Artefactual ST-segment elevation mimicking ST-segment–elevation acute myocardial infarction. In the limb leads, ST-segment deviation lasts only ≈120 ms, an interval that is too short to account for the entire ST segment, because it would correspond to a QTc interval of ≈230 ms. However, the QTc interval is normal (≈450 ms), as can be inferred from lead II (vertical dashed lines mark the end of the T wave). Thus, it becomes apparent that, in the limb leads, the ST segment incorporates a deviated and nondeviated part, and that the transition between these distinct parts of the ST segment is sharp and nonphysiological (arrows). In addition, similarly timed nonphysiological deflections of the ST segment are also present in all precordial leads (arrowheads), and other sharp nonphysiological deflections of opposite polarities are also present in opposite leads (asterisk). In lead II, however, the tracing is completely normal, with no abnormal deflections seen in any of its components, including the ST segment (box). The ECG pattern of abnormal deflections (most notably ST-segment deviations) in all leads except 1 limb lead is highly suggestive of a malfunctional limb electrode. See text for further details.