Guide — Cardiac
Cardioversion vs Defibrillation
Both cardioversion and defibrillation deliver electrical energy to the heart to restore normal rhythm, but they differ critically in timing, indication, and technique. Understanding when to use each — and how to assist safely — is an essential cardiac nursing competency.
9 min read · Clinical Practice
Educational use only. Electrical therapy is performed under direct provider supervision and per institutional protocols. This guide supports learning — it does not replace clinical training, credentialing, or ACLS certification. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
The Core Distinction
The fundamental difference between cardioversion and defibrillation is synchronization:
- Cardioversion — shock is delivered synchronized to the R wave (QRS complex) to avoid shocking during the vulnerable T wave period, which can precipitate ventricular fibrillation
- Defibrillation — shock is delivered asynchronously (not timed to any cardiac event) because the patient is already in a disorganized or absent rhythm where timing is irrelevant
Memory anchor: If there is an organized rhythm with a pulse → consider synchronized cardioversion. If there is no organized rhythm or no pulse → defibrillate.
Definitions
| Feature | Cardioversion | Defibrillation |
|---|---|---|
| Synchronization | Yes — timed to R wave | No — asynchronous |
| Patient Status | Usually with pulse (may be conscious) | Pulseless, unresponsive |
| Energy (typical) | Lower (50–200 J biphasic, rhythm-dependent) | Higher (120–200 J biphasic for initial shock) |
| Setting | Elective or urgent (patient may need sedation) | Emergency (cardiac arrest) |
| Device Mode | Sync mode ON | Sync mode OFF |
Indications
Synchronized Cardioversion:
- Unstable atrial fibrillation or atrial flutter with rapid ventricular response
- Unstable supraventricular tachycardia (SVT) not responding to vagal maneuvers or adenosine
- Stable monomorphic ventricular tachycardia (with pulse) that fails pharmacologic management
- Hemodynamic instability: hypotension, chest pain, altered mental status, or signs of shock attributable to the dysrhythmia
Defibrillation:
- Ventricular fibrillation (VF) — pulseless
- Pulseless ventricular tachycardia (pVT)
- Both are shockable rhythms under ACLS protocols
Contraindications
Cardioversion contraindications and cautions:
- Atrial fibrillation of unknown duration (> 48 hours or unknown) without anticoagulation or ruling out intracardiac thrombus — risk of thromboembolism/stroke
- Digitalis toxicity — electrical shock can precipitate malignant arrhythmias in this setting
- Junctional or sinus tachycardia — rate-related, not a re-entrant arrhythmia; cardioversion will not be effective
Defibrillation contraindications:
- Non-shockable rhythms: asystole and pulseless electrical activity (PEA) — defibrillation is ineffective and wastes time that should be spent on CPR and reversible cause management
- Confirmed DNR/DNI status — always clarify code status before initiating any resuscitation
Nursing Considerations
Before the procedure:
- Verify informed consent (for elective cardioversion) and confirm patient identity
- Obtain IV access; ensure resuscitation equipment is at bedside
- Assess and document NPO status, current medications, and allergies
- Administer procedural sedation per order (for elective cardioversion) — common agents include midazolam, propofol, or etomidate
- Apply monitoring leads; ensure clear rhythm display on the defibrillator screen
- For cardioversion: confirm SYNC mode is active (device will display a marker on R waves)
During the procedure:
- Announce “Clear” and visually confirm no personnel are in contact with the patient or bed before discharging
- Apply firm pressure with paddles or ensure good pad contact to minimize resistance
- For cardioversion: hold the discharge button until the shock is delivered (device waits for R wave synchronization and may have a brief delay)
- For defibrillation: minimize interruptions to CPR — aim for < 10-second pause
After the procedure:
- Assess rhythm, pulse, blood pressure, and level of consciousness immediately
- Continue monitoring for recurrence and post-procedure complications
- Document: rhythm before and after, energy used, number of shocks, patient response, and medications given
- Inspect skin under pads for burns; apply care as needed
Safety Considerations
- Remove supplemental oxygen from the immediate area before shocking — oxygen supports combustion and can cause fire/burns
- Ensure all personnel are clear — electrical current can conduct through anyone in contact with the patient or the bed frame
- Implanted pacemakers and ICDs: Avoid placing pads directly over device; position them at least 8 cm away and use anterior-posterior pad placement when possible
- Transdermal medication patches: Remove nitroglycerin, hormone, and nicotine patches from the chest before placing pads to prevent burns and arcing
- Wet or diaphoretic skin: Dry the chest before pad application to ensure adequate conductance and reduce burn risk
- Double-check SYNC mode every time before cardioversion — many defibrillators automatically revert to unsynchronized mode after each shock delivery
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Heart Association (AHA) · American College of Cardiology (ACC) · AHA ACLS Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →