Thallium-201 myocardial imaging in young asymptomatic subjects with "ischaemic" changes in exercise electrocardiogram

In order to assess the significance of a positive electrocardiographic response to exercise test in 10 asymptomatic subjects with normal resting ECG, a myocardial perfusion scanning with Thallium-201 at rest and during exercise was performed. The following ECG tests were also performed on these subjects: forced hyperventilation, exercise test after nitroglycerin (TNG), exercise test after propranolol. Myocardial perfusion scans did not reveal any defect at rest nor during exercise. Hyperventilation determined abnormalities of ventricular repolarization in all subjects. TNG did not improve the response to exercise test and even decreased the ischemic threshold. After propranolol the electrocardiographic response to exercise became normal in 9 cases, while in 1 subject the ST depressions were impressively reduced. All subjects had a follow-up of 14 to 91 months. During this period none presented symptoms suggesting a coronary disease. This study suggests that combined evaluation of Thallium myocardial perfusion imaging during exercise and exercise ECG test after TNG is most useful in differentiating ischemic from nonischemic exercise ST depressions in asymptomatic population.