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Since PR and PT interval are regarded as baseline, ST segment elevation is regarded as a sign of myocardial ischemia. The opposing leads (such as V3 and V4 versus posterior leads V7–V9) always show reciprocal ST segment changes (ST elevation in one lead is followed by ST depression in the opposing lead).
The 2018 European Society of Cardiology/American College of Cardiology Foundation/American Heart Association/World Health Federation Universal Definition of Myocardial Infarction for the ECG diagnosis of the ST segment elevation type of acute myocardial infarction require new ST elevation at J point of at least 1mm (0.1 mV) in two contiguous leads with the cut-points: ≥1 mm in all leads ...
Illustration of ST segment elevation and depression The normal ST segment has a slight upward concavity. Flat, downsloping, or depressed ST segments may indicate coronary ischemia. ST elevation may indicate transmural myocardial infarction. An elevation of >1mm and longer than 80 milliseconds following the J-point.
12-lead electrocardiogram showing ST-segment elevation (orange) in I, aVL and V1-V5 with reciprocal changes (blue) in the inferior leads, indicative of an anterior wall myocardial infarction. The primary purpose of the electrocardiogram is to detect ischemia or acute coronary injury in broad, symptomatic emergency department populations. A ...
ST segment depression in eight or more leads, associated with ST segment elevation in aVR and V1 are associated with left main coronary artery disease or three-vessel disease (blockage of all three major branches of coronary arteries). ST segment depression most prominent from V1 to V3 is suggestive of posterior infarction.
The TIMI risk score can identify high risk patients in ST-elevation and non-ST segment elevation MI ACS [30] [31] and has been independently validated. [ 32 ] [ 33 ] Based on a global registry of 102,341 patients, the GRACE risk score estimates in-hospital, 6 months, 1 year, and 3-year mortality risk after a heart attack. [ 34 ]
ST segment depression and T-wave changes may be seen in patients with unstable angina; Depressed but upsloping ST segment generally rules out ischemia as a cause. Also, it can be a normal variant or artifacts, such as: Pseudo-ST-depression, which is a wandering baseline due to poor skin contact of the electrode [3]
ST segment elevation — 54 percent sensitivity; Abnormal Q waves — 31 percent sensitivity; Cabrera's sign — 27 percent sensitivity, 47 percent for anteroseptal MI; Initial positivity in V1 with a Q wave in V6 — 20 percent sensitivity but 100 percent specificity for anteroseptal MI