Symmetric T waves, inverted or upright (as in "hyperacute" T waves), characteristic of ECG "ischemia," have been considered to reflect a type, or degree, of cellular affection resulting only in action potentials of increased duration.7,10,16 Because the QT interval recorded at the body surface can be considered as the sum of all action potentials (i.e., of the QT intervals of individual cells), any process (such as ECG ischemia) that increases action potential duration will cause prolongation of ventricular depolarization and QT interval. T-wave inversions710 do not always reflect "physiologic" ischemia (due to decreased blood supply) because they also can be seen in evolving pericarditis, myocardial contusion, and increased intracranial pressure, as well as in the right chest leads of young patients (persistent juvenile pattern).43


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