Prognosis in Medically Stabilized Unstable Angina: Early Holter ST-Segment Monitoring Compared with Predischarge Exercise Thallium Tomography

Objective: To assess the relative value of invasive and noninvasive predictors of outcome in patients after unstable angina.

Design: Cohort of 54 patients with unstable angina who had 6-month follow-up after stabilization on medical therapy.

Setting: University-based hospital, tertiary referral center.

Patients: Consecutive patients with unstable angina whose symptoms resolved while receiving medical therapy.

Measurements and Main Results: We prospectively compared 24-hour Holter ST-segment monitoring at admission, quantitative exercise thallium tomography, and cardiac catheterization 5 ± 2 days after admission and analyzed their value for predicting a cardiac event in patients with unstable angina within 6 months. When patients with a favorable outcome (n = 40) were compared with patients with an unfavorable outcome (n = 11) no statistical difference was found in duration of ST shift of 1 mm or more on Holter monitoring (51 ± 119 min compared with 37 ± 43 min), exercise duration by the standard Bruce protocol (8.0 ± 3.6 min compared with 7.9 ± 3.1 min), exercise-induced ST depression (0.6 ± 0.9 mm compared with 1.0 ± 1.0 mm), and contrast left ventricular ejection fraction (70% ± 10% compared with 69% ± 15%). Patients with a favorable outcome were distinguished from those with an unfavorable outcome by a higher maximum rate-pressure product (24 x 10³ ± 6 x 10³ compared with 18 x 10³ ± 7 x 10³, P = 0.0025), smaller size of the reversible scintigraphic perfusion defect expressed as a percentage of total myocardium imaged (6% ± 11% compared with 17% ± 18%, P = 0.05) and a smaller number of vessels with stenosis of 50% or more (1.1 ± 1.2 compared with 2.1 ± 1.0, P = 0.01). On multiple logistic regression analysis, a history of previous myocardial infarction was the most powerful predictor of outcome. In patients without myocardial infarction, reversible exercise thallium perfusion defect size was the only predictor.

Conclusion: After stabilization of an episode of unstable angina, quantitative tomographic exercise thallium scintigraphy has greater value for risk stratification than Holter ST-segment monitoring, particularly in patients who have not had a previous infarction.