In ventricular fibrillation the heart quivers instead of pumping, and blood stops moving
When the heart's lower chambers lose their electrical order, the muscle twitches at random rather than squeezing from the tip upward. No blood leaves the heart, the person collapses without a pulse, and without CPR and a defibrillator death follows quickly. Survival outside hospital is roughly one in six.
Ventricular fibrillation, or VF, is the rhythm first found in about 10 percent of cardiac arrests. On an electrocardiogram it appears as ragged, shapeless waves with no clear pattern; one classic description calls it chaotic, asynchronous, fractionated activity. Clinicians grade it as coarse or fine by amplitude. Coarse VF may respond better to a shock, while fine VF can look almost like a flat line on a monitor set to low sensitivity, so some teams give CPR and drugs to build it up before shocking.
Most cases arise in diseased hearts, above all from ischaemic heart disease, but cardiomyopathy, myocarditis and valve disease can cause it too, as can electrolyte imbalances, overdoses of heart-toxic drugs, near drowning, major trauma, electric shock and bleeding inside the skull. A person may show agonal breathing, gasps that can fool a bystander into thinking they are breathing normally, when in fact the brainstem is starved of blood.
A puzzling minority happens in hearts with no visible disease. This idiopathic VF accounts for roughly 1 percent of out-of-hospital arrests and about 14 percent of VF resuscitations in people under 40. Inherited conditions offer clues: in Brugada syndrome, sodium channels in heart cells are faulty, and certain forms of long QT syndrome involve a potassium channel. Researchers admit that some of the mechanisms behind sudden death in apparently healthy hearts are still not fully understood.
The standard response is cardiopulmonary resuscitation plus defibrillation, with biphasic shocks possibly outperforming monophasic ones, and epinephrine or amiodarone given if first measures fail. Where the rhythm is caught matters enormously: about 17 percent survive when it strikes outside hospital, against about 46 percent inside. As long ago as 1899, researchers found that VF was usually what actually killed people executed in the electric chair.
Source: Ventricular fibrillation
