Pulmonary arterial hypertension (PAH), once considered a rare complication of sickle cell disease (SCD) and thalassemia, appears to be more common in adults with hemoglobinopathy than previously appreciated. On prospective screening of adults with SCD, approximately one-third of adults are found on echocardiography to have a tricuspid regurgitant jet velocity (TRV) of 2.5 m/s or higher, many of whom are asymptomatic. Dyspnea on exertion is the most common presenting symptom. This TRV abnormality is a marker for approximately 40% 3-year mortality in adults, and it is associated with laboratory values suggestive of more severe intravascular hemolysis. Release of hemoglobin and arginase from lysed red cells causes scavenging of nitric oxide (NO) and catabolism of L-arginine, the obligate substrate for NO synthase. The resulting impairment in NO bioavailability is associated with pulmonary vasoconstriction, endothelial dysfunction, thrombosis, and eventual development of plexogenic arterial lesions, the histological hallmark of all forms of PAH. Undoubtedly, additional pathophysiological mechanisms will also play a role in its multifactorial pathogenesis. Early data from children with SCD indicate a similar prevalence of elevated TRV, but the prognostic implications of this remain to be established. Individual patient diagnosis of PAH requires confirmation by right heart catheterization studies and individualized management. Hemolysis-associated PAH with impairments in NO bioavailability is being identified in thalassemia and other hemolytic disorders, and may be a general consequence of long-standing, severe intravascular hemolytic anemia.Keywords sickle cell; thalassemia; pulmonary hypertension; nitric oxide; arginase Pulmonary hypertension is a complication of sickle cell disease (SCD) and thalassemia gaining considerable attention in the past 4 years. Cor pulmonale, the clinical syndrome of right ventricular failure, has been considered for decades to be a rare, but well-known, terminal complication in adults with both hemoglobinopathies [1,2]. As the survival of patients with hemoglobinopathies has improved dramatically in the last forty years, the prevalence of such chronic complications has increased. Well-documented studies of pulmonary arterial hypertension (PAH) have drawn the attention of the hematology community to its frequent occurrence and poor prognosis [3][4][5][6][7]. This article will review the current understanding of hemoglobinopathy-associated pulmonary hypertension, with special attention to the most recently developing data in children.
PREVALENCE AND PROGNOSISIn the last few years, echocardiographic screening studies have suggested that the prevalence of hemoglobinopathy-associated PAH is much higher than previously known. In SCD, approximately one-third of adult patients have an elevated tricuspid regurgitant jet velocity (TRV) of 2.5 m/s or higher, a threshold that correlates in right heart catheterization studies to a pulmonary artery systolic pressure of at least 30 mm Hg [8][9]...