5.1 Acute Ischemic Stroke: Thrombolysis & Blood Pressure Control

5.1 Acute Ischemic Stroke: Thrombolysis & Blood Pressure Control

Acute ischemic stroke (AIS) represents a hyperacute medical emergency in which rapid diagnostic assessment and prompt pharmacotherapeutic intervention directly dictate long-term neurological recovery. Under the pathophysiologic paradigm that "time is brain," an estimated 1.9 million neurons, 14 billion synapses, and 7.5 miles of myelinated axons are destroyed every minute an ischemic stroke remains untreated. The primary pharmacotherapeutic objective in the emergency department (ED) is the rapid restoration of cerebral blood flow to the salvageable ischemic penumbra before irreversible infarction ensues, while concurrently controlling blood pressure to prevent secondary hemorrhagic transformation.

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Thrombolytic Pharmacotherapy: Alteplase vs. Tenecteplase

Recombinant tissue plasminogen activators (tPA) promote fibrinolysis by selectively binding to fibrin on the thrombus surface and converting clot-bound plasminogen into active plasmin. Plasmin cleaves fibrin polymers into soluble fibrin degradation products, dissolving the occlusive intravascular thrombus.

Alteplase (rt-PA)

Alteplase remains the historically established standard of care for AIS within guideline-directed treatment windows:

• Dosing: 0.9 mg/kg IV (maximum total dose of 90 mg).
• Administration Architecture:
  • Initial 10% of the calculated dose administered as a rapid intravenous bolus over 1 minute.
  • Remaining 90% of the calculated dose administered as a continuous intravenous infusion over 60 minutes via an automated infusion pump.
• Preparation & Line Flushing: Discard the excess volume from the vial prior to initiating the infusion to prevent accidental total overdose. At the conclusion of the 60-minute infusion, a 0.9% sodium chloride flush at the same infusion rate is mandatory to ensure all residual alteplase in the IV tubing is delivered to the patient.

Tenecteplase (TNK-tPA)

Tenecteplase is a genetically engineered variant of native tPA with three modifications: Thr103Asn, Asn117Gln, and replacement of the Lys-His-Arg-Arg sequence at positions 296–299 with four alanines. The TNKase label lists these advantages over native tPA:

• 80-fold greater resistance to inactivation by plasminogen activator inhibitor-1 (PAI-1).
• 14-fold greater fibrin specificity, resulting in enhanced thrombus targeting and reduced systemic depletion of circulating fibrinogen, alpha-2 antiplasmin, and clotting factors.
• Prolonged terminal elimination half-life (~20 to 24 minutes vs. 4 to 5 minutes for alteplase), enabling delivery as a single rapid IV bolus.
• AIS Dosing: 0.25 mg/kg IV single bolus (maximum dose of 25 mg) administered over 5 to 10 seconds.

Clinical Trial Evidence: Alteplase vs. Tenecteplase

1. EXTEND-IA TNK (2018): Evaluated AIS patients with large vessel occlusions (LVO) scheduled for endovascular thrombectomy (EVT). Patients receiving tenecteplase 0.25 mg/kg achieved significantly higher pre-thrombectomy reperfusion rates (22% vs. 10%, p=0.002) and superior 90-day functional recovery compared to alteplase.
2. AcT Trial (2022): A large pragmatic Canadian registry trial (n=1,577) comparing tenecteplase 0.25 mg/kg against alteplase 0.9 mg/kg in all-comer AIS patients within 4.5 hours. Tenecteplase met non-inferiority criteria for the primary endpoint of 90-day modified Rankin Scale (mRS) 0 to 1 (36.9% vs. 34.8%), with identical rates of symptomatic intracranial hemorrhage (3.4% vs. 3.2%).
3. TIMELESS Trial (2024): Tenecteplase 0.25 mg/kg given 4.5 to 24 hours after onset to patients with large vessel occlusion and salvageable penumbra, most of whom then had thrombectomy, did not improve 90-day functional outcome.
4. TRACE-III (2024): In patients with large vessel occlusion 4.5 to 24 hours from onset who could not get thrombectomy, tenecteplase improved the chance of excellent functional outcome. This trial supports late-window thrombolysis where thrombectomy is unavailable.

