Breed-Specific Variations in Vertebral Right Heart Index (VRHi): Implications for Detection of True and False Right Heart Enlargement (RHE) in Dogs

This study investigated breed-specific variations in vertebral right heart index (VRHi) values and their diagnostic accuracy in detecting right heart enlargement (RHE) in dogs. A total of 359 dogs from various breeds, including brachycephalic and non-brachycephalic groups, were evaluated using radiographic and echocardiographic methods. The VRHi was measured from lateral (RL) and ventrodorsal (VD) thoracic radiographs. Certain breeds, such as brachycephalic dogs, Schnauzers, Dachshunds, Pomeranians, Yorkshire Terriers, and Miniature Pinschers, demonstrated significantly higher VRHi values than non-brachycephalic breeds, even without true RHE. The RL VRHi showed stronger clinical relevance than the VD VRHi, correlating better with the echocardiographic findings. Breed-specific diagnostic cutoff values were established: RL VRHi ≥ 3.45 vertebral units (v) (sensitivity: 75%, specificity: 75%) and VD VRHi ≥ 2.75 v (sensitivity: 72%, specificity: 72%) for brachycephalic breeds and RL VRHi ≥ 3.25 v (sensitivity: 78%, specificity: 80%), VD VRHi ≥ 2.4 v (sensitivity: 61%, specificity: 61%) for non-brachycephalic breeds not belonging to the aforementioned categories. Body weight and chest conformation showed no significant association with VRHi values. These findings highlight the necessity of considering breed-specific factors in radiographic cardiac evaluations, as some breeds may present radiographic signs of RHE despite a normal cardiac anatomy and function.