Pathophysiology and treatment of pulmonary hypertension in sickle cell disease

Abstract

Pulmonary hypertension affects ∼10% of adult patients with sickle cell disease (SCD), particularly those with the homozygous genotype. An increase in pulmonary artery systolic pressure, estimated noninvasively by echocardiography, helps identify SCD patients at risk for pulmonary hypertension, but definitive diagnosis requires right-heart catheterization. About half of SCD-related pulmonary hypertension patients have precapillary pulmonary hypertension with potential etiologies of (1) a nitric oxide deficiency state and vasculopathy consequent to intravascular hemolysis, (2) chronic pulmonary thromboembolism, or (3) upregulated hypoxic responses secondary to anemia, low O2 saturation, and microvascular obstruction. The remainder have postcapillary pulmonary hypertension secondary to left ventricular dysfunction. Although the pulmonary artery pressure in SCD patients with pulmonary hypertension is only moderately elevated, they have a markedly higher risk of death than patients without pulmonary hypertension. Guidelines for diagnosis and management of SCD-related pulmonary hypertension were published recently by the American Thoracic Society. Management of adults with sickle-related pulmonary hypertension is based on anticoagulation for those with thromboembolism; oxygen therapy for those with low oxygen saturation; treatment of left ventricular failure in those with postcapillary pulmonary hypertension; and hydroxyurea or transfusions to raise the hemoglobin concentration, reduce hemolysis, and prevent vaso-occlusive events that cause additional increases in pulmonary pressure. Randomized trials have not identified drugs to lower pulmonary pressure in SCD patients with precapillary pulmonary hypertension. Patients with hemodynamics of pulmonary arterial hypertension should be referred to specialized centers and considered for treatments known to be effective in other forms of pulmonary arterial hypertension. There have been reports that some of these treatments improve SCD-related pulmonary hypertension.

Figure 1

Schematic representations of pulmonary hypertension. (A) Schematic cross-sectional representation of a normal pulmonary arteriole and a pulmonary arteriole affected by pulmonary hypertension. (Adapted from Pugliese et al.) (B) Schematic representation of site of initiation of elevated pulmonary arterial pressure of precapillary pulmonary hypertension, postcapillary pulmonary hypertension, and CTEPH. L.V., left ventricle; PH, pulmonary hypertension; R.A., right atrium; R.V., right ventricle.

Figure 2

Proposed algorithm for evaluation of pulmonary hypertension related to sickle cell disease. 6MWD, 6-minute walk distance; ANA, anti-nuclear antibody; CXR, chest X-ray; EKG, electrocardiogram; LFTs, liver function tests; mPAP, mean pulmonary artery pressure; NT-pro-BNP, N-terminal pro–brain natriuretic peptide; PAWP, pulmonary artery wedge pressure; PH, pulmonary hypertension; PVR, pulmonary vascular resistance; SCD, sickle cell disease; TRV, tricuspid regurgitation velocity. Note: Echocardiography should be performed while patients are clinically stable. PAH therapy is to be considered on the basis of a weak recommendation and very low-quality evidence. Reprinted with permission of the American Thoracic Society. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society.