CT Scan-Measured Pulmonary Artery to Aorta Ratio and Echocardiography for Detecting Pulmonary Hypertension in Severe COPD

Abstract

COPD is associated with significant morbidity primarily driven by acute exacerbations. Relative pulmonary artery (PA) enlargement, defined as a PA to ascending aorta (A) diameter ratio greater than one (PA:A>1) identifies patients at increased risk for exacerbations. However, little is known about the correlation between PA:A, echocardiography, and invasive hemodynamics in COPD. A retrospective observational study of patients with severe COPD being evaluated for lung transplantation at a single center between 2007 and 2011 was conducted. Clinical characteristics, CT scans, echocardiograms, and right-sided heart catheterizations were reviewed. The PA diameter at the bifurcation and A diameter from the same CT image were measured. Linear and logistic regression were used to examine the relationships between PA:A ratio by CT scan and PA systolic pressure (PASP) by echocardiogram with invasive hemodynamics. Receiver operating characteristic analysis assessed the usefulness of the PA:A ratio and PASP in predicting resting pulmonary hypertension (PH) (mean pulmonary artery pressure [mPAP]>25 mm Hg). Sixty patients with a mean predicted FEV1 of 27%±12% were evaluated. CT scan-measured PA:A correlated linearly with mPAP after adjustment for multiple covariates (r=0.30, P=.03), a finding not observed with PASP. In a multivariate logistic model, mPAP was independently associated with PA:A>1 (OR, 1.44; 95% CI, 1.02-2.04; P=.04). PA:A>1 was 73% sensitive and 84% specific for identifying patients with resting PH (area under the curve, 0.83; 95% CI, 0.72-0.93; P<.001), whereas PASP was not useful. A PA:A ratio>1 on CT scan outperforms echocardiography for diagnosing resting PH in patients with severe COPD.