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Figure 4 Cellular basis for the T-wave. (A) The electrocardiogram (ECG) tracings were recorded in patients with various serum potassium concentrations. A pathologic U-wave was seen under hypokalemia, whereas a tall and upright T-wave was associated with hyperkalemia. (B) Simultaneous recording of action potentials (APs) from epicardial (Epi) and M cells or endocardial cells (Endo), together with a transmural ECG under various extracellular potassium concentrations. Extracellular potassium primarily influenced the AP phase 3 slope (repolarization rate); hyperkalemia accelerated phase 3 repolarization, whereas hypokalemia reduced it. The alteration of AP phase 3 slopes and their interplay among different myocardial layers determined the T-wave morphologies under various extracellular potassium concentrations. A pathologic U-wave was present with hypokalemia. Reprinted from Yan et al. (32), with permission.
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