Nursing care
Defibrillation and Cardioversion: the nurse's role, start to finish
Written and reviewed by Dana Whitfield, RN, MSN · 5 min read · Updated September 2026
Short answer
Defibrillation delivers an unsynchronised shock for pulseless VF or VT, while cardioversion delivers a synchronised shock timed to the R wave for unstable but perfusing rhythms such as AF or SVT. Synchronising on a pulseless patient wastes time; failing to synchronise on a perfusing patient can strike during the T wave and induce VF.
Indications and contraindications
Defibrillation is for pulseless ventricular fibrillation and pulseless ventricular tachycardia. There is no pulse to protect, so the shock fires immediately, unsynchronised, as soon as the machine is charged. Delay for rhythm analysis or pad placement is the only acceptable delay.
Cardioversion is for a patient who still has a pulse but is haemodynamically unstable on a shockable rhythm: unstable atrial fibrillation or flutter, unstable supraventricular tachycardia, or unstable ventricular tachycardia with a pulse. The machine is set to synchronised mode so the shock falls on the R wave and avoids the T wave, where a shock can provoke VF instead of correcting the rhythm. Elective cardioversion for stable AF is planned, often with prior anticoagulation and a transoesophageal echo to exclude atrial thrombus, since restoring sinus rhythm can dislodge a clot. Cardioversion is contraindicated, or at least deferred, in known digoxin toxicity and in unstable atrial thrombus, and used cautiously in the presence of a pacemaker or ICD.
Getting the patient ready
For an unstable, conscious patient going to synchronised cardioversion, obtain consent if time allows, secure IV access, and prepare short-acting sedation or analgesia per protocol, since the shock is painful and the patient is awake for it. Attach a 3- or 5-lead ECG that the defibrillator can read for synchronisation, not just a rhythm strip, because the sync marker depends on a clean R wave.
Remove transdermal patches and metal jewellery from the chest, dry diaphoretic skin, and clip rather than shave excess chest hair if it will compromise pad contact. Place pads in the recommended anterior-lateral or anterior-posterior position, clear of any implanted device by several centimetres. For defibrillation there is no time for sedation or consent: the patient is pulseless, CPR continues until the moment of the shock, and readiness means pads on and the team clear.
Technique and safety checks
The single fact that separates these two procedures: cardioversion is synchronised to the R wave, defibrillation is not. Confirm the mode on the machine display before every shock, because a machine left in sync mode during a cardiac arrest can wait indefinitely for an R wave that a fibrillating heart never produces, delaying the shock that would restart it. Conversely, an unsynchronised shock delivered to a perfusing rhythm risks landing on the T wave and inducing the very arrest the procedure was meant to prevent.
Announce charging and shocking clearly, confirm nobody is touching the bed or the patient, and visually check that oxygen is not flowing across the chest. Select the energy per the rhythm and local protocol, deliver the shock, and check the rhythm immediately after. For cardioversion, if the first synchronised shock fails, escalate energy and reconfirm sync mode before the next attempt, since some machines revert to default settings between shocks.
What can go wrong
The most dangerous error is confusing the two modes: shocking a pulseless arrest in synchronised mode delays defibrillation while the machine searches for an R wave, and shocking a perfusing tachyarrhythmia in unsynchronised mode risks inducing VF by striking during repolarisation. Both are avoidable with a mode check before every shock.
Skin burns occur from poor pad contact, excess chest hair, or diaphoresis. Embolic stroke can follow cardioversion of AF with an unrecognised atrial thrombus, which is why anticoagulation status and clot exclusion matter before elective procedures. Bradyarrhythmia or transient asystole can follow cardioversion, so a resuscitation team and equipment stay at the bedside. Failure to synchronise correctly can also occur if T waves are tall enough to be misread as R waves, so watch the sync markers on the monitor rather than trusting the mode setting alone.
Ongoing care
After either procedure, monitor the airway, breathing, vital signs and level of consciousness closely, particularly if sedation was used for cardioversion. Obtain a 12-lead ECG to confirm the resulting rhythm and check pad sites for skin burns.
Following successful defibrillation for VF or VT, continue post-arrest care: targeted temperature management where indicated, haemodynamic support, and a search for the reversible cause. Following cardioversion, watch for recurrence of the original arrhythmia, document energy levels and number of attempts, and continue any anticoagulation plan already in place. Reassure the patient once awake, since waking mid-procedure or with chest soreness and no memory of events is common and unsettling.
Common exam questions
NCLEX items on this topic hinge on the synchronised-versus-unsynchronised distinction and on picking the correct rhythm for each. Expect a stem describing pulseless VF or VT that tests whether you reach for defibrillation without delay, and a separate stem describing unstable AF or SVT with a pulse that tests whether you select synchronised cardioversion instead.
Distractor answers often reverse the two procedures, or describe defibrillating a rhythm that actually needs cardioversion. Other favourites: recognising that a shockable pulseless rhythm never waits for sedation, that pre-cardioversion anticoagulation and thrombus screening matter for elective AF conversion, and that oxygen must be moved away from the chest before any shock is delivered.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our cardiovascular practice questions are the closest set to what this page covers.
Common questions
Can you defibrillate a patient who has a pulse?
No. Defibrillation is unsynchronised and reserved for pulseless VF and pulseless VT. A patient with a pulse and an unstable shockable rhythm needs synchronised cardioversion instead, because an unsynchronised shock risks landing during repolarisation and inducing VF.
What happens if the defibrillator is left in sync mode during a cardiac arrest?
The machine will wait for an R wave to time the shock against, which a fibrillating or pulseless rhythm may never reliably produce. This delays or prevents the shock from firing, so mode must be checked and switched to unsynchronised before defibrillating a pulseless arrest.
Why does elective cardioversion for atrial fibrillation need anticoagulation first?
AF allows blood to stagnate in the atria, particularly the left atrial appendage, and clot can form. Restoring sinus rhythm can dislodge that clot into the circulation, so anticoagulation or a transoesophageal echo to exclude thrombus usually precedes elective cardioversion.
Is sedation used for both procedures?
Sedation is used for cardioversion because the patient is conscious and the shock is painful. Defibrillation is performed on a pulseless, unresponsive patient, so there is no sedation and no delay for it.
What energy level is used for cardioversion versus defibrillation?
Energy settings vary by rhythm, device and local protocol rather than a single fixed number, so follow your institution's algorithm and the manufacturer's guidance for the specific arrhythmia being treated. What stays constant is the mode: synchronised for a perfusing rhythm, unsynchronised for pulseless VF or VT.
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