Echocardiographic evidence of left atrial mechanical dysfunction after conversion of atrial fibrillation to sinus rhythm in 5 horses.

The research article investigates the presence of left atrial contractile dysfunction in horses, after they are treated for atrial fibrillation (an irregular and often rapid heart rate) and restored to normal sinus rhythm. It used transthoracic echocardiography (ultrasound imaging of the heart) to detect this dysfunction in a small group of Standardbred horses.

Study Methodology

• Five Standardbred horses suffering from atrial fibrillation were included in the study alongside a control group of six healthy Standardbreds of similar age, weight, and athletic condition.
• Four horses were treated with quinidine, a pharmacological method, while one horse underwent transvenous electrical cardioversion, a more physical treatment of correcting heart rhythm.
• Echocardiographic examinations, including 2-dimensional echocardiography (2DE), transmitral flow Doppler, and tissue Doppler imaging (TDI) techniques, were performed on the healthy horses once and on the horses with atrial fibrillation 24 hours and 72 hours after converting to normal sinus rhythm. This allowed for a comparative analysis of left atrial (LA) mechanical function before and after treatment.

Study Findings

• The study found that there were significant decreases in left atrial contractile function as well as LA reservoir function 24 hours after conversion from atrial fibrillation to normal sinus rhythm. This was detected through the 2-dimensional echocardiography and TDI indices created during the echocardiographic examinations.
• Some recovery was noted as the significant decrease observed was no longer statistically significant 72 hours after conversion, but it was observed that there was still variability in echocardiographic variables amongst different horses between the 24-hour and 72-hour mark post-conversion.

Conclusions Drawn

• The study concludes that left atrial contractile dysfunction can be evaluated in horses using 2DE, transmitral Doppler flow velocity profiles, and TDI analysis of left atrial wall motion.
• The results found are consistent with atrial fibrillation-induced atrial remodeling. Yet, it acknowledges that the possibility of residual effects from treatment or the influence of underlying primary myopathy (muscle disease) cannot be completely discounted.