Ventricular fibrillation (VF) is a chaotic rhythm that originates in the ventricles (the lower chambers of the heart).
In ventricular fibrillation, there is no organized depolarization of the ventricles. The ventricular muscle quivers. As a result, there is no effective myocardial contraction and no pulse.
The resulting rhythm looks chaotic with deflections that vary in shape and amplitude. No normal-looking waveforms are visible.
Ventricular fibrillation is normally broken down into coarse or fine ventricular fibrillation.
Ventricular fibrillation with waves that are 3 or more mm high is called "coarse" VF.
Ventricular fibrillation with low amplitude waves (less than 3 mm) is called "fine" VF.
Fine ventricular fibrillation is even more dangerous than coarse ventricular fibrillation, because there is even less contractility of the myocardium, which results in a smaller amplitude.
Usually when a person experiences ventricular fibrillation, it first starts off as coarse ventricular fibrillation. If untreated, it then may progress to fine ventricular fibrillation, which can then progress to asystole (which is no ventricle contractility at all, just a flat line).
With ventricular fibrillation, the rate cannot be determined, because there are no discernible waves or complexes to measure. The rhythm is rapid and chaotic with no pattern or regularity. No part of the EKG is discernible, including the p waves, PR interval, or QRS complex.
Aehlert, Barbara. Pocket Reference for ECGs Made Easy. Mosby JEMS/Elsevier, 2006.
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