Cardiovascular responses to transvenous electrical cardioversion of atrial fibrillation in anaesthetized horses.

The research investigates the cardiovascular responses in horses that undergo direct current shock treatment for atrial fibrillation, a common arrhythmia in the species. The results suggest that cardioversion to regular sinus rhythm does not severely affect cardiovascular function under anaesthesia, paving the way for safe and effective treatment protocols for equine atrial fibrillation.

Study Design and Methods

• The study followed a prospective clinical design with eight horses diagnosed with atrial fibrillation (AF) and subsequently treated through transvenous electrical cardioversion after pre-treatment with amiodarone, a medication used to help restore normal heart rhythm.
• Under sedation, cardioversion catheters and a pacing catheter were inserted. Anaesthesia was then induced through a combination of detomidine, methadone, ketamine, and midazolam, and maintained with isoflurane in oxygen – this process prepares the horses for the shock treatment.
• Flunixin meglumine was administered intravenously to manage pain. The shock-delivering procedure was synchronized with the R-wave of the horses’ electrocardiogram and was presented as biphasic truncated exponential waves.
• Several critical factors such as pulse oximetry, electrocardiography, capnography, arterial blood pressure, cardiac index (CI), and arterial blood gases were monitored before and after the shock treatment.

Study Results

• The measured parameters before the delivery of the first direct current shock were reportedly identical with values of healthy horses under anaesthesia.
• Reliable Cardiac Index measurements could not be obtained using the PulseCO technique. Most horses required intermittent positive pressure ventilation due to bradypnea (slow breathing) and/or high PaCO2 levels, while two horses were administered dobutamine.
• After the first unsuccessful shock application, the systolic arterial pressure (SAP) was decreased, but other recorded values remained stable.
• Conversion to sinus rhythm (SR) led to increases in cardiac index and stroke index but a decrease in systolic arterial pressure.

Study Conclusions

• In horses with AF, cardiovascular function was well maintained during anaesthesia and remained unaffected by the introduction of direct current shock treatment. Additionally, the conversion to SR resulted in an increase in cardiac and stroke indices, albeit with a decrease in SAP.
• The study posits the feasibility of this method to treat horses with AF without severe disruptions to cardiovascular function during anaesthesia.