In a patient with new ischemic stroke evident on magnetic resonance imaging (MRI) and an elevated National Institutes of Health Stroke Scale (NIHSS), should I initiate heparin therapy?

Do Not Start Heparin for Acute Ischemic Stroke

Heparin is not recommended for routine treatment of acute ischemic stroke, regardless of NIHSS score or MRI findings. The evidence consistently shows no net benefit and increased risk of hemorrhagic complications 1.

What You Should Do Instead

Immediate Management (First 24-48 Hours)

1. Assess for thrombolysis eligibility first

   • If within 3-4.5 hours of symptom onset, prioritize IV alteplase (0.9 mg/kg, max 90 mg) 1, 2
   • If large vessel occlusion on imaging, consider mechanical thrombectomy

2. Start aspirin 160-325 mg within 24-48 hours 1, 2

   • Delay aspirin for 24 hours if patient received IV alteplase
   • This is the standard acute antiplatelet therapy with proven benefit (Grade 1A evidence)

3. For minor stroke (NIHSS ≤3-4)

   • Consider dual antiplatelet therapy (aspirin + clopidogrel) for 21 days if started within 24 hours 1
   • This provides early secondary stroke prevention for up to 90 days

VTE Prophylaxis Only

Use prophylactic-dose heparin (5,000 units subcutaneous every 8-12 hours) or pneumatic compression devices ONLY for DVT/PE prevention in immobilized patients 2, 3. This is distinct from therapeutic anticoagulation and is the only appropriate heparin use in acute stroke.

Why Heparin Doesn't Work

The 2018 AHA/ASA Guidelines explicitly state that urgent anticoagulation with heparin does not improve outcomes in acute ischemic stroke 1. The International Stroke Trial and Chinese Acute Stroke Trial (>40,000 patients combined) demonstrated that while heparin reduced recurrent ischemic stroke, this benefit was completely offset by increased symptomatic intracranial hemorrhage 4.

Limited Exceptions (Uncertain Benefit)

The guidelines acknowledge only two scenarios where short-term heparin might be considered, though evidence remains weak 1:

1. Non-occlusive intraluminal thrombus (IIb recommendation, C-LD evidence)

   • Small observational studies suggest possible safety 5
   • Consider if visible thrombus on vessel imaging without complete occlusion
   • Risk-benefit remains uncertain

2. Severe ipsilateral carotid stenosis (IIb recommendation, B-NR evidence)

   • Usefulness "not well established"
   • No strong evidence to support routine use

Critical Pitfalls to Avoid

• Do not use heparin as a substitute for proven acute stroke therapies (thrombolysis, thrombectomy, aspirin)
• Do not confuse VTE prophylaxis dosing with therapeutic anticoagulation - these are entirely different indications 3
• Atrial fibrillation is NOT an indication for acute heparin - the IST trial showed no benefit even in AF patients 4
• Higher NIHSS scores increase both thrombotic AND hemorrhagic risk - there is no NIHSS threshold where heparin becomes beneficial 6

Long-Term Anticoagulation Planning

If the patient has atrial fibrillation or another cardioembolic source, plan for oral anticoagulation but delay initiation based on stroke size and hemorrhage risk. This is a separate decision from acute management and typically starts days to weeks after the acute event, not immediately.

The evidence is clear: aspirin, not heparin, is the appropriate antithrombotic for acute ischemic stroke management 1, 2, 4.