Urinary Electrolyte Excretion in Dogs with Myxomatous Mitral Valve Disease

Abstract: Background Progressive myxomatous mitral valve disease (MMVD) is associated with reflex neuroendocrine responses, including fluid retention associated with excess renal sodium avidity. Hypothesis/Objectives We hypothesized that urinary sodium fractional excretion (FENa) will be lowest in dogs with late stage B2 MMVD, and highest in stage C; Stage C dogs receiving quadruple therapy will have higher FENa than those on dual therapy; and duration of furosemide therapy will be negatively correlated with FENa. Animals Client-owned dogs with MMVD (135): 45 dogs in Stages B1, B2 and C, respectively. Methods Retrospective cross-sectional study using archived samples collected between November 2007 and June 2024. Demographic information, medical history and echocardiographic measurements were obtained from clinical records. Creatinine and electrolyte (Na+, K+, Cl-) concentrations were measured in urine and serum samples. Kruskal-Wallis, Mann-Whitney U and Spearman’s rank correlation tests were used. Results Stage C dogs had higher FENa (median 0.53%, IQR 0.11-0.78) compared to B1 dogs (0.28%, IQR 0.11-0.42; P = 0.04), whereas FENa was not different comparing stage B2 (0.31%, IQR 0.16-0.5) with stage B1 (P = 1.00) or C dogs (P = 0.294). In stage C dogs, FENa was not different with quadruple therapy (0.47%, IQR 0.19-0.7) compared with dual therapy (0.59%, IQR 0.07-1.17; P = 0.830). There was no correlation between FENa and duration of furosemide therapy (P = 0.630). Conclusions and clinical importance Diuresis is a primary driver for urinary sodium excretion in dogs with MMVD. Stage B2 dogs cannot be differentiated from other stages based on urinary sodium excretion.