), but the impact of wall shear stress in the lung is actually poorly defined. We examined information from patients having cardiac lesions which impact the pulmonary circulation in distinct ways, as well as experimental studies, asking how altered hemodynamics impact the risk of developing PVO. Our results are as follows: (1) with atrial septal defect (ASD; increased PBF but low PAP), shear stress may be increased but there is little tendency to develop PVO; (2) with normal PBF but increased pulmonary vascular resistance (PVR; mitral valve disease) shear stress may also be increased but risk of PVO still low; (3) with high PVR and PBF (e.g., large ventricular septal defect), wall shear stress is markedly increased and the likelihood of developing PVO is much higher than with high PBF or PAP only; and (4) with ASD, experimental and clinical observations suggest that increased PBF plus another stimulus (e.g., endothelial inflammation) may be required for PVO. We conclude that modestly increased wall shear stress (e.g., ASD) infrequently provokes PVO, and likely requires other factors to be harmful. Likewise, increased PAP seldom causes PVO. Markedly increased wall shear stress may greatly increase the likelihood of PVO, but we cannot discriminate its effect from the combined effects of increased PAP and PBF. Finally, the age of onset of increased PAP may critically impact the risk of PVO. Some implications of these observations for future investigations are discussed.

Congenital heart disease and pulmonary hypertension

Many patients with congenital heart disease and systemic-to-pulmonary shunts develop pulmonary arterial hypertension (PAH), particularly if the cardiac defect is left unrepaired. A persistent increase in pulmonary blood flow may lead to obstructive arteriopathy and increased pulmonary vascular resistance, a condition that can lead to reversal of shunt and cyanosis (Eisenmenger syndrome). Cardiac catheterization is crucial to confirm diagnosis and facilitate treatment. Bosentan is the only medication to date to be compared with placebo in a randomized controlled trial specifically targeting congenital heart disease-associated PAH. Lung transplantation with repair of the cardiac defect or combined heart-lung transplantation is reserved for recalcitrant cases.

Updated clinical classification of pulmonary hypertension

The aim of a clinical classification of pulmonary hypertension (PH) is to group together different manifestations of disease sharing similarities in pathophysiologic mechanisms, clinical presentation, and therapeutic approaches. In 2003, during the 3rd World Symposium on Pulmonary Hypertension, the clinical classification of PH initially adopted in 1998 during the 2nd World Symposium was slightly modified. During the 4th World Symposium held in 2008, it was decided to maintain the general architecture and philosophy of the previous clinical classifications. The modifications adopted during this meeting principally concern Group 1, pulmonary arterial hypertension (PAH). This subgroup includes patients with PAH with a family history or patients with idiopathic PAH with germline mutations (e.g., bone morphogenetic protein receptor-2, activin receptor-like kinase type 1, and endoglin). In the new classification, schistosomiasis and chronic hemolytic anemia appear as separate entities in the subgroup of PAH associated with identified diseases. Finally, it was decided to place pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis in a separate group, distinct from but very close to Group 1 (now called Group 1'). Thus, Group 1 of PAH is now more homogeneous.

Eisenmenger syndrome and atrial septal defect: nature or nurture?

BACKGROUND

It has long been debated whether patients with atrial septal defect (ASD) Eisenmenger syndrome have idiopathic pulmonary arterial hypertension with an incidental ASD or severe pulmonary hypertension on the basis of their ASD shunt magnitude alone.

HYPOTHESIS

It was hypothesized that if ASD Eisenmenger patients had idiopathic pulmonary arterial hypertension with an incidental ASD, a mutation in the bone morphogenetic protein receptor-2 (BMPR2) would be found in some of these patients.

PATIENTS AND METHODS

All adult patients with ASD Eisenmenger syndrome were identified from the databases of two adult congenital cardiac units, and were matched to a control group with similar types of ASDs and no pulmonary hypertension. Gene coding for BMPR2 was examined for mutation using denaturing high-performance liquid chromatography of the entire coding sequence.

RESULTS

Eighteen adult patients with ASD Eisenmenger syndrome and 18 control patients were identified. ASD Eisenmenger patients had significantly larger ASDs than the control patients (3.7+/-1.2 cm versus 1.9+/-0.7 cm, P<0.01). A mutation in BMPR2 was not detected in either group.

CONCLUSION

ASD Eisenmenger syndrome may occur without BMPR2 mutation. Whether shunt magnitude alone or in combination with yet another genetic mutation is responsible for the development of pulmonary hypertension in these patients remains to be determined.

Hypertensive pulmonary vascular disease in adults with secundum or sinus venosus atrial septal defect

BACKGROUND

The development of hypertensive pulmonary vascular disease (HPVD) is considered a risk factor in the long-term course of patients with secundum atrial septal defects (ASD). The aim of this study was to assess the prevalence and histologic degree of HPVD and pulmonary hypertension in relation to preoperative clinical and hemodynamic data, intraoperative findings, and operative outcome in adults.