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Time Windows and Strict Eligibility Criteria

Treatment Windows

• Standard Window (0 to 3 hours): Supported by the original NINDS rt-PA trial. Initiated within 3 hours from symptom onset or last known normal (LKN).
• Expanded Window (3 to 4.5 hours): Supported by the ECASS III trial, which excluded age over 80 years, NIHSS over 25, diabetes plus prior stroke, and oral anticoagulant use. Later AHA/ASA guidance no longer treats most of those trial exclusions as absolute in this window.
• Extended Windows (2026 AHA/ASA guideline): Thrombolysis may be reasonable for patients with salvageable ischemic penumbra on advanced imaging who wake up with symptoms (within 9 hours of the midpoint of sleep) or are 4.5 to 9 hours from last known well (EXTEND), and for patients with large vessel occlusion and salvageable tissue up to 24 hours when thrombectomy is not available (TRACE-III).
• Non-disabling Deficits: For minor, non-disabling stroke within 4.5 hours, thrombolysis has not shown benefit, and dual antiplatelet therapy (aspirin plus clopidogrel) is preferred.

Absolute Exclusion Criteria for Intravenous Thrombolysis

Prior to administering alteplase or tenecteplase, the emergency medicine pharmacist must rigorously review absolute contraindications:

1. Acute Intracranial Hemorrhage: Confirmed on non-contrast head CT.
2. Recent Head Trauma or Stroke: Severe head trauma or ischemic stroke within the preceding 3 months.
3. Severe Uncontrolled Blood Pressure: Systolic blood pressure (SBP) $\ge 185\text{ mmHg}$ or diastolic blood pressure (DBP) $\ge 110\text{ mmHg}$ refractory to acute antihypertensive therapy.
4. Thrombocytopenia: Platelet count $<100,000/\mu\text{L}$.
5. Active Anticoagulant Use:
   • Warfarin with INR >1.7 or PT >15 seconds.
   • Unfractionated heparin within 48 hours resulting in an elevated aPTT >40 seconds.
   • Therapeutic Low Molecular Weight Heparin (LMWH, e.g., enoxaparin 1 mg/kg q12h) within 24 hours.
   • Direct Oral Anticoagulants (DOACs: apixaban, rivaroxaban, edoxaban, dabigatran) ingested within 48 hours, unless specific laboratory assays (calibrated anti-Xa level or diluted thrombin time) are undetectable, or $>48$ hours have elapsed with documented normal creatinine clearance.
6. Structural Intracranial Lesions: Intra-axial intracranial neoplasm is a contraindication. A small, unruptured, unsecured intracranial aneurysm (under 10 mm) or a benign extra-axial tumor such as a meningioma is not a reason to withhold treatment, and the 2026 guideline frames these as individualized decisions. The safety of thrombolysis with an unruptured arteriovenous malformation is uncertain, so it may be considered for severe deficits.
7. Active Internal Bleeding: Acute gastrointestinal malignancy or GI hemorrhage within the preceding 21 days.
8. Infective Endocarditis & Aortic Dissection: High risk of catastrophic secondary intracranial mycotic aneurysm rupture or hemorrhagic dissection propagation.

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Blood Pressure Targets & Emergency Antihypertensive Protocols

Elevated blood pressure during acute ischemic stroke is often a compensatory physiological response to maintain cerebral perfusion through collateral vessels. However, excessive hypertension significantly elevates the risk of fatal hemorrhagic transformation when thrombolytics are administered.

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Specific Hemodynamic Thresholds

• Pre-Thrombolytic Threshold: SBP must be lowered to $<185\text{ mmHg}$ and DBP to $<110\text{ mmHg}$ BEFORE initiating alteplase or tenecteplase. If blood pressure cannot be maintained below 185/110 mmHg with first-line agents, thrombolytic therapy must be abandoned.
• Post-Thrombolytic Maintenance: SBP must remain $<180\text{ mmHg}$ and DBP $<105\text{ mmHg}$ for at least the first 24 hours post-thrombolysis. The 2026 guideline adds that intensive lowering to an SBP below 140 mmHg after thrombolysis or thrombectomy is not recommended, because it does not improve outcomes and may harm after thrombectomy.
• Monitoring Protocol: Check blood pressure every 15 minutes for 2 hours, then every 30 minutes for 6 hours, then every 60 minutes for 16 hours.
• Permissive Hypertension: For AIS patients not receiving thrombolytics or EVT, blood pressure should not be treated acutely unless SBP $>220\text{ mmHg}$ or DBP $>120\text{ mmHg}$ or there is co-existing target end-organ damage (acute coronary syndrome, acute aortic dissection, hypertensive encephalopathy, or pulmonary edema). If treating, lower blood pressure conservatively by 15% within the first 24 hours.

