Introduction

Stroke

“An interruption of the oxygen supply to the brain typically due to an occlusion or rupture”

• Approximately 795,000 people in the United States experience a stroke, of which 87% (690,000) are ischemic.

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Pathophysiology

1. ‘Ischemic occlusion generates thrombotic and embolic conditions in the brain’ 
2. Thrombus versus embolus 
   • Thrombus
     • An aggregation of platelets and fibrin formed in response either to an atherosclerotic lesion or to vessel injury
     • In response to vessel or tissue injury, the blood coagulation system is activated, which initiates the following cascade of processes transforming prothrombin and resulting in a fibrin clot
       1. Prothrombin🡪 Thrombin 🡪 Fibrinogen🡪 Fibrin🡪 Fibrin Clot
   • Embolus 
     • Particles that act as traveling “clots” 
     • Example
       1. Platelet aggregate dislodged from an atherosclerotic lesion
       2. This is transported via bloodstream through the cerebrovasculature until it reaches vessels too small for further propagation
       3. The clot then clogs the vessel thus preventing blood flow to enter the distal vasculature

3. Atherosclerosis

• Blood flow is affected by narrowing of vessels due to atherosclerosis
• Plaque buildup leads to constriction of the vascular chamber and form clots, causing thrombotic stroke

4. Embolic stroke

• A decrease in blood flow to the brain causes an embolism
• A reduction in blood to the brain causes severe stress and untimely leads to cell death

‘Necrosis is followed by disruption of the plasma membrane, organelle swelling and leaking of cellular contents into extracellular space, and loss of neuronal function

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5. Cellular level

a. Neuronal cell death occurs secondary to necrosis and apoptosis

• Necrosis
  • A process that is not regulated or programmed and is the predominant mechanism that follows acute permanent focal vascular occlusion
  •  Typically, a consequence of disruption of cellular homeostasis due to energy failure and is accompanied by cellular swelling, membrane lysis, inflammation, vascular damage, and edema formation
• Apoptosis
  • Programmed cell death

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b. Types of Stroke 

• Ischemic Stroke (subtypes)
  • Lacunar Stroke
    • Due to small vessel disease 
  • Cardioembolic Stroke
    • ‘A stroke attributable to arterial occlusion from an embolus that presumably arose from the heart’
  • Large Artery Atherosclerosis
    • ‘Ischemic stroke in the vascular distribution of a major intracranial or extracranial artery with >50% stenosis or occlusion on vascular imaging’ 
  • Cryptogenic Stroke
    • Ischemic stroke that is confirmed with imaging, but the source is unknown 
• Transient Ischemic Attack (TIA)
  • A brief episode of neurologic dysfunction caused by ischemia without acute infarction 
  • Symptoms typically resolve 
• Hemorrhagic Stroke
  • Bleeding in the brain typically caused by ruptured blood vessels 
  • Associated with severe morbidity and mortality

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Risk Factors

1. Hypertension 
   • medical condition in which the blood pressure in the arteries is persistently elevated.
2. Dyslipidemia 
   • Abnormally high levels of lipids in the blood.
3. Diabetes Mellitus 
   • a disease of inadequate control of blood levels of glucose.
4. Atrial Fibrillation 
   • A disease of the heart characterized by irregular and often faster heartbeat.
5. Cigarette Use