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

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.

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.

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).

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.

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).

SMI detects reduced renal microvascular perfusion in dogs with cardiac disease, which is associated with venous congestion rather than cardiac output.