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
can deteriorate or go into cardiac arrest. Thus, the procedure should
be done in a resuscitation area, with the appropriate monitoring
and standby resuscitation equipment. Cardioversion should be synchronized,
which means the electric current will be timed with the patient’s
intrinsic R wave, and thus minimize the risk of inducing Vfib.
Remove all metallic objects and nitroglycerin patches from
the patient to avoid causing skin burns. Ensure correct placement
of defibrillation paddles/pads and remove any direct
source of oxygen facing these paddles/pads to avoid fire
risk.2,3 If paddles are used, do not allow the
conducting gel to spread to within 5 cm of the other paddle. In
patients with an internal pacemaker who require defibrillation,
ensure that the paddles/pads are placed well away (12.5
cm or 5 in.) from the pacemaker before discharging.
Avoid prolonged pauses in CPR when defibrillating. This
was emphasized in the 2005 International Liaison Committee on Resuscitation
(ILCOR) guidelines.4 Thus, the emphasis is now
on minimal interruptions to CPR for analysis, a single shock instead
of three “stacked” shocks, and immediate resumption
of CPR without a pulse or rhythm check immediately after defibrillation.
1. Defibrillator: This can be a manual, semi-, or fully
automated external defibrillator.
2. Paddles or self-adhesive defibrillation pads.
3. Conductive gel or gel pads for defibrillation paddles.
4. Related resuscitation equipment (e.g., bag-valve mask device,
airway devices, suction, IV cannulation, and drugs).
Defibrillators should be properly maintained and in a constant
state of readiness. The use of checklists5 is recommended
to prevent defibrillator malfunction and ensure proper maintenance
of batteries. Users should be trained in the proper use of checklists,
and checks should be performed frequently (as often as every shift).
Place the patient in a supine position. Expose the chest and
remove any jewelry. Look for and remove any medication patches from
the patient’s chest (e.g., nitroglycerine). If the chest
is very hairy in the areas where electrodes are to be placed, quickly
shave this hair. This is necessary to ensure the electrodes stick
onto the chest. If the chest is wet (patient is sweaty or has been in
water), wipe dry immediately. Sweat or moisture on the chest will
reduce good contact and adhesion of the electrodes onto the chest
For a patient in cardiac arrest, defibrillation is part of the
immediate resuscitation process. However, for an elective or semi-elective
cardioversion, adequate anesthesia and procedural monitoring is
essential. The patient should be monitored in an area with resuscitation
equipment, including cardiac, blood pressure, and pulse oximetry
monitoring. Airway equipment, suction, and oxygen should be immediately
available. An IV line must be in place, and the procedure should
be explained to the patient and informed consent obtained when possible.
Once preparations are completed, sedate the patient with an IV agent,
such as etomidate, propofol, or midazolam (see Chapter 41, Procedural Sedation and Analgesia). Maintain cardiac monitoring
immediately after ...