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 risk in symptom-free patients who have had coronary-artery-bypass grafting (CABG) is unclear. Practice guidelines have argued against routine screening of these patients. We sought to find out the independent and incremental prognostic value of exercise thallium-201 single-photon-emission computed tomography (SPECT) for prediction of death and non-fatal 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 had undergone CABG and none had recurrent angina or other major intercurrent coronary events. Exercise and thallium-perfusion variables were analysed to determine their prognostic importance during 3 years of follow-up. Findings Myocardial-perfusion defects were noted in 508 (58%) patients. There were 57 deaths and 72 patients had major events (death 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 variable with the strongest predictive power was an impaired (≤6 METs [measure of oxygen consumption equal to 3•5 mL/kg/min]) exercise capacity; poor exercise capacity was predictive of death (18% vs 4%, p<0•0001) and death or non-fatal MI (19% vs 5%, p<0•0001). After adjusting for baseline clinical variables, surgical variables, time elapsed since CABG, and standard cardiovascular risk factors, thallium-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). Similarly, 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 confounders. 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-fatal MI. Recommendations against routine screening exercise myocardial-perfusion studies in this setting should be reconsidered.