• Biplane area-length method;
  • Canine;
  • Echocardiography;
  • Myxomytous mitral valve disease


Left atrial size is prognostically important in dogs with myxomatous mitral valve disease (MMVD).


To compare the level of agreement in identification of left atrial enlargement (LAE) between the left atrial-to-aortic root ratio (LA : Ao) and left atrial volume using the biplane area-length method indexed to body weight (LA Vol/BW).


Sixty dogs with MMVD and 22 normal dogs were prospectively studied with 2-dimensional echocardiography.


The upper limit of normal for LA Vol/BW was defined as 1.1 mL/kg. LA : Ao was deemed normal if ≤1.5. To define overall disease severity, each dog was assigned a mitral regurgitation severity score (MRSS) based on echocardiographic parameters that did not include left atrial size. ACVIM staging also was utilized.


Of 60 affected dogs, 20 were ACVIM Stage B1, 25 were Stage B2, and 15 were Stage C. LA Vol/BW identified LAE in 12 cases in which LA : Ao was normal; 7 of these were Stage B1 and 5 were Stage B2. This diagnostic disagreement was significant (P = .00012). Of the 12 cases in which diagnostic discrepancies were identified, 5/5 of the B2 dogs and 3/7 B1 dogs had a moderate MRSS, whereas 4/7 B1 dogs had a mild MRSS. No diagnostic discrepancies between LA : Ao and LA Vol/BW were apparent in dogs with a severe MRSS.

Conclusions and Clinical Importance

This study shows evidence of diagnostic disagreement between LA : Ao and LA Vol/BW for assessment of LAE. LA Vol/BW may be superior to LA : Ao for identification of mild LAE.