Ability of the exercise electrocardiogram test to detect ischemia in stable coronary artery disease patients with ST-segment depression on the resting electrocardiogram

Background The appearance of ST-segment depression on the exercise electrocardiogram (ETT) generally indicates myocardial ischemia. Disorders that produce ST-segment depression on the resting electrocardiogram can confound the results of the ETT. The purpose of this study was to assess the reliability of exercise ST-segment depression as an indicator of ischemia in patients with a resting electrocardiographic ST depression, presumably caused by coronary disease. Methods We studied 882 patients 1 to 6 months after a hospitalization for myocardial infarction or unstable angina as part of the Multicenter Study of Myocardial Ischemia. An ETT and thallium-201 perfusion scan were performed in all patients. For the purpose of this study, the perfusion scan was considered the "gold standard" for ischemia. We correlated the ETT ST-segment responses with the perfusion scan in a group with a normal electrocardiogram baseline ST segment (NO ST DEP group) and in a group with resting electrocardiographic ST depression greater than or equal to 0.5 mm (ST DEP group). Results Although the frequency of ischemia by perfusion scan was similar in the ST DEP group (48%) to that in the NO ST DEP group (40%), the ST DEP group had a significantly higher (p = 0.03) sensitivity (54%) in detecting ischemia than the NO ST DEP group (35%). The ST DEP group, however; had a lower (58% vs 74%) specificity than the NO ST DEP group (p = 0.056). Baseline characteristics of the two groups probably account for these differences. The overall diagnostic accuracy is similar (58% vs 56%) in the two groups. Conclusion We conclude that in a stable population with known coronary disease, the presence of ST depression on the resting electrocardiogram does not impair the detection of ischemia by the ETT, but may be associated with a higher false-positive rate.