The evolution of electrocardiographic changes in ST-segment elevation myocardial infarction

Acute myocardial infarction (AMI) is a not uncommon diagnosis in the emergency department. During ST-segment elevation AMI (STEMI), the electrocardiogram (ECG) typically follows a progression of abnormality, beginning with hyperacute T waves and culminating with ST-segment elevation; pathologic Q waves can appear early and/or late in the process. Other findings include T-wave inversion and ST-segment depression which can occur before, during, or after the STEMI event. The evolution of ECG through these changes can occur rapidly after coronary artery occlusion. The emergency physician should be aware of the ECG findings that characterize the evolution of an STEMI with a sound understanding of the associated pathophysiology and clinical implication. This review discusses the changing ECG during an AMI. The pathogenesis of these findings is discussed. Finally, the clinical implications at each stage are reviewed.