What percentage of patients with cardioverted atrial fibrillation (AFib) without anticoagulation experience strokes?

From the Guidelines

Patients with cardioverted atrial fibrillation (AFib) without anticoagulation have approximately a 1% to 5% risk of stroke, as reported in case-control series 1. The risk of stroke in these patients is a significant concern, and anticoagulation is often recommended to mitigate this risk. The stroke risk varies based on individual risk factors, with higher rates in those who have additional risk factors such as heart failure, hypertension, advanced age (≥75 years), diabetes, prior stroke, vascular disease, or female sex. Some key points to consider include:

• The risk of thromboembolism in patients with AFib is between 1% and 5% without anticoagulation 1
• Anticoagulation with warfarin (INR 2.0 to 3.0) for 3 to 4 weeks before and after cardioversion can reduce the risk of thromboembolism 1
• The CHADS2 score can be used to stratify stroke risk in patients with AFib, with higher scores indicating a greater risk of stroke 1
• Current practice guidelines recommend anticoagulation for at least 3 weeks before and 4 weeks after cardioversion for AFib lasting longer than 48 hours or of unknown duration 1
• If cardioversion must be performed urgently without prior anticoagulation, transesophageal echocardiography should be performed to rule out left atrial thrombus, and anticoagulation should be started immediately and continued for at least 4 weeks afterward 1 The mechanism behind these strokes involves thrombus formation in the left atrium or left atrial appendage due to blood stasis during atrial fibrillation, which can embolize to the brain when normal atrial contraction resumes after cardioversion. It is essential to weigh the benefits and risks of anticoagulation in each patient, considering factors such as bleeding risk, patient preferences, and access to good INR monitoring 1.

From the Research

Stroke Risk in Patients with Cardioverted Atrial Fibrillation without Anticoagulation

• The risk of stroke in patients with cardioverted atrial fibrillation (AFib) without anticoagulation is a significant concern, with studies suggesting that the majority of post-cardioversion strokes occur in patients not using oral anticoagulation before cardioversion of acute AF 2.
• A study found that post-cardioversion strokes accounted for 6.4% of strokes in patients with paroxysmal or persistent AF, with 63 events occurring in patients not using anticoagulation 2.
• Another study suggested that patients with AFib and a CHA2DS2-VASc score >1 benefit from oral anticoagulation prior to cardioversion, with a higher risk of thromboembolic complications in patients without oral anticoagulation 3.
• The risk of thromboembolic events in patients with acute AFib without anticoagulation is estimated to be in the range of 10% in patients with multiple classic risk factors for thromboembolism 4.

Percentage of Patients Experiencing Strokes

• While the exact percentage of patients with cardioverted AFib without anticoagulation who experience strokes is not directly stated, a study found that the incidence of ischemic stroke was 4.1% in the overall cohort of patients with AFib who were not treated with oral anticoagulants due to increased bleeding risk 5.
• Another study suggested that every sixteenth stroke of patients with paroxysmal/persistent AF is preceded by a cardioversion, with most post-cardioversion strokes occurring in patients not using oral anticoagulation before cardioversion of acute AF 2.

Risk Factors for Stroke

• The risk of stroke in patients with cardioverted AFib without anticoagulation is increased in patients with certain risk factors, including heart failure, hypertension, diabetes, prior stroke, female sex, and age above 65-75 years 4.
• The CHA2DS2-VASc score is a useful tool for assessing the risk of stroke in patients with AFib, with a score >1 indicating a higher risk of stroke 3, 6.