Temporal evolution of ECG-based indexes in patients with myocardial ischemia induced by prolonged balloon occlusion

The time course of ischemic ECG changes induced by prolonged occlusion have been studied. The authors have analyzed the evolution along angioplasty of an Ischemic Changes Sensor (ICS) parameter estimated for different ECG-based indexes in 83 patients. They compared traditional indexes (e.g. ST level, QT interval, T wave measurements, etc.) and global measurements derived using the Karhunen-Loeve transform applied on different ECG intervals. The KLT-based indexes showed a better sensitivity to ischemic changes than did the traditional indexes (89% in KLT index for ST-T complex, vs. 61% in ST level index). Further, it was found that changes in the ST-T complex usually appeared earlier than in the QRS complex (77% of patients vs. 23%). A similar percentage occurred earlier in the T wave (41%) and in the ST segment (36%). It was also found that the largest changes occurred during the first minute of occlusion