The ECG findings of ischemia or infarction can result in changes to the J point, ST segment, and T waves. This makes the diagnostic process challenging in some patients because there are other diagnoses that will also change the J point, ST segment, and T waves, including:
Therefore, changes to the J point, ST segment, and T wave are non-specific. In other words, they can be caused by many different processes.
- early repolarization
- left ventricular hypertrophy (LVH) with repolarization abnormalities
- left bundle branch block (LBBB)
- ventricular rhythms
- pace rhythms
- drugs (digoxin is a common example)
- electrolytes (potassium is a common example)
- central nervous system events (for example, a stroke)
Further, in order to accurately diagnose ischemia or infarction, you need to also know the diagnostic criteria of the diagnoses that mimic ischemia and infarction to help increase your diagnostic accuracy.
Ischemia is a condition of oxygen deprivation that does not result in cell death. Infarction is a condition of oxygen deprivation that does result in cell death. The ECG patterns of ischemia vs. infarction has some similarities and some differences.
ECG Diagnostic criteria of myocardial ischemia:
- J point depression
- ST segment depression
- Inverted T waves
- Biphasic T waves
- the findings above occur in 2 anatomically contiguous leads (2 leads from the same area of the heart)
1. Wagner GS, Macfarlane P, Wellens H, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part VI: acute ischemia/infarction: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology. Circulation. 2009;119(10):e262-e270.