Using a computerized diagnostic algorithm, the defibrillator analyzes the ECG tracing and attempts to detect either ventricular tachycardia or ventricular fibrillation. Many years of testing and application have made this process highly reliable. If the AED detects ventricular fibrillation, it will prompt the user to deliver a shock or automatically deliver the shock itself, depending upon its design and programming. Most AEDs include a memory system to allow for post-event monitoring and review of incidents, and a few also incorporate a simple ECG display. The other unique characteristic of more recent AEDs is the biphasic nature of the delivered shock.
Most defibrillators deliver a monophasic voltage, which can be pictured as half of a sine wave.
Biphasic voltage is best thought of as the complete sine wave, having both negative and positive components. In a way, the biphasic shock is a type of alternating current. Both the lower voltage and biphasic current also seem to cause less myocardial damage as a result of the shock. Another significant result from using a lower voltage is that a smaller battery and capacitor can be used, allowing for a much more compact and lighter weight unit. In the context of an airline, when every extra pound adds to costs, this development has made AEDs more feasible.