Should patients with new‑onset atrial fibrillation receive continuous intravenous heparin?

Anticoagulation for New-Onset Atrial Fibrillation

Yes, patients with new-onset atrial fibrillation should receive continuous intravenous heparin if cardioversion is planned or if they are hemodynamically unstable, with an initial bolus followed by continuous infusion targeting an aPTT of 1.5-2 times control. 1, 2

Clinical Decision Algorithm

Hemodynamically Unstable Patients (Immediate Action Required)

Perform immediate cardioversion WITHOUT waiting for anticoagulation if the patient has:

• Angina pectoris 1, 2
• Acute myocardial infarction 1, 2
• Cardiogenic shock 1, 2
• Pulmonary edema 1, 2
• Symptomatic hypotension 1

Concurrent with cardioversion, administer:

• IV heparin bolus immediately, followed by continuous infusion 1, 2
• Target aPTT 1.5-2 times control 1
• Continue heparin until therapeutic oral anticoagulation (INR 2-3) is achieved 2
• Maintain anticoagulation for at least 4 weeks post-cardioversion regardless of rhythm 2

Hemodynamically Stable Patients

AF Duration <48 Hours

Cardioversion can proceed with concurrent heparin initiation:

• Start IV heparin bolus followed by continuous infusion 1
• Target aPTT 1.5-2 times control 1
• Cardioversion does not require 3-week pre-treatment delay 1
• Continue anticoagulation for 4 weeks post-cardioversion 1

Important caveat: Recent evidence suggests even AF <48 hours carries thromboembolic risk, so anticoagulation should not be omitted 3, 4

AF Duration >48 Hours or Unknown Duration

Two acceptable approaches:

Option 1 - Traditional approach:

• Anticoagulate for 3-4 weeks before cardioversion 1
• Use IV heparin initially, then transition to warfarin (INR 2-3) 1
• Continue anticoagulation for 4 weeks post-cardioversion 1

Option 2 - TEE-guided approach:

• Perform transesophageal echocardiography to rule out left atrial thrombus 1
• If no thrombus: give IV heparin bolus before cardioversion, then continuous infusion 1
• Target aPTT 1.5-2 times control 1
• Continue anticoagulation for 4 weeks post-cardioversion 1
• If thrombus present: treat with oral anticoagulation (INR 2-3), delay cardioversion 1

Heparin Administration Details

Dosing protocol:

• Initial IV bolus followed by continuous infusion 1, 2
• Adjust dose to maintain aPTT 1.5-2 times control 1
• Monitor aPTT at least daily during initiation 1

Alternative to unfractionated heparin:

• Low molecular weight heparin (LMWH) subcutaneously is supported by limited data 1
• One randomized trial showed LMWH (tinzaparin) was safe and effective with zero strokes versus 5 strokes in the unfractionated heparin group 4

Critical Pitfalls to Avoid

Do not delay cardioversion for anticoagulation in hemodynamically unstable patients - this is a Class I recommendation that prioritizes mortality over stroke risk 1, 2

Do not assume AF <48 hours is "safe" without anticoagulation - thrombus formation can occur rapidly, and recent evidence challenges the traditional 48-hour cutoff 3, 4

Do not stop anticoagulation early after cardioversion - the 4-week post-cardioversion period is critical regardless of whether sinus rhythm is maintained, as atrial stunning persists 1, 2

Do not use digoxin alone for rate control in new-onset AF - this is a Class III recommendation (harmful) 1

Transition to Oral Anticoagulation

Overlap heparin with warfarin for several days:

• Start warfarin concurrently with heparin 1
• Continue heparin until INR is therapeutic (2-3) for at least 24 hours 1
• Check INR at least weekly during initiation, then monthly when stable 1

Total anticoagulation duration:

• Minimum 4 weeks post-cardioversion 1, 2
• Long-term anticoagulation based on CHA₂DS₂-VASc score and stroke risk factors 1, 5