Dynamic QRS-complex and ST-segment monitoring by continuous vectorcardiography during carotid endarterectomy

Abstract

Many authors report a high incidence of cardiac events during carotid endarterectomy. The aim of the present study was to evaluate the usefulness of dynamic continuous on-line vectorcardiography for monitoring the occurrence of myocardial ischaemia during carotid endarterectomy. We studied 21 patients undergoing carotid endarterectomy. Patients underwent general anaesthesia with isoflurane or sevoflurane. The vectorcardiogram was monitored continuously during carotid endarterectomy. Electrodes were placed according to the previously described lead system and connected to a computerized system for on-line vectorcardiography. Two trend variables were recorded: the QRS vector difference, which reflects changes in the shape of the QRS complex; and the ST vector magnitude, which represents deflection of the ST segment from the isoelectric level. The ST segment deflection was measured 60 ms after termination of the QRS complex. Vectorcardiography was successfully recorded in all 21 patients. Three patients showed intraoperative vectorcardiogram abnormalities. In one of these three patients, both ST vector magnitude and QRS vector difference increased after induction of anaesthesia and ST vector magnitude returned to baseline after administration of nitroglycerin. In the other two patients, both ST vector magnitude and QRS vector difference gradually increased after cross-clamping of the internal carotid artery and ST vector magnitude returned to baseline after unclamping. QRS vector difference remained elevated for several hours in all three patients. Monitoring ST vector magnitude and QRS vector difference by vectorcardiography may be useful for identifying myocardial ischaemia during carotid endarterectomy.