48 Hours.

Dear Readers,

Patients who present to the emergency department (ED) with new onset or recurrent sustained atrial fibrillation (AF) are often not taking oral anticoagulation. There is always the challenge of knowing precisely when the AF started in these patients. Patients frequently report with confidence a specific time of AF onset, only to later express uncertainty after further questioning. It is possible that in some of these patients, AF had been present for days and only later resulted in symptoms such as heart failure or palpitations. Yet there are also patients who seem to be able to reliably identify the onset of their AF and come to the ED highly symptomatic in need of cardioversion. In these patients, it is common practice to perform, or recommend the performance of, electrical cardioversion without anticoagulation, or a transesophageal echocardiogram (TEE), when the AF has been present for less than 48 hours.

Where does the 48-hour cut-off come from? It appears to come from expert opinion and observations from imaging studies. However, there is also evidence from TEE studies that a left atrial appendage thrombus can develop in less than 48 hours in some patients with AF. These more recent observations have led to a more conservative approach of recommending a TEE and anticoagulation when there is any uncertainty about the patient’s story or when the patient has high-risk features for stroke. 

In a Research Letter to the Editor in the Journal of the American Medical Association last summer, investigators from the Finnish CardioVersion study provided a unique temporal analysis of the outcomes of 2,481 patients who underwent 5,116 successful electrical cardioversions within 48 hours in the absence of anticoagulation.¹ The team had previously shown that age, female sex, heart failure, and diabetes were independent predictors of thromboembolic complication.² This further analysis divided patients into three groups based on the time between the onset of the AF and the cardioversion (<12 hours, 12-24 hours, and 24-48 hours). The overall incidence of a thromboembolic stroke was low at 0.7%, and was comparable to the risk of stroke in patients with AF of longer duration who undergo cardioversion in the presence of anticoagulation. However, compared to patients with AF <12 hours in duration, the risk of stroke for patients with AF for 12-24 hours was 4 times as high (OR 1.7-9.1; p<0.001), and for patients with AF 24-48 hours was 3.3 times as high (OR 1.3-8.9; p<0.02).

Despite the limitations of this study, which include its retrospective design, the lack of a control group that was treated with anticoagulation and therefore exposed to the risk of bleeding, and the uncertainty related to the duration of the AF based on patient reporting, the study included a large number of patients, and the data are compelling. Based on this temporal substudy of the Finnish CardioVersion study, it would be reasonable when contemplating cardioversion in a patient with acute AF without anticoagulation to begin using a more conservative cut-off of 12 hours of AF duration (in which the risk of stroke is only 0.3% compared to 1.1% when the AF duration is 12-48 hours), especially in patients with heart failure or other risk factors for stroke.

References

1. Nuotio I, Kartikainen JEK, Grönberg T, et al. Time to cardioversion for acute atrial fibrillation and thromboembolic complications. JAMA. 2014;312:647-648.
2. Airaksinen KE, Grönberg T, Nuotio I, et al. Thromboembolic complications after cardioversion of acute atrial fibrillation: the FinCV (Finnish CardioVersion) study. J Am Coll Cardiol. 2013;62:1187-1192.