You are working the weekend overnight shift at a small community hospital. You agreed to cover the shift as a favor to a colleague. During the wee hours, two unrelated, previously healthy young patients present one hour apart with the complaint of palpitations. In both cases this was of acute onset, only a few hours ago. The first patient has a heart rate of 190 bpm, and the second 160 bpm. For each patient, the electrocardiogram reveals atrial fibrillation, with a rapid ventricular response. You see no ECG indication of ischemia, and neither patient is having chest pain. They do not have any history of atrial fibrillation.
This particular hospital has cardiology coverage and a hospitalist program. After giving each patient an intravenous bolus of diltiazem, their heart rate slows to below 100 bpm, and they are much more comfortable. They are, however, both still in atrial fibrillation. What you really want to do is go back to your call room and get a nap, but you are faced with a treatment decision.
You now have to choose between conservative or aggressive treatment for these patients. Conservative treatment typically consisting of rate control, anticoagulation, and a hospital admit for possible delayed cardioversion by cardiology.
Or, do you try to get these patient discharged home after cardioversion in your department? You could be preventing an unnecessary hospital admission, end an uncomfortable rhythm, and avoid the prolonged use of rate control and anticoagulation drugs. If this is your approach, do you choose chemical or electrical cardioversion? If you use electrical cardioversion, what setting of joules do choose?
Atrial fibrillation is the most common acute arrhythmia presenting to the emergency department (ED).1 There is no consensus at to the optimal management of recent-onset atrial fibrillation or flutter, and a great deal of controversy surrounds the issue. There is, however, a small but growing body of literature to support an aggressive approach in the emergency department. Additionally, it appears that when patients are left in atrial fibrillation for long durations, eventual cardioversion attempts will be less successful.2 In 2008, Ian Stiell, et al., presented a consecutive cohort study totaling 660 patients who presented to the University of Ottawa ED with an atrial arrhythmia of less than 48 hour duration.3 They applied their aggressive cardioversion protocol to these patients, with the result that 96.8% of these patient were discharged home, 93.3% of whom were in sinus rhythm. They had no cases of torsades de pointes, stroke, or death. The protocol called for the administration of procainamide at one gram over one hour. This resulted in a 58.3% conversion rate. For those patients who failed to convert with procainamide, they underwent subsequent electrical cardioversion with a 91.7% success rate. The median length of stay in the ED was 4.9 hours overall, with 3.9 hours for those undergoing conversion with procainamide, and 6.5 hours for those requiring electrical cardioversion.
The Ottawa physicain’s choice of procainamide seems to have been the result of their personal experience and comfort with this drug.4 They had previously published a consecutive cohort study of 341 patients with new atrial arrhythmia, using the same procainamide protocol.4 In that study, the largest of it kind up to that point involving procainamide, they reported a conversion rate of 52.2% for atrial fibrillation, and 28% for atrial flutter. Adverse events occurred in 10% of cases: hypotension 8.5%; bradycardia; 0.6%; atrioventricular block, 0.6%; ventricular tachycardia 0.3%. They had no cases of stroke, torsades, or death. They concluded that conversion with IV procainamide is both safe and effective.
Regarding the choice of agent for pharmacologic cardioversion, The American College of Cardiology, American Heart Association, and European Society of Cardiology, have published practice guidelines. They include class I – proven efficacy (dofetilide, IV flecanide, ibutilide, propafenone); class IIa – usefulness (amiodarone, oral flecainide); class IIb – less effective (procainamide, quinidine); and class III – should not be used (digoxin, sotalol).5 Most of the studies involving the use of these drugs for acute-onset cardioversion are small. For example, in 2000, Martinez-Marcos, et al., did a prospective, head-to-head, comparison of flecainide, propafenone, and amiodarone.6 He enrolled 150 consecutive patients, and after one hour the conversion rates were flecanide (58%), propafenone (60%), amiodarone (14%). No ventricular arrhythmia occurred in this study.
For the conversion of atrial arrhythmia, meta-analysis suggests that amiodarone may be no more effective than placebo after the first hour of infusion.7,8 Ibutilide, the only FDA-approved drug for this purpose, has shown a conversion rate of about 61%, but an incidence of torsades de pontes of 4.3%, with 1.7% of these cases being sustained.9,10 It is recommended that potassium, magnesium, and the QT interval be checked prior to using this drug.
Regarding the choice of shock energy for the conversion of atrial fibrillation, the older recommendations of starting with a low energy setting (i.e. 50 J, monophasic), with sequential small increases may be more dangerous and less effective than starting with a higher energy setting (> 200 J). In 2008, Gallagher et al., published a study evaluating the relationship shock energy to arrhythmic complications.11 They hypothesized that most cases of shock-induced ventricular fibrillation occurred from a lack of proper synchronization, with the shock occurring during ventricular repolarisation. They theorized that higher energy shocks (> 200J) would exceed the upper limit of vulnerability for ventricular fibrillation. They found, in 2522 attempts of electrical cardioversion, with 6398 shocks delivered, that ventricular fibrillation was significantly more common after shocks of < 200 J (5 of 2959 shocks vs. 0 or 3439). Conversion of atrial flutter or atrial tachycardia to atrial fibrillation was also more common at < 200 J (20 or 930 shocks vs. 1 or 313). It has been proposed that starting with lower energy may decreases the risk of shock-induced myocardial damage. Gallager, however, found that the initial use of higher energy reduces the total number of shocks required, and as a result, a lower amount of total energy delivered. At > 200 J, a far higher number of patients were converted with a single shock. They advise that in electrical cardioversion, monophasic shocks < 200 J, or biphasic shock < 100 J should be avoided. With the exceptional safety of higher energy electrical cardioversion, the primary adverse events with this strategy should be related primarily to the use of procedural sedation.
In patients with symptoms greater than 48 hours, or of unclear duration, aggressive protocols must be avoided unless the patient is already therapeutically anticougulated for greater than 3-4 weeks. The only possible exception is if a negative transesophageal echocardiogram is preformed immediately prior to cardioversion.12 But, even with a negative transesophageal echocardiogram, many of these patients will still require anticoagulation prior to, and after, cardioversion. Unless the patient is truly unstable, cardiology should be involved in cases of ischemia, hypotension, or acute congestive heart failure. In these days of ED overcrowding, and limited hospital bed availability, aggressive treatment of new-onset atrial arrhythmia with rapid discharge home now appears to be a viable therapeutic option.
You decide to try the aggressive protocol for your two patients. As mentioned before, they are healthy with a clear onset of less than 48 hours. They also have both been NPO for greater than 6 hours. You do not anticoagulate either patient. The first patient converts to sinus rhythm after 45 minutes on his procainamide drip. The second does not convert with procainamide. After obtaining informed consent, that patient is sedated with a single dose each of IV fentanyl and propofol, and successfully cardioverted with one shock of 150 J biphasic, synchronized. He awakes without complication. Both patients are discharged home from your ED on no medications, with the recommendation of outpatient cardiology follow up.
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