Prognostic Value of Intrarenal Venous Flow Analysis Using Pulsed‐Wave Doppler Ultrasonography in Dogs with Myxomatous Mitral Valve Disease

ABSTRACT Background The predictive value of intrarenal Doppler ultrasonography (IRD) analysis using pulsed‐wave Doppler for survival in dogs with myxomatous mitral valve disease (MMVD) remains unknown. Hypothesis/Objectives Impaired IRD indices, such as a high venous impedance index (VII), are associated with a short survival time in dogs with MMVD. Animals Seventy‐one client‐owned dogs with MMVD. Methods Prospective cohort study. Dogs diagnosed with various stages of MMVD between July 2019 and February 2024 were enrolled. Echocardiography and an IRD analysis were performed. Resistance index and VII were estimated using the following formula: (maximum flow velocity—minimum flow velocity)/maximum flow velocity from renal interlobar arteries and veins, respectively. Intrarenal venous flow waveforms were categorized into continuous and discontinuous patterns. Discontinuous IRVF pattern is defined as a minimum velocity of 0. The primary endpoint was defined as a composite of cardiac‐ and renal‐related death. Results During the follow‐up period, 18 dogs met the primary endpoint. A multivariable Cox proportional hazard analysis adjusted for the Mitral INsufficiency Echocardiographic score and plasma creatinine concentrations identified VII > 0.37 (hazard ratio, at least 4.62; 95% CI, 1.47–14.56) and discontinuous intrarenal venous pattern (hazard ratio, at least 3.62; 95% CI, 1.22–10.73) as an independent predictors of cardiac‐ and renal‐related death. No association between resistance index and outcomes was observed in the multivariable analysis. Conclusions and Clinical Importance Worse outcomes in dogs with MMVD could be predicted by an intrarenal venous flow analysis.