The degree of ST-segment depression on symptom-limited exercise testing: Relation to the myocardial ischemic burden as determined by thallium-201 scintigraphy

This study sought to determine the relation between the magnitude of exercise-induced ST depression and the ischemic burden as determined by quantitative thallium-201 scintigraphy. One hundred forty-four consecutive patients were prospectively studied with symptom-limited exercise testing and thallium-201 scintigraphy. Of these patients, 37 had between 1.0 and <2.0 mm (group 1) and 17 had ≥2.0 mm (group 2) of exercise-induced ST depression. There were no significant differences between groups 1 and 2 with respect to all exercise parameters including peak exercise heart rate (134 ± 21 vs 144 ± 26 beats/min), metabolic equivalents achieved (7.9 ± 3.0 vs 8.6 ± 3.3), and exercise time (7.4 ± 2.7 minutes in both groups). There was no significant difference in the prevalence of thallium-201 redistribution defects in group 1 versus group 2 patients (17 of 37 [46%] vs 8 of 17 [47%]), and in the extent of ischemia as determined by the number of redistribution defects per patient (1.2 ± 1.8 vs 1.2 ± 1.5, respectively). Thus, in this consecutive group of patients with exercise-induced ST depression, those with ≥2.0 mm of ST depression, relative to patients with a lesser degree of ST depression, had comparable exercise capacity and comparable ischemic burden by thallium-201 scintigraphic assessment. We conclude that the magnitude of ST depression on symptom-limited exercise testing does not correlate with the extent of ischemia as assessed by quantitative thallium-201 scintigraphy.