ventricular fibrillation
Ventricular fibrillation is the heart's electrical equivalent of total panic. Instead of contracting in an organized pump, the muscle of the ventricles quivers in a chaotic, uncoordinated shimmer — so no blood is pumped at all. Within seconds the brain is starved of oxygen, the person collapses unconscious, and without treatment death follows in minutes. It is the commonest rhythm in sudden cardiac arrest.
On a monitor the trace becomes a wild, irregular, coarse-then-fine squiggle with no recognizable beats. The usual trigger is an acute heart attack or severe ischemia, but it can also arise from inherited channel disorders, electrolyte derangement, or as the lethal end-stage of ventricular tachycardia.
There is only one rhythm-restoring treatment: an immediate electrical shock from a defibrillator, which momentarily stuns all the muscle so the natural pacemaker can resume control. High-quality chest compressions buy time until a shock can be delivered. Survival falls sharply with every minute of delay, which is why public defibrillators and bystander CPR save lives.
A man collapses at a gym; a bystander starts chest compressions and an automated external defibrillator advises a shock, which converts his ventricular fibrillation back to a normal rhythm before the ambulance arrives.
Early defibrillation and bystander CPR are the strongest determinants of survival.
Ventricular fibrillation is a “shockable” rhythm: defibrillation is the definitive treatment, whereas drugs alone will not restore an organized beat. Every minute without a shock cuts survival substantially.