Evaluation of renal microvascular perfusion in dogs with cardiac disease using Superb Microvascular Imaging.

BACKGROUND: Renal dysfunction in cardiac disease is attributed to both reduced cardiac output and venous congestion; however, relative contributions of these mechanisms are difficult to evaluate clinically. HYPOTHESIS/OBJECTIVES: Renal microvascular perfusion assessed by Superb Microvascular Imaging (SMI) would be associated with indices of cardiac output and venous congestion in dogs with cardiac disease. ANIMALS: Forty-three client-owned dogs were enrolled: 15 healthy dogs (Control), 21 dogs with cardiac disease but without right-sided heart failure (non-RHF), and 7 dogs with signs of right-sided heart failure (RHF). METHODS: Prospective cross-sectional observational study. SMI images were obtained from renal cortex, and mean SMI signal intensity (SMI-SI) was calculated as an index of renal perfusion. The left ventricular outflow tract velocity-time integral (LVOT-VTI) was used as an index of cardiac output, while caudal vena cava short-to-long axis ratio at minimal inspiratory diameter (CVC SD/LD) was used to indicate venous congestion. RESULTS: Median SMI-SI was 41.3 (95% CI, 39.1-43.8) in Control, 21.6 (95% CI: 19.4-23.9) in non-RHF, and 18.6 (95% CI, 16.4-21.0) in RHF. Both cardiac disease groups had lower values than Control (P < .001). SMI-SI was negatively correlated with CVC SD/LD (ρ = -0.59, P < .001) and positively correlated with LVOT-VTI (ρ = 0.43, P = .007). In full multivariable analysis, only CVC SD/LD was independently associated with SMI-SI (P = .001). CONCLUSIONS AND CLINICAL IMPORTANCE: SMI detects reduced renal microvascular perfusion in dogs with cardiac disease, which is associated with venous congestion rather than cardiac output.