Temporal evolution of traditional versus transformed EGG-based indexes in patients with induced myocardial ischemia

The time course of changes in the electrocardiogram as a result of myocardi al ischemia induced during prolonged coronary angioplasty has been studied. We have analyzed the electrocardiogram evolution during the occlusion in t erms of the Ischemic Changes Sensor, which is a parameter that describes th e capacity of different indexes to detect induced changes. Traditional inde xes at specific time locations (ST level, T wave amplitude and position, an d durations of QT interval and QRS complex) and global indexes (based on th e Karhunen-Loeve transform as applied to the QRS complex, ST-T complex, ST segment and T wave) have been considered. The global indexes better detecte d ischemic changes than the traditional indexes. The most sensitive were th e index for the ST-T complex (89%) in the Karhunen-Loeve transform-derived group and for the ST level (61%) in the traditional group. Changes in the v entricular repolarization period usually appeared earlier (77% of patients) than changes in the depolarization period (23% of patients). A similar per centage of patients exhibited the earliest ischemic changes in the T wave ( 41%) and in the ST segment (36%). The evolution of the Ischemic Changes Sen sor parameters showed thar the majority (60%) of the total changes occurred during the first minute of occlusion. The results suggest that the use of global electrocardiogram indexes better reflect ischemic changes than do tr aditional indexes, such as the ST segment deviation.