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 ele ctrocardiogram (ETT) generally indicates myocardial ischemia. Disorder s 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 indicat or of ischemia in patients with a resting electrocardiographic ST depr ession, presumably caused by coronary disease. Methods We studied 882 patients 1 to 6 months after a hospitalization for myocardial infarcti on or unstable angina as part of the Multicenter Study of Myocardial I schemia. An ETT and thallium-201 perfusion scan were performed in all patients. For the purpose of this study, the perfusion scan was consid ered the ''gold standard'' for ischemia. We correlated the ETT ST-segm ent responses with the perfusion scan in a group with a normal electro cardiogram baseline ST segment (NO ST DEP group) and in a group with r esting electrocardiographic ST depression greater than or equal to 0.5 mm (ST DEP group). Results Although the frequency of ischemia by perf usion 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 th an the NO ST DEP group (p = 0.056). Baseline characteristics of the tw o groups probably account for these differences. The overall diagnosti c accuracy is similar (58% vs 56%) in the two groups. Conclusion We co nclude that in a stable population with known coronary disease, the pr esence of ST depression on the resting electrocardiogram does not impa ir the detection of ischemia by the ETT, but may be associated with a higher false-positive rate.