Novel Computed Tomography Angiography Parameter Is Associated with Low Cardiac Index in Patients with Chronic Thromboembolic Pulmonary Hypertension: A Retrospective Analysis

Chronic thromboembolic pulmonary hypertension (CTEPH) is a complication of incomplete resolution of acute pulmonary embolism. We hypothesize changes in CT Hounsfield Unit gradient (HU-Delta) created by the dispersion of IV contrast through the downstream blood pool correlate with cardiac index (CI). We sought to compare HU-Delta with invasively obtained CI. Methods: We completed a retrospective analysis of CTEPH patients in which individuals with low CI (<2.2-L/min/m(2)) were identified. Both absolute and fractional HU-Delta were derived from pulmonary CTA by subtracting the HU value of the left atrium (LA) and left ventricle (LV) from the main pulmonary artery (MPA) (absolute) and expressing them as a percentage of MPA-HU (fractional) on static axial images. These were compared between low and normal CI. Results: Of the 237 patients, 50.2% were female, 53.2% were White, 36.7% were Black. Hemodynamics were mean pulmonary artery (PA) pressure = 45.4 +/- 11.2-mmHg, pulmonary vascular resistance = 9.2 +/- 4.4-WU, CI = 2.05 +/- 0.48-L/min/m(2). There was a higher mean MPA-HU = 391.1 +/- 113.6 than LA-HU = 251.6 +/- 81. In patients with low CI, the HU-Delta was higher, HU-Delta MPA-LA was 148.9 +/- 78.4 vs. 124.5 +/- 77.2 (p = 0.02), and HU-Delta MPA-LV was 170.7 +/- 87 vs. 140 +/- 82 (p = 0.009). A HU-Delta MPA-LA = 118 had a sensitivity of 75.6% and specificity of 77% to detect low CI, AUC 0.61, p = 0.003. A HU-Delta PA-LV = 156 had a sensitivity of 77% and specificity of 53% to detect low CI, AUC = 0.62, p = 0.001. A fractional reduction HU-Delta MPA-LA of 35% had a sensitivity and specificity of 79% and 53%, respectively, to detect low CI (AUC 0.65, p < 0.001). A fractional reduction of the HU-Delta MPA-LV of 40% had a sensitivity and specificity of 80% and 55%, respectively, to detect low CI (AUC 0.65, p < 0.001). HU Delta were highly reproducible (Kappa = 0.9, p < 0.001, 95% CI 0.86-0.95). Conclusions: High HU Delta between MPA-LA and MPA-LV were associated with low CI in patients with CTEPH.