Myocardial Ischemia, Injury, and Infarction

While myocardial ischemia, injury, and infarction may be used nearly interchangeably in modern parlance, they each have specific definitions. The main factor that separates infarction from the other two terms is the presence of pathological Q-waves—a strong indicator of myocardial tissue death and, given enough time, scar formation. This is an important distinction, as the presence of ST-segment elevations (STEs) is not pathognomonic for an ST-segment elevation myocardial infarction (STEMI). In fact, less worrisome diagnoses, such as pericarditis and benign early repolarization, are present with STEs. This exemplifies the notion that not all STEs are consistent with STEMI; furthermore, ST-segment changes need not be related to ischemia, injury, or infarction. As such, the reader must be able to identify not only the individual components of the ECG (such as STEs) but also integrate these findings into the clinical picture. By reviewing potentially dangerous ECGs, such as those indicative of acute coronary syndrome (ACS), as well as less concerning findings (like benign early repolarization), the learner will be able to correctly interpret the ECG and use that to direct the patient's care.