Transient coronary occlusion during elective PTCA: QRS changes are consistent with the timing of regional ventricular activation

BACKGROUND Electrocardiographic assessment of acute myocardial ischemia has traditionally emphasized ST-segment changes, whereas QRS alterations have received comparatively less attention. Whether the timing of ischemia-induced QRS changes is related to the normal timing of regional ventricular activation remains unknown. OBJECTIVE To determine whether the timing of QRS changes during acute coronary occlusion follows the timing of regional ventricular activation according to the occluded coronary artery. METHODS Electrocardiograms from 45 patients were recorded during controlled balloon occlusion of the left anterior descending (LAD), right coronary (RCA), and left circumflex (LCx) arteries. High-resolution, time-aligned analysis (1-ms) was performed using standard and derived leads, including regional loops and precordial bipolar and averaged signals. The timing and distribution of ischemia-induced QRS changes were compared between baseline and coronary occlusion. RESULTS The onset of ischemia-induced QRS changes differed according to the occluded coronary artery. In LAD occlusions, QRS vector changes occurred significantly earlier (40.7 ms), whereas RCA occlusions showed later changes (53.6 ms, p = 0.003 for LAD vs RCA comparison). Overall, the timing of QRS vector changes was consistent with the expected activation sequence of the myocardial territory supplied by the occluded artery. CONCLUSIONS During acute coronary occlusion, ischemia-induced QRS changes were consistent with the expected activation timing of the myocardial territory supplied by the occluded artery. These exploratory findings support a physiological framework for interpreting QRS changes during ischemia and suggest that the standard ECG contains underrecognized temporal information. Whether these temporal features can help identify the occluded coronary territory remains a hypothesis that requires prospective diagnostic-performance studies.