Influence of halothane and catecholamines on heart rate and rhythm in the horse

Abstract

Summary1. Ventricular ectopic beats were recorded in eight of thirteen conscious horses following the intravenous administration of adrenaline in doses of 3 t4g/kg. Following pre-treatment with either atropine sulphate (0-1 mg/kg) or propranolol hydrochloride (0O1 mg/kg), the same dose level of adrenaline failed to produce ventricular ectopic beats. 2. Halothane anaesthesia sensitized the equine heart to the arrhythmogenic actions of adrenaline; the incidence and duration of ventricular arrhythmias being greater than in conscious animals. In comparison with the findings in conscious horses, ether anaesthesia appeared to protect the heart against adrenaline-induced arrhythmias.3. From a comparison of the arrhythmogenic, chronotropic and pressor actions of adrenaline, noradrenaline and isoprenaline during halothane anaesthesia. it was concluded that sensitization to the arrhythmogenic actions of catecholamines resulted primarily from the action of halothane on the ventricle. The results also indicated that the pressor responses to catecholamines during halothane anaesthesia probably played some part in the genesis of arrhythmias. 4. No " spontaneous " ventricular arrhythmias were recorded in twenty-four horses anaesthetized with halothane or in sixteen animals under ether anaesthesia. 5. The available evidence indicates that a moderate to fairly severe degree of hypercapnia produced little increase in sympathetic control of the myocardium during halothane anaesthesia; the absence of irregularities in ventricular rhythm during halothane anaesthesia were attributed to this factor.

Anesthesia of the critically ill equine patient

“…Although all three inhalants depress cardiorespiratory function in a dose-dependent manner, isoflurane and sevoflurane act similarly at equipotent concentrations, with both causing less depression of cardiac output and more depression of respiratory rate compared with halothane [10]. Halothane, unlike isoflurane and sevoflurane, has been reported to cause cardiac rhythm irregularities because of sensitization of the myocardium [64,65]. With the introduction of isoflurane, currently at a comparable cost, it is difficult to rationalize the continued use of halothane in the critically ill equine patient.…”

Anesthetic recovery and hemodynamic effects of continuous thiopental infusion versus halothane for maintenance anesthesia in patients undergoing ocular surgery

“…shown that the halothane has a potential role on the conducting tissues of the ventricle and even its increased sensitivity to catecholamine blood pressure alterations and arrhythmias resulted primarily from its action on these tissues 10 . Moreover, it has been confirmed that halothane caused a significant and dose-dependent decrease in cardiac output and this reduction was dependent to halothane effects on antipyrine disposition profoundly affected by this anesthetic agent 11 .…”

Negative chronotropic and antiarrhythmic properties of atropine and other tropane analogues on isolated cat heart preparations.

“…As illustrated, the doseeffect curves obtained are parallel to each other. However, figure 2 illustrates the nonparallel nature of the dose-effect curve obtained with procaine amide in the Dose-effect curves obtained on the whole isolated cat heart preparation illustrating the diminution of heart rate produced by quinidine (13), l-atropine (20), d,l-atropine (13), d,l-homatropine (18), and l-scopolamine (9) (number of individual determinations in parentheses). same preparation in comparison to d,/-atropine and /scopolamine.…”