Left Ventricular Volume Indexing in Athletic Brazilian Sport Horses Using Body Weight.

Overview

• This study measured the size of the left ventricle in healthy Brazilian Sport Horses using a 3D echocardiographic method and compared the accuracy of estimating body weight from thoracic girth versus using an actual scale measurement for normalizing heart volume data.

Background and Purpose

• The left ventricle (LV) volume is an important indicator of heart size and remodeling in horses, especially athletes, and is assessed using echocardiography.
• The single-plane Simpson method of discs (SMOD) is a volumetric technique used to measure the LV volumes, providing data such as LV end-diastolic volume (LVEDV), LV end-systolic volume (LVESV), and ejection fraction (EF%).
• To compare heart volumes accurately across different horses, these volumes need to be indexed or normalized to body size.
• This study aimed to describe LV volumes in Brazilian Sport Horses (BH) using SMOD, and to evaluate the practicality and accuracy of estimating body weight using thoracic girth (BWe) versus using a scale-measured weight (BWs) for indexing volumes.

Methods

• Sample: 30 healthy Brazilian Sport Horses (15 males and 15 females) aged 4 to 16 years.
• Measurements:
  • LV volumes measured with echocardiography using SMOD: LVEDV, LVESV, and EF%.
  • Body weight measured by two methods:
    • Actual measured weight using a scale (BWs).
    • Estimated body weight calculated using a formula based on thoracic girth measurement (BWe).
• Normalization/Indexing:
  • LV volumes were indexed by dividing them by BWs and BWe to compare the methods.
  • Additionally, volumes were normalized to a reference body weight of 500 kg to standardize comparisons.

Key Results

• LV volume measurements averaged:
  • LVEDV: 1060 ± 154 mL (range roughly 1003–1118 mL).
  • LVESV: 318 ± 77 mL (range roughly 290–347 mL).
  • EF%: 70.0 ± 5.4%, indicating normal systolic function in these horses.
• Comparison of body weight methods:
  • The estimated weight (BWe) correlated moderately well with scale weight (BWs) with R² = 0.61, which is statistically significant (P < 0.0001).
  • However, BWe had a mean bias of +33.25 kg, with limits of agreement from -37.59 to +104.09 kg, indicating considerable variability and potential for error.
  • The mean absolute error was 39 ± 28.83 kg, and percentage error was approximately 8.92 ± 7.27%, showing estimation inaccuracies.
• Indexed volumes:
  • LVEDV per scale weight (LVEDV/BWs) averaged 2.30 ± 0.29 mL/kg.
  • LVEDV per estimated weight (LVEDV/BWe) averaged 2.15 ± 0.26 mL/kg.
  • Normalization to 500 kg body weight gave mean LVEDV values of:
    • 1151 ± 146 mL (using scale weight normalization).
    • 1069 ± 131 mL (using estimated weight normalization).
  • LVESV similarly normalized to 346 ± 83 mL (scale) versus 321 ± 70 mL (estimated).
  • There was a moderate to strong linear association between indexed volumes regardless of the body weight method used.
• No significant differences in LV volume or EF were found related to sex or age within the sample.

Conclusions and Implications

• Indexing LV volumes to body weight improves comparability between individual animals by accounting for size differences.
• Estimating body weight from thoracic girth (BWe) is a practical and useful field method when scales are not available.
• However, the estimation method can introduce considerable error in individual measurements, which could affect precise clinical or research assessments.
• Therefore, for more accurate individual evaluations, actual scale-measured body weight (BWs) remains the preferred method for normalization.
• This study provides important reference LV volume values for Brazilian Sport Horses and informs best practices for cardiac volume assessment in large animal athletes.