Thrombolysis in Stroke: rtPA Eligibility Criteria and Protocol for Acute Ischemic Stroke

Introduction

Acute ischemic stroke (AIS) remains a major cause of death and disability worldwide. One of the most critical interventions in its early management is the administration of recombinant tissue plasminogen activator (rtPA), also known as Alteplase. This thrombolytic agent can dissolve the clot obstructing cerebral blood flow.

The administration of rtPA is time-sensitive and governed by strict eligibility criteria. Understanding these criteria is essential for prompt and safe treatment.

1. Pathophysiology of Ischemic Stroke

An ischemic stroke occurs when a cerebral artery is occluded by a thrombus or embolus, leading to brain tissue ischemia and infarction. Rapid restoration of blood flow is crucial to prevent permanent neuronal injury.

Time is Brain: It is estimated that 1.9 million neurons die every minute during an untreated stroke.
Therefore, early identification and treatment are key to improving outcomes.

2. What is rtPA?

rtPA (Alteplase) is a serine protease enzyme that converts plasminogen to plasmin, which then dissolves fibrin clots.

Mechanism of Action:

Binds to fibrin in a thrombus.
Activates plasminogen to plasmin.
Plasmin breaks down fibrin and dissolves the clot.

3. Indications for rtPA Use

The primary indication is acute ischemic stroke diagnosed within a specific therapeutic window and after ruling out contraindications.

Main goal: Salvage the ischemic penumbra (reversible damage).
Early administration = better outcomes.

4. Time Window for rtPA Administration

Time Frame	Recommendation
0–3 hours	Strongest recommendation for rtPA administration
3–4.5 hours	Still acceptable, with additional exclusion criteria
>4.5 hours	Not recommended unless selected by advanced imaging
Wake-up stroke	Eligible only if a mismatch is seen on DWI-FLAIR MRI or CTP

🧠 Remember: Always calculate from “Last Known Well (LKW)”, not from presentation time.

5. Inclusion Criteria for rtPA (Based on AHA/ASA Guidelines)

✅ Must meet all of the following:

Age ≥ 18 years.
Clinical diagnosis of acute ischemic stroke with measurable neurologic deficit.
Symptom onset within 4.5 hours.
No evidence of hemorrhage on non-contrast CT.
No rapidly resolving symptoms (i.e., not a TIA).
NIHSS ≥ 4 or disabling symptoms.

6. Exclusion Criteria for rtPA

❌ Absolute Contraindications:

Any intracranial hemorrhage on imaging.
Bleeding diathesis:
- Platelet count < 100,000/mm³
- INR > 1.7
- aPTT > 40 seconds
Recent surgery or trauma (within 14 days).
GI or urinary tract hemorrhage within 21 days.
Severe uncontrolled hypertension: SBP >185 mmHg or DBP >110 mmHg.
Blood glucose <50 or >400 mg/dL.
Known intracranial neoplasm or vascular malformation.

⚠️ Relative Contraindications (use clinical judgment):

Minor or rapidly improving stroke symptoms.
Seizure at onset with post-ictal deficits.
Recent myocardial infarction.
Pregnancy (not an absolute contraindication).
Age >80 in extended window (see below).

7. Extended Time Window (3–4.5 hours): Additional Exclusion Criteria

If rtPA is being considered in the 3 to 4.5-hour window, exclude if:

Age > 80 years
Oral anticoagulant use, regardless of INR.
NIHSS > 25
History of both stroke and diabetes

8. NIH Stroke Scale (NIHSS) and rtPA

The NIHSS helps quantify stroke severity. While there is no strict cutoff, most guidelines recommend rtPA if NIHSS is ≥ 4.

NIHSS 0–4: Minor stroke, observe unless disabling symptoms (e.g., aphasia).
NIHSS >25: Consider risk-benefit; associated with higher hemorrhage risk.

9. Step-by-Step Eligibility Assessment Algorithm

📝 Step 1: Identify Time of Last Known Well (LKW)

Must be within 4.5 hours
Wake-up strokes: Use imaging to determine eligibility (MRI mismatch or CT perfusion).

📝 Step 2: Perform Rapid Assessment

Vitals, glucose, and NIHSS.
Get a non-contrast CT brain: Rule out hemorrhage.

📝 Step 3: Screen for Contraindications

Recent surgery, bleeding, labs (platelet count, INR, glucose).
Manage BP if SBP >185 or DBP >110 (labetalol, nicardipine).

📝 Step 4: Calculate rtPA Dose

Weight (kg)	Total Dose (0.9 mg/kg)	10% Bolus (1 min)	Infusion over 1 hr
60	54 mg	5.4 mg	48.6 mg
70	63 mg	6.3 mg	56.7 mg
80	72 mg	7.2 mg	64.8 mg
Max Dose	90 mg	9 mg	81 mg

10. Post-rtPA Monitoring Protocol

First 24 Hours – Intensive monitoring:

Time Post rtPA	Monitoring
First 2 hours	Vitals & NIHSS q15 minutes
Hours 2–8	Vitals q30 minutes
Hours 8–24	Vitals hourly

Do not give antiplatelets, anticoagulants, or perform invasive procedures within 24 hours.

Repeat non-contrast CT brain at 24 hours to rule out hemorrhagic transformation.

11. Imaging and Special Considerations

Initial Imaging:

CT Brain (non-contrast): Rule out hemorrhage.
CT Angiogram or MRI: Consider if large vessel occlusion is suspected (for thrombectomy).

Advanced Imaging (if LKW unclear or wake-up stroke):

DWI-FLAIR mismatch on MRI: Suggests acute ischemia.
CT Perfusion (CTP): Shows salvageable brain tissue ("penumbra").

12. Adverse Effects of rtPA

Intracerebral hemorrhage (ICH): Occurs in ~6% of treated patients.
Angioedema (esp. in ACE inhibitor users).
Hypotension, allergic reactions (rare).

🩸 If bleeding occurs:

Stop rtPA.
Administer cryoprecipitate, platelets, TXA or aminocaproic acid if needed.
Neurosurgery consult.

13. Key Takeaways and Mnemonic: “S.T.R.O.K.E.”

S – Symptom onset < 4.5 hours T – Time = brain (act fast) R – Rule out hemorrhage via CT O – Obtain labs (glucose, INR, platelets) K – Know contraindications E – Evaluate for eligibility using NIHSS, BP, and exclusions

Conclusion

rtPA remains a life-saving intervention for ischemic stroke when used appropriately. Timely action, precise calculation, and strict adherence to contraindications are the cornerstones of effective thrombolytic therapy.

This structured approach improves patient outcomes and prepares you to perform confidently in clinical exams and real-life emergencies. Always remember: the faster the door-to-needle time, the better the prognosis.