defibrillator

This is a device used in the treatment of life-threatening disturbances of the rhythm of the heart beat which may occur as the result of a heart attack or a variety of serious injuries or illnesses. Its effect is to ‘reset’ the electrical activity of the heart in the hope that the natural pacemaker cells can then regain control of the rhythm. Defibrillation using direct current, in the form of an unsynchronized countershock, is usually the only way to halt ventricular fibrillation. The countershock from the defibrillator produces a sustained simultaneous excitation (and hence contraction) of all cardiac muscle fibres, which can terminate ventricular fibrillation and other abnormal rhythms. The countershock is administered by pressing a button on each of two defibrillator ‘paddles’ placed on the chest wall. Firm pressure is applied to these paddles to ensure good electrical contact with the skin; this also forces air out of the lungs to bring the chest wall in closer contact with the heart. While the shock is discharged, the patient often ‘jumps’ because motor nerves and skeletal muscles are simultaneously, unavoidably stimulated.

— David J. Miller, Niall MacFarlane

See also cardiac arrest; electrocardiogram; heart; heart attack.

An apparatus for defibrillating the ventricles of the heart.

An apparatus used to produce defibrillation by application of brief electroshock to the heart, directly or through electrodes placed on the chest wall.

• chemical d. — certain antiarrhythmic drugs are effective as antifibrillation agents and may be used in emergency situations to overcome ventricular fibrillation.