Defibrillation is the therapeutic use of electricity to depolarize
the myocardium and thus allow more coordinated contractions to occur.
The term defibrillation is usually applied to an
attempt to terminate a nonperfusing cardiac arrest rhythm [e.g.,
ventricular fibrillation (Vfib) or pulseless ventricular tachycardia
(Vtach)], allowing normal electrical activity to occur.
Cardioversion, by contrast, is the application of electricity
to attempt to terminate a still perfusing rhythm (e.g., Vtach with
a pulse, supraventricular tachycardias, including atrial arrhythmias),
hopefully to allow a normal sinus rhythm to restart. By this definition,
cardioversion is a less urgent procedure compared to defibrillation,
although the patient may be hypotensive or hemodynamically unstable,
rather than in cardiac arrest.
Indications for defibrillation include Vfib (Figure
36-1) and pulseless Vtach (Figure 36-2). Defibrillation
is contraindicated for asystole, pulseless electrical activity,
sinus rhythm, a conscious patient with a pulse, or where there is
danger to the operator or others (e.g., from a wet patient
Cardioversion is indicated for a hemodynamically unstable patient
with Vtach, supraventricular tachycardia, atrial
flutter, or atrial fibrillation. It is also possibly indicated after
failed pharmacologic therapy for the previously mentioned arrhythmias,
especially if the patient becomes hemodynamically unstable.
Electrical energy can terminate an abnormal rhythm, but if inappropriately
delivered, it can also induce Vfib. This can happen if the electric shock
occurs during the relative refractory portion of cardiac electrical activity.1 This
coincides with the middle and terminal phases of the T wave and
is also referred to as the vulnerable period.
When performing defibrillation, check the patient and rhythm
to ensure that a shock is truly indicated. Movement artifacts
or loose leads may lead to a misinterpretation of the rhythm. When
using automated external defibrillators (AEDs), it is important
to stop all movement (e.g., during transport) and confirm cardiac
arrest before initiating analysis mode.
Make sure that no rescuer is inadvertently in contact with the
patient when a shock is delivered—thus the emphasis on “stand
clear” drills during defibrillator training. If the patient
is on a wet or conducting surface, move the patient to a safe area
and dry the body before delivering the shock. When using manual
defibrillation paddles, always make sure that the paddles are either
on the defibrillator cradle or on the patient’s chest, with
minimal time in transit. Always point the paddles downward and never
wave the paddles around or face them toward each other, especially when
paddles are charged. This is to prevent inadvertent discharges. Sparking
can occur when the paddles are in close proximity to each other.
During cardioversion, there is a possibility that the patient