Cardioversion for Atrial Fibrillation

Published - Written by Michael Mi, MD

As a cardiology fellow, I receive consultation requests for management of atrial fibrillation (AF) on a daily basis from both inpatient and outpatient settings. AF accounts for 0.5% of U.S. emergency department (ED) visits, and our ED colleagues commonly ask whether a patient should undergo cardioversion, admission, or both. Patients may present with acute symptoms of shortness of breath, palpitations, and exertional fatigue or even with congestive heart failure. Others may be asymptomatic and have had AF detected incidentally in the outpatient office. For symptomatic patients, restoration of sinus rhythm via cardioversion can quickly resolve symptoms, but cardioversion is by no means a benign process.

At my institution in the U.S., electrical cardioversion is generally the preferred method, and the requirement for sedation comes with its own cost and risk. Alternatively, pharmacologic cardioversion still requires the expertise and availability of a cardiologist and the resources for monitoring afterwards. We know that regardless of cardioversion methods, the procedure can trigger thromboembolic complications in the absence of anticoagulation, even if duration of AF is short (<48 hours). Although cardioversion may be an effective solution for acute-onset AF, it only addresses one moment in the management of what is often a chronic condition. Many patients develop self-limited episodic AF before progressing to recurrent and more–persistent disease. For a first episode, rates of spontaneous conversion of AF to sinus rhythm are quite high.

Given the costs and risks of cardioversion and uncertain long-term benefits, investigators of the RACE 7 ACWAS trial examined whether delaying cardioversion in the acute management of symptomatic AF is as effective and safe as immediate cardioversion in the ED. They compared a wait-and-see approach (consisting of administration of rate-control medications to control symptoms and delayed cardioversion the next day if AF was still present) with an immediate cardioversion approach on presentation to the ED. The wait-and-see approach was found to be noninferior to immediate cardioversion for the primary outcome of sinus rhythm 4 weeks later. Further observations from the trial confirmed that recent-onset AF is indeed paroxysmal: 69% of patients in the delayed-cardioversion group had spontaneous conversion to sinus rhythm within 48 hours and 29% of patients in the early-cardioversion group had recurrent AF within 4 weeks of the index visit. Overall, both approaches were safe with timely administration of anticoagulation to high-risk patients.

The following NEJM Journal Watch summary provides more details of the trial and findings.


Can Cardioversion of New-Onset Atrial Fibrillation Be Safely Delayed in the ED?

Mark S. Link, MD reviewing Pluymaekers NAHA et al. N Engl J Med 2019 Mar 18 Healey JS and McIntyre WF. N Engl J Med 2019 Mar 18

For achieving sinus rhythm within 4 weeks and avoiding cardiovascular complications, immediate cardioversion in the emergency department was no better than cardioversion at 48 hours.

Atrial fibrillation (AF) is a common presentation in the emergency department (ED), but it's not always clear whether a patient with new-onset AF should undergo cardioversion immediately or be allowed some time for spontaneous conversion. Patients with marked AF symptoms certainly have no luxury to wait, but what about patients whose symptoms are less dramatic?

At two EDs in the Netherlands (NCT02248753), investigators randomized 437 adults with hemodynamically stable, symptomatic AF of recent onset (<36 hours) to undergo cardioversion either early (immediately) or after a delay (48 hours after symptom onset). The primary analysis included 427 patients (mean age, 65). About 40% were taking an anticoagulant at enrollment; another 29% started anticoagulation during the index visit.

Incidence of the primary endpoint — normal sinus rhythm at 4 weeks — was 94% in the early-cardioversion group and 91% in the delayed-cardioversion group, meeting the criterion for noninferiority of the delayed strategy. In the delayed group, conversion to sinus rhythm occurred spontaneously in 69% of patients and after the delayed cardioversion in 28%. Rates of cardiovascular complications were <0.5% in both the early and delayed groups; notably, only one stroke or transient ischemic attack occurred in each group.

Comment: Immediate cardioversion is not necessary for patients with recent-onset AF. Allowing a short time for spontaneous conversion to sinus rhythm is reasonable, as long as the total time in AF is <48 hours. Anticoagulation is critical, however, especially for patients with AF lasting >24 hours, as stroke has been associated with AF durations of 24 to 48 hours.


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Mike was a 2017-2018 NEJM Editorial Fellow and a hospitalist at Beth Israel Deaconess Medical Center. He graduated from Harvard Medical School and completed his internal medicine training at BIDMC.