Changes in QRS duration and R-wave amplitude in electrocardiogram leads with ST segment elevation differentiate epicardial and transmural myocardial injury

Background: Acute transmural ischemia increases QRS duration and R-wave amplitude owing to depressed intramyocardial activation. Theoretically, when myocardial injury is confined to the epicardium, the intramyocardial activation is preserved without affecting QRS duration.

Objective: The purpose of this study was to distinguish epicardial from transmural myocardial injury based on the analysis of the QRS complex in leads with ST segment elevation.

Methods: Electrophysiological effects of epicardial injury induced by topical application (n = 7) or intrapericardial injection (n = 10) of potassium were assessed in pigs in local electrograms recorded with needles in the left ventricle and in the peripheral 12-lead electrocardiogram (ECG), respectively, and were compared with transmural injury induced by acute left anterior descending (LAD) occlusion in the same pig.

Results: Epicardial application of 50 mM potassium induced ST segment elevation in epicardial (0.2 ± 0.06 to 0.5 ± 0.09 mV; P <.05) but not in midmyocardial local electrograms (0.1 ± 0.07 to -0.1 ± 0.09 mV). Local midmyocardial activation times were not affected by epicardial applied potassium (182 ± 5.9 vs. 183 ± 5.8 ms) but increased significantly during acute LAD occlusion (246 ± 20.9 ms; P <.01). Intrapericardial injected potassium induced ST segment elevation on average in nine of 12 ECG leads but did not change QRS duration and R-wave amplitude. Acute LAD occlusion induced ST segment elevation (five of 12 leads) associated with increased QRS duration (69 ± 1.2 to 89 ± 3.6 ms; P <.001) and R-wave amplitude (0.1 ± 0.01 to 0.7 ± 0.09 mV; P <.001) in the ECG.

Conclusion: Transmural but not epicardial myocardial injury delays intramural local activation and is associated with QRS prolongation and enlarged R-wave amplitude in leads with ST segment elevation. This differential ECG pattern may help to distinguish acute pericarditis (epicardial injury) from acute transmural ischemia in clinical practice.