Prevalence and risk factors for pulmonary artery systolic hypertension among sickle cell disease patients in Nigeria

Abstract

Pulmonary artery systolic hypertension is common and associated with increased mortality among adult sickle cell disease (SCD) patients in the United States. Although the prevalence of SCD is highest in sub-Saharan Africa, the frequency of pulmonary artery systolic hypertension and the risk factors for the development of pulmonary hypertension have not been reported from Africa. We studied 208 hydroxyurea naïve Nigerian SCD patients at steady state and 94 healthy controls. Pulmonary artery systolic hypertension was defined prospectively as tricuspid regurgitant jet velocity > or =2.5 m/sec. Results were compared with a previously published US prospective SCD cohort. Only 7% of Nigerians compared with 46% of US adults with SCD were >35 years. Tricuspid regurgitant jet velocity was > or =2.5 m/sec in 25% of Nigerian SCD patients. Higher jet velocity was associated with greater serum globulin (P = 0.002), blood urea nitrogen (P = 0.019) and lactate dehydrogenase concentrations (P = 0.026) and with inability to walk >300 m in 6 min (P = 0.042). Compared with the US cohort, Nigerian patients had more hemolysis as indicated by lower hemoglobin and higher lactate dehydrogenase concentrations (P < or = 0.003). Pulmonary hypertension is common among Nigerian SCD patients. The public health implication of this finding is significant considering the potential number of individuals at risk for this complication. Better understanding of the long term outcome of pulmonary hypertension and causes of death in SCD and the institution of preventive measures are major public health challenges for Africa. The inclusion of African sites in sickle cell pulmonary hypertension clinical trials should be encouraged.

Figure 1

Box plots depicting median and interquartile ranges of tricuspid regurgitant jet velocity (TRV) values in controls and patients with sickle cell disease.

Figure 2

Functional consequence of elevated tricuspid regurgitant velocity in patients with sickle cell disease. Increasing proportions of patients are unable to walk more than 300 minutes in six minutes according to three categories of increasing jet velocity.

Figure 3

Comparison of age distributions and tricuspid regurgitant jet velocities between the present Nigerian cohort and the previously published (5) NIH-Howard University US cohort of sickle cell disease patients. Proportions with jet velocities ≥2.5 m/sec according to age categories shown in a. Jet velocity declined with increasing age in the Nigerian cohort (R = −0.15; P = 0.053) but increased with increasing age in the US cohort (R = 0.18; P = 0.012) (Figure 3b).