New onset atrial fibrillation: to anticoagulate or not to anticoagulate?

By Zach Adams, OSUEM Resident // Edited by Michael Barrie, OSUEM Assistant Professor

A 34 year-old female with a prior history of arrhythmia presents to the ED with palpitations.  The patient reports the symptoms began suddenly this AM at about 8AM.  The monitor shows atrial fibrillation at a rate of 157.  You do not have a prior ECG for review.  After discussing options with the patient, the decision is made to attempt cardioversion.  What are the risks, and do we need to anticoagulate afterwards?

As we well know, patients with atrial fibrillation (AF) are at an increased risk of thromboembolic events, most commonly stroke.  Overall risk for patients with non-valvular atrial fibrillation can be calculated using the CHADS2 score or the more recent CHA2DS2-VASc score and helps guide long-term anticoagulant therapy for prevention.  The HAS-BLED score furthermore stratifies bleeding risk in subsets of individuals who will require long-term anticoagulation. The overall risk of stroke in AF increases from baseline after both spontaneous and chemical or electrical cardioversion, with most events occurring within 10 days for patients on either warfarin or non-vitamin-K antagonist antithrombotics (1-4).  In any instance of new onset atrial fibrillation, the risk of thrombus increases with risk factors and length of duration of AF, with up to 13 percent of patients having evidence of left atrial thrombus on TEE (5-7). 

Guidelines suggest for patients with unknown duration of atrial fibrillation or duration >48 hours, 3 weeks of anticoagulation or TEE to document lack of atrial thrombus be utilized prior to cardioversion, with long-term anticoagulation guided by risk stratification above.  Such patients are a relatively easy disposition depending on presentation.  For patients with new onset atrial fibrillation of <48 hours, however, things can get tricky, especially considering that the vast majority of individuals with atrial fibrillation (up to 90%) are asymptomatic (8).  Should we reliably use symptom onset to make a decision to perform ED cardioversion? 

Historically, many practitioners perform cardioversion in patients with acute (<48 hour) symptoms attributed to atrial fibrillation.  Some  have even vouched for a “wait and see” approach in the ED, in which patients with onset of symptoms <48 are discharged with 24 hour follow-up and cardioversion as needed or observational protocol, as the spontaneous cardioversion rate is high – upwards of 70% (9).  However, while embolization after return of sinus rhythm was previously attributed to dislodgment of a left atrial thrombus at the time of conversion, evidence shows that LA thrombi can also form in the immediate post-cardioversion state, regardless of the method (i.e. electrical, chemical, spontaneous) (10-13).  In such instances, “stunning” of the atria secondary to conversion to sinus rhythm leads to thrombus formation, with recent guidelines calling this practice into question.  More precisely, the Finnish CardioVersion study measured this risk, and found a pretty conclusive 0.7% 30-day risk of embolic stroke depending on patient risk factors (risk factors: age >60, OR 1.05; female sex, OR 2.1; heart failure, OR 2.9; diabetes, OR 2.3) (14).  The aforementioned CHADS2 and CHA2DS2-VASc scores were also highly predictive of thromboembolic events for those undergoing cardioversion of AF <48 hours in the study population.  The authors concluded that consideration should be given to periprocedural and postpostprocedural anticoagulation and broader group of patients with AF <48 hours.   So what should we do?  Should we anticoagulant during the cardioversion in these patients?  What about after?

These are some difficult questions to answer, and various recommendations have been made.  Recent AHA/ACC 2014 AF guidelines strongly recommend for heparin or a newer anticoagulant (NOAC) as soon as possible before cardioversion followed by long-term oral anticoagulation in patients at high risk.  They further recommend for cardioversion with or without periprocedural anticoagulation followed by no long-term anticoagulation in patients at low risk (15).  Alternatively, the 2011 European Society of Cardiology AF guidelines make a weak recommendation for periprocedural heparin in ALL patients with AF <48 hours with long-term oral anticoagulation in high risk patients (16).  Sort of confusing. 


In patients with unknown duration of AF or duration >48 hours, initiation of anticoagulation for 3 weeks prior to elective cardioversion or a TEE based approach with post-cardioversion anticoagulation is warranted.  Such patients presenting in the ED should be dispositioned depending on the decision of rate versus rhythm control as well as anticoagulation therapy in conjunction with cardiology and the patient.

In patients with new onset AF or duration <48 hours, the decision to cardiovert the patient (either chemically or electrically if they haven’t spontaneously converted) warrants careful assessment of risk factors and periprocedural and post-cardioversion anticoagulation depending on the overall risk.  Consideration might be given to utilization of pre-cardioversion heparin or NOAC before cardioversion in moderate to high risk patients (CHAD2DS2-VASc 1) followed by long-term anticoagulation.  For low risk patients (CHA2DS2-VASc = 0), recommendations are either for no anticoagulation or pre-procedural anticoagulation and 4 weeks of anticoagulation thereafter to further reduce the risk of stroke.  Bleeding risk assessment can guide therapy using the HAS-BLED score. 


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