First-Line Intravenous Antihypertensive Agents

1. Labetalol:
   • Mechanism: Combined competitive antagonist at alpha-1, beta-1, and beta-2 adrenergic receptors (7:1 beta-to-alpha blockade ratio intravenously).
   • Dosing: 10 to 20 mg IV push over 1 to 2 minutes; may repeat or double the dose every 10 to 20 minutes (up to a cumulative maximum of 300 mg), or initiate a continuous infusion at 2 to 8 mg/min.
   • Clinical Pearls: Avoid in severe bradycardia (HR <60 bpm), second- or third-degree heart block, and active acute decompensated heart failure.
2. Nicardipine:
   • Mechanism: Second-generation dihydropyridine calcium channel blocker that selectively inhibits L-type calcium channels in vascular smooth muscle, producing potent peripheral and cerebral arterial vasodilation without negative inotropic or dromotropic effects.
   • Dosing: Initial continuous IV infusion at 5 mg/h; titrate by 2.5 mg/h every 5 to 15 minutes to target blood pressure (maximum dose 15 mg/h).
   • Clinical Pearls: Highly titratable with a predictable linear dose-response. Ensure infusion site rotation or large-vein access to minimize superficial phlebitis.
3. Clevidipine:
   • Mechanism: Third-generation ultra-short-acting dihydropyridine calcium channel blocker rapidly hydrolyzed by blood and tissue esterases (elimination half-life ~1 minute).
   • Dosing: Initial continuous IV infusion at 1 to 2 mg/h; double the dose every 90 seconds until approaching target, then titrate by 2 to 4 mg/h every 5 to 10 minutes (maximum dose 32 mg/h).
   • Clinical Pearls: Formulated in a 20% lipid emulsion (provides 2 kcal/mL; 0.2 g fat/mL). Strict aseptic technique required; discard vial and infusion line within 12 hours of puncture. Contraindicated in severe egg or soybean allergies and defective lipid metabolism (e.g., severe hypertriglyceridemia).

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Thrombolytic & Antihypertensive Reference Matrix

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Life-Threatening Post-Thrombolytic Complications

1. Symptomatic Intracranial Hemorrhage (sICH)

Occurring in approximately 2% to 6% of patients, sICH is defined as new intracranial hemorrhage documented on neuroimaging associated with an acute neurological deterioration (drop in GCS or increase in NIHSS by $\ge 4$ points), acute severe headache, sudden vomiting, or acute secondary hypertension.

Immediate Reversal Protocol:

1. STOP the thrombolytic infusion immediately if still running.
2. Order an emergent non-contrast head CT and STAT neurosurgery consult.
3. Draw STAT laboratory tests: CBC, PT/INR, aPTT, fibrinogen, and type and crossmatch.
4. Cryoprecipitate: Administer 10 units IV bolus immediately. Cryoprecipitate is the primary source of concentrated fibrinogen, factor VIII, and von Willebrand factor. Recheck fibrinogen level at 1 hour post-infusion; if fibrinogen remains $<150\text{ mg/dL}$, administer an additional 10 units.
5. Antifibrinolytic Therapy: Administer Tranexamic Acid (TXA) 1000 mg IV infused over 10 minutes OR Aminocaproic acid 4 to 5 g IV over 1 hour followed by 1 g/h for 8 hours.

2. Orolingual Angioedema

Orolingual angioedema occurs in 1% to 5% of thrombolytic recipients. It is characterized by acute swelling of the tongue, lips, and oropharynx, often asymmetric. The risk is elevated 4- to 5-fold in patients taking ACE inhibitors due to impaired degradation of bradykinin, which is further amplified by plasmin-mediated activation of the contact kallikrein-kinin cascade.

Emergency Management Protocol:

1. Airway Protection: Maintain airway patency; prepare for immediate fiberoptic nasal or endotracheal intubation if stridor or laryngeal edema develops.
2. Discontinue Thrombolytic Infusion.
3. Corticosteroids & Antihistamines:
   • Methylprednisolone: 125 mg IV push.
   • Diphenhydramine: 50 mg IV push.
   • Famotidine: 20 mg IV push (H2 receptor blockade).
4. Epinephrine: For progressive airway compromise, administer epinephrine 0.3 mg IM (1:1,000 solution) into the anterolateral thigh or nebulized racemic epinephrine (0.5 mL of 2.25% solution).
5. Targeted Bradykinin Blockade: For refractory ACE-inhibitor-associated angioedema, administer Icatibant 30 mg subcutaneous injection (selective bradykinin B2 receptor antagonist) or Ecallantide 30 mg SC (plasma kallikrein inhibitor).