What are the phases of ventricular fibrillation (VF)?

Phases of ventricular fibrillation (VF)


Here is what has been called as the three phase model of ventricular fibrillation:

  1. Electrical phase: Initial 4 minutes of VF.
  2. Hemodynamic phase: 4 minutes to 10 minutes after the onset of VF.
  3. Metabolic phase: Beyond 10 minutes after the onset of VF.

If EMS (Emergency medical service) arrives within 4 min (electrical phase) – defibrillation first – It is likely to be coarse VF and responds better to defibrillation. Moreover, metabolic acidosis which makes ventricular fibrillation refractory to defibrillation, would not have set in.
If after 4 min, but before 10 min, cardiopulmonary resuscitation (CPR) followed by defibrillation. It is likely that by this time lack of circulation would have caused metabolic acidosis and ventricular fibrillation would have degenerated into fine ventricular fibrillation. Defibrillation first strategy may have limited success at this stage and hence CPR first strategy is adopted. CPR will get the circulation started and there will be improvement in metabolic acidosis. This will enhance the chances of successful defibrillation.
If EMS arrives beyond 10 min, only limited success can be anticipated. CPR followed by defibrillation may achieve return of spontaneous circulation (ROSC) in some cases. Induction of hypothermia (revised term: targeted temperature management) is recommended as a measure of cerebral protection, though trial results have been controversial.

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