Forms of defibrillation
A distinction is basically drawn between synchronous and asynchronous defibrillation as well as between automatic and manual defibrillation. The operating mode of a defibrillator is also either monophasic or biphasic.
Asynchronous defibrillation versus synchronous defibrillation
Asynchronous and synchronous defibrillation differ by the timing of the shock delivery in relation to the ECG. A reference to just defibrillation will generally be referring to asynchronous defibrillation. Synchronous defibrillation by contrast is described as cardioversion.
Cardioversion or synchronous defibrillation is normally performed as part of an elective treatment of, say, atrial arrhythmia or as an emergency procedure with instable ventricular tachycardia. It is performed synchronized with the R wave in the ECG to avoid disrupting the vulnerable phase.
Asynchronous defibrillation, however, takes place with no synchronization with the ECG, as there is no coordinated excitation of the heart. Asynchronous defibrillation is an emergency technique.
Automatic versus manual defibrillation
An ECG analysis of the underlying heart rhythm must be performed before any defibrillation in order to determine whether there is a shockable rhythm or not. If the defibrillator detects a shockable rhythm the device is charged and prepares the shock. Automatic and manual defibrillation then differ in terms of who or what eventually delivers the shock.
Manual defibrillation involves the users deciding themselves whether and when a shock is delivered.
In the case of automatic defibrillation, the device decides when and whether a shock is delivered. However, with a semiautomatic defibrillator, the users trigger the shock by pressing a button.
Monophasic versus biphasic defibrillation
For a defibrillation there are various pulse configurations: monophasic and biphasic. They differ by virtue of the type of current pulse. Studies show that biphasic shocks with a defibrillation tend to be more effective and better suited than conventional monophasic shocks4.