defibrillator

defibrillator device that delivers an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances ( arrhythmias ). The shock changes a fibrillation to an organized rhythm or changes a very rapid and ineffective cardiac rhythm to a slower, more effective one. In a typical hospital defibrillator, voltage stored by the defibrillator pushes electrical current through the chest to deliver a muscle-contracting jolt to the heart; the current is transmitted by means of electrodes or paddles placed on the chest. Automated external defibrillators are now available for use by persons with minimal medical training in emergencies when medical professionals are unavailable, and miniaturization has led to the development of the implanted internal defibrillator (also called an internal cardioverter). In the latter a microcomputer uses an electrode to monitor the heartbeat. Upon detecting a minor arrhythmia, it activates a built-in conventional pacemaker to restabilize the heart's rhythm. If that fails, it delivers a small defibrillating electrical shock to the heart. In an extreme case, it resorts to a far stronger shock to reset the heart rate.

defibrillator (dee-fib-ri-lay-ter) n. the apparatus used for issuing a measured electrical current to a patient's heart in defibrillation. Defibrillators may be semi- or fully automated to recognize abnormal rhythms and to deliver the appropriate shock, fully operator-dependent, or implanted into the patient's body like a pacemaker.

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, and Niall MacFarlane