Long-term follow-up of atrial function after cardioversion of atrial fibrillation in horses.

The study investigates the recovery timeline and functioning of the left atrial contraction in horses that have undergone treatment for naturally-occurring atrial fibrillation (AF). It discusses how, after cardioversion treatment, atrial contractile function improved over a period of several weeks, but observed some persistent differences compared to the healthy control group.

Research Objective

The purpose of this study was to understand and quantify the recovery and functioning of left atrial (LA) contractile ability following cardioversion of naturally occurring AF in horses. The effects of two different treatments for AF were studied – transvenous electrical cardioversion (TVEC) and quinidine sulfate.

Study Design and Methodology

• The research included 42 horses suffering from AF that were successfully treated using either TVEC (39 horses) or quinidine sulfate (3 horses). Out of these, 25 had a trivial to mild presence of mitral regurgitation, a leakage in one of the heart valves.
• A group of 37 healthy horses were used as a control group for comparison.
• The duration of each horse’s AF condition was estimated based on previous examinations and history.
• Echocardiography, an ultrasound-based diagnostic method, was performed on the horses during general anaesthesia after TVEC (day 0), and on days 1, 2, 6, and at the end of 7 weeks after the cardioversion treatment.
• The researchers made use of two-dimensional (2D) echocardiography to measure the LA diameter, area, and ejection phase indices such as fractional shortening. TDI or Tissue Doppler Imaging measurements to evaluate myocardial velocity during atrial contraction, time to onset, time to peak, and duration were also used.

Key Findings

• The study found that the atrial contractile function, as measured by 2D echocardiography and TDI, gradually improved following cardioversion.
• Seven weeks after the cardioversion treatment, TDI-determined myocardial velocities returned to reference values typical for healthy horses.
• Despite this recovery, AF horses still showed significantly larger atrial dimensions, lower 2D ejection phase indices, and longer TDI-based conduction time compared to the healthy control group. These differences imply that even after treatment and a certain recovery period, full recovery of the atrial function is yet to be achieved.

Conclusion

The research concluded that the dysfunction in atrial contraction resulting from AF in horses gradually improves in the weeks following cardioversion treatment. However, seven weeks post-treatment, the atrial function still showed significant differences from that of healthy horses. This seems to suggest that more time or further treatment may be necessary for a full recovery.