Ischemia
Also calledMyocardial ischemia · Cardiac ischemia · Ischaemia
Definition
An imbalance between myocardial oxygen supply and demand; its onset is the first step toward myocardial infarction. On the ECG it mainly alters the ST segment and T wave: ischemia limited to the inner (subendocardial) layer classically causes horizontal or downsloping ST depression and/or deep, symmetric T-wave inversion, while ischemia from acute coronary occlusion produces hyperacute T waves and then ST elevation in the leads over the ischemic region. Ischemic ST changes can be transient, returning to normal as the episode settles, whereas infarction is defined as myocardial cell death caused by prolonged ischemia. The first ECG can also look normal: as many as 1 in 5 patients with acute myocardial infarction have a normal or near-normal trace.
Sources
- Channer K, Morris F. ABC of clinical electrocardiography: myocardial ischaemia. BMJ. 2002;324(7344):1023-1026. doi.org/10.1136/bmj.324.7344.1023
- 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. Circulation. 2009;119(10):e262-e270. doi.org/10.1161/CIRCULATIONAHA.108.191098
- Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018). Circulation. 2018;138(20):e618-e651. doi.org/10.1161/CIR.0000000000000617
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.