Cerebrovascular Accident (CVA) and Transient Ischemic Attack (TIA)

Introduction

For the MCCQE1, understanding Cerebrovascular Accidents (Stroke) and Transient Ischemic Attacks (TIA) is critical. Stroke is a leading cause of disability and the third leading cause of death in Canada. Mastery of this topic requires a solid grasp of the CanMEDS Medical Expert role—specifically in acute recognition, rapid management (“Time is Brain”), and secondary prevention.

This guide focuses on the Canadian approach to stroke care, aligning with the Canadian Stroke Best Practice Recommendations (CSBPR).

Definitions and Classification

Understanding the distinction between TIA and Stroke is fundamental for MCCQE1 preparation.

Pathophysiology Classification

Clinical Presentation

Rapid identification is key. The Heart and Stroke Foundation of Canada promotes the FAST signs.

Vascular Syndromes

Recognizing the territory aids in localization, a frequent MCCQE1 testing point.

Diagnosis and Investigations

Time is of the essence. The goal is to rule out hemorrhage and identify salvageable tissue.

Acute Management (Ischemic Stroke)

1. Thrombolysis (IV Alteplase/Tenecteplase)

• Mechanism: Recombinant tissue plasminogen activator (tPA).
• Time Window: Within 4.5 hours of symptom onset (Last Known Well).
• Inclusion: Clinical diagnosis of disabling stroke, age ≥18.
• Key Contraindications:
  • Hemorrhage on CT.
  • Recent major surgery/trauma (within 14 days).
  • Active internal bleeding.
  • BP >185/110 mmHg (must be lowered before treatment).
  • Current anticoagulant use with elevated INR (>1.7) or DOAC use within 48h (unless normal renal function and >48h, or specific reversal available).

2. Endovascular Thrombectomy (EVT)

• Indication: Large Vessel Occlusion (LVO) in anterior circulation.
• Time Window: Up to 6 hours standard; extended window 6–24 hours for select patients (based on perfusion imaging showing salvageable penumbra - DAWN/DEFUSE-3 criteria).
• Note: Can be done in conjunction with tPA (“Bridging therapy”).

3. Blood Pressure Management

• Candidates for tPA: Keep BP <185/110 mmHg before bolus and <180/105 mmHg for 24h after.
• Not candidates for tPA: Permissive hypertension is allowed to maintain perfusion. Treat only if BP >220/120 mmHg or if there is end-organ damage (e.g., aortic dissection, MI). Lower by 15% initially.

4. Antiplatelet Therapy

• ASA (Aspirin): 160–325 mg PO/PR stat after CT rules out bleed.
  • If tPA given: Delay ASA for 24 hours.
  • If no tPA: Give immediately.

Secondary Prevention (Canadian Guidelines)

Prevention strategies depend on the etiology determined by the workup (Holter monitor, Echocardiogram, Carotid Doppler).

1. Non-Cardioembolic Stroke (Atherosclerotic/Lacunar)

• Antiplatelets:
  • Single agent: ASA (81mg daily) OR Clopidogrel (75mg daily).
  • Dual Antiplatelet Therapy (DAPT): ASA + Clopidogrel for 21 days only, then switch to monotherapy. Indicated for High-risk TIA (ABCD2 ≥4) or Minor Ischemic Stroke (NIHSS ≤3). (Reference: CHANCE and POINT trials).
• Lipids: High-intensity statin (Atorvastatin 80mg). Target LDL <1.8 mmol/L (or <1.4 mmol/L in very high risk).
• Carotid Stenosis: Carotid Endarterectomy (CEA) recommended for symptomatic stenosis 70–99%. Benefit for 50–69% is moderate (NASCET trial). Perform ideally within 2 weeks.

2. Cardioembolic Stroke (Atrial Fibrillation)

• Anticoagulation: DOACs (Apixaban, Rivaroxaban, Dabigatran, Edoxaban) are preferred over Warfarin in Canada.
• Timing: “1-3-6-12 rule” (rough guide for restarting anticoagulation after stroke to minimize hemorrhagic transformation risk):
  • 1 day: TIA.
  • 3 days: Mild stroke.
  • 6 days: Moderate stroke.
  • 12 days: Severe stroke.

