Indications
- Atrial fibrillation / flutter — symptomatic, or to restore rhythm in a rhythm-control strategy
- Hemodynamically unstable SVT, AF, flutter, or VT with a pulse — urgent synchronized cardioversion
- Stable SVT refractory to vagal maneuvers and adenosine (less common)
- Elective restoration of sinus rhythm after adequate anticoagulation
Pulseless VT/VF is defibrillation, not synchronized cardioversion.
Anticoagulation — the safety core
- AF/flutter <48 h of known onset: cardiovert with anticoagulation started, lower thromboembolic risk (still anticoagulate per stroke risk afterward)
- AF/flutter ≥48 h or unknown duration: either ≥3 weeks of documented therapeutic anticoagulation or a TEE excluding LAA thrombus before cardioversion
- After cardioversion: anticoagulate ≥4 weeks regardless of CHA2DS2-VASc — the atrium is mechanically stunned and thrombus can form even in sinus rhythm
- Longer-term anticoagulation follows the patient’s CHA2DS2-VASc score
Setup & equipment
- Confirm consent, NPO status, and a current potassium and digoxin assessment (avoid in digoxin toxicity)
- Place pads anterior-posterior (often superior for AF) or anterior-lateral
- Attach defibrillator ECG leads so the device can sense R waves for synchronization
- Pre-oxygenate; sedate with propofol or etomidate to brief unconsciousness
Technique
- Engage SYNC mode and confirm the device is marking the R waves (sync markers on the QRS, not the T)
- Select energy: biphasic AF 120–200 J, flutter/SVT 50–100 J, monomorphic VT ~100 J
- Ensure everyone is clear; deliver during sedation
- Reassess rhythm. On failure, re-arm SYNC (it often disengages), escalate energy, and consider switching pad position or pretreating with an antiarrhythmic
- For VT, if the rhythm degenerates to VF, switch to unsynchronized defibrillation immediately
Troubleshooting a failed cardioversion
- Re-confirm SYNC and good R-wave sensing
- Escalate energy and optimize pad contact/position (AP for AF)
- Pretreat with ibutilide or amiodarone to lower the defibrillation threshold and improve success/maintenance
- Correct hypokalemia and hypomagnesemia
- Reconsider the diagnosis (e.g., atrial tachycardia that won’t shock-convert)
Complications
- VF from an unsynchronized shock — the reason SYNC discipline matters
- Thromboembolism / stroke — from inadequate anticoagulation
- Bradycardia / sinus arrest post-conversion — be ready to pace, especially with sinus node dysfunction
- Sedation-related hypotension or hypoventilation
- Skin burns at the pad sites
Post-procedure care
- Monitor on telemetry through sedation recovery; document the post-shock rhythm with a 12-lead
- Continue anticoagulation ≥4 weeks, then per long-term stroke risk
- Arrange rhythm follow-up and, where relevant, an antiarrhythmic plan to maintain sinus rhythm