Action potentials relative refractory period

Figure 6. An action potential. The diagram illustrates the sequential changes in membrane potential that occur during an action potential. The refractory period is divided into absolute (solid line) and relative (dashed line). See text for details.

However, there is a period of time following the absolute refractory period during which a premature electrical stimulus can be conducted, and is often conducted abnormally. This period of time is called the relative refractory period (Fig. 6-2).2 The relative refractory period corresponds roughly to the latter half of phase 3 repolarization on the action potential and to the latter half of the T wave on the ECG. If a new... 

The effective refractory period is followed by a relative refractory period that lasts for the remaining 50 msec of the ventricular action potential. During this period, action potentials may be generated however, the myocardium is more difficult than normal to excite. 

FIGURE 23-1 T The cardiac action potential recorded from a Purkinje cell. The effective refractory period is the time during which the cell cannot be depolarized, and the relative refractory period is the time in which a supranormal stimulus is required to depolarize the cell. Action potential phases [0-4] and the ionic basis for each phase are discussed in the text. From Keefe DLD, Kates RE, Harrison DC. New antiarrhythmic drugs their place in therapy. Drugs. 1981 22 363 with permission.]... 

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