Jake Johnson, Jenelle Soppet, James Sutherland-Smith, Amy Sato, Suzanne M. Cunningham, Keaton Cortez, Agustina Anson
Background
Left atrial enlargement (LAE) in dogs is a key prognostic indicator for cardiac diseases, especially myxomatous mitral valve disease (MMVD). Echocardiography and thoracic radiography are standard methods for assessing left atrial size, but there are limited data on using computed tomography (CT) for this purpose. Given that non-ECG-gated CT is commonly performed for non-cardiac reasons, this study aimed to determine whether the left atrium-to-aortic diameter ratio (LA:Ao) measured on non-ECG-gated CT could accurately detect LAE when compared with echocardiography.
Methods
This retrospective study analyzed records from 123 dogs that underwent both non-ECG-gated thoracic CT and echocardiography within one month at the Cummings School of Veterinary Medicine (2008–2019). Echocardiography served as the gold standard, with LAE defined as a 2D echocardiographic LA:Ao ≥ 1.6. CT measurements were performed on post-contrast transverse images by blinded observers, measuring the widest left atrial diameter and the corresponding descending aortic diameter on the same slice. Logistic regression and receiver operating characteristic (ROC) analyses evaluated the diagnostic performance of CT LA:Ao for detecting LAE. Intra- and interobserver variability were also assessed.
Results
Out of 123 dogs, 33 had LAE on echocardiography and 90 had normal atrial size. The CT LA:Ao ratio demonstrated poor sensitivity but high specificity. A cutoff value of 3.4 yielded 97% specificity, 15% sensitivity, 71% positive predictive value, and 76% negative predictive value. The area under the ROC curve was 0.61, indicating poor overall performance. Observer measurements were consistent across raters and timepoints. Body weight differed significantly between groups, but age and aortic diameter did not.
Limitations
Key limitations included the retrospective design, variable sedation and anesthesia protocols, differing CT slice thicknesses (3–5 mm), and absence of ECG gating. The study also used the descending aorta instead of the aortic cusps for measurements, which may have affected comparability with echocardiographic ratios. Additionally, most LAE cases were mild, potentially underrepresenting dogs with severe enlargement.
Conclusions
Non-ECG-gated CT measurement of the left atrium-to-aorta diameter ratio is not a sensitive tool for detecting left atrial enlargement in dogs. Although a CT LA:Ao ≥ 3.4 is highly specific and may warrant echocardiographic follow-up, the overlap between normal and abnormal dogs limits clinical utility. Future studies should consider standardized protocols, use of multiplanar reconstructions, and comparison with advanced imaging modalities to improve diagnostic accuracy.
Postcontrast transverse CT image of the thorax at thelevel of the left atrium in a 19.6 kg Beagle dog with left atrial enlargementidentified on 2D echocardiography. The CT left atrium-to-aorta (LA:Ao)measurement technique is demonstrated. The left atrial transverse diam-eter was measured at the point of maximal left atrial width, not includingthe pulmonary veins or left auricle (solid line, 19.9 mm). The short-axisaortic diameter was measured (dashed line, 8.8 mm). The CT LA:Ao ratioin this dog was 2.3
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