Atropine reduces dobutamine-induced side effects in ponies undergoing a pharmacological stress protocol.

This research evaluates the use of atropine to mitigate the side effects of the drug dobutamine in ponies, in the context of stress echocardiography—a test to study the heart function during physical stress conditions. The results suggest that a low dose of dobutamine, when used after administering atropine, is a potential pharmacological protocol for performing these stress tests in equids, whereas high doses of dobutamine could be harmful.

Objective and Methodology

• The main objective of this study was to study the impact of administering a low dose of dobutamine on the cardiac performance of ponies that were previously given atropine. The end goal was to devise a pharmacological protocol that permits examining the equine heart under stimulated conditions.
• Thirteen healthy Shetland ponies were considered for this research. Their heart rate, stroke index, and cardiac index were collected using pulsed-wave Doppler ultrasound measurements both at rest and during dobutamine infusion at increasing rates.
• The ponies were divided into two groups. Group 1 (seven ponies) received dobutamine infusion beginning at 2 microg/kg bwt/min for 5 minutes, which was then increased every 5 minutes from 5 to 40 microg/kg bwt/min.
• Group 2 (six ponies) also received dobutamine infusion, but at incremental rates of 1 microg/kg bwt/min every 5 minutes, started from 2 microg/kg bwt/min to 5 microg/kg bwt/min, after they were premedicated with 2 injections of 25 microg/kg bwt of atropine administered 5 minutes apart.

Results

• It was observed that the increase in the cardiac index was more significant in Group 2 during the pharmacological challenge, reaching about 2.5 times of the resting value. This increase in the cardiac index was attributable to an increase in the heart rate in both groups, though the stroke index decreased significantly in Group 1, with no significant change in Group 2.
• Ponies in Group 1 showed extreme restlessness and instances of cardiac arrhythmias during the pharmacological challenge. They also had a high intragroup variability in the cardiac response. The ponies in Group 2 did not exhibit such behaviors or symptoms.

Conclusions

• The study suggests that administering a low dose of dobutamine in ponies that have been pre-treated with atropine could be a beneficial pharmacological protocol to perform stress echocardiography in equids.
• The researchers also concluded that further studies are required to evaluate the left ventricular wall motion in horses undergoing the low-dose dobutamine protocol after pretreatment with atropine.