There is another Chris Lam(b)

Journal of Veterinary Internal Medicine, 2021

Author

Obi Veterinary Education
August 27, 2025

Christopher Lam, Brad J. Gavaghan, Fiona E. Meyers

Background
Myxomatous mitral valve disease (MMVD) is the most common acquired cardiac condition in dogs, leading to left atrial (LA) enlargement, which is a predictor of congestive heart failure (CHF). While echocardiography is the gold standard for diagnosing LA enlargement, it is not always available in general practice. Radiographic methods, such as vertebral heart size (VHS) and vertebral left atrial size (VLAS), have been proposed for assessing cardiac size. This study introduces the modified-vertebral left atrial size (M-VLAS) method and evaluates its accuracy compared to existing radiographic indices.

Methods
A retrospective case-control study was conducted using 64 dogs with various stages of MMVD and 6 healthy controls. LA measurements were obtained using M-VLAS, VLAS, VHS, and radiographic left atrial dimension (RLAD) from thoracic radiographs. These values were correlated with echocardiographically measured LA-to-aortic root ratio (LA/Ao). Receiver operating characteristic (ROC) curve analysis was performed to determine the diagnostic performance of each method.

Results
M-VLAS showed a strong correlation with LA/Ao (r = 0.77, P < 0.001), performing better than VHS (r = 0.67, P < 0.001). ROC analysis demonstrated M-VLAS had the highest area under the curve (AUC = 0.97), significantly outperforming VHS (P = 0.03). A cutoff of ≥3.4 vertebrae in M-VLAS predicted LA enlargement with 92.7% sensitivity and 93.1% specificity.

Limitations
The retrospective design limited control over case selection, and breed-related variations in cardiac dimensions were not assessed. Interobserver variability, though evaluated, may still influence results. The study population was relatively small, particularly for the control group.

Conclusions
M-VLAS provides a reliable and repeatable method for identifying LA enlargement in dogs with MMVD, outperforming VHS and offering an alternative when echocardiography is unavailable. The method enhances the diagnostic accuracy of thoracic radiographs, aiding in the early identification of dogs that may benefit from medical management. Further studies are needed to evaluate its applicability across different breeds.

Measurements of M-VLAS, VLAS, VHS, and RLAD demonstrated on the same right lateral inspiratory radiograph of a dog with stage B2 MMVD. All methods take their respective measurements from the cranial edge of the T4 vertebral body extending caudally, parallel to the vertebral column, rounded to the nearest 0.1 vertebrae. A. MVLAS—an initial line (yellow)—is drawn from the centre of the most ventral aspect of the carina to the intersection between the most caudal aspect of the left atrium and the dorsal border of the caudal vena cava. A second additional line (red) is then drawn from the most distal border of the left atrium towards the first line, intersecting it perpendicularly. Two separate straight lines corresponding to the lengths of the first 2 lines (yellow + red) were then drawn from the cranial edge of the T4 vertebral body extending in a caudal direction, ventral and parallel to the vertebral canal. The M-VLAS for this dog is 2.2 + 1.4 = 3.6 vertebrae (v). (Note: the first value being the VLAS.) B. Vertebral left atrial size (VLAS = 2.2v)—yellow line C. Vertebral heart score (VHS = 5.7 + 4.6 = 10.3v), vertical axis—thick white line; horizontal axis—thin white line. D. Radiographic left atrial dimension (RLAD = 2.0v)—dashed white lines represent the VHS vertical and horizontal axes, constituting the foundation for the RLAD measurement (green line), which bisects the VHS intersection.

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