Preoperative evaluation of cardiac risk by means of atrial pacing and thallium 201 scintigraphy

Abstract

Atrial pacing and thallium 201 scintigraphy were done in 61 patients with known or suspected coronary artery disease referred for evaluation of cardiac risk before elective vascular surgery. All patients had noncardiac limitations precluding performance of an adequate exercise stress test. Before atrial pacing all were considered to be at low risk of a postoperative cardiac event based on assessment of clinical parameters. Vascular surgery was subsequently performed in 47 patients. In these patients, pacing-induced ST segment depression ≥ 1 mm occurred in 18, a fixed perfusion defect occurred in 11, and a reversible defect occurred in six. Two of the six patients with reversible perfusion defects had preoperative coronary angiography; both had significant coronary artery disease (one or more lesions ≥50%). Two patients (one of whom had a reversible perfusion defect) underwent preoperative coronary revascularizaton and tolerated subsequent vascular surgery well. All other patients received only medical therapy. None of the 47 patients undergoing vascular surgery had a postoperative cardiac event (unstable angina, congestive heart failure, myocardial infarction, or cardiac death). Of the 14 patients in whom vascular surgery was deferred or canceled, surgery was canceled for noncardiac reasons in seven. Six of these seven patients had a normal perfusion scan; none had a reversible perfusion defect or marked (≥2 mm) ST segment depression. No cardiac event occurred during a 3-month period after atrial pacing in any of these patients. Six of the remaining seven patients had reversible perfusion defects. Four of these six patients underwent cardiac catheterization; all had significant coronary artery disease. One patient with a reversible perfusion defect and another with a fixed defect died suddenly while awaiting coronary revascularization. We conclude that a normal thallium 201 scan outcome or a scan showing only a fixed perfusion defect during atrial pacing confirms low risk for postoperative cardiac events. Although medical treatment of patients with a reversible perfusion defect does not preclude a postoperative course free of cardiac events, cardiac catheterization and, if clinically indicated, coronary revascularization should be considered because of a high incidence of coronary artery disease in these patients.