Thallium-201 exercise myocardial imaging to evaluate myocardial perfusion after coronary artery bypass surgery.

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Abstract
To assess the usefulness of thallium 201 exercise scintigraphy in evaluating myocardial perfusion after coronary artery bypass surgery imaging was performed after submaximal bicycle ergometry and at rest in 54 patients before and within 24 .+-. 10 (SD) weeks after operation. According to the postoperative scintigram the patients were assigned to 3 groups: Group 1 comprised 31 patients whose perfusion returned to normal after exercise and at rest within the preoperatively ischemic regions; group 2 comprised 16 patients with identical pre- and postoperative exercise-induced perfusion defects; and group 3 comprised 7 patients with enlarged or new perfusion defects postoperatively. Clinically, 14 of 31 patients in group 1 were symptom-free after operation, 2 of whom showed an abnormal exercise ECG; the other 17 patients complained of chest pain, and in 6 the exercise ECG was pathological. In group 2, 8 of 16 patients were symptom-free after operation and showed normal exercise ECG and the other 8 continued to suffer from angina, and 7 had a pathological exercise ECG. All 7 patients in group 3 were symptomatic and showed an abnormal exercise ECG. Scintigraphy identified 8 of 20 patients (40%) who were symptom-free and showed normal exercise ECG as still having exercise-induced ischemia and not truly benefiting from the surgical intervention. Improvement in perfusion was documented in 17 of 31 patients (53%) despite further complaints of chest pain and persistence of a pathological exercise ECG in 6 of them. Bypass graft patency rate paralleled the scintigraphic findings in the 35 patients who were restudied arteriographically. In group 1 (16 patients restudied) the graft patency rate was 81%, significantly different from the 38% in group 2 (13 patients restudied); it was 15% in group 3 (6 patients restudied). The degree of vascular obstruction decreased in group 1, remained unchanged in group 2, and tended to increase in group 3. Thallium-201 exercise scintigraphy is a useful technique to document changes in regional perfusion after surgery and is superior to the clinical evaluation of patients including the exercise ECG.