Should heparin be given before and after cardioversion for atrial fibrillation, and can anticoagulation be omitted if the arrhythmia duration is ≤48 hours and the CHA₂DS₂‑VASc (Congestive heart failure, Hypertension, Age ≥ 75 years, Diabetes mellitus, Stroke/TIA, Vascular disease, Age 65–74 years, Sex category) score is zero?

Anticoagulation for Cardioversion in Atrial Fibrillation

Yes, heparin (or another anticoagulant) should be given for cardioversion, with the specific approach determined by AF duration and stroke risk—even for AF <48 hours with CHA₂DS₂-VASc score of zero, anticoagulation may be considered peri-cardioversion, though it is not mandatory in this lowest-risk group.

AF Duration ≥48 Hours or Unknown Duration

For AF lasting 48 hours or longer, or when duration is unknown, you must anticoagulate with warfarin (INR 2.0-3.0), a factor Xa inhibitor, or direct thrombin inhibitor for at least 3 weeks before and at least 4 weeks after cardioversion, regardless of CHA₂DS₂-VASc score or cardioversion method (electrical or pharmacological). 1 This Class I recommendation from the 2019 AHA/ACC/HRS guidelines reflects the well-established risk of thromboembolism when cardioverting patients with prolonged AF duration. 1

Alternative TEE-Guided Strategy

If you cannot wait 3 weeks for anticoagulation, perform transesophageal echocardiography to exclude left atrial thrombus. 1 If no thrombus is identified, proceed with cardioversion immediately after initiating heparin (IV unfractionated heparin or weight-adjusted therapeutic dose LMWH), then continue anticoagulation for at least 4 weeks post-cardioversion. 1, 2 If thrombus is present, anticoagulate for at least 3 weeks before attempting cardioversion. 1

AF Duration <48 Hours with High Stroke Risk

For patients with AF <48 hours and CHA₂DS₂-VASc score ≥2 in men or ≥3 in women, administer heparin, a factor Xa inhibitor, or direct thrombin inhibitor as soon as possible before cardioversion, followed by long-term anticoagulation therapy. 1, 2 This is a Class IIa recommendation (reasonable to perform), downgraded from Class I in 2014 guidelines due to recognition that the evidence base is less robust than for longer-duration AF. 1

The rationale is compelling: retrospective data show that patients with AF <48 hours who did not receive therapeutic anticoagulation had nearly 5 times higher risk of thromboembolism compared to those anticoagulated with warfarin or heparin. 1 In one study, patients with CHA₂DS₂-VASc ≤1 had low overall event rates (0.4%), but this low-risk group still accounted for 26% of all thromboembolic events. 1 Additionally, up to 14% of patients with presumed short-duration AF have left atrial thrombus on TEE. 2

Continue anticoagulation for at least 4 weeks post-cardioversion due to atrial stunning (transient atrial mechanical dysfunction that persists even after restoration of sinus rhythm). 1, 2 Long-term anticoagulation beyond 4 weeks should be based on CHA₂DS₂-VASc score, not rhythm status. 1, 2

AF Duration <48 Hours with Low Stroke Risk (CHA₂DS₂-VASc Score 0 in Men, 1 in Women)

For this lowest-risk group, administration of heparin, a factor Xa inhibitor, or direct thrombin inhibitor versus no anticoagulant therapy may be considered before cardioversion, without the need for post-cardioversion oral anticoagulation. 1 This is a Class IIb recommendation (may be considered), reflecting genuine clinical equipoise. 1

The European Society of Cardiology guidelines suggest that IV heparin or LMWH may be considered peri-cardioversion for patients with clearly <48 hours duration and no thromboembolic risk factors, without need for post-cardioversion oral anticoagulation. 1 However, observational data show that even in this low-risk population, peri-cardioversion anticoagulation reduces stroke risk. 2

In real-world practice, I recommend erring on the side of caution and administering at least peri-cardioversion heparin or LMWH even for CHA₂DS₂-VASc score 0/1 patients, given the low bleeding risk and potential catastrophic consequences of stroke. 2, 3

Emergency/Immediate Cardioversion for Hemodynamic Instability

For patients requiring immediate cardioversion due to hemodynamic instability (angina, myocardial infarction, shock, or pulmonary edema), perform cardioversion without delay, but initiate heparin (IV UFH bolus followed by infusion, or weight-adjusted therapeutic dose LMWH) as soon as possible. 1 Continue anticoagulation for at least 4 weeks after cardioversion. 1 If AF duration was >48 hours or unknown, continue anticoagulation for at least 4 weeks; if high stroke risk, continue long-term. 1

Practical Anticoagulation Regimens

For peri-cardioversion anticoagulation, use one of the following: 2

• Unfractionated heparin: IV bolus followed by continuous infusion
• LMWH: Weight-adjusted therapeutic dose (full VTE treatment doses)
• DOACs: Standard dosing (apixaban, rivaroxaban, edoxaban, or dabigatran)
• Warfarin: Target INR 2.0-3.0

DOACs are now considered effective and safe alternatives to warfarin for cardioversion, supported by three prospective RCTs and multiple retrospective analyses. 1 The 2019 guidelines upgraded DOACs to Class I/Level B-R for use around cardioversion. 1

Critical Pitfalls to Avoid

1. Do not assume AF <48 hours is safe without anticoagulation in patients with any stroke risk factors. The traditional "48-hour rule" oversimplifies risk—CHA₂DS₂-VASc score matters significantly even in short-duration AF. 3

2. Do not discontinue anticoagulation before 4 weeks post-cardioversion, even if sinus rhythm is maintained. Atrial stunning persists for weeks after cardioversion regardless of apparent rhythm restoration. 1, 4

3. Do not forget that pharmacological cardioversion carries the same thromboembolic risk as electrical cardioversion. The same anticoagulation rules apply to both methods. 1, 2

4. Do not rely on patient-reported symptom onset to determine AF duration. Many patients have asymptomatic AF episodes before their symptomatic presentation. When duration is uncertain, treat as >48 hours. 2