Is atrial fibrillation (A fib) managed with synchronized or unsynchronized cardioversion?

Atrial Fibrillation Requires Synchronized Cardioversion

Atrial fibrillation must be treated with synchronized cardioversion, not unsynchronized defibrillation, to avoid potentially dangerous ventricular arrhythmias. 1 Synchronized cardioversion is essential because it times the electrical shock delivery with the QRS complex, preventing shock delivery during the vulnerable period of the cardiac cycle when ventricular fibrillation could be induced.

Understanding Synchronized vs. Unsynchronized Cardioversion

Synchronized Cardioversion

• Definition: Shock delivery timed (synchronized) with the QRS complex
• Purpose: Avoids shock delivery during the relative refractory period of the cardiac cycle
• When to use: For atrial fibrillation, atrial flutter, supraventricular tachycardia, and monomorphic ventricular tachycardia with pulses
• Initial energy settings for AF: 200 J monophasic shock 1

Unsynchronized Cardioversion (Defibrillation)

• Definition: Asynchronous electrical shock delivery
• Purpose: Immediate termination of disorganized rhythms
• When to use: For ventricular fibrillation, pulseless ventricular tachycardia, and polymorphic (irregular) VT
• Never use for: Atrial fibrillation, as it may induce ventricular fibrillation 1

Clinical Approach to Cardioversion in AF

Hemodynamically Unstable Patients

1. Immediate synchronized cardioversion is recommended for AF patients with:
   • Ongoing myocardial ischemia
   • Symptomatic hypotension
   • Angina
   • Heart failure
   • Pre-excitation with very rapid tachycardia 1

Hemodynamically Stable Patients

1. Synchronized cardioversion is still the method of choice when:
   • Pharmacological therapy is ineffective or contraindicated
   • Symptoms are unacceptable to the patient despite adequate rate control 1

Technical Considerations for Synchronized Cardioversion

• Energy levels: Start with 200 J for monophasic waveform for AF (50 J for atrial flutter) 1
• Preparation: Brief general anesthesia or conscious sedation whenever possible
• Positioning: Proper paddle placement (typically anterolateral or anteroposterior)
• Safety: Take precautions to minimize sparking during cardioversion; avoid oxygen-enriched atmosphere near the chest 1

Common Pitfalls to Avoid

1. Never use unsynchronized shocks for AF - this can induce ventricular fibrillation by delivering energy during the vulnerable period of repolarization 1

2. Do not attempt cardioversion in digitalis toxicity or hypokalemia - increased risk of ventricular arrhythmias 1

3. Ensure proper synchronization - confirm the machine is in "sync" mode and that it's detecting R waves (markers visible on QRS complexes)

4. Be prepared for post-cardioversion arrhythmias - patients often have atrial or ventricular premature complexes immediately after cardioversion that may induce further episodes of arrhythmia 1

5. Maintain anticoagulation - ensure appropriate anticoagulation before cardioversion for AF lasting >48 hours to prevent thromboembolism

The evidence is clear and consistent across multiple guidelines that atrial fibrillation requires synchronized cardioversion to safely and effectively restore normal sinus rhythm while minimizing the risk of inducing more dangerous arrhythmias.