Perioperative myocardial ischemia in carotid endarterectomy under cervical plexus block and prophylactic nitroglycerin infusion

Perioperative myocardial ischemia was evaluated in 36 consecutive carotid endarterectomy procedures carried out on patients with a high (72.2%) prevalence of ischemic heart disease. The procedures were performed under cervical plexus block plus a prophylactic intravenous nitroglycerin infusion. Findings of myocardial ischemia on perioperative (48 hours) continuous electrocardiogram recordings were correlated with preoperative cardiac status, perioperative continuous intra-arterial blood pressure measurements, and postoperative cardiac outcome. In two patients, ST segment analysis was un-interpretable because of bundle-branch blocks. Altogether, 64 episodes of significant ST segment depression were detected in 18 (52.9%) of the remaining procedures. In 8 (23.5%) procedures, ST segment depressions occurred either during carotid artery clamping at the time of the largest rise in blood pressure or within 2 hours of declamping, when blood pressure tended to decline. There were four (11.7%) postoperative cardiac events: three myocardial infarctions (one Q wave and two non-Q wave) and one episode of unstable angina pectoris. All four patients with cardiac events had early signs of myocardial ischemia either at the time of cross-clamping, or soon after declamping of the carotid artery. All myocardial infarctions developed following prolonged (> 10 hours) myocardial ischemia, starting with the first 20 hours after surgery. Thus, ST segment depression occurring during clamping or soon after carotid declamping was associated with cardiac complications (sensitivity 100% and specificity 86.6%) and suggests the possible usefulness of on-line ST segment trend monitoring.