Principles of External Defibrillators

Abstract

Electrical defibrillation is the only effective therapy for cardiac arrest caused by ventricular fibrillation (VF) [1, 2] or pulseless ventricular tachycardia (VT). Scientific evidence to sup‐ port early defibrillation is overwhelming [3-5], being delay from collapse to delivery of the first shock the single most important determinant of survival [6, 7]. If defibrillation is deliv‐ ered promptly, survival rates as high as 75% have been reported [8, 9]. The chance of a fa‐ vourable outcome decline at a rate of about 10% for each minute cardiac defibrillation is delayed [3, 10]. The guidelines on cardiopulmonary resuscitation of the European Resuscitation Council and American Heart Association (AHA) strongly recommend attempting defibrillation with minimal delay in victims of VF/VT cardiac arrest. As this event occurs most often in the vic‐ tim’s private home or in public spaces away from healthcare facilities, the need for early de‐ fibrillation has led to the development of automatic, portable defibrillators (Automated External Defibrillator - AED). The purpose of this chapter is to review the mechanisms of external defibrillation, the availa‐ ble types of AEDs including the wearable cardioverter-defibrillator, its uses and limitations.