Afib of Less than 48 Hours: A Look at Thromboembolic Risk

November 15, 2016

New research suggests that even a short time spent in atrial fibrillation increases thromboembolic risk nearly 5-fold.

Dan Smith is a 69-year-old with a history of hypertension who presents to the emergency room 4 hours after the onset of palpitations. His heart rate is 149 beats/min and blood pressure is 129/74 mmHg. The ECG reveals atrial fibrillation (AF). He says he knows the exact time the palpitations began in the morning and that he has never had these symptoms before.

According to the current guidelines, what is the recommended next step in management?A. Synchronized cardioversion

B. Warfarin or novel oral anticoagulant for 4 weeks followed by cardioversion

C. Transesophageal echocardiogram (TEE) followed by cardioversion

D. Any of the above

Answer and discussion>>



Answer: A. Synchronized cardioversion  

According to the current (2014) AHA/ACC/HRS guidelines,1 there is no need to anticoagulate patients or perform a TEE prior to cardioversion if the onset of AF is <48h. The other two options are acceptable for when patients present with AF of unknown duration.

A recent study2 published in JACC Electrophysiology challenges this guideline-recommended practice, pointing out that even AF of <48h duration can significantly increase risk for thromboembolism. The study used a database of Cleveland Clinic patients who presented with AF <48h (as assessed by symptom onset and electrocardiographic/telemetry evidence) and underwent cardioversion. Patients were retrospectively divided into three groups:

               Group 1 (mean CHA2DS2-Vasc 2.3 ± 1.7):

- 567 total cardioversions
- 484 non-anticoagulated
   . 190 (33.5%) no anticoagulation or antiplatelet agents
   . 310 (54.7%) on aspirin alone
   . 67 (11.8%) warfarin with an INR ≤1.5

              Results: 6 (1.06%) neurologic events (all in pts on aspirin alone)

               Group 2 (mean CHA2DS2-Vasc 2.1 ± 1.6):

          - 116 cardioversions INR between 1.5 and 2

               Group 3 (mean CHA2DS2-Vasc 2.6 ± 1.6):

                        - 898 cardioversions
                        - 709 patients therapeutically anticoagulated
                            . 567 (63.1%) on warfarin with INR ≥ 2
                            . 331 (36.9%) on heparin with aPTT ≥ 50

    Results: 2 (0.22%, OR 4.8, p=0.03) neurologic events, both in pts off anticoagulation at time of stroke.

As the results show, all strokes in this small study occurred in patients who were not receiving anticoagulation. There are multiple explanations for this increased risk of thromboembolism. Evidence suggests that AF of even a few minutes’ duration can lead to slow flow and early thrombus formation in the atrial appendage. Furthermore, there is significant atrial stunning following electrical cardioversion which can also become a nidus for thrombus formation in the appendage.

Notably, no events occurred in patients with CHA2DS2-Vasc <2. Therefore this small study provides important clinical observations. Firstly, the CHA2DS2-Vasc risk score estimator provides relatively good risk estimation even in patients undergoing cardioversion with short duration of AF. Secondly, caution should be exercised in patients with a CHA2DS2-Vasc >2 undergoing cardioversion when AF duration is <48 hours. Although larger studies are needed to validate these findings (as the total number of patients and the rate of thromboembolism was low) and no NOACs were included, these results do raise the question of whether the guidelines need to be revised.



1. January CT, Wann L, Alpert JS, et al. 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2014;64:2246-2280.

2. Garg A, Khunger M, Seicean S, Chung MK, Tchou PJ. Incidence of thromboembolic complications within 30 days of electrical cardioversion performed within 48 hours of atrial fibrillation onset.JACCCEP. 2016;2:487-494.