Parasympathetic influence on the arrhythmogenicity of graded dobutamine infusions in halothane-anesthetized horses.

The research is about studying the effect of parasympathetic control on the propensity for arrhythmias in horses under anesthesia and administered steady, graded doses of dobutamine.

Objective and Methodology

• The scientists wanted to understand the parasympathetic tone’s impact on the occurrence of arrhythmias in halothane-anesthetized horses, in clinical conditions, administered with steady increments of dobutamine infusions.
• The experimental design included using six horses for nine trials. The researchers administered two series of graded dobutamine infusions intravenously, each infusion lasting for twenty minutes.
• The dobutamine dosage was incremented at intervals of five minutes starting at 5 micrograms per kilogram of body weight per minute, reaching to 20 micrograms per kilogram of body weight per minute.

Interventions and Observations

• Before the second series of dobutamine infusions, either an isotonic saline solution (v), atropine (A), or a bilateral vagotomy (VG), was administered as a treatment. The first set of dobutamine infusions were given without any prior treatment.
• They observed significant interaction between the treatment type and dosage of dobutamine for values differentiating from baseline for mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, heart rate, and cardiac index when the dobutamine dosages were 5 and 10 micrograms per kilogram of body weight per minute. This observation was also valid for heart rate, when given at the dosage of 15 micrograms of dobutamine per kilogram of body weight per minute.
• From results, horses in group-V showed different results from groups A and VG, except on heart rate and cardiac index at the dosage of 5 micrograms of dobutamine/kg/min. The results were not markedly different between group A and group VG horses in most cases.

Arrhythmias Findings

• The type of arrhythmia observed varied with the type of treatment. During low dobutamine infusion rates in the first series (no treatment) and in group V during the second series, normal sinus rhythm, second-degree atrioventricular block, and bradyarrhythmias were found to be prevailing.
• In contrast, during the second infusion series in the A and VG groups, mostly tachyarrhythmias, a type of arrhythmia where heart rate exceeds the normal limit, were observed.