Radiographic Comparison of Pulmonary Lobar Vasculature Dimensions in Medically Managed and Drug-Naive Dogs With Left Heart Failure Secondary to Myxomatous Mitral Valve Disease.

Myxomatous mitral valve disease (MMVD) is the most common acquired cause of left heart failure (LHF) in dogs, and radiographic identification of pulmonary venous enlargement is traditionally used to support the diagnosis of LHF. However, the absence of venous enlargement has been anecdotally observed after initiation of therapy. Therefore, we aimed to compare radiographic pulmonary vessel size in LHF patients with ongoing medical management ± receiving acute rescue therapy. Dogs with echocardiographically confirmed MMVD and radiographic cardiogenic pulmonary edema were retrospectively selected. Pulmonary lobar artery and vein widths were measured using standardized rib-to-vessel ratios: cranial vessels at the intersection with the fourth rib on lateral projections and caudal vessels at the ninth rib on ventrodorsal/dorsoventral projections. Pulmonary vein-to-artery (PV/PA) and vessel-to-rib ratios were calculated, with enlargement defined as >1.2 and small vessel size as <0.8, and treatment groups were compared using Welch-corrected t-tests. 200 radiographic studies from 163 dogs were reviewed. In all dogs, the veins measured larger than the arteries in all lung lobes. Chronically untreated dogs who received furosemide immediately before radiographs had no venous enlargement. All other groups had vascular asymmetry or venous enlargement in at least two lung lobes. All control dogs with reoccurrence of LHF had absence of venous enlargement after initiation of therapy. Pulmonary venous enlargement was most pronounced in the right caudal lung lobe. These findings indicate that dogs chronically managed for MMVD may decompensate into LHF without radiographic pulmonary venous enlargement and that furosemide administration prior to imaging can normalize vessel size.