Stroke

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A stroke (syn. Cerebral Vascular Accident or "CVA") is a sudden, often focal, loss of brain function. There are many different causes of stroke, but all involve a loss of vital blood and oxygen to all or part of the brain. Strokes can have many different clinical presentations. Approximately 700,000 Americans per year experience a stroke. Stroke is a medical emergency and can cause permanent neurologic damage or death if not promptly diagnosed and treated. It is the third leading cause of death and the leading cause of long-term adult disability in the United States.[1] On average, a stroke occurs every 45 seconds and someone dies from a stroke every 3 minutes.[2][3]

Risk factors for stroke include atherosclerosis, advanced age, hypertension (high blood pressure), diabetes mellitus, high cholesterol, cigarette smoking, atrial fibrillation, ethnic identity, and some blood clotting disorders.

The term "brain attack" has been advocated for use in the United States for stroke, just as the term "heart attack" is used for myocardial infarction, where a cutoff of blood causes necrosis to the tissue of the heart. Many hospitals have multidisciplinary "stroke teams" specifically for swift treatment of stroke.

A transient ischemic attack (TIA) is a brief loss of neurologic function, and is disussed elsewhere.

Strokes can be classified as ischemic or hemorrhagic.

Etiology

Ischemic Stroke

Atherosclerosis is responsible for the majority of ischemic strokes. Atheroembolism can occur within the cerebral circulation or can originate outside the cerebral circulation. The etiology of atherosclerosis-related strokes is very similar to that of heart attacks. An atherosclerotic plaque in a cerebral artery can gradually develop an associated thrombus or rupture suddenly causing a rapid occlusion, or the thrombus can break off and lodge in a vessel even deeper in the brain. "Thrombotic stroke" usually refers to in-situ thrombus, "embolic stroke" to thrombosis from distant sites.

Thrombotic Stroke

Thrombotic and thromboembolic strokes can originate in either large or small blood vessels, and are usually due to abnormalities in the vessel (most commonly atherosclerosis). One of the most important etiologies is carotid artery disease. Lacunae are also a subset of thrombotic stroke.

Embolic Stroke

Embolism of thrombi from outside the cerebral circulation are responsible for a large and important subset of ischemic strokes. In these cases a thrombus (blood clot) travels from its origin and