Fig. 3.

Changes in epicardial action potential duration, ventricular effective refractory period, and local critical interval after exposure to hypokalemia and to lidocaine. Epicardial MAP waveforms during regular stimulation in hearts exposed to normokalemic (5.2 mM K⁺, A) and hypokalemic (3.0 mM K⁺, B) test solutions and normokalemic (C) and hypokalemic (D) test solutions containing lidocaine (10 μM) for 20 min comparing action potential duration at 90% repolarization; APD₉₀ (vertical solid lines), VERP (vertical broken lines), and local critical interval (shading; a). Action potential duration at 90% repolarization, APD₉₀ (dense hashing), VERP (sparse hashing) and critical interval (shading) under these conditions (b). Asterisks indicate values that are significantly (P < 0.05) larger and daggers those that are smaller than those recorded in normokalemic hearts