Thoracic epidural anaesthesia decreases the incidence of ventricular arrhythmias during acute myocardial ischaemia in the anaesthetized rat

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Abstract
The aim of the present investigation was to study the effect of high thoracic epidural anaesthesia (TEA) on the incidence of ventricular arrhythmias after ligation of the left coronary artery in chloralose-anaesthetized rats. Forty animals were randomly assigned to receive either 40-50 .mu.l of bupivacaine (5 mg/ml) or saline in implanted thoracic epidural catheters. TEA decreased mean arterial pressure (MAP) from 118 .+-. 5 mm Hg to 72 .+-. 4 mm Hg and heart rate (HR) from 450 .+-. 9 to 387 .+-. 8 beats/min, while epidural saline did not affect MAP and HR. In both groups coronary artery ligation induced a transient decrease in MAP within the first 5-10 min after ligation. In the control group HR increased, during the 30-min post-ligation period, from 453 .+-. 9 to 474 .+-. 10 beats/min (P < 0.05) while no significant change was seen in the TEA group. In both groups the mortality rate was 10%. In the TEA group 30% and in the control group 0% had normal sinus rhythm during the recording period (P < 0.001). The incidence of ventricular fibrillation and/or tachycardia was significantly lower (P < 0.05) in the TEA group (20%) compared to the control group (53%). The incidence of ventricular extrasystoles did not differ between the two groups. We conclude that TEA-induced blockade of sympathetic afferents and efferents may offer protection against malignant ventricular arrhythmias in the early phase of acute myocardial infarction.