# Phase Angle as a Non-Invasive Biomarker of Fluid Overload in Canine Right Heart Failure: A Bioelectrical Impedance Approach

## TL;DR

This study shows that a non-invasive electrical measurement called phase angle can help detect fluid overload in dogs with right heart failure, offering a safer alternative to invasive tests.

## Contribution

The study validates phase angle as a novel non-invasive biomarker for fluid overload in canine right heart failure using bioelectrical impedance analysis.

## Key findings

- Dogs with right heart failure had significantly lower phase angle values compared to healthy dogs and those with left heart failure.
- Phase angle strongly correlated with plasma osmolality and showed associations with body weight and age.
- The InBody M20 device is feasible for non-invasive monitoring of fluid status in veterinary cardiology.

## Abstract

Heart failure is a common and serious condition in dogs, but monitoring changes in fluid levels is often difficult without invasive tools. This study investigated a noninvasive device that sends a weak electrical current through the dog’s body to measure a value called “phase angle”, which may reflect the amount of fluid inside and outside cells. We focused on dogs with right heart failure, a condition that causes fluid accumulation. Comparing dogs with heart failure with healthy dogs, we found that the phase angle was lower in the affected group and significantly correlated with blood test results related to fluid balance. These findings suggest that this approach could help veterinarians monitor dogs with heart failure more safely and easily. In the future, this approach may reduce the need for more invasive testing and enable faster adjustments to treatment plans. This represents a step toward improving quality of life and outcomes for dogs with heart disease.

Background: Right heart failure (RHF) in dogs is marked by pathological fluid redistribution and extracellular fluid (ECF) accumulation, which intensifies cardiac work-load and disrupts systemic homeostasis. This study aimed to validate the clinical utility of phase angle (PhA), a key biomarker derived from bioelectrical impedance analysis (BIA), as a non-invasive and real-time indicator of fluid distribution abnormalities in canine RHF. PhA reflects cellular integrity and fluid balance, making it a promising tool for detecting ECF accumulation, one of the hallmark features of RHF. Additionally, the study assessed the feasibility and clinical applicability of the InBody M20 device in veterinary cardiology, supporting its potential role in monitoring and managing fluid-related complications in dogs with RHF. Methods: A total of 110 canine patients presenting to the Tokyo University of Agriculture and Technology Veterinary Hospital were enrolled and categorized into three groups: right-sided heart failure (RHF), left-sided heart failure (LHF), and healthy controls. Phase angle (PhA) was measured using the InBody M20 device, and plasma osmolality (OSM) was also assessed. Additionally, the effects of body weight and age on PhA values were analyzed to account for potential confounding factors. Results: Dogs in the RHF group exhibited significantly lower phase angle (PhA) values and higher plasma osmolality (OSM) compared to those in the LHF and control groups. A strong positive correlation was observed between PhA and OSM (r = 0.9211, p < 0.0001). Additionally, PhA measured at 5 kHz demonstrated a significant negative correlation with body weight (r = –0.4536, p = 0.0007), while PhA at 50 kHz showed a significant negative correlation with age (r = –0.3219, p = 0.0176). Conclusions: PhA is a reliable and non-invasive biomarker for assessing extracellular fluid accumulation and diagnosing right heart failure in dogs. Its strong correlation with plasma osmolality, as well as its associations with body weight and age, highlights its clinical relevance for comprehensive fluid status evaluation. The findings support the feasibility and applicability of using the InBody M20 device in veterinary cardiology to monitor and manage fluid-related complications in canine patients.