Halothane-catecholamine arrhythmias in swine (Sus scrofa).

Area of Science:

• Veterinary Anesthesiology
• Cardiovascular Pharmacology
• Comparative Physiology

Background:

• Epinephrine can induce cardiac arrhythmias, especially during anesthesia.
• Alpha-1 and beta-1 adrenergic receptors play critical roles in cardiovascular regulation.
• Understanding the protective effects of adrenergic blockade against epinephrine-induced arrhythmias is vital for anesthetic safety.

Purpose of the Study:

• To determine the arrhythmogenic dose of epinephrine (ADE) in pigs under different anesthetic conditions.
• To compare the protective effects of alpha-1 (prazosin) and beta-1 (metoprolol) adrenergic blockade against epinephrine-induced arrhythmias during halothane-xylazine anesthesia.

Main Methods:

• The study involved 6 pigs under steady-state anesthesia (1.5% halothane).
• ADE was determined during halothane-xylazine anesthesia, with and without prazosin or metoprolol blockade.
• Epinephrine was infused at increasing doses to identify the threshold for ventricular arrhythmias.

Main Results:

• Xylazine did not significantly alter ADE but increased mean arterial pressure.
• Prazosin significantly increased ADE, indicating enhanced protection against arrhythmias.
• Metoprolol also increased ADE, but to a lesser extent than prazosin.
• Prazosin administration was associated with increased heart rate and decreased mean arterial pressure.

Conclusions:

• Alpha-1 blockade with prazosin provides superior protection against epinephrine-induced arrhythmias compared to beta-1 blockade with metoprolol in pigs under halothane-xylazine anesthesia.
• These findings have implications for managing anesthetic protocols and preventing cardiac complications.