METHODS

Lung biopsies of 75 patients, mean age 44 +/- 14 years (18-71 years), with secundum ASD or sinus venosus defect including ten patients with partial anomalous pulmonary venous return were analyzed in accordance with preoperative and intraoperative findings as well as operative outcome. Lung biopsy was performed at the time of defect closure and was classified according to Heath and Edwards.

RESULTS

Structural changes of the pulmonary vasculature were found in 59% of patients; grade 3 and higher changes were present in 19%. There were no statistically significant relations between histologic findings and preoperative clinical and hemodynamic data, intraoperative findings, and operative outcome. The prevalence of moderate (32-50 mm Hg) and severe (> 50 mm Hg) systolic pulmonary hypertension was 27% and 17%, respectively. Increased systolic pulmonary arterial pressure was associated with increased pulmonary vascular resistance (p < 0.000) and patients' age (p = 0.001). Patients with a lower functional capacity had a higher prevalence of pulmonary hypertension (p = 0.011).

CONCLUSIONS

The prevalence of HPVD and pulmonary hypertension in adult patients with secundum ASD or sinus venosus defect is considerable. Preoperative hemodynamic data do not predict the degree of HPVD in lung biopsy. Closure is generally advised to prevent increasing pulmonary arterial pressure and decreasing functional capacity over time.

Long-term outcome after surgical closure of atrial septal defect in childhood with extensive assessment including MRI measurement of the ventricles

Surgical closure of the secundum type of atrial septal defect (ASD) in childhood leads to excellent survival. However, relevant morbidity has been reported. Transcatheter closure of these defects has now become an alternative approach. To compare the results of the two different interventions, reliable data are needed on the long-term morbidity after defect closure with both methods. Patients were evaluated after a minimum of 10 years after surgical closure of an ASD in childhood. Assessment included analysis of perioperative data, interview, clinical examination, electrocardiogram, (ECG), 24-hour ECG, ergometry, chest radiograph, echocardiography, and MRI. A total of 66 patients underwent operation between 1971 and 1986 at our institution. Forty-eight of them (73%) were interviewed and 38 (58%) participated fully in the study program. Eighteen (27%) either refused to participate or were lost to follow-up. There were no substantial residual disorders, such as arrhythmias, right-sided heart dilatation, pulmonary hypertension, or reduced work capacity. Surgical closure of an ASD in childhood has an excellent long-term outcome. Surgical closure is thus the standard against which transcatheter closure needs to be measured.

Need for closure of secundum atrial septal defect in infancy

OBJECTIVES

Closure of isolated secundum atrial septal defect is generally recommended at the age of 4 to 5 years. However, there are children with isolated secundum atrial septal defect in whom early closure should be performed. We aimed to assess the underlying conditions that led to earlier closure in this special patient group and to analyze the outcome.

METHODS AND RESULTS

From January 1990 through August 2002, 24 infants with isolated secundum atrial septal defect underwent surgical closure within the first year of life. All children were symptomatic. Signs of pulmonary hyperperfusion, such as tachydyspnea, failure to thrive, recurrent respiratory infections, or heart failure, were present. Four infants required artificial ventilation. Ten patients had additional problems, such as prematurity with chronic lung disease, hepato-omphalocele and congenital diaphragmatic hernia, which were present in 1 patient each. Eleven patients had defined dysmorphic syndromes. All but 1 infant underwent preoperative invasive hemodynamic evaluation. Thirteen patients had pulmonary hypertension preoperatively. The follow-up time was 46 +/- 33 months (range, 4-125 months). At follow-up, pulmonary artery pressure proved to be normal in 11 of the 13 children who had pulmonary hypertension previously. One patient died of persistent pulmonary hypertension. Clinical performance, growth, and development improved in nearly all patients. All ventilator-dependent children could be weaned shortly after atrial septal defect closure.

CONCLUSIONS

If lungs are compromised, even a minor left-to-right shunt might be poorly tolerated in infancy. In these children early surgical closure of an isolated secundum atrial septal defect should be performed to support thrive and growth and to prevent the onset of irreversible changes of the pulmonary vasculature.

Classification and epidemiology of pulmonary hypertension

Pulmonary hypertension is a complex disease that can be idiopathic, familial, or associated with a wide range of disease processes. This article outlines the classification of primary pulmonary hypertension and discusses the various types of the disease.

