VLAS calculator for dogs
Enter the vertebral left atrial size from a lateral thoracic radiograph, choose the breed, and copy the summary.
For educational purposes only. This is not veterinary advice and does not replace clinical judgment. Check every result against the source guideline.
Carina to where the left atrium meets the caudal vena cava, counted along the spine from the cranial edge of T4, to the nearest 0.1.
Intervals come from right lateral radiographs.
Enter the VLAS to compare it with the reference interval.
The calculator runs in your browser, and the numbers you enter are never sent anywhere. A VLAS outside a reference interval is a finding to interpret, not a diagnosis.
How to measure VLAS
- On a lateral thoracic radiograph, draw a line from the centre of the most ventral part of the carina to the most caudal part of the left atrium, where it meets the dorsal border of the caudal vena cava.
- Lay a line of the same length along the spine, starting at the cranial edge of T4 and running caudally just ventral and parallel to the vertebral canal.
- Count the vertebrae the line covers, to the nearest 0.1. That count is the VLAS.
Measuring the long and short axis as well? The vertebral heart score calculator takes all three.
VLAS reference intervals by breed
95 percent reference intervals from right lateral radiographs of clinically healthy dogs. The all-breeds interval is from 80 healthy adult dogs in Vezzosi and colleagues. The Borzoi is left out because its paper prints different intervals in the abstract and the tables.
Where the cutoffs come from
Malcolm and colleagues described VLAS in 103 dogs and found 2.3 vertebrae or more a useful predictor of left atrial enlargement on echocardiography. The 2019 ACVIM consensus suggests 3 vertebrae or more where echocardiography is not available. Each figure on this page comes from the paper named beside it.
Common questions
- What is VLAS?
- Vertebral left atrial size is a measurement of the left atrium on a lateral thoracic radiograph, given in vertebrae. Malcolm and colleagues described it in 2018 in dogs with myxomatous mitral valve disease.
- How do you measure VLAS?
- On a lateral thoracic radiograph, draw a line from the centre of the most ventral part of the carina to the most caudal part of the left atrium, where it meets the dorsal border of the caudal vena cava. Lay a line of the same length along the spine, starting at the cranial edge of T4 and running caudally just ventral and parallel to the vertebral canal. Count the vertebrae the line covers, to the nearest 0.1. That count is the VLAS.
- What is a normal VLAS in dogs?
- Vezzosi and colleagues measured 80 healthy adult dogs on right lateral radiographs and found a median of 1.9 vertebrae and a reference interval of 1.4 to 2.2. Body weight, sex and age had no effect. Some breeds sit higher, so a breed interval is a better comparison where one exists.
- What VLAS cutoff suggests left atrial enlargement?
- In Malcolm and colleagues' study of 103 dogs, 88 with mitral valve disease and 15 controls, VLAS of 2.3 or more best matched a long-axis LA:Ao of 2.6 or more, 2.5 or more matched a short-axis LA:Ao of 1.6 or more, and 2.4 or more matched both. The cutoff depends on the echocardiographic definition used.
- How does VLAS relate to ACVIM stage B2?
- The 2019 ACVIM consensus says VLAS of 3 or more likely identifies stage B2 mitral valve disease, and suggests it where echocardiography is not available. It does not stage a dog on its own.
- Should I use the right or left lateral view?
- The reference interval and the breed intervals on this page come from right lateral radiographs. Malcolm and colleagues measured both lateral views.
Also useful: the vertebral heart score calculator and the LVIDDN calculator.
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