Value of Tracheal Bifurcation Angle Measurement as a Radiographic Sign of Left Atrial Enlargement in Dogs

Abstract

An increased tracheal bifurcation angle on the dorsoventral projection is described as a sign of left atrium enlargement in dogs, with a normal range of 60-90 degrees reported. However in people, this angle is a poor indicator of left atrial size. Our purpose was to evaluate the value of the tracheal bifurcation angle for differentiating normal from enlarged left atrium in dogs. Dorsoventral radiographs and echocardiograms of 33 healthy and 73 dogs with confirmed degenerative myxomatous mitral valve disease were evaluated. Left atrial size was classified according to the echocardiographic left atrium to aorta ratio, as normal, mildly, moderately, or severely enlarged. Independent samples t-tests were used to compare the bifurcation angle between groups. A significant difference was observed between the angle of dogs with normal left atrium (68.1 +/- 8.5 degrees, range: 51.3-92.4 degrees) and dogs with enlarged left atrium (75.8 +/- 8.2 degrees, range: 57.3-91.7 degrees). A significant difference was also noted between the angle of normal dogs and those with moderate (75.5 +/- 6.8 degrees, range: 62.8-88.7 degrees) and severe (80.4 +/- 7.7 degrees, range: 64.7-91.7 degrees) left atrial enlargement, as well as between dogs with mild (70.7 +/- 7.2 degrees, range: 57.3-89.9 degrees) and severe enlargement. Using two discriminators, 85.1 degrees and 76.6 degrees, the bifurcation angle had a specificity of 92.6% and 88.9%, respectively, for identifying left atrial enlargement, and a sensitivity of 15.4% and 40.4%. Although significant differences were observed between dogs with normal and increased left atrial size, the large degree of overlap in the range of bifurcation angles and its poor sensitivity make the measurement of this angle of little value for diagnosing left atrial enlargement.

Diagnostic Accuracy of Tests Based on Radiologic Measurements of Dogs and Cats: A Systematic Review

“…Initial literature search found 4264 papers, which were reduced to 244 on the basis of title, to 43 of the basis of abstract, and to 26 by detailed review (Fig. ).…”

“…Radiologic measurements used in studies retrieved by search were predominantly linear or ratio, with relatively few examples of angle, area or volume measurements. The studies retrieved by this search represent a more heterogeneous group than is usually obtained by systematic reviews focused on a single diagnosis.…”

Measurements of the Pulmonary Vasculature on Thoracic Radiographs in Healthy Dogs Compared to Dogs With Mitral Regurgitation

“…The following was measured on thoracic radiographs of both groups: (1) the diameter of the right cranial pulmonary artery and vein at the level of the fourth rib; (2) the diameter of the fourth rib at a point just distal to the spine; (3) the distal and left sides of the summation shadow created by the right caudal pulmonary artery and vein with the ninth rib were measured by two radiologists (OHJ and OJY) who were blinded to the group (Fig. 1).…”

“…Thus, early detection of these changes with high sensitivity is useful to diagnose mitral regurgitation. Several studies have been performed about atrial enlargement on radiographs; 2,3 however, no study has addressed pulmonary vein enlargement. Furthermore, not much is known about the correlation between pulmonary vein enlargement and severity of mitral regurgitation in dogs.…”

Pulmonary Hypertension in the Dog

“…In dogs with PH associated with MMVD, cardiomegaly and left atrial and ventricular dilation are often the main radiographic features (Fig 1 C and D). These aspects are evident as an increased long axis and short axis of the cardiac silhouette [54] and increased tracheal bifurcation angle [55]; moreover, dilated pulmonary vessels, and an interstitial and/or alveolar pattern can be present in cases of cardiogenic pulmonary oedema [56]. In a recent study evaluating the radiographic features of dogs with MMVD and PH, a short-axis diameter of the cardiac silhouette on lateral projection of > 5.2 thoracic vertebrae and a sternal contact of > 3.3 thoracic vertebrae were signifi cantly correlated with PH with a predictive accuracy of 85.9%…”