Primary pulmonary hypertension: insights into pathogenesis from epidemiology

Primary pulmonary hypertension (PPH) is a rare disease that affects young people predominantly of female gender. Early epidemiologic studies have shown that the diagnosis is usually made 1 to 2 years after symptoms onset, and the mean survival is reduced to 2 to 3 years thereafter. New insights into the pathogenesis of PPH by epidemiologic studies may be obtained through the utilization of informatic technologies coupled to a clear definition of the disease. Early stages of precapillary pulmonary hypertension could be identified through screening tests like echocardiography in populations with higher incidence, such as familial PPH and the conditions associated with pulmonary hypertension. These latter conditions are hemodynamically and pathologically similar to the primary form, and they can give insight into several possible aspects of the pathogenesis of PPH. Prospective registries are very useful in coordinating the collection of epidemiologic data, and new technologies, such as informatics, may improve the management and the continuous updating of the databases.

Pulmonary hemodynamics modify the rat pulmonary artery response to injury. A neointimal model of pulmonary hypertension

Hemodynamic factors have profound influences on blood vessels. To test the hypothesis that hemodynamic conditions modify the pattern of remodeling in response to injury, monocrotaline (MCT) injury in Sprague-Dawley rats was followed 1 week later by left pneumonectomy to increase blood flow to the right lung. Right pulmonary artery remodeling in these MCT plus pneumonectomy animals was compared with animals receiving MCT or pneumonectomy alone. Neointimal changes developed in more than 90% of all right lung intra-acinar vessels 5 weeks after MCT injury (4 weeks after pneumonectomy). Neointimal lesions did not develop in untreated animals or in animals receiving MCT or pneumonectomy only. Animals with a neointimal pattern of remodeling developed severe right ventricular hypertrophy (RVH) whereas animals with a medial hypertrophy pattern of remodeling (MCT only) developed moderate RVH compared with control animals. Neointimal lesions and RVH were similar whether injury preceded pneumonectomy or vice versa. To exclude the possibility that neointimal lesions resulted from injury plus post-pneumonectomy compensatory lung growth, rather than injury plus increased flow, a left subclavian-pulmonary artery anastomosis was substituted for pneumonectomy. Neointimal lesions and severe RVH developed in these animals but were not seen in animals receiving either MCT or anastomosis only. These studies demonstrate an important role for hemodynamics in determining the pattern of pulmonary vascular remodeling after injury.

Pulmonary vascular disease in a child with atrial septal defect of the secundum type and type I glycogen storage disease

A rare combination of atrial septal defect of the secundum type and type I glycogen storage disease was seen with early fatal outcome due to rapidly progressive severe pulmonary vascular disease. Possible reasons for the unexpected, rapidly progressive pulmonary vascular disease are discussed.

Pulmonary vascular disease in secundum atrial septal defect in childhood: an unusual evolution

Reported is a case of a 16-month-old girl with an isolated atrial septal defect in whom severe pulmonary hypertension has developed in 26 months in spite of an important functional gradient across the pulmonic valves at a first catheterization. Individual susceptibility to an increased pulmonary blood flow is evoked.

Secundum atrial septal defect with severe pulmonary hypertension. Open lung biopsy diagnosis of operative indication

In 14 of 15 patients ranging in age from 1 to 62 years (mean of 34) with secundum atrial septal defect (ASD) and pulmonary hypertension over 60 mm Hg peak pressure, operative indication was determined by morphometric diagnosis of open biopsy of lung specimens. In one patient, open lung biopsy was also performed during corrective surgery. Pulmonary arterial changes in the 15 patients were grouped into four classifications as follow: (1) plexogenic pulmonary arteriopathy (six patients); (2) thromboembolism in small pulmonary arteries (three patients); (3) "musculoelastosis," intimal proliferation of longitudinal smooth muscle bundles and elastic fibers (three patients); and (4) combinations of (1), (2) or (1), (3) (three patients). We conclude concerning the operative indication that group 2 patients are operable in all cases and group 1 patients with Yamaki's index of pulmonary vascular disease of 2.2 or less; group 3 patients with the absence of complete occlusion of the small pulmonary arterial lumen are operable, and patients with clear evidence of severe plexogenic pulmonary arteriopathy in group 4 are not operable. Comparative analysis of pulmonary pathology and hemodynamic performance revealed that open lung biopsy should be performed to determine operative candidacy in cases with a pulmonary vascular resistance greater than 8 unit X m2, which is considered to represent the borderline of operability.

Pulmonary hypertension in isolated secundum atrial septal defect: high frequency in young patients

Out of 709 consecutive patients with isolated secundum atrial septal defect, the pulmonary artery systolic pressure was greater than 50 mm Hg in 118 patients (17%). Pulmonary hypertension was present in 13% of patients under 10 years and in 14% aged 11 to 20 years. The Eisenmenger reaction was present in 9% of the 709 patients. The frequency of the Eisenmenger reaction was high in young patients and was not significantly different in patients in the first and second decades as compared to older patients. None of our patients with pulmonary hypertension resided at high altitude. The high frequency of pulmonary hypertension in our young patients cannot be satisfactorily explained. Autopsy studies suggest that in some, pulmonary hypertension is due to the persistence of the fetal pulmonary vascular pattern.

