When should a non‑contrast head CT be obtained after intravenous alteplase administration for an acute ischemic stroke?

Post-Alteplase Cranial CT Timing

Obtain a follow-up non-contrast head CT or MRI at 24 hours after IV alteplase administration before starting any anticoagulants or antiplatelet agents. 1

Routine Post-Treatment Imaging

The American Heart Association/American Stroke Association guidelines establish a clear protocol for post-alteplase neuroimaging:

• Perform routine follow-up CT or MRI scan at 24 hours after IV alteplase infusion before initiating anticoagulant or antiplatelet therapy 1
• This 24-hour imaging serves to detect hemorrhagic transformation and assess infarct evolution before starting antithrombotic medications 1
• The timing is standardized regardless of clinical course, provided the patient remains neurologically stable 1

Emergency Imaging Indications

If clinical deterioration occurs at any time during or after alteplase administration, obtain an emergent non-contrast head CT immediately—do not wait for the scheduled 24-hour scan. 1

Specific triggers requiring immediate CT imaging include:

• Severe headache 1
• Acute hypertension (systolic BP >180 mmHg or diastolic >105 mmHg despite treatment) 1
• Nausea or vomiting 1
• Worsening neurological examination (any decline in NIHSS or level of consciousness) 1

Management During Deterioration

• Discontinue the alteplase infusion immediately if still running 1
• Obtain emergent non-enhanced head CT to evaluate for symptomatic intracranial hemorrhage 1
• If hemorrhage is confirmed, initiate reversal protocol with cryoprecipitate (10 units), tranexamic acid (1000 mg IV) or ε-aminocaproic acid (4-5 g loading dose), and obtain hematology and neurosurgery consultations 1, 2

Clinical Monitoring Schedule

The guidelines mandate intensive neurological surveillance that determines when imaging may be needed:

• Every 15 minutes during and for 2 hours after IV alteplase infusion 1
• Every 30 minutes for the subsequent 6 hours (hours 2-8) 1
• Hourly from 8 to 24 hours after treatment 1

This frequent monitoring allows early detection of complications that would trigger emergency imaging before the routine 24-hour scan 1.

Rationale for 24-Hour Timing

The 24-hour timepoint balances several considerations:

• Hemorrhagic transformation typically manifests within the first 24-36 hours after alteplase, with symptomatic intracranial hemorrhage rates of 2.4-6.4% across major trials 3, 4
• Antiplatelet and anticoagulant therapy must be delayed until hemorrhage is excluded, as these agents would exacerbate any bleeding 1
• The Canadian Stroke Best Practice guidelines similarly recommend maintaining blood pressure <180/105 mmHg for 24 hours after alteplase, aligning with the imaging timeframe 1

Common Pitfalls

• Do not delay the 24-hour CT beyond this timeframe, as it gates initiation of secondary stroke prevention therapies 1
• Do not obtain routine imaging earlier than 24 hours unless clinically indicated, as early ischemic changes may be difficult to interpret and do not change management in stable patients 1
• Do not start antiplatelet or anticoagulant therapy before the 24-hour imaging is completed and reviewed, even if the patient appears clinically improved 1