Purpose: CT pulmonary angiography(CTPA), which is often performed for suspected pulmonary embolism(PE), may suggest the presence of pulmonary hypertension(PH) by the diameter of the pulmonary artery(PA), the size of the right ventricle and reflux.
The aim of this study is to examine the association between CTPA parameters known to suggest PH, and another parameter – Time to Threshold(TTT), which is defined as the duration of time it takes the contrast material to reach a 100HU threshold in the PA in a large cohort of patients.
Material & Methods: A retrospective analysis of consecutive patients who had CTPA during 01/2014-12/2015, with TTT data. The CTPA were reviewed to assess the diameter of the PA, grade the degree of reflux of contrast into the IV(1-6), while the volumes of the right ventricle(RV) and atrium(RA) were calculated with a volumetric analysis software, and adjusted for body surface area(BSA). We used Pearson’s and Spearman’s correlation coefficients to study the association between TTT and PA diameter, and RV and RA volumes, and T-test for the association between TTT and reflux, categorized into negligible(grades 1-3), or substantial (grades 4-6). Multivariate linear regression for the association between TTT and other cardiac parameters while controlling for patients’ age.
Results: Following exclusion of patients diagnosed by the CTPA with PE, the final cohort included 1098 patients, (42.4% Males), mean age 68.0±17.58, mean TTT 11.3±3.3 seconds.
A significant positive moderate correlation was found between TTT and increased RA volume (r=0.32), RV volume (r=0.32), and PA diameter (r =0.23), (p‹0.001 in all).
After excluding patients with background of left heart diseases and atrial fibrillation (n=280), and following adjustment to age, within the remaining cohort without cardiac diseases (n=818), increased TTT remained to be associated with increased RA volume (r=0.22), RV volume (r=0.26), and PA diameter (r =0.20), (p‹0.001). Also, the mean TTT was higher among patients with substantial grades of reflux (grades 4-6) when compared to those with negligible reflux (1-3), (12.01±3.0 seconds vs. 10.82±2.97 seconds, p=0.001).
Conclusions: Longer TTT is associated with increased RV and RA volumes, larger PA diameter and substantial reflux of contrast. This association remains after excluding patients with cardiac disease. Our findings suggest that TTT may be used as a parameter indicating PH. Further studies using echocardiography measurements of the systolic pulmonary arterial pressure as the reference, are on the way to further clarify the factors influencing the TTT of contrast in the PA on CTPA.
