The purpose of this study was to investigate the effects of three anesthetic agents, with premedication of medetomidine and midazolam, on electrocardiographic variables in dogs. Ten adult mixed breed dogs were used in a crossover design study, where they received ketamine, propofol and isoflurane treatments with a one-week washout period between them. In all three groups, medetomidine was administered first followed by midazolam after 15 min. Then, after 20 min, group 1 received ketamine intravenously (IV), group 2 received propofol (IV), and group 3 received isoflurane (inhalation). In all dogs, electrocardiographs were taken before and after premedication’s, as well as every 15 min during anesthesia. Medetomidine significantly decreased heart rate and P wave amplitude and increased PR interval, R wave amplitude, QT interval, and T wave amplitude. Midazolam increased the amplitude of the R and T waves. Ketamine increased the heart rate and PR interval. Propofol increased the heart rate for up to 15 min, decreased the PR interval for up to 30 min, and the QT interval for up to 45 min. Isoflurane increased the heart rate and decreased the amplitude of R and T waves. The results showed that the drugs used in this study did not have many side effects on electrocardiographic variables and could be used without serious concern. The most important side effects observed were a severe reduction in heart rate and 1st degree atrioventricular (AV) block and, to a lesser extent, 2nd degree AV block caused by medetomidine and midazolam which were masked by the anesthetics.

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