Measurement of cardiac dimensions with two-dimensional echocardiography in the living horse.

The study used two-dimensional echocardiography (2DE) to establish normal values for cardiac dimensions in Thoroughbred and part Thoroughbred horses. Measurements were made on unsedated horses during examinations, and various cardiac parameters were determined and compared against values in existing literature. A significant correlation was found between certain parameters and body weight.

Methodology

• The study involved 22 unsedated Thoroughbred and part Thoroughbred horses, each weighing between 411 and 650 kg.
• 2DE was used to measure the heart dimensions of the horses which stood during the examination. The investigation used a 3.5 MHz mechanical sector transducer at various positions and tomographic planes.
• The researchers measured the right ventricular diameter (RVD), ventricular septal thickness (VSTh), aortic diameter (AoD), area of the chordal lumen of the left ventricle (CTA), left ventricular diameter (LVD), and left atrial diameter (LAD) either at ventricular end-diastole (Ed) or end-systole (Es).
• The investigators also calculated fractional shortening (FS) of the left ventricle and end-systolic left atrial to aortic ratio (LAD-Es:AoD-Es).

Results

• Echocardiographic data were analyzed against body weight through linear regression.
• Intra-observer variability was assessed in five horses, with each parameter measured during 10 consecutive cardiac cycles.
• The measurements from the study were compared with M-mode values reported in other research articles.
• Repeatable and good-quality recordings could be obtained, and accurate measurements could be made using intra-cardiac reference points in 18 of the horses whose weight was not more than 551 kg.
• For the heavier horses, the existing machine and transducer had limitations. Lower frequency probes or higher-quality equipment might be needed to overcome this issue.
• There was a significant correlation noted between body weight and the following parameters: VSTh-Es, AoD-Es, and CTA-Es.

Conclusion

• This study established normal reference values for 2DE measurements in Thoroughbred horses, providing a valuable tool for further research and clinical applications. It highlighted the potential limitations with heavier animals and suggested alternatives for improving accuracy in these cases.