DC Cardioversion

Indications

• Tachyarrhythmia (broad or narrow complex) with adverse features per the RCUK 2025 tachycardia algorithm: shock, syncope, myocardial ischaemia, heart failure, or an arrhythmia immediately post-ROSC (new life-threatening feature in the 2025 guidelines).
• These features indicate the patient is haemodynamically unstable because of the tachycardia and needs synchronised cardioversion as first-line treatment, rather than drug therapy alone.
• Elective cardioversion for stable arrhythmia (e.g. persistent AF) is typically a planned procedure with anticoagulation considerations addressed in advance — this page focuses on the emergency indication.

Anticoagulation considerations

• Life-threatening instability — proceed to emergency cardioversion without delaying for anticoagulation.
• Stable patient, AF onset <48 hours — rhythm control (including cardioversion) can usually proceed without a pre-cardioversion anticoagulation delay, per NICE NG196.
• Stable patient, AF onset >48 hours or uncertain — cardioversion should generally be delayed until the patient has been therapeutically anticoagulated for a minimum of 3 weeks, or a transoesophageal echocardiogram has excluded left atrial thrombus, per NICE NG196.
• Discuss with cardiology/senior review where the duration of onset is uncertain or borderline in an otherwise stable patient.

Sedation & preparation

• A conscious patient needs sedation or brief general anaesthesia before shock delivery — cardioversion without adequate sedation is distressing and should not be performed in an awake, unanaesthetised patient outside of extreme peri-arrest circumstances.
• Full monitoring: continuous ECG, pulse oximetry, non-invasive blood pressure, capnography if sedated.
• Airway equipment and resuscitation drugs immediately available.
• IV access secured before starting.
• Involve an anaesthetist or appropriately trained sedationist per local policy, particularly outside genuine peri-arrest emergencies.

Equipment

Pad positions

Either antero-lateral or antero-posterior placement is acceptable; antero-posterior may improve efficacy for atrial arrhythmias, but antero-lateral is the more familiar, faster default in an emergency.

Step-by-step technique

1. Confirm the indication

   Reconfirm adverse features are present and that this is genuinely a cardioversion (not defibrillation) situation with an organised rhythm and a pulse.

2. Attach pads and monitor

   Self-adhesive pads in the chosen position; continuous ECG display on the defibrillator.

3. Sedate

   Administer sedation/anaesthesia per local protocol; confirm adequate depth before proceeding.

4. Select SYNC mode

   Activate synchronised mode on the defibrillator — confirm the machine marks the R wave correctly on each complex before shocking. Synchronisation must be re-selected before every shock; most defibrillators default back to unsynchronised mode after each delivered shock.

5. Select energy and shock

   Choose an appropriate starting energy for the rhythm (see below), ensure everyone is clear of the patient and bed, and deliver the shock. There will be a short discharge delay while the machine waits for the next R wave — hold the button until the shock fires.

6. Reassess and escalate

   Check the rhythm and pulse. If unsuccessful, re-select sync mode and increase the energy for the next attempt, following a stepwise increase per the algorithm.

7. After three unsuccessful shocks

   If adverse features persist after three synchronised shocks, give amiodarone 300 mg IV over 10–20 minutes, then attempt a further synchronised shock; expert help should be sought if not already involved.

Energy levels (RCUK 2025)

• Broad-complex tachycardia (e.g. VT) — initial shock 120–150 J biphasic, with stepwise increases for subsequent shocks if unsuccessful.
• Atrial flutter or regular narrow-complex tachycardia (SVT) — initial shock 70–120 J biphasic, with stepwise increases for subsequent shocks.
• Atrial fibrillation — the 2021 update (unchanged in 2025) states an initial synchronised shock at maximum defibrillator output, rather than an escalating low-to-high strategy, is a reasonable approach based on current evidence; some departments still use an initial lower energy with escalation depending on local protocol and device — confirm your local policy and the defibrillator manufacturer's guidance before use.
• Up to three synchronised shock attempts before amiodarone 300 mg IV over 10–20 minutes and a further attempt, per the standard peri-arrest tachycardia sequence.

Complications

Aftercare & documentation

• Continuous monitoring until fully recovered from sedation and rhythm is confirmed stable.
• 12-lead ECG post-cardioversion.
• Document: indication, adverse features present, sedation used, energy and number of shocks, rhythm before/after, complications, anticoagulation plan.
• Address the underlying cause and arrange appropriate follow-up (cardiology, anticoagulation review) as indicated.

Pitfalls & pearls

• Confirm adverse features are genuinely present before shocking — a fast but stable patient should generally receive drug therapy first.
• Re-select SYNC mode before every single shock — most machines revert to unsynchronised mode by default.
• Don't skip a considered anticoagulation discussion in the stable patient with AF of uncertain or prolonged duration — only bypass it when instability truly demands immediate action.
• Have a clear sedation and airway plan before the first shock, not improvised afterwards.

References