Prognostic value of myocardial perfusion SPECT versus exercise electrocardiography in patients with ST-segment depression on resting electrocardiography

Background. The value of exercise-induced ST-segment depression for the prognostic evaluation of patients with I mm of ST depression or greater on the resting electrocardiogram is controversial. Methods and Results. Patients who underwent exercise myocardial perfusion single photon emission computed tomography (MPS) and had resting ST depression of I mm or greater with a nondiagnostic exercise electrocardiographic response (n = 1122) were followed up for 3.4 +/- 2.3 years. Those with paced rhythm, pre-excitation, left bundle branch block, or myocardial revascularization within the first 60 days after MPS were excluded. Additional exercise-induced ST-segment depression was considered significant if >= 2 mm MPS was scored semiquantitatively by use of a 20-segment model of the left ventricle; the percentage of myocardium involved with stress defects (% myo) was derived by normalizing to the maximal possible score of 80. Hard events were defined as nonfatal myocardial infarction or cardiac death. A Cox analysis was used to determine independent predictors of hard events among clinical, exercise, and nuclear variables. Hard event rates increased as a function of % myo for either patients with exercise-induced ST depression (1.4%/y for normal MPS vs 4.1%/y for % myo > 10%, P < .03) or those without it (0.7%/y for normal MPS vs 3.0%/y for % myo > 10%, P = .0001). Age, diabetes mellitus, shortness of breath as the presenting symptom, and % myo were independent predictors of hard events. Exercise-induced ST depression was predictive of hard events only when it was 3 mm or greater. The presence and extent of perfusion defects, reflected in the % myo, had incremental prognostic value over clinical variables and also over all degrees of exercise-induced ST depression. Conclusions. Although MPS effectively risk-stratifies patients with resting ST depression of I mm or greater, the prognostic value of exercise-induced ST depression is limited in these patients, with a small added risk when severe (>= 3 mm).