Characterization of silent ischemia in patients with unstable angina: prognostic and therapeutic implications

The occurrence of silent ischemia in various ischemic myocardial syndromes has attracted increasing attention. In unstable angina hemodynamic monitoring has suggested that the symptomatic and silent episodes of ischemia do not differ significantly. In two discrete studies we determined the characteristics and prognostic significance of silent ischemic episodes in unstable angina. In one study with 41 patients, there were 781 episodes of ischemia in Holter recordings: 392 (50%) with ST-segment depression, 242 (31%) with ST-elevation, 45 (6%) with ST-elevation and depression in different leads, 70 (9%) with pseudonormalization of T waves and 32 (4%) with T wave augmentation. Ventricular arrhythmias were associated with 18% of the episodes. The mean duration of ischemia was 14 minutes (range 30 seconds to almost twelve hours), the majority being less than five minutes. Only 154 (20%) of the 781 episodes of ischemia were associated with pain. Conversely, 77 episodes of chest pain were not associated with electrocardiographic changes. Analysis of the temporal sequence of heart rate during the development of ischemia (analysed in 415 episodes) showed that in only 43 (10%) the heart rate at the beginning of ischemia was significantly (exceeding 6 beats/minute) greater than that at five minutes (baseline) preceding the onset of ischemia. At the peak of ischemia, the mean heart rate increase was 10% and returned to baseline at the end of the ischemic episode. The data indicate that 80% of ischemic episodes in unstable angina are silent and over 90% are not triggered by increases in heart rate indicating that increased oxygen demand is an uncommon cause of ischemia in unstable angina.(ABSTRACT TRUNCATED AT 250 WORDS)