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Cardiac cells have two refractory periods, the first from the beginning of phase 0 until part way through phase 3; this is known as the absolute refractory period during which it is impossible for the cell to produce another action potential. This is immediately followed, until the end of phase 3, by a relative refractory period, during which a ...
During the relative refractory period, a new action potential can be elicited under the correct circumstances. The cardiac refractory period can result in different forms of re-entry, which are a cause of tachycardia. [1] [B: 3] Vortices of excitation in the myocardium (autowave vortices) are a form of re-entry.
Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the ventricles of the heart quiver. [2] It is due to disorganized electrical activity. [2] Ventricular fibrillation results in cardiac arrest with loss of consciousness and no pulse. [1] This is followed by sudden cardiac death in the absence of treatment. [2]
Effective refractory period in green. In electrocardiography, during a cardiac cycle, once an action potential is initiated, there is a period of time that a new action potential cannot be initiated. This is termed the effective refractory period (ERP) of the tissue.
Timing the shock to the R wave prevents the delivery of the shock during the vulnerable period (or relative refractory period) of the cardiac cycle, which could induce ventricular fibrillation. If the patient is conscious, various drugs are often used to help sedate the patient and make the procedure more tolerable.
Ibutilide is a Class III antiarrhythmic agent that is indicated for acute cardioconversion of atrial fibrillation and atrial flutter of a recent onset to sinus rhythm. It exerts its antiarrhythmic effect by induction of slow inward sodium current, which prolongs action potential and refractory period of myocardial cells.
Phase 2 may be interrupted due to augmented opening of calcium channels, while phase 3 interruptions are due to the opening of sodium channels. Early afterdepolarizations can result in torsades de pointes , tachycardia , and other arrhythmias . [ 3 ]
The drug was used in emergency medicine, cardiology, and other specialties throughout the 1980s-1990s for the acute management of ventricular tachycardia and ventricular fibrillation refractory to other first line treatments such as defibrillation or lidocaine.