What is the usual initial energy setting for synchronized cardioversion in a hemodynamically unstable patient with atrial fibrillation of less than two days' duration?

From the Guidelines

For synchronized cardioversion in a hemodynamically unstable patient with atrial fibrillation of less than two days' duration, the usual initial energy setting is 120-200 joules with a biphasic defibrillator. This recommendation is based on the most recent and highest quality study available, which suggests that an initial energy dose of 120 to 200 J is recommended for cardioversion of atrial fibrillation with a biphasic waveform 1. The procedure involves several key steps, including:

• Placing defibrillator pads on the chest
• Ensuring the synchronization mode is activated
• Charging to the appropriate energy level
• Delivering the shock Synchronization is critical as it ensures the shock is delivered during the QRS complex and not during the T wave, which could induce ventricular fibrillation. If the first shock is unsuccessful, energy levels can be escalated for subsequent attempts, with some studies suggesting that higher initial energies may be more effective in achieving successful cardioversion 1. The goal of the procedure is to deliver an electrical current through the heart, depolarizing cardiac cells simultaneously and allowing the sinoatrial node to resume control of the heart rhythm, thereby correcting the rapid, irregular rhythm of atrial fibrillation that is compromising cardiac output in hemodynamically unstable patients. Key factors to consider in the decision to perform cardioversion include the duration of atrial fibrillation, the presence of underlying heart disease, and the patient's overall clinical status, with shorter duration of AF and younger age being independent predictors of success 1.

From the Research

Synchronized Cardioversion Energy Settings

• The usual initial energy setting for synchronized cardioversion in a hemodynamically unstable patient with atrial fibrillation of less than two days' duration is 100 joules, as recommended by a study published in The American journal of emergency medicine 2.
• This energy setting is based on the optimization of initial energy for cardioversion of atrial tachyarrhythmias with biphasic shocks, which found that an initial energy of 100 J achieved the lowest total cumulative energy in patients with AF of 2 days or less 2.
• Another study published in the Journal of the American College of Cardiology found that an initial energy setting of 100 J was effective in cardioverting atrial flutter, with a success rate of 68% 3.
• However, it's worth noting that other studies have suggested that higher initial energy settings, such as 150 J or 360 J, may be more effective in certain patient populations, such as those with chronic AF or AF of longer duration 3, 4.
• The choice of initial energy setting may depend on various factors, including the patient's clinical characteristics, the type and duration of the arrhythmia, and the specific cardioversion protocol being used.

Key Findings

• A study published in Circulation found that low-energy cardioversion using a biphasic shock waveform was effective in terminating spontaneous AF, with a mean energy of 3.3 +/- 1.3 J required to restore sinus rhythm in patients with chronic AF 5.
• Another study published in Arquivos brasileiros de cardiologia found that patients who received an initial energy of >=150J had a tendency towards greater efficacy of the initial shock and received fewer counter shocks compared to those who received 100J 4.
• However, in patients with recent-onset AF, the cumulative energy level was lower in the 100J group, suggesting that a lower initial energy setting may be sufficient in this patient population 4.