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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]
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.
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.
Right after the ventricles contract, the cells enter into a refractory period, where they can’t be stimulated to contract again, and during the upslope of the T wave, some cells are starting to come out of refractory, so those cells might be ready to go again, whereas other cells might still be in a refractory phase.
Ashman beats are described as wide complex QRS complexes that follow a short R-R interval preceded by a long R-R interval. [3] This short QRS complex typically has a right bundle branch block morphology and represents an aberrantly conducted complex that originates above the AV node, rather than a complex that originates in either the right or left ventricle.
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.
The refractory period of cardiac muscle is distinct from that of skeletal muscle. Nerves that innervate skeletal muscle have an extremely short refractory period after being subjected to an action potential (of the order of 1 ms). This can lead to sustained or tetanic contraction. In the heart, contractions must be spaced to maintain a rhythm.