The effect of an infusion of esmolol on the incidence of myocardial ischaemia during tracheal extubation following coronary artery surgery

Introduction

Silent myocardial ischaemia (SMI) has been shown to be temporally associated with tracheal extubation in up to 27% of patients after coronary artery bypass operations [1]. Patients who develop SMI during tracheal extubation are more likely to have a higher heart rate [1,2] and arterial pressure [2]. The aim of this study was to determine whether an esmolol infusion could affect the incidence of SMI during the weaning from intermittent positive pressure ventilation and tracheal extubation following coronary artery surgery. Patient haemodynamics and adverse events were also assessed.

Methods

Ethics Committee Approval and informed consent were obtained. The study was conducted in the intensive care unit (ICU) on patients who had undergone elective coronary artery surgery. Preoperative exclusion criteria were: digoxin therapy, electrocardiographic (ECG) evidence of left ventricular hypertrophy or left bundle branch block, cardiac pacemaker, asthma, a previous intolerance to beta adrenergic blockade or renal impairment. Postoperative exclusion criteria were first degree heart block or beta adrenergic agonist infusion at the time of study entry. Thirty-eight patients were randomized to the control group (group C) and 34 to receive a sliding scale infusion of esmolol (group E) with a target heart rate between 55-75 bpm. The study period extended from 120 min before until 180 min after tracheal extubation. Myocardial ischaemia, reversible ST segment depression ≥ 2 mm or elevation ≥ 3 mm for more than 60 s was detected using the Compas computerized ambulatory ECG system (S-pace Medical, Sheffield, UK). Heart rate and arterial pressure were recorded at 10-min intervals. A P value < 0.05 was considered significant.

Results

One patient from each group was withdrawn because of ECG lead faults. Two patients from group E were withdrawn because of hypotension. The patient characteristics were comparable between the two groups. The esmolol group had a lower incidence of myocardial ischaemia compared with the control group (3/31 versus 12/37; Χ² analysis, P = 0.05). Heart rate increased in group C (analysis of variance, P = 0.002) and was unchanged in group E. Arterial pressure in both groups showed increases during tracheal extubation. Four patients from group E had a high heart rate that was difficult to control and a further three patients developed hypotension.

Conclusions

Esmolol does reduce the incidence of myocardial ischaemia in association with tracheal extubation following coronary artery surgery. However, the high incidence of adverse events limits its use in this patient population.