From the Guidelines
For unstable atrial fibrillation requiring immediate cardioversion, use synchronized electrical cardioversion starting at 120-200 joules with a biphasic defibrillator or 200 joules with a monophasic defibrillator. This recommendation is based on the most recent and highest quality study available, which suggests that an initial energy of 120-200 J with a biphasic defibrillator is effective for cardioversion of atrial fibrillation 1. If the first shock is unsuccessful, energy can be escalated to the maximum available (typically 200 joules for biphasic and 360 joules for monophasic). Unstable atrial fibrillation is characterized by hypotension, acute heart failure, ongoing chest pain, or altered mental status, and requires immediate intervention. Prior to cardioversion, ensure the patient is adequately sedated if conscious, and have resuscitation equipment readily available. After successful cardioversion, monitor the patient closely for recurrence, maintain oxygenation, and consider antiarrhythmic medications to maintain sinus rhythm. The higher energy levels are recommended for atrial fibrillation compared to other arrhythmias because the chaotic electrical activity in the atria can be more difficult to terminate, requiring greater energy delivery to simultaneously depolarize enough cardiac tissue to restore normal sinus rhythm.
Some key points to consider when performing cardioversion for unstable atrial fibrillation include:
- Using a biphasic defibrillator, which is more effective than a monophasic defibrillator for cardioversion of atrial fibrillation 1
- Starting with an initial energy of 120-200 J, which is recommended by the American Heart Association guidelines 1
- Escalating energy levels if the first shock is unsuccessful, up to a maximum of 200 joules for biphasic and 360 joules for monophasic defibrillators
- Ensuring the patient is adequately sedated and has resuscitation equipment readily available prior to cardioversion
- Monitoring the patient closely for recurrence and considering antiarrhythmic medications to maintain sinus rhythm after successful cardioversion.
The evidence from the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care supports the use of synchronized electrical cardioversion starting at 120-200 joules with a biphasic defibrillator or 200 joules with a monophasic defibrillator for unstable atrial fibrillation 1. This recommendation is based on the best available evidence and prioritizes the patient's morbidity, mortality, and quality of life.
From the Research
Atrial Fibrillation Energy Requirements
- The energy required for cardioversion of atrial fibrillation (AF) can vary depending on several factors, including the type of defibrillator used and the patient's characteristics 2, 3, 4.
- Studies have shown that biphasic defibrillators are more effective than monophasic defibrillators for cardioversion of AF, and that lower energy levels can be used with biphasic defibrillators 2, 3.
- One study found that an initial energy setting of 100 J was effective in 71% of patients with AF, while an initial energy setting of 50 J was effective in 61% of patients 2.
- Another study found that the average selected energy threshold for AF using a rectilinear biphasic waveform was 70.6 J, compared to 193.4 J for a monophasic damped sine waveform 3.
- The BEST AF Trial found that a non-escalating energy protocol with an initial energy setting of 200 J resulted in higher first-shock success rates, particularly in patients with a body mass index (BMI) >25 kg/m2 4.
Energy Settings for Unstable Atrial Fibrillation
- For unstable AF, the American Heart Association recommends using an initial energy setting of 200 J for biphasic defibrillators 4.
- However, the optimal energy setting for unstable AF may depend on the individual patient's characteristics and the specific defibrillator being used.
- It is generally recommended to start with a lower energy setting and escalate as needed, rather than starting with a high energy setting and risking unnecessary tissue damage 2, 3.