ACLS Electrical Therapy: Defibrillation, Cardioversion and Pacing

Three electrical therapies appear in the ACLS algorithms, and confusing them is one of the commonest errors in practice and in the Megacode. The ACLS course teaches when to use each one.

Defibrillation

An unsynchronised shock for VF and pulseless VT. Biphasic energy follows the manufacturer’s recommendation. Resume compressions immediately after each shock.

Synchronised cardioversion

A shock timed to the QRS complex, to avoid delivering it during a vulnerable part of the cycle. Used for unstable tachycardia with a pulse — see the tachycardia algorithm. The initial energy depends on the rhythm: lower for regular narrow-complex rhythms, higher for irregular narrow-complex rhythms such as atrial fibrillation, and an intermediate dose for regular wide-complex rhythms. An irregular wide-complex rhythm is treated with a defibrillation dose. Sedate a conscious patient if it will not delay treatment, and check the sync marker before each shock.

Transcutaneous pacing

Pads deliver pacing impulses through the chest wall for symptomatic bradycardia when atropine is ineffective, while a longer-term solution is arranged — see the bradycardia algorithm. Confirm electrical and mechanical capture by feeling a pulse, and give analgesia and sedation.

Safety

• Everyone clear, including oxygen away from the chest.
• Pads away from implanted devices and medication patches — see using an AED.
• If the patient loses their pulse during cardioversion, turn sync off and defibrillate.

Rhythm recognition is covered in ACLS rhythms.

This guide summarises what the ACLS course teaches for education only. It is not a clinical protocol: follow the current American Heart Association guidelines, linked below, and your institution’s policies.

More ACLS guides: ACLS algorithms and skills

• ACLS Course in Abu Dhabi — dates, format and booking
• ACLS Algorithms Explained: Cardiac Arrest, Bradycardia, Tachycardia and Post-Arrest Care
• The ACLS Systematic Approach: BLS, Primary and Secondary Assessment
• ACLS Cardiac Arrest: VF and Pulseless VT (the Shockable Pathway)
• ACLS Asystole and PEA: The Non-Shockable Pathway
• ACLS Bradycardia Algorithm: Atropine, Pacing and Infusions
• ACLS Tachycardia Algorithm: Stable vs Unstable Tachycardia
• ACLS Post-Cardiac Arrest Care: What Happens After ROSC
• The H's and T's of ACLS: Reversible Causes of Cardiac Arrest
• ACLS Drugs: Adrenaline, Amiodarone, Atropine, Adenosine and More
• ACLS Rhythms: The ECG Rhythms You Need to Recognise
• ACLS Airway Management: From Bag-Mask to Advanced Airway
• Waveform Capnography in ACLS: What End-Tidal CO2 Tells You
• Acute Coronary Syndromes in ACLS: Recognition and First Steps
• Acute Stroke in ACLS: Recognition, Timing and First Steps
• ACLS Megacode: How It Works and How to Pass as Team Leader
• All ACLS guides, by topic

Other life support and first aid courses: BLS Course · PALS Course · First Aid Course · Training calendar

Frequently asked questions

What is the difference between defibrillation and cardioversion?

Defibrillation is an unsynchronised shock for VF and pulseless VT; cardioversion is synchronised to the QRS for unstable tachycardia with a pulse.

When is pacing used?

For symptomatic bradycardia that does not respond to atropine.

What if a patient in VT loses their pulse during cardioversion?

Turn off sync and defibrillate.

How do you confirm pacing capture?

Electrical capture on the monitor and mechanical capture by feeling a pulse.

Is sedation needed for cardioversion?

For conscious patients, if it does not delay treatment.

Sources and further reading

What we teach follows the awarding body and the UAE health authorities. For the definitive position on a course or licensing question, these are the places to check.

• CPR and ECC Guidelines — American Heart Association
• Advanced Cardiovascular Life Support (ACLS) — American Heart Association

Last reviewed 21 September 2026 by the training team at Safety First Medical Services, an American Heart Association training centre at Addax Office Tower, Al Reem Island, Abu Dhabi. Call +971 55 761 9841 or email training@safetyfirstmed.ae.