Synchronized Cardioversion for Arrhythmias
Synchronized cardioversion should be performed immediately for any hemodynamically unstable patient with supraventricular or ventricular tachycardia (with a pulse), and for stable patients when pharmacological therapy fails or is contraindicated. 1
Immediate Indications (Hemodynamically Unstable Patients)
Perform synchronized cardioversion without delay when patients exhibit signs of hemodynamic instability including hypotension, altered mental status, shock, chest pain, or acute heart failure symptoms. 2, 3
Specific Arrhythmias Requiring Immediate Synchronized Cardioversion:
AVRT (Atrioventricular Reentrant Tachycardia): Use synchronized cardioversion if vagal maneuvers or adenosine are ineffective or not feasible in unstable patients. 1
Pre-excited Atrial Fibrillation: Perform immediate synchronized cardioversion in unstable patients, as rapid pre-excited AV conduction can lead to ventricular fibrillation. 1
Monomorphic Ventricular Tachycardia with pulse: Start with 100J (biphasic or monophasic) for unstable patients. 4, 2
Wide Complex Tachycardia: Immediate synchronized cardioversion is indicated when hemodynamic instability is present. 3
Supraventricular Tachycardia in Acute Heart Failure: Poorly tolerated SVT should be treated with synchronous cardioversion at relatively low energies (50-100J biphasic). 1
Indications in Hemodynamically Stable Patients
Use synchronized cardioversion when pharmacological therapy is ineffective or contraindicated in stable patients with adequate sedation or anesthesia. 1
Specific Scenarios:
AVRT or AVNRT: Most stable patients respond to pharmacological therapy (80-98% success with verapamil, diltiazem, or adenosine), but synchronized cardioversion is highly effective when drugs fail. 1
Atrial Flutter/Fibrillation: DC cardioversion achieved 98% success rate in one prospective study of 53 patients with various tachyarrhythmias. 5
Critical Contraindications - When NOT to Use Synchronized Cardioversion
Never use synchronized cardioversion for the following rhythms:
Ventricular Fibrillation: The device may not sense a QRS wave, potentially resulting in no shock delivery—use unsynchronized high-energy shocks instead. 4
Pulseless Ventricular Tachycardia: Treat exactly like VF with unsynchronized high-energy shocks to avoid delays in cardiac arrest treatment. 4
Polymorphic (irregular) VT: Even with a pulse, synchronization is usually not possible—use unsynchronized shocks. 4
Digitalis toxicity or hypokalemia: Electrical cardioversion is contraindicated in these conditions. 2
Energy Dosing Algorithm
Initial Energy Levels:
- Monomorphic VT with pulse: 100J (biphasic or monophasic) 4
- SVT/Atrial Flutter: 50-100J (biphasic) 1
- AVRT/AVNRT: Standard cardioversion energies with stepwise escalation if initial attempt fails 1
If Initial Cardioversion Fails:
- Increase energy in stepwise fashion for subsequent attempts 4
- Consider adjusting electrode location or applying pressure over electrodes 2
- Administer antiarrhythmic medication (amiodarone 150mg IV over 10 minutes) before subsequent attempts 2
Important Clinical Pitfalls to Avoid
Do not delay cardioversion in hemodynamically unstable patients to attempt pharmacological conversion—this prioritizes morbidity and mortality outcomes. 3
Avoid calcium channel blockers (verapamil, diltiazem) in patients with ventricular tachycardia, as they can worsen hemodynamic status. 3
Have equipment immediately available when treating unstable VT, as patients may deteriorate to pulseless VT or VF at any moment. 4
Be prepared for post-cardioversion arrhythmias: Patients often have atrial or ventricular premature complexes immediately after cardioversion that may induce further episodes, requiring antiarrhythmic drugs to prevent acute reinitiation. 1
Post-Cardioversion Management
- Consider antiarrhythmic medication (amiodarone preferred in heart failure patients) to prevent recurrent arrhythmias 2
- Beta-blockers may be beneficial for recurrent and refractory ventricular arrhythmias 2
- For atrial fibrillation, recurrence rates are high (71-84% at 1 year), making maintenance antiarrhythmic therapy important 6