CT scan-measured pulmonary artery to aorta ratio and echocardiography for detecting pulmonary hypertension in severe COPD

Abstract

Background: 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.

Methods: 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).

Results: 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.

Conclusions: A PA:A ratio>1 on CT scan outperforms echocardiography for diagnosing resting PH in patients with severe COPD.

Figure 1.

Measurement of the PA and A diameters at the PA bifurcation. A = aorta; PA = pulmonary artery.

Figure 2.

Linear relationships between invasive hemodynamics, PA diameter and PA:A ratio from CT scan as well as PA systolic pressure by echocardiography. mPAP = mean PA pressure; mPCWP = mean pulmonary capillary wedge pressure; PASP = echocardiographic PA systolic pressure; sPAP = systolic PA pressure. See Figure 1 legend for expansion of other abbreviations.

Figure 3.

A, Receiver operator characteristic curve with the PA:A ratio at identifying mPAP > 25 mm Hg. B, Receiver operating characteristic curve with the echocardiographic PA systolic pressure at identifying mPAP > 25 mm Hg. AUC = area under the curve. See Figure 1 and 2 legends for expansion of other abbreviations.