The Effect of Thalassemia and Other RBC Hemolytic Disorders and Splenectomy on the Frequency of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) has been accepted to be a clinical entity associated with hemoglobinopthies, mostly reported in sickle disease and thalassemia intermedia (TI). Anecdotal cases of PAH in other chronic hemolytic disorders have been reported; many of which have been associated with a prior splenectomy. The pathogenesis of PAH in the non sickle-cell RBC hemolytic disorders has not been well defined and the large variability in its frequency and severity are not clear. We aimed to characterize biomarkers in thalassemia and in other RBC disorders and evaluate the specific role of splenectomy (spleen.) in these diseases.

A total of 106 patients were analyzed: Forty two were regularly transfused thalassemia major (TM), 34 had TI (16 with Hb E/beta thalassemia, 11 with beta thalassemia, and 7 with hemoglobin H-Constant Spring (Hb H-CS); 18 with hereditary spherocytosis (HS) or pyruvate kinase (PK) deficiency, 2 with an unstable Hb (Hb Koln), and 10 with a history of splenectomy for non-RBC related reasons (trauma or chronic ITP). PAH was determined by using a Doppler echocardiogram showing a tricuspid regurgitation jet velocity (TRV) of >2.5m/s. Markers of platelet activation (P- selectin, soluble CD40 (sCD40L); abnormal exposure of Phosphatidyl Serine (PS) on RBCs, thrombin generation (thrombin-anti-thrombin, TAT); increased ventricular pressure strain (brain natriuretic peptide (BNP); plasma free Hb, LDH and NOx, and endothelin-1, soluble vascular cell adhesion molecule (sVCAM) were analyzed.

Nineteen (56%) of the TI patients (15 with beta-TI and 4 with Hb H-CS) had abnormally elevated TRV (Mean 3.0±0.5). The 2 patients with Hb Koln had increased TRV. There were no PAH cases detected among patients with membrane or RBC enzyme deficiencies, neither was there an increased TRV in patients who had been splenectomized without a RBC disorder. There were also no cases of increased TRV in the transfused TM cohort. Patients with TI, in addition to a prior splenectomy and increased hemolysis had increased platelet activation, abnormal RBC PS exposure and anemia. TI patients also had an increase in ET-1 levels, a potent vasoconstrictor. The 2 patients with Hb Koln had increased thrombin generation in addition to hemolysis and absence of spleen.

PAH was not detected in splenectomized patients with only a mild chronic hemolytic disorder or in those without a RBC disorder. In addition to the absence of spleen, a higher rate of hemolysis, resulting in NO scavenging and increase in ET-1 and the involvement of platelet activation or thrombin generation are likely required for the development of dysregulation of the pulmonary vascular function. PAH is rare in TI patients which have not undergone splenectomy; absence of spleen likely enhances the effects of thrombocytosis and platelet activation. Our data indicates that PAH is common in patients with Hb H-CS, mostly splenectomized, and should be screened for. In addition our data shows that blood transfusions reduce the elements of anemia, hemolysis and coagulation activation and prevent the development of PAH in splenectomized and non-splenectomized patients.

No relevant conflicts of interest to declare.