Echocardiographic Investigation of Canine Myxomatous Mitral Valvular Disease

Objectives: To further characterize the echocardiographic anatomy of the canine mitral valve in healthy dogs and those affected by myxomatous mitral valve disease (MMVD), and to compare the level of agreement between two methods of assessment of left atrial size in identification of left atrial enlargement in dogs with MMVD.

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

Methods: The length (AMVL), width (AMVW) and area (AMVA) of the anterior mitral valve leaflet and the diameter of the mitral valve annulus in systole (MVAs) and diastole (MVAd) were measured. Left atrial size was evaluated with the left atrial to aortic root ratio (LA:Ao) and by measuring left atrial volume indexed to body weight (LA Vol/BW). All patients were staged using published ACVIM guidelines and separated into groups B1 and B2/C.

Results: Measurements of AMVL, AMVW, AMVA, MVAs and MVAd were all significantly greater in the B2/C group than in the control group. AMVW was significantly greater in group B1 than control. Twelve dogs had left atrial enlargement identified with LA Vol/BW that were considered normal using LA:Ao. Diagnostic disagreement between these two measurements was significant (P = 0.00012). The majority of dogs with diagnostic disagreement had concurrent echocardiographic evidence of more advanced mitral regurgitation.

Conclusions: Relative to normal dogs, AMVL, AMVW, AMVA, MVAs and MVAd are greater in patients with advanced MMVD. LA Vol/BW may be superior to LA:Ao for identification of mild left atrial enlargement.