An echocardiographic study of atrial fibrillation in horses: before and after conversion to sinus rhythm.

The research focuses on studying the effects of atrial fibrillation in horses, specifically its impact on ventricular function, and how these effects change when the condition is treated and the heart rhythm is returned to normal.

Objective of the Research

• The primary aim of the study was to investigate the influence of atrial fibrillation on the heart function of horses, particularly the ventricles, and to observe how this impact shifts when the horses are treated to restore normal heart rhythm.

Methodology

• The researchers used two types of echocardiograms (2D and M-mode) to monitor the heart activity of 41 horses both before and after they had been treated for atrial fibrillation. A smaller group of 20 horses also underwent these examinations post-treatment, with their results compared to the pre-treatment results.

Findings

• In these horses, atrial fibrillation was noted to be linked with a decrease in mean left ventricular fractional shortening (an indication of how well the ventricles are pumping out blood), with 22 out of the 41 horses falling below the reference range.
• The rest of the M-mode variables fell within the normal range. However, 12 horses showed increased left ventricular lumen dimensions during contraction (systole), and eight horses demonstrated shorter ejection times (the duration blood is pushed out of the ventricles).
• All horses showed abnormal movement in the mitral valve (the valve that lets blood flow from the left atrium to the left ventricle). This was characterized by missing A peaks, which were substituted by small diastolic undulations in 55 percent of the horses.
• In horses 1 to 20, a meaningful increase in mean fractional shortening was observed following the restoration of a normal sinus rhythm. Despite this, no significant changes were recorded in heart rate or left ventricular lumen diameters in systole or diastole.

Conclusion

• The results suggest that atrial fibrillation might adversely affect ventricular function in horses. However, these negative effects appear to lessen as the irregular rhythm is corrected and sinus rhythm is restored.