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contentuptodate· Content· item f26_24_27023
©2013 UpToDate ® Print Email Relationship between myocardial action potential and surface electrocardiogram Each phase of the myocardial action potential (numbers, upper panel) corresponds to a deflection or interval on the surface electrocardiogram (lower panel). Phase 4, the resting membrane potential, is responsible for the TQ segment; this segment has a prominent role in the ECG manifestations of ischemia during exercise testing.