Measurement and estimation of normal mitral annular size using computed tomography in 248 small-breed dogs

Surgical mitral valve repair is gaining recognition as an essential treatment option for dogs with myxomatous mitral valve disease despite the lack of established criteria for suture annuloplasty. Therefore, measuring normal mitral annular size in small-breed dogs without heart abnormalities may help determine the appropriate target annular size.

Dogs weighing <10 kg without evidence of heart disease that underwent three-phase computed tomography under anesthesia were retrospectively collected. Mitral annular measurements including trigone-to-trigone distance (TT) and the fourth thoracic vertebral body length (T4) were measured using multiplanar reformatting. The correlations between mitral annular measurements and body size, including body weight (BW) and T4, were examined. The regression equations for estimating annular circumference (AC) were then calculated.

The study population comprised 248 dogs weighing 1.2-9.9 kg. Mean values (±standard deviation) of TT and AC were 1.56 (±0.27) and 5.81 (±0.95) cm, respectively. All annular measurements presented a correlation coefficient >0.7 with both BW and T4. Regression equations using BW, T4, and TT explained the AC in our population with sufficient coefficients of determination, with values of 0.68, 0.65, and 0.80, respectively.

Synchronous electrocardiogram recordings were not available in this study, and the use of electrocardiogram-gated computed tomography may provide a more accurate assessment.

Mitral annular size was strongly correlated with BW and T4 in small-breed dogs. A normal AC can be estimated through regression equations using BW, T4, or TT. The TT calculated using CT images is the most valuable index for accurate estimation.