3. Lifestyle Modification

• Smoking cessation.
• Exercise (150 min/week moderate).
• Diet (Mediterranean/DASH).
• Diabetes control (HbA1c ≤7.0%).

Key Points to Remember for MCCQE1

• Hypoglycemia is the most common stroke mimic; always check glucose first.
• Non-contrast CT is the mandatory first imaging study.
• Time is Brain: tPA window is strict (4.5h). Do not delay CT.
• Permissive Hypertension: Do not aggressively lower BP in ischemic stroke unless tPA is planned or BP is extreme (>220/120).
• Posterior Circulation: Vertigo + Diplopia + Dysarthria suggests brainstem/cerebellum, not peripheral vestibular disease.
• Aphasia: Almost always Left MCA (dominant hemisphere).
• Neglect: Almost always Right MCA (non-dominant hemisphere).

Sample Question

Clinical Scenario

A 68-year-old male presents to the Emergency Department with sudden onset of right-sided weakness and difficulty speaking. The symptoms began 2 hours ago while he was eating breakfast. Past medical history is significant for hypertension and type 2 diabetes.

Physical Examination:

• BP: 175/95 mmHg
• HR: 88 bpm (regular)
• Neurology: Global aphasia, right facial droop, right arm paralysis (0/5), and right leg weakness (3/5).
• Glucometer: 6.5 mmol/L.

Investigations:

• CT Head (Non-contrast): No hemorrhage, no acute hypodensity. Early signs of MCA territory ischemia are equivocal.

Which one of the following is the most appropriate immediate management step?

Options

• A. Administer ASA 325 mg orally immediately.
• B. Administer IV Alteplase (tPA).
• C. Administer IV Labetalol to lower SBP <140 mmHg.
• D. Order an urgent MRI Brain to confirm the diagnosis.
• E. Start Heparin infusion.

Explanation

The correct answer is:

• B. Administer IV Alteplase (tPA).

Detailed Explanation: This patient presents with a clinical diagnosis of acute ischemic stroke (Left MCA syndrome) within the therapeutic window for thrombolysis (2 hours onset, window is 4.5 hours). The non-contrast CT has ruled out hemorrhage. His blood pressure (175/95 mmHg) is below the exclusion threshold for tPA (>185/110 mmHg). Therefore, the immediate priority is to administer IV Alteplase to restore perfusion and save brain tissue.

• Option A (ASA): While ASA is indicated in acute stroke, it should be withheld for 24 hours if thrombolytic therapy is administered to reduce bleeding risk. It would be the correct choice if the patient were outside the tPA window or had a contraindication.
• Option C (Labetalol): Aggressive blood pressure lowering is contraindicated in acute ischemic stroke as it may compromise collateral perfusion to the penumbra. BP only needs to be lowered if >185/110 for tPA candidates or >220/120 for non-candidates.
• Option D (MRI): While MRI is more sensitive, waiting for an MRI would delay time-critical thrombolysis. CT is sufficient to rule out bleed.
• Option E (Heparin): Full anticoagulation with Heparin is generally not indicated in the acute phase of ischemic stroke due to high risk of hemorrhagic transformation and lack of proven benefit over antiplatelets/thrombolysis.

References

1. Heart & Stroke Foundation of Canada. Canadian Stroke Best Practice Recommendations (CSBPR). Acute Stroke Management (2022 Update). https://www.strokebestpractices.ca/ 
2. Medical Council of Canada. MCCQE Part I Objectives: Stroke.
3. Canadian Cardiovascular Society (CCS). 2020 Comprehensive Guidelines for the Management of Atrial Fibrillation.
4. Boulanger, J. M., et al. (2018). Canadian Stroke Best Practice Recommendations for Acute Stroke Management. International Journal of Stroke.
5. Gladstone, D. J., et al. (2021). Atrial Fibrillation Screening in High-Risk Patients. New England Journal of Medicine.