Characterizing acute ischemia via ECG: A study of severity, extent, and spatial variability in myocardial infarction and non-infarction groups

Ischemic heart disease remains the leading cause of mortality worldwide. Its diagnosis largely relies on detecting dynamic changes in the ST segment of the electrocardiogram (ECG). However, alterations in other ECG waves and intervals have also been reported. One factor that is often overlooked is the presence of a prior myocardial infarction and its influence on the myocardial response to a new ischemic event. This study aimed to quantify the magnitude and temporal dynamics of ECG changes during acute myocardial ischemia and to evaluate how a previous infarction modifies these changes. Twelve-lead ECG recordings obtained before and during acute ischemia induced by percutaneous coronary intervention in one of the three major coronary arteries were analyzed. Dynamic heartbeat averages were computed to extract and track features related to ECG depolarization (QRS width, amplitude, and area) and repolarization (T-wave amplitude and area, ST-segment deviation and area, and T-to-QRS amplitude ratio). The results show that, beyond ST-segment deviation, multiple ECG markers evolve over time during coronary artery occlusion. Repolarization features showed earlier and more pronounced alterations than depolarization features, reaching approximately 37-fold and 23-fold changes at 4 minutes of occlusion compared with baseline, respectively. Males showed faster and more sustained ST increases (up to ~47-fold vs ~30-fold in females); older patients had abrupt early ST peaks (~38-fold at ~2 min after occlusion), whereas younger patients exhibited a more gradual increase. Moreover, patients with a prior infarction showed a stronger association between ECG changes and both the extent and severity of ischemia, reaching maximum correlation coefficients of 0.75 for repolarization markers and 0.57 for depolarization markers. Distinct spatial lead patterns were also identified according to the occluded artery and the presence of a prior infarction. In conclusion, acute ischemia induces dynamic changes across multiple ECG markers beyond the ST segment, where repolarization changes precede and exceed depolarization. These responses are modulated by age and sex; furthermore, prior infarction tightens their correlation with ischemic burden and alters spatial lead patterns.