This is an opportune time to reappraise primary pulmonary hypertension. The disease is still incurable but recent laboratory studies are beginning to provide clues to its pathogenesis, and we now know that survival is improved by sustained intravenous prostacyclin treatment and by chronic anticoagulation. In 1991, before these treatments were generally available, the median survival was given as 2.8 years, based on the National Institute of Health Registry.1 In patients with a cardiac index of less than 2 l/min/m², the median survival was 17 months, and untreated patients with a right atrial pressure exceeding 20 mm Hg lived for one month. Recent reports show a 49% survival rate at 30 months and a 25% survival rate at five years in older children and adults treated with continuous intravenous prostacyclin.2Survival is better in younger children.2 In general, the disease is similar in adults and children but there are important differences.

Primary pulmonary hypertension is diagnosed when there is no explanation for the increase in pulmonary arterial pressure. The mean pressure exceeds 25 mm Hg at rest and 30 mm Hg on exercise. The disease is progressive, leading to a gradual increase in right ventricular pressure, right heart failure, functional incapacity, and death. In 1975, a WHO committee defined primary pulmonary hypertension according to morphological criteria, as being caused either by pulmonary …