Electrical cardioversion is a time-honored highly effective method for converting AF to sinus rhythm. Urgent cardioversion is indicated when the ventricular response is greater than 130/beats/min in association with:

Rate control can improve hemodynamics even if the patient remains in AF. Digoxin is commonly used in the treatment of AF in ICU patients. Yet, in the critically ill ICU patient digoxin is probably the least effective drug in controlling the ventricular response in AF. Digoxin decreases ventricular response in AF by vagotonic mechanisms. In critically ill patients, AF occurs in the setting of high sympathetic tone and frequently with the use of vasopressors and inotropic agents, a situation in which digoxin is likely to be ineffective. In addition, this drug has a very narrow therapeutic index and should be avoided except in patients with poor LV function.

Diltiazem is an effective agent for rate control in most patients with a response rate of between 93 and 97 %. Diltiazem is given as a 5 mg bolus every 5 min until rate control is achieved or a maximal dose of 15 mg is administered, followed by an infusion of up to 15 mg/h. Esmolol, an ultrashort acting selective beta-blocker has been demonstrated to be effective in controlling the ventricular response in AF. Similarly, IV metoprolol (5 mg boluses) may used for rate control. However, beta-blockers may cause hypotension particularly in patients with poor LV function. Amiodarone (or digoxin) may be used for rate control in patients with poor LV function. Magnesium has been shown to reduce the ventricular response in AF, with a greater effect when combined with digoxin. Magnesium may act by increasing the atrio-His interval and atrioventricular nodal refractoriness.

Digoxin and calcium channel blockers should not be given to patients who have atrial fibrillation with an anterogradely conducting accessory pathway, because blocking atrioventricular nodal conduction may provoke conduction down the accessory pathway, leading to an increase rather than decrease in the ventricular rate and hemodynamic collapse.

A number of randomized controlled studies (RCT’s) have evaluated procainamide, amiodarone, flecainide, sotalol, propafenone and ibutilide in patients presenting to hospital with acute atrial fibrillation (non-ICU setting). In general these studies have found the rate of conversion to be similar with the antiarrhythmic drug as with placebo, with approximately 60 % of patients spontaneously converting to sinus rhythm within 24 h [10]. The natural history of AF in acutely ill ICU patients has not been studied. However, it is likely that untreated the arrhythmia will persist until the underlying medical condition which precipitated the arrhythmia has improved or resolved. The role of anti-arrhythmic agents in facilitating pharmacological cardioversion is unclear; however it would appear that these agents have a limited role in the critically ill patient. Amiodarone is the agent most commonly used to facilitate cardioversion in the ICU. Amiodarone is not without risks, with hypotension and bradycardia being the most common adverse events, usually occurring during the loading infusion. Acute hepatotoxicity with liver function test abnormalities has been reported in 9–17 % of patients Amiodarone has also been associated with acute pulmonary toxicity presenting as ARDS. High inspired oxygen concentration and pre-existing ARDS may be risk factors for acute amiodarone pulmonary toxicity. Sleeswijk et al. reported the efficacy of a magnesium-amiodarone step-up scheme in critically ill patients with new-onset atrial fibrillation [11]. A MgSO₄ bolus (0.037 g/kg body weight in 15 min) was followed by continuous infusion (0.025 g/kg body weight/h) [bolus of 2–3 g followed by infusion at 2 g/h in 70 kg patient]. Intravenous amiodarone (loading dose 300 mg, followed by continuous infusion of 1,200 mg/24 h) was given to those not responding to MgSO₄ within 1 h. Clinical response was defined as conversion to sinus rhythm or decrease in heart rate <110 beats/min. Sixteen of the 29 patients responded to MgSO₄ monotherapy, whereas the addition of amiodarone was required in 13 patients. Median time until conversion to sinus rhythm after MgSO₄ was 2 h while the median conversion time in patients requiring amiodarone was 4 h. The 24-h conversion rate was 90 %. As this approach obviates the need for anticoagulation, it may be the preferable approach to AF in ICU patients. Kanji et al. determined the outcome of patients in a mixed ICU who had preexistent AF (186 pts) or developed new onset AF (139 pts) in the ICU (10.5 % of all patients) [9]. Hemodynamic instability developed in 37 % of patients with new-onset AF with pharmacologic rhythm conversion was attempted in 76 % those with new-onset AF. Although initially successful in 87 % of new-onset cases, 42 % reverted back to AF. Only 18 % of patients with new-onset AF who survived to ICU discharge left the ICU in AF.