Pathophysiology
Pathophysiology
The modern “plaque rupture”
In both embolic and thrombotic stroke, an unstable plaque can lead to disease (if not cardiac source). Whether embolic or thrombotic, this plaque can originate both in the brain and extracranially in the carotid and vertebrobasilar arteries and even the aorta. The plaque rupture, which is similar in ACS, helps explain the mechanism of action. In this disease process, there is an interplay between the blood vessel, coagulative pathway, and inflammation. The majority of patients will have underlying atherosclerosis in either vertebrobasilar or carotid arteries. With increasing inflammation, there will be a higher risk of instability and rupture that can precipitate stroke. A thrombus will develop due to the activation of platelets, fibrin as well as other chemical mediators to obstruct the artery. As the artery is obstructed, blood flow is impaired, leading to ischemia and infarction if not reversed. Of note, a stationary thrombus can become dislodged, causing embolic events.
Pathophysiology downstream of obstruction
Downstream of obstruction, the brain will lose blood supply, causing ischemia, infarct, and necrosis. The innermost area will infarct or necrose first and surrounding areas will have ischemia. This threatened area is called the ischemic shadow (penumbra) and may still be saved from irreversible damage. Fibrinolytics (rtPA) can help save these areas that would otherwise eventually undergo permanent necrosis.
Key Takeaway
Time = Brain
Stroke is an urgent condition; “brain attack” indicates the urgency.
Once the artery is occluded, there is a limited time to reverse it to save brain tissue.
Minimize delays and treat patients quickly!
Related Video: Pathophysiology of Cerebrovascular Accidents
Other underlying etiologies
Atrial fibrillation (AFib)
Afib is the most common underlying cause of cardioembolic etiology. In Afib, the fibrillation of the atrium encourages the creation of small emboli that can be propagated towards the brain. Patients with Afib have a 5% incidence of stroke each year.
Hypertension
Chronic hypertension affects small arterial walls by hardening them and increasing the risk of thrombosis. A lacunar infarct, in which the small subcortical perforating arteries are occluded, is commonly seen in hypertensive patients. Additionally, hypertension can lead to hemorrhagic stroke.