PREDICTION OF DEATH AND MYOCARDIAL-INFARCTION BY SCREENING WITH EXERCISE-THALLIUM TESTING AFTER CORONARY-ARTERY-BYPASS GRAFTING

Background The role of myocardial-perfusion imaging in calculating ris k in symptom-free patients who have had coronary-artery-bypass graftin g (CABG) is unclear. Practice guidelines have argued against routine s creening of these patients. We sought to find out the independent and incremental prognostic value of exercise thallium-201 single-photon-em ission computed tomography (SPECT) for prediction of death and non-fat al myocardial infarction (MI) in these patients.Methods Analyses were based on 873 symptom-free patients undergoing symptom-limited exercise thallium-201 SPECT between September, 1990, and December, 1993. All h ad undergone CABG and none had recurrent angina or other major intercu rrent coronary events. Exercise and thallium-perfusion Variables were analysed to determine their prognostic importance during 3 years of fo llow-up. Findings Myocardial-perfusion defects were noted in 508 (58%) patients, There were 57 deaths and 72 patients had major events (deat h or non-fatal MI), Patients with thallium-perfusion defects were more likely to die (9% vs 3%, p=0.0004) or suffer a major event (11% vs 4% , p=0.0002). Reversible defects were also predictive of death (12% vs 5%, p=0.002) and major events (13% vs 7%, p=0.004). The exercise varia ble with the strongest predictive power was an impaired (less than or equal to 6 METs [measure of oxygen consumption equal to 3.5 mL/kg/min] ) exercise capacity; poor exercise capacity was predictive of death (1 8% vs 4%, p<0.0001) and death or non-fatal MI (19% vs 5%, p<0.0001). A fter adjusting for baseline clinical variables, surgical variables, ti me elapsed since CABG, and standard cardiovascular risk factors, thall ium-perfusion defects remained predictive of death (adjusted relative risk 2.78, 95% CI 1.44-5.39) and major events (2.63, 1.49-4.66), Simil arly, impaired exercise remained strongly predictive of death (4.16, 2 .38-7.29) and major events (3.61, 2.22-5.87) after adjusting for confo unders. Interpretation In this group of patients who were symptom-free after CABG, thallium-perfusion defects and impaired exercise capacity were strong and independent predictors of subsequent death or non-fat al MI. Recommendations against routine screening exercise myocardial-p erfusion studies in this setting should be reconsidered.