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For all procedures, ask yourself, 'does this need to be done 'now vs later'? And should this be done by 'me vs someone else?' Very often the answers will be 'now' and 'me' - so read on!

Synchronised cardioversion


How to perform synchronised cardioversion for 'unstable' tachycardias.



'Unstable' tachycardias - see ACLS Tachycardia algorithm 2020.

In ACLS, 'unstable' is defined as the presence of one or more of

  • hypotension
  • new altered level of consciousness
  • signs of shock
  • ischaemic chest pain
  • new or worsening cardiac failure


This procedure is not for pulseless VT or for VF. Both of these should be treated with unsynchronized defibrillation.

Cardioversion of atrial fibrillation requires caution to reduce the risk of embolic stroke from the procedure. The patient should be:

  • fully anticoagulated for 3 weeks prior OR
  • unstable and in rapid need of rhythm control (thus accepting the higher risk of stroke)  OR
  • onset within 12 hours OR
  • rhythm is AF with onset within 48 hours AND with a CHADS2 risk score of <2
Otherwise rate control may be preferable in terms of avoiding stroke risk from cardioversion. NB AF with Wolf-Parkinson-White (ventricular pre-excitation via an accessory pathway) is a special case where rate control via the AV node may create risk of VF - if unstable, electrically cardiovert, if stable, procainamide can control rate and may also cardiovert - expert consultation is recommended.


IV cannula
Resuscitation equipment


Cardioversion electrode position image
Pad positions for cardioversion
R wave synchronisation

  • the defibrillation pads will probably already be in place, if not, place them on the patients chest in the positions indicated on the pads
  • if there is time and the patient can comprehend, explain to the patient what you propose to do and get consent
  • explain to the team what you are going to do
  • sedation is necessary if the patient is awake, depending on the urgency of the situation
    • brief sedation with propofol is usually adequate - alternatively midazolam could be used
    • evidence suggests no need for adding an opiate (which increases the hypotension and apnoea risk)
  • select 'Sync' on the monitor and ensure it is marking the R waves (this is to avoid delivering a shock on the T wave which can precipitate VF)
  • select the energy level.

    Initial energy levels in Joules
    VT (monomorphic) 100 100
    AF 120-200 200
    Atrial flutter / SVT 50-100 50-100
    VT (polymorphic eg. Torsades) Unsyncrhonized 200 Unsyncrhonized 200
  • ensure everyone is clear, before briefly re-checking the monitor and pressing and holding the Shock button. Say 'you're clear, I'm clear, still in (whichever rhythm), shocking....'
  • you may need to hold the 'Shock' button for a brief time to allow the defibrillator to deliver the shock at the correct, synchronised time
  • if tachycardia persists, increase the energy by perhaps 50 J or more, re-select Sync, and repeat the process

Potential pitfalls

Improperly positioned or adhered defibrillation pads.
Inadequate safety when delivering a shock.
Not checking that the defib is 'synched' every shock.
Not holding the Shock button long enough for a shock to be delivered.

"Plan B"

Synchronised cardioversion is usually successful.
In case of failure, review pharmacological options and/or attempt to discuss with a cardiologist.

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Last modified: Thursday, 19 May 2022, 2:47 PM