Should heparin (unfractionated heparin) be held before cardioversion?

Should Heparin Be Held Before Cardioversion?

No, heparin should NOT be held before cardioversion—it should be initiated and continued throughout the peri-cardioversion period to prevent thromboembolic complications. The evidence consistently demonstrates that anticoagulation with unfractionated heparin (or low-molecular-weight heparin) is essential for stroke prevention in the cardioversion setting.

Anticoagulation Strategy Based on AF Duration

AF Duration >48 Hours or Unknown Duration

For elective cardioversion:

• Therapeutic anticoagulation is required for at least 3 weeks before cardioversion 1
• Continue anticoagulation for at least 4 weeks after cardioversion 1
• This applies to both electrical and pharmacological cardioversion 1

TEE-guided alternative approach:

• If no thrombus is identified on TEE, heparin should be initiated immediately before cardioversion and continued until therapeutic oral anticoagulation is established 1
• Anticoagulation must still be maintained for at least 4 weeks post-cardioversion 1

AF Duration <48 Hours

For patients with CHA₂DS₂-VASc ≥2 (men) or ≥3 (women):

• Heparin (unfractionated or LMWH at full treatment doses) should be started at presentation before proceeding to cardioversion 1
• This recommendation is supported by data showing lower stroke rates with anticoagulation (0.1% vs 0.7%, p=0.001) 1
• Continue therapeutic anticoagulation for at least 4 weeks post-cardioversion 1

For patients with CHA₂DS₂-VASc 0 (men) or 1 (women):

• Heparin administration may be considered but is not mandatory 1
• Post-cardioversion oral anticoagulation is not required in this low-risk group 1

Hemodynamically Unstable AF Requiring Urgent Cardioversion

Critical management principle:

• Immediate cardioversion should NOT be delayed to achieve therapeutic anticoagulation 1
• However, intravenous unfractionated heparin or subcutaneous LMWH must be initiated before cardioversion whenever possible 1
• Initiation of anticoagulation must not delay emergency interventions required to stabilize the patient 1
• After successful cardioversion, therapeutic anticoagulation should continue for at least 4 weeks regardless of baseline stroke risk 1

Physiologic Rationale for Continuous Anticoagulation

Atrial stunning phenomenon:

• Cardioversion causes transient mechanical dysfunction of the left atrium and left atrial appendage that can persist for weeks 1
• Recovery of mechanical function is delayed depending on AF duration before conversion 1
• Thrombus can form during this stunning period and embolize after mechanical function returns 1
• This explains why 98% of thromboembolic events cluster within the first 10 days after cardioversion 1

Common Pitfalls to Avoid

Never discontinue heparin during the peri-cardioversion period:

• Even when TEE shows no thrombus, heparin must be continued because atrial stunning occurs after cardioversion regardless of pre-existing thrombus 1
• The risk of stroke remains elevated for weeks post-cardioversion due to delayed recovery of atrial mechanical function 1

Do not assume short AF duration eliminates thrombus risk:

• Left atrial thrombus has been documented on TEE in up to 14% of patients with AF <48 hours duration 1
• Asymptomatic AF episodes make accurate duration assessment difficult 1

Long-term anticoagulation decisions are independent of cardioversion success:

• Continue anticoagulation based on CHA₂DS₂-VASc score, not rhythm status 2
• Approximately 50% of patients experience AF recurrence at 1 year after cardioversion 2
• Strokes occur during documented sinus rhythm in paroxysmal AF patients 2