12- Ischemic Strokes

What is an ischemic stroke?

no blood flow to area of brain due to blockage

Etiologies of Ischemic Stroke

Anything that causes lack of perfusion:

1. thromboembolism in aorta, heart, carotid (carotid artery disease), circle of willis (atherosclerosis in circle)

2. Compression by tumor

3. Hypoperfusion due to hypotension or heart attack

4, Clotting disorder

What is the epidemiology of ischemic strokes?

1. previous stroke

2. transient ischemic attack

3. amaurosis fugax

4. previous myocardial infarction

5. Evidence of atherosclerotic plaques (calcium crystals, hollenhorst)

6. anyone at risk for atherosclerosis (diabetic, poor cholesterol, alcohol, smoking).

What are ocular warning signs of a potential ischemic stroke?

BRAO + CRAO

loss of vision/visual field

What is a BRAO? What does it cause?

occlusion of branch of retinal artery causing infarct downstream

causes pallor + sudden, unilateral, painless partial vision loss

What is a CRAO? What does it cause?

occlusion fo central retinal artery

causes:

cherry red spot

pallor

sudden, unilateral, painless complete vision loss

When does irreversible damage of retina occur with a CRAO?

>/= 90 mins

What is the workup for retinal artery occlusions?

carotid workup (carotid doppler, bruits)

heart workup

Treatment for retinal artery occlusions?

decrease atherosclerosis + clotting

endarterectomy

What is a transient ischemic attack?

temporary (<1hr), ischemia causing functional deficits of brain or body

Pathogenesis of a stroke

1. Ischemia of brain

2. Hydropic change due to decreased blood flow (TIA)

3. After 60 mins of ischemia, infarct, causing liquefactive necrosis of core/umbra

4. Pneumbra flooded with glutamate + NO, triggering apoptosis + necrosis

5. Pneumbra grows

Why does the death of umbra trigger apoptosis + necrosis of penumbra?

When cells of umbra/core die, they release glut (which causes excitotoxity, triggering apoptosis) and NO (free radical, triggers apoptosis + necrosis) of nearby cells

What are the treatments for an ischemic stroke?

1. Reperfusion: give tPA immediately to break up clot

2. Neuroprotection: give Memantine/Namenda for 4 weeks to decrease size of penumbra

3. Decrease swelling: mannitol or craniotomy

4. Treat underlying disease that caused CVA

Why do you need to give tPA within 3 hours of ischemic stroke?

need to break up fibrin polymer to dissolve clot

but after 3 hours, repair would have started + tPA would interfere causing brain to bleed

Why does memantine decrease size of penumbra after ischemic stroke?

inhibits NMDA channels of glutamenergic neurons so Ca2+ cannot enter cell + trigger apoptosis

How does mannitol decrease swelling after ischemic stroke?

increases osmotic/solute pressure in blood, drawing H2O out of tissue and into blood vessels