# Assessment of renal congestion in a rat model with congestive heart failure using superb microvascular imaging

## TL;DR

This study shows that superb microvascular imaging can effectively assess kidney congestion in rats with heart failure.

## Contribution

The study introduces IRPI as a novel metric for evaluating renal congestion using superb microvascular imaging in a rat model.

## Key findings

- IRPI was significantly higher in the heart failure group compared to the control group.
- IRPI correlated strongly with medullary time-to-peak and renal medullary pressure.
- Renal function and left ventricular ejection fraction did not differ significantly between groups.

## Abstract

Renal congestion is a therapeutic target in congestive heart failure. However, its detailed evaluation in a clinical setting is challenging. This study sought to assess renal congestion impairment using superb microvascular imaging (SMI), a simple and accessible method.

Dahl salt-sensitive rats, used as a model for congestive heart failure, underwent central venous pressure (CVP) measurements. Renal congestion was evaluated through measurements of renal medullary pressure (RMP) and assessment of renal perfusion using contrast-enhanced ultrasonography at both the early (control group) and heart failure phases (HF group). All rats were assessed with SMI. The region of interest (ROI) was set in interlobular vessels, interlobar vessels, and a combination of these areas. The area ratio was calculated from the color pixel count in the ROI divided by the total pixel count in the ROI. Intrarenal perfusion index (IRPI) was defined as (maximum area ratio—minimum area ratio) / maximum area ratio.

There were no significant differences in renal function and left ventricular ejection fraction between the two groups. CVP, time-to-peak (TTP) in the medulla, and RMP were higher in the HF group than in the control group. In the HF group, IRPI, evaluated in the interlobular vessels, was significantly higher than in the control group. IRPI was positively correlated with TTP in the medulla (p = 0.028, R = 0.60) and RMP (p < 0.001, R = 0.84), indicating that IRPI reflected renal congestion.

IRPI is a useful tool for assessing renal congestion in rats with congestive heart failure.

The online version contains supplementary material available at 10.1007/s10396-023-01396-7.