Prognostic value of SPECT myocardial perfusion imaging when exercise is submaximal

Introduction. For patients undergoing myocardial perfusion imaging (MPI), pharmacological stress is increasingly recommended when there is any doubt about exercise capacity. This approach is based on the observation that the sensitivity for detecting coronary disease is reduced when exercise stress is submaximal. This would be of little importance clinically if the sensitivity for predicting irreversible cardiac events were maintained. We investigated the prognostic value of a normal SPECT MPI study when exercise produced submaximal stress. Methods. Between 1995-1998, 1398 patients underwent SPECT MPI (73% 99mTc-tetrofosmin, 27% 201Tl), 1290 (92%) with exercise stress (72% treadmill, 28% upright bicycle). 574 (41%) failed to achieve 80% of the maximum predicted heart rate: age 60±10 years, 63% male, 5% diabetic, 19% previous myocardial infarction, 28% previous revascularisation, 18% angiographically documented coronary disease. 203 (35%) of these MPI studies were normal, and the patients were followed-up by GP questionnaire with review of the hospital notes. Cardiac events were cardiac death or nonfatal myocardial infarction. Results. Follow-up was complete for 155 patients, with a mean (±SD) duration of 2.2±0.8 years. 3 patients died, all of definite noncardiac causes. There was 1 cardiac event (nonfatal myocardial infarction) in a patient who had previously had coronary artery bypass surgery. Conclusion. A normal SPECT MPI study following submaximal exercise predicts a very low risk of cardiac events during follow-up in a relatively high risk population. Patients with reduced exercise capacity do not automatically require pharmacological stress for accurate risk assessment.