Effects of atropine on the arrhythmogenic dose of dobutamine in xylazine-thiamylal-halothane-anesthetized horses.

The research explores the effect of Atropine on the dosage of Dobutamine which triggers arrhythmia in horses under Xylazine-Thiamylal-Halothane anesthesia. The experiment found a significant difference in the arrhythmia-inducing dose of Dobutamine between those administered saline and Atropine.

Study Design

• The study was conducted with six horses used in twelve randomized trials. Horses were premedicated with Xylazine, anesthetized with guaifenesin and thiamylal, and maintained with halothane in oxygen.
• After stabilizing the end-tidal halothane concentration at 1.1% in oxygen, either saline solution or Atropine was administered intravenously (IV). Dobutamine infusion began five minutes later.
• The infusion of Dobutamine was maintained for 10 minutes or stopped if certain criteria were met indicating arrhythmia. If the criteria for termination were not met, the dobutamine infusion was increased. Horses were then allowed to recover and rest for at least one week before the next trial.
• The arrhythmogenic dose of Dobutamine was calculated by multiplying the infusion rate by the elapsed time when arrhythmia occurred.

Findings

• The research found a notable difference between the arrhythmogenic doses of Dobutamine in horses treated with saline solution and in those treated with Atropine. The arrhythmogenic dose was significantly lower in horses treated with Atropine.
• No significant differences in prearrhythmia or immediate postarrhythmia ventricular heart rate and arterial pressures between the treated and control groups were observed.
• Changes in hemodynamic variables (HR, SAP, DAP, MAP) from prearrhythmia to immediate postarrhythmia were also not significantly different between the groups

This research highlights the influence of parasympathetic tone on the amount of Dobutamine needed to induce arrhythmia in horses and shows that Atropine significantly reduces this dosage. However, there was no recorded difference in the hemodynamic variables before and after arrhythmia onset. The effect of these findings on the veterinary application of Dobutamine and Atropine requires further exploration.