Atrial septal defect in the older patient. A clinical and hemodynamic study in patients operated on after age 35

Twenty-four patients over 35 years of age with a secundum atrial septal defect (ASD) had a clinical and hemodynamic assessment prior to surgical closure and a follow-up assessment an average of 6 years afterward. All were initially in functional class III or IV. Twenty-three patients had a moderate to large left-to-right shunt. Five had elevated pulmonary vascular resistance (PVR); all had moderate to severe pulmonary hypertension. Left ventricular dysfunction (LVD) was found in 17.

Following surgical closure, 22 patients showed sustained clinical improvement and were in class I or II. The mean pulmonary artery pressure fell to normal or mildly elevated values in 21. The PVR was now elevated in 14 patients, suggesting continued progression of obliterative pulmonary vascular disease. Three had small residual shunts. LVD, however, persisted after operation, which may reflect underlying myocardial pathology unrelated to the ASD.

Operative closure of ASD, therefore, is recommended for disabled patients over 35, even if they have moderate pulmonary hypertension or congestive heart failure.

Natural history of atrial septal defect

The natural history of atrial septal defect becomes increasingly difficult to determine with the number of patients having operations. The expectation of life has been calculated for those surviving their first year by two quite independent methods: (I) from 121 reported necropsies and (2) by calculating the mortality rates each decade from 25 deaths among 167 personal or reported patients followed for 663 patient-years. They were patients rather than the ideal of unselected children, but many were symptomless when first seen and sent only because of their physical signs. The two methods gave close agreement about the percentages still living at the end of each decade, generally within +/- 1 or 2 per cent and only as much as +/- 4.5 per cent in the second decade. With the relatively small numbers involved, such close agreement is probably fortunate. The mortality rates are low for the first two decades, 0.6 and 0.7 per cent per annum. In successive decades they rise from 2.7, to 4.5, to 5.4, and 7.5 per cent per annum. One-quarter have died just before their 27th year, half by their 36th year, three-quarters by 50, and 90 per cent by 60 years. The arithmetical mean age of death is 37.5 +/- 4.5 years. The median is also 37 years. The mode is widely spread through the 3rd to 6th decades. All these figures are better than those for aortic stenosis, coarctation of the aorta, and pulmonary stenosis. In and after the fourth decade they approximate more closely to the figures for aortic stenosis and coarctation but are still better than those for pulmonary stenosis. They are improved on only by those with a persistent ductus.

Natural history and prognosis of atrial septal defect

A series of 128 consecutive cases of atrial septal defect in adult patients was analyzed from the standpoint of the course and prognosis. The ages of the patients ranged from 18 to 67 years and the ratio of men to women was 1 to 2. Age distribution when compared with life expectancy tables indicated reduced life expectancy. Clinical analysis revealed that three quarters of the patients were symptomatic, but symptoms were mild to moderate and usually nonprogressive. Hemodynamic analysis revealed significant pulmonary hypertension in 22% of the series, of which 15% had high pulmonary vascular resistance, and significant arterial hypoxemia in 14%. The most serious risk factor in atrial septal defect is severe pulmonary hypertension. This complication, which develops in about 14% of patients with atrial septal defect when they are between 20 and 40 years of age, may be rapidly progressive, leading to shunt reversal, disability, and death. Once established, pulmonary hypertension may progress even when the defect is surgically closed. Heart failure occurs usually in older individuals and is associated mostly with chronic atrial arrhythmias rather than pulmonary hypertension.

Effect of flow and pressure on pulmonary vessels. A semiquantitative study based on lung biopsies

Of a total of over 1,000 lung biopsies, carried out over a 3½-year period on patients, the great majority of whom were operated on for various acquired or congenital cardiac diseases, 86 were on patients operated upon for atrial septal defect, 99 on patients with a ventricular septal defect, and 82 on patients with patent ductus arteriosus. The morphological data, particularly with regard to the lung vessels, were correlated with hemodynamic findings in these patients. In atrial septal defect the pulmonary vessels did not differ significantly from those in normal controls of the same ages. Notably there were no differences between patients with relatively low pulmonary arterial flow and those with high flow. In patent ductus arteriosus the only difference was an increase in intimal fibrosis of the pulmonary arteries as compared to normals. In ventricular septal defect, on the other hand, there was an increase in thickness of both media and intima and also in incidence of hemosiderosis. These changes did show a correlation with increased pulmonary arterial pressure but not with pulmonary arterial flow. It is concluded that pulmonary hypertension may provoke these vascular lesions and conversely may be maintained or increased by these lesions, while an increased flow in itself has little or no effect with regard to the morphological alterations, if it is not accompanied by pulmonary hypertension.