The most dramatic and worrisome ST segment elevations occur as a result of severe coronary ischemia. The elevation occurring with transmural myocardial infarction is the best known and may be the earliest ECG finding during the acute process. Less frequent, but still a result of coronary ischemia, is the elevation seen in a small percentage of treadmill exercise tests and in patients with Prinzmetal's variant angina. Usually, the ST segment must be 1 mm above baseline to merit attention.
Adding spice to the evaluation is the fact that a goodly proportion of normal ECGs will have significant ST elevation.
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This is attributed to the early repolarization phenomenon and can be seen in healthy individuals. Of help in differentiating normal from abnormal elevations is the shape of the initial portion of the segment.
In normals, it has an upward concavity, whereas in severe ischemia it usually has an upward convexity. The normal is often accompanied by a notched J point and prominent T wave.