Prevalence and significance of transient--predominantly asymptomatic--myocardial ischemia on Holter monitoring in unstable angina pectoris, and correlation with exercise test and thallium-201 myocardial perfusion imaging.

The prevalence and clinical significance of transient myocardial ischemia was evaluated prospectively in 43 patients with a clinical diagnosis of unstable angina. Continuous 2-channel Holter electrocardiographic monitoring was begun < 24 hours after admission. In 3,558 hours of recordings (mean 83 +/- 20 hours/patient), there were 1,671 episodes of transient ischemia; > 90% were asymptomatic. All patients but 1 had at least 1 episode of transient ischemia. Twenty-two patients (group 1) had a total ischemic duration of > or = 30 minutes/day, whereas 21 patients (group 2) had a total ischemic duration of < 30 minutes/day. A predischarge symptom-limited exercise test was performed in 40 of these patients after medical stabilization and 39 patients underwent exercise thallium-201 imaging, an average of 3 days after the exercise test. During a follow-up period of 39.9 +/- 9 months (range 28 to 49), 4 patients developed myocardial infarction and 22 required revascularization because of medically refractory angina. There were significantly more patients with total cardiac events (myocardial infarction or a need for revascularization) in group 1 than in group 2 (p < 0.05). Among patients undergoing an exercise test and exercise thallium-201 imaging, a positive exercise electrocardiogram and the presence of a reversible thallium-201 perfusion defect were also significant predictors of subsequent cardiac events (p < 0.05 and p < 0.001, respectively). The results of the Holter recordings did not add significantly more prognostic information.(ABSTRACT TRUNCATED AT 250 WORDS)