Echocardiography, 6-Minute Walk Distance, and Distance-Saturation Product as Predictors of Pulmonary Arterial Hypertension in Idiopathic Pulmonary Fibrosis

BACKGROUND: Pulmonary arterial hypertension (PAH) is frequently seen in patients with idiopathic pulmonary fibrosis (IPF). We sought to examine the performance of echocardiography, 6-min walk test (6MWT) distance, distance-saturation product (DSP), and pulse oximetry (S_pO2) in detecting underlying PAH in IPF.

METHODS: 626 lung transplanted patients from February 1990 to December 2007 were considered. Subjects with pre-transplant diagnosis of IPF were evaluated. Based on findings in pre-transplant right heart catheterization, the presence or absence of PAH was recorded. Right-ventricle systolic pressure, 6MWT distance, DSP, and lowest S_pO2 during 6MWT were compared in PAH and non-PAH groups. Receiver operating characteristic curves for each variable to assess prediction of PAH were constructed.

RESULTS: 131 patients were transplanted due to IPF. Of these 131 patients, 58 (44%) were eligible. PAH was diagnosed by right heart catheterization in 25 (43%) of 58 eligible patients. The mean pulmonary arterial pressure in PAH patients was 33 mm Hg, and 19 mm Hg in non-PAH patients (P = .001). 6MWT distance was 321 m in the PAH group, and 346 m in the non-PAH one (P = .38). DSP in PAH subjects was 272 meters% and 286 meters% in those with no PAH (P = .57). The lowest S_pO2 in the PAH and non-PAH groups were 84% and 82%, respectively (P = .38). The diagnostic accuracy of the echocardiography exceeded that of the other variables (area under the curve 0.72).

CONCLUSIONS: Right-ventricle systolic pressure measured by echocardiography, by 6MWT distance, by DSP, or by S_pO2 performs poorly in detecting PAH in IPF. Measured by right heart catheterization, right-ventricle systolic pressure performs better to predict PAH in IPF.