When should patients taking oral anticoagulation (Low Molecular Weight Heparin (LMWH)) for stroke prevention be switched to parenteral anticoagulation (Unfractionated Heparin (UFH))?

Scenarios for Switching from Oral to Parenteral Anticoagulation in Stroke Prevention

Parenteral anticoagulation should be used as a substitute for oral anticoagulation in specific clinical scenarios where oral therapy is temporarily inappropriate or contraindicated, particularly during perioperative periods, acute illness, or when rapid anticoagulation is needed. 1

Key Scenarios for Switching to Parenteral Anticoagulation

1. Perioperative Management

• For patients requiring temporary interruption of oral anticoagulation for surgical procedures:
  • Bridging therapy with LMWH is recommended for high-risk patients (stroke or TIA within 3 months, CHADS₂ score of 5-6, mechanical or rheumatic valve disease) 1
  • Preferred method is full treatment doses of LMWH administered subcutaneously rather than prophylactic doses 1
  • For patients with mechanical heart valves, unfractionated heparin may be preferred 1

2. Acute Illness with NPO Status

• When patients cannot take oral medications:
  • During hospitalization for acute illness
  • When gastrointestinal absorption is compromised
  • During periods of severe nausea/vomiting
  • LMWH is generally preferred over UFH for most patients 1, 2

3. Post-Stroke Management

• After an ischemic stroke while on oral anticoagulation:
  • Timing of reinitiation of anticoagulation depends on stroke severity 1
  • For mild stroke: anticoagulation may be initiated >3 days after stroke
  • For moderate stroke: anticoagulation may be initiated >6-8 days after stroke
  • For severe stroke: anticoagulation may be initiated >12-14 days after stroke
  • Bridging with heparin is generally not recommended due to increased risk of symptomatic intracranial hemorrhage 1

4. Post-Hemorrhagic Stroke

• After intracranial hemorrhage:
  • Anticoagulation should be discontinued for at least 1-2 weeks 1
  • For patients requiring anticoagulation soon after cerebral hemorrhage, intravenous heparin may be safer than oral anticoagulation 1
  • Oral anticoagulants may be resumed after 3-4 weeks with rigorous monitoring 1

5. Pregnancy

• For pregnant women requiring anticoagulation:
  • Oral anticoagulants should be replaced by heparin during the first trimester and last 6 weeks before delivery 1
  • Options include adjusted-dose UFH or LMWH with factor Xa monitoring throughout pregnancy 1

Considerations for Parenteral Anticoagulant Selection

LMWH vs. UFH

• LMWH advantages over UFH:

  • Higher bioavailability
  • More predictable anticoagulant effects
  • Less interaction with platelets
  • Lower risk of heparin-induced thrombocytopenia
  • Can be administered subcutaneously in outpatient setting 2, 3

• UFH may be preferred when:

  • Rapid reversal may be needed
  • Patient has severe renal impairment
  • Mechanical heart valves are present 1

Important Caveats

• Avoid bridging in low-risk scenarios: Bridging increases bleeding risk without clear benefit in patients at low risk for thromboembolism 1

• Do not use parenteral anticoagulation immediately after acute ischemic stroke: The European Society of Cardiology and American Heart Association/American Stroke Association recommend against immediate anticoagulation with heparin after an acute ischemic stroke 1, 4

• Consider alternatives in patients with contraindications to both oral and parenteral anticoagulation: Left atrial appendage occlusion may be considered for patients with AF at high risk for stroke but with contraindications to anticoagulation 5

• Monitor closely for bleeding complications: Parenteral anticoagulants carry significant bleeding risks that require careful monitoring, especially when transitioning between agents 6

By following these guidelines for appropriate switching between oral and parenteral anticoagulation, clinicians can maintain effective stroke prevention while minimizing risks during periods when oral anticoagulation is not feasible.