COMPUTED TOMOGRAPHIC MEASUREMENT OF THE MAIN PULMONARY ARTERY TO AORTIC DIAMETER RATIO IN HEALTHY DOGS: A COMPARISON TO ECHOCARDIOGRAPHICALLY DERIVED RATIOS.

ABSTRACT

Indicators of pulmonary hypertension in dogs examined with thoracic computed tomography (CT) are not well established in the veterinary literature. In humans, the main pulmonary artery to aortic diameter ratio (MPAAo) measured via CT, has been shown to be more sensitive than echocardiographic variables for predicting presence and severity of pulmonary hypertension, in some cases. In veterinary literature, the MPAAo has been determined echocardiographically to have an upper limit of about 11. Measurement of this ratio has not been described in dogs using CT. The objectives of this cross-sectional, prospective study were to compare echocardiographic measurement of MPAAo with that obtained via CT, determine if measurement of MPAAo via CT is repeatable and reproducible, and determine the effect of respiration and contrast administration on the measurement of MPAAo via CT. Ten healthy dogs without pulmonary hypertension were anesthetized to undergo thoracic CT using three protocols and echocardiography. The MPAAo was measured three times by three observers for each of the three CT protocols and compared to echocardiographic measurements. The mean MPAAo measured among all observers and CT protocols was 1.108 ± 0.152 (SD). The effect of CT scan protocol on MPAAo significantly differed among the three methods (P = 0.0014), where expiratory scans had lower MPAAo than inspiratory scans. The ratio measured on inspiratory CT scans consistently overestimated MPAAo when compared to echocardiography (bias = 0.226). Findings did not support the echocardiographically derived upper limit of MPAAo as an upper limit for determination of main pulmonary arterial enlargement on CT.