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Direct current (DC) cardioversion is a medical procedure to restore sinus rhythm in certain arrhythmias. It involves delivering a synchronised electric current using a defibrillator.
A synchronised shock involves delivering a shock that coincides with the R-wave of the QRS complex. This is essential because an unsynchronised shock may coincide with a T-wave, leading to ventricular fibrillation.
This guide provides a step-by-step approach to DC cardioversion in an OSCE setting; it is NOT intended to be used to guide patient care.
The guide does not focus on cardiac arrest management. For further information, read the Geeky Medics guide to advanced life support.
Indications
DC cardioversion is not indicated in all arrhythmias but should be used in:
- Unstable tachyarrhythmias: characterised by the presence of life-threatening features
- Stable tachyarrhythmias: unresponsive to simple interventions and pharmacological management, i.e. vagal manoeuvres, adenosine, flecainide
- Atrial fibrillation (AF): elective cardioversion where rhythm control is appropriate
Life-threatening features
There are four life-threatening features that suggest unstable tachyarrhythmias:
- Shock
- Syncope
- Myocardial ischaemia
- Severe heart failure
The presence of any one of these requires urgent cardioversion.
Defibrillator
Types of machine
Monophasic defibrillators
The current flows in a single direction, from one electrode to another. They are less efficient, and higher energy levels are needed to achieve effective defibrillation. They are less commonly used today.
Biphasic defibrillators
The current flows in one direction and then reverses. They are more efficient, and lower energy levels are needed to achieve effective defibrillation. They are more commonly used.
Key elements
While all defibrillators operate similarly, there might be differences due to the machine’s model. Familiarise yourself with the machine available in your healthcare setting.
- Power switch: turns the defibrillator on and off
- Screen: shows ECG, heart rate, and other vital data
- Mode selector button: allows the selection of different modes (manual, AED, pacing, etc.)
- Energy control knobs or buttons: allows the setting of shock energy level (e.g. 50J, 100J, 200J)
- Sync button: activates synchronisation with R-wave on ECG; essential for DC cardioversion
- Charge button: charges the machine to the chosen energy level
- Shock button: delivers the shock when pressed; when synchronisation is active, this needs to be pressed and held to deliver a shock
- Disarm button: safely discharges the stored energy without delivering a shock
- Handheld paddles or adhesive pads: these are connected by wires to the machine and deliver the shock to the patient’s chest
Therapeutic uses
Defibrillators are essentially used for three purposes:
1. Defibrillation: delivery of an unsynchronised shock in a patient in cardiac arrest with a shockable rhythm. The shock is unsynchronised as there is typically no coordinated electrical activity
2. DC cardioversion: involves the delivery of a synchronised shock to restore sinus rhythm in patients with certain arrhythmias
3. Pacing: delivery of controlled electrical impulses to restore or maintain an adequate heart rate in bradyarrhythmias, including heart blocks
Gather equipment
Gather the appropriate equipment for DC cardioversion:
- Resuscitation trolley
- Defibrillator
- Self-adhesive defibrillation pads
- ECG monitoring
- Skin cleaning wipes (alcohol/chlorhexidine)
- Razor (if hair needs to be removed for better pad attachment)
- Conductive gel sheath or conducting liquid gel (if manual paddles are used)
Sedation
Conscious sedation or general anaesthesia is required to perform DC cardioversion, as the procedure is painful and stimulating.
A competent healthcare professional (typically an anaesthetist) must carry out the sedation and provide airway support.
Introduction
Wash your hands using alcohol gel. If your hands are visibly soiled, wash them with soap and water.
Don PPE if appropriate.
Introduce yourself to the patient including your name and role.
Confirm the patient’s name and date of birth.
Briefly explain what the procedure will involve using patient-friendly language.
Example explanation
“This procedure is called cardioversion. It’s done to restore normal heartbeat rhythm by delivering an electrical shock to your chest. We will be sedating you for the procedure so that you don’t feel any discomfort. While you are sedated, we will be monitoring your breathing and heart activity throughout.
For the procedure, you will need to lie flat on your back, and we’ll place sticky pads on your chest, which will be used to deliver the shock.
The main risks of the procedure are mild skin irritation or soreness and, in rare cases, serious disturbance to your heartbeat. We will monitor you closely during and after the procedure to keep you safe.”
Gain consent to proceed with DC cardioversion. Written consent should be obtained as best practice, although this may not be possible in emergency situations.
Check if the patient has any allergies (e.g. latex).
Pre-procedure
Contraindications
Contraindications to DC cardioversion include:
- Patient refusal (absolute contraindication)
- Severe electrolyte disturbances: should be corrected before attempting cardioversion unless an emergency
- Inadequate anticoagulation for elective cardioversion in AF: if AF is present for >48 hours, elective cardioversion should be delayed to allow therapeutic anticoagulation for at least 3 weeks to prevent thromboembolic events
- Left atrial thrombus: cardioversion should be delayed until clot resolution, with therapeutic anticoagulation
Patient positioning
The patient should be in a supine position.
Required monitoring
It is important to monitor the patient’s vital signs throughout the procedure, particularly continuous cardiac monitoring.
As the procedures involve sedation, airway monitoring, and assessment are required throughout. Airway manoeuvres or adjuncts are typically required, but this should be led by the anaesthetist.
DC cardioversion
Preparation
1. Bring the resuscitation trolley and defibrillator
2. Make sure the patient is supine and expose the patient’s chest, if not already done
3. Clean, dry, or shave the skin if time permits to ensure better pad attachment
4. Attach the pads in the appropriate position as determined by the type of tachyarrhythmia
5. Attach the defibrillator’s three-lead monitoring
6. Prepare for sedation and airway management with an anaesthetist present
Pad positions
Pad placement can vary depending on the arrhythmia, as specific positions are shown to be more effective than others.
- Anterolateral (standard pad position): used for all tachyarrhythmias. One pad is placed to the right of the upper sternum below the clavicle and the other in the patient’s left mid-axillary line, approximately level with the V6 ECG electrode.
- Anterioposterior: where practicable, this should be used for atrial fibrillation and atrial flutter. One pad is placed anteriorly over the left precordium and the other on the back behind the heart, inferior to the left scapula.
Defibrillator machine settings
1. Turn on the defibrillator and ensure the machine displays the expected rhythm. If the rhythm is unclear, try switching leads
2. Press the sync button and confirm that synchronisation is on
3. Select the appropriate energy level as determined by the type of tachyarrhythmia
4. Press the charge button
Shock energy levels
The initial energy level is dependent on the arrhythmia involved:
- Atrial flutter and regular narrow complex tachyarrhythmias: start with 70–120J (biphasic shock)
- Broad complex tachyarrhythmias or atrial fibrillation: start with 120–150J (biphasic shock)
To increase the likelihood of initial shock success and reduce the duration of sedation, higher initial energy may be considered, particularly in obese patients or in patients known to be difficult to cardiovert.
If the initial shock fails, increase the energy in increments of 50–100J for subsequent shocks. The maximum energy level depends on the specific defibrillator used in your healthcare setting. Seek senior input to determine appropriate escalation.
Shock delivery
1. Ensure it is safe to deliver the shock and clearly announce “all clear“
2. Press and hold the shock button until the shock is delivered. There might be a delay as the defibrillator synchronises with the cardiac rhythm
Defibrillator safety
Before delivering the shock, always shout “all clear” and confirm that no one is touching the patient or their surroundings.
Oxygen masks and nasal cannula should be removed more than one metre from the patient’s chest. Closed-circuit oxygen delivery systems, such as tracheal tubes or supraglottic airway devices, don’t need to be removed.
For DC cardioversion, always double-check that the sync mode is on. An unsynchronised shock may coincide with the T-wave, triggering ventricular fibrillation.
If the defibrillator is charged but the shock is not delivered, always press the disarm button to discharge the stored energy safely.
Rhythm confirmation
Once the DC shock is delivered, it’s important to review the cardiac rhythm:
1. Confirm the cardiac rhythm. If cardioversion is unsuccessful, the energy may need to be increased in increments for subsequent shocks
2. Ensure that synchronisation remains activated. Synchronisation settings may vary between defibrillators; in some, synchronisation remains active after a shock, while in others, it needs to be reactivated
The approach can vary between elective and emergency situations when cardioversion is unsuccessful:
- In elective cardioversion, if unsuccessful, the procedure is typically abandoned
- However, in emergency cardioversion, senior input should be sought to determine the next steps
Defibrillator machines using paddles
Defibrillators often use adhesive pads instead of paddles due to ease of use and increased safety. However, if your healthcare setting has a machine using paddles, the process will be altered slightly.
Conducting material should be applied between the paddles and chest to prevent skin burns, e.g. conducting gel sheath or liquid gel placed on paddles.
To deliver the shock, place the paddles in the appropriate position, press down firmly on the chest wall, and press both buttons on the paddles simultaneously to deliver the shock.
To complete the procedure…
Confirm electrical cardioversion.
Ensure continuous monitoring including cardiac monitoring.
Allow the patient to reposition to a position that is comfortable for them.
Dispose of sharps, PPE, and other clinical waste into an appropriate clinical waste bin.
Wash your hands.
Document the procedure, including the number and energy of the shocks required.
Reviewer
Dr Chandrashekhar Mankar
Cardiac Anaesthetist
Dr Roger Clark
Acute Medicine Consultant
Editor
Dr Jamie Scriven
References
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Resuscitation Council UK. Chapter 11: Peri-arrest Arrhythmias. In: Advanced Life Support (8th Edition). 2021. Available from: [LINK]
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