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

## TL;DR

A new CT scan measurement helps identify heart function issues in patients with a type of lung hypertension.

## Contribution

A novel CT angiography parameter (HU-Δ) is shown to correlate with low cardiac index in CTEPH patients.

## Key findings

- Higher HU-Δ values in the pulmonary artery compared to the left atrium and ventricle were associated with low cardiac index.
- Thresholds of HU-Δ showed moderate sensitivity and specificity for detecting low cardiac index in CTEPH patients.
- The HU-Δ measurement was highly reproducible across evaluations.

## Abstract

Chronic thromboembolic pulmonary hypertension (CTEPH) is a complication of incomplete resolution of acute pulmonary embolism. We hypothesize changes in CT Hounsfield Unit gradient (HU-Δ) created by the dispersion of IV contrast through the downstream blood pool correlate with cardiac index (CI). We sought to compare HU-Δ with invasively obtained CI. Methods: We completed a retrospective analysis of CTEPH patients in which individuals with low CI (<2.2-L/min/m2) were identified. Both absolute and fractional HU-Δ 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/m2. There was a higher mean MPA-HU = 391.1 ± 113.6 than LA-HU = 251.6 ± 81. In patients with low CI, the HU-Δ was higher, HU-ΔMPA-LA was 148.9 ± 78.4 vs. 124.5 ± 77.2 (p = 0.02), and HU-ΔMPA-LV was 170.7 ± 87 vs. 140 ± 82 (p = 0.009). A HU-ΔMPA-LA = 118 had a sensitivity of 75.6% and specificity of 77% to detect low CI, AUC 0.61, p = 0.003. A HU-ΔPA-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-ΔMPA-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-ΔMPA-LV of 40% had a sensitivity and specificity of 80% and 55%, respectively, to detect low CI (AUC 0.65, p < 0.001). HU Δ were highly reproducible (Kappa = 0.9, p < 0.001, 95% CI 0.86–0.95). Conclusions: High HU Δ between MPA-LA and MPA-LV were associated with low CI in patients with CTEPH.