What is the preferred method of cardioversion for atrial fibrillation (AFib), synchronized or unsynchronized cardioversion?

Synchronized Cardioversion is the Preferred Method for Atrial Fibrillation

Synchronized cardioversion is the recommended method for electrical cardioversion of atrial fibrillation, as it ensures electrical stimulation does not occur during the vulnerable phase of the cardiac cycle. 1

Rationale for Synchronized Cardioversion

• Synchronized cardioversion involves delivery of an electrical shock synchronized with the intrinsic activity of the heart by sensing the R wave of the ECG, preventing stimulation during the vulnerable phase of the cardiac cycle 1
• Unsynchronized cardioversion (defibrillation) is appropriate only for ventricular fibrillation, where R-wave synchronization is not feasible 1
• Synchronized cardioversion reduces the risk of inducing ventricular fibrillation by avoiding shock delivery during the vulnerable period of ventricular repolarization 1

Clinical Applications of Synchronized Cardioversion for AFib

Indications for Immediate Synchronized Cardioversion

• When rapid ventricular response does not respond promptly to pharmacological measures with ongoing myocardial ischemia, symptomatic hypotension, angina, or heart failure 1
• For patients with AF involving pre-excitation when very rapid tachycardia or hemodynamic instability occurs 1
• When symptoms of AF are unacceptable to the patient despite adequate rate control 1

Technical Considerations

• Current density delivered to the heart depends on defibrillator capacitor voltage, output waveform, electrode size/position, and thoracic impedance 1
• Recommended paddle diameter is 8-12 cm for optimal current delivery 1
• Rectilinear biphasic shocks have shown higher success rates (94%) compared to monophasic shocks (79%) and require less energy 1
• Shocks delivered during expiration or chest compression deliver higher energy to the heart due to reduced pulmonary tissue interference 1

Pharmacological Considerations with Cardioversion

• Antiarrhythmic medications may be administered before cardioversion to increase success rates and prevent early recurrence 1
• For patients with AF or atrial flutter of less than 48 hours' duration who are at low thromboembolic risk, anticoagulation should be initiated before or immediately after cardioversion 1
• Anticoagulation should be continued for at least 4 weeks after cardioversion unless contraindicated 1

Common Pitfalls and Caveats

• Electrical cardioversion is contraindicated in patients with digitalis toxicity or hypokalemia due to increased risk of ventricular arrhythmias 1
• Patients often have atrial or ventricular premature complexes immediately after cardioversion that may induce further episodes of AF, requiring antiarrhythmic medication to prevent acute reinitiation 1
• Frequent repetition of direct-current cardioversion is not recommended for patients with relatively short periods of sinus rhythm between relapses despite prophylactic antiarrhythmic therapy 1
• When AF occurs in patients with ventricular pre-excitation and a short accessory pathway refractory period, rapid pre-excited conduction can lead to unstable tachycardia or ventricular fibrillation, making early synchronized cardioversion crucial 1

Special Considerations

• For refractory cases, adjusting electrode position, applying pressure over electrodes, or administering antiarrhythmic medication before repeated attempts may improve success rates 1
• In hemodynamically stable patients with pre-excited AF, ibutilide or intravenous procainamide can be beneficial before attempting cardioversion 1
• Higher energy synchronized cardioversion (up to 720J using two defibrillators) has been shown to be safe and effective in patients refractory to standard energy cardioversion 2

By following these evidence-based recommendations, synchronized cardioversion offers the safest and most effective electrical approach to restore sinus rhythm in patients with atrial fibrillation.