Hankin EJ, Sutherland-Smith J, Cunningham S.
Introduction/Purpose: Pulmonary hypertension (PH) is a complex and serious clinical syndrome. Main pulmonary artery (PA) ratio to ascending aorta (Ao) diameter (PAAo), derived from thoracic CT is a well established means of diagnosing PH in people. Echocardiography is the current gold standard for the diagnosis of PH in dogs, however with the advent of routine thoracic CT imaging in veterinary medicine an accurate and simple means for determining the presence of PH would be advantageous.
Methods: This retrospective study of 67 dogs investigated the relationship between echocardiography parameters used to diagnose PH and the PA:Ao ratio. The maximal PA and Ao diameters were measured on transverse slices, near the bifurcation of the right and left pulmonary arteries and the mid-point of the aortic arch respectively.
Results: Peak TR gradient pressures were measured in 36 dogs. Twenty-three of 36 dogs had TR >30 mmHg, suggestive of systolic PH, of which 9/36 dogs had mild (30- 50mmHg), 8/36 had moderate (50-75mmHg), and 6/36 had severe (>75mmHg) elevations in TR. Pulmonic AT:ET was measured in 53 dogs and 15/53 dogs had AT:ET ratio <0.31, suggestive of systolic PH. A significant linear correlation was shown between TR gradient pressures and CT PAAo, both without (r=0.71, p-value < 0.001) and with IV contrast (r=0.70, p-value <0.001). The mean CT PAAo of dogs with moderate (p=0.0004) and severe (p<0.0001) TR pressures were significantly higher than dogs with normal TR pressures. A significant correlation was noted between a CT PA:Ao of >1:1 in dogs with moderate or severe PH (TR >50 mmHg), with a sensitivity of 92% and specificity of 57%. Furthermore, ROC Curve analysis for a PAAo ratio of >1:1 and a cut-off TR pressure gradient of >50mmHg determined a performance accuracy of c = 0.9532. Inter-observer agreement for measurements performed on post-contrast images was good (kl=1 = 0.77, k 1=2= 0.74) and fair on pre-contrast images (kl=1 = 0.40,
k 1=2 = 0.33). Further analysis revealed an estimated difference in ratio measurement between the two radiologists of 0.06 (p=0.01 03).
Discussion/Conclusion: Main pulmonary artery to aorta ratio, as measured on transverse CT images, is a sensitive and repeatable test for the detection of moderate and severe pulmonary hypertension in dogs. This ratio is easily calculated and can be used as an adjunct to echocardiography particularly with the increasing use of thoracic CT in veterinary medicine.