Spectral Doppler of aortic and carotid blood flow in horses with aortic valve regurgitation.

Overview

• This study investigated the use of various echocardiographic and Doppler ultrasound techniques to assess aortic regurgitation severity in horses.
• It specifically compared spectral Doppler measurements of the aortic valve and common carotid artery blood flow in horses with different degrees of aortic regurgitation.

Background and Purpose

• Aortic valve regurgitation (AR) is a condition where the aortic valve does not close properly, causing blood to flow backward into the left ventricle during diastole.
• Assessing the severity of AR in horses traditionally uses echocardiography, including 2D, M-mode, color Doppler, pulsed-wave Doppler (PWD), and continuous-wave Doppler (CWD).
• The study aimed to compare these imaging modalities with PWD ultrasonography of the common carotid artery (CCA) to evaluate AR severity in Warmblood horses.

Study Design and Methods

• Retrospective descriptive study involving 80 Warmblood horses:
• 20 normal (without AR)
• 60 with varying AR severity (mild, moderate, severe)
• Measurements included cardiac dimensions, Doppler flow velocities in the aorta and common carotid artery, non-invasive blood pressure, and presence of ventricular arrhythmia.
• Horses were categorized into groups based on AR severity for comparative analysis.
• Statistical analyses utilized included analysis of variance (ANOVA), chi-square tests, Spearman’s rho correlation, and Kruskal-Wallis tests.

Key Findings

• Aortic antegrade flow velocity:
• Maximal antegrade flow velocity through the aortic valve was significantly higher in moderate and severe AR groups compared to normal horses.
• Severe AR group had higher velocity than the mild AR group (P < 0.001).
• Common carotid artery (CCA) antegrade flow velocity:
• Mean antegrade flow velocities increased with AR severity:
• Normal: 0.9 m/s (± 0.3 m/s)
• Mild AR: 1.0 m/s (± 0.2 m/s)
• Moderate AR: 1.2 m/s (± 0.3 m/s)
• Severe AR: 1.5 m/s (± 0.4 m/s)
• Retrograde flow in common carotid artery:
• Pathologic retrograde diastolic flow was detected in horses with moderate (6 out of 20) and severe AR (13 out of 20).
• This retrograde flow was associated with increased left ventricular size and pulse pressures greater than 60 mmHg, indicating hemodynamic overload.
• Continuous-wave Doppler (CWD) regurgitant jet pressure half-time:
• This measure failed to reliably differentiate between AR severity grades, suggesting it is an unreliable parameter for severity assessment in horses.

Limitations of the Study

• Retrospective study design led to missing data points in the dataset.
• The AR classification system used was not validated through longitudinal (long-term) clinical follow-up.
• Very low retrograde velocities (<10 cm/s) in the CCA were not measured, potentially limiting detailed flow characterization.

Conclusions and Clinical Implications

• Pulsed-wave Doppler ultrasonography of the common carotid artery is a useful non-invasive tool to identify moderate and severe AR in horses experiencing hemodynamic overload.
• The presence of retrograde flow in the CCA during diastole is a marker of significant AR and is linked with left ventricular dilation, a marker of structural cardiac changes.
• Continuous-wave Doppler measurement of the regurgitant jet pressure half-time is not a reliable method to assess AR severity in horses.
• This study suggests that evaluating blood flow in the carotid artery can complement traditional cardiac imaging techniques to improve AR severity assessment in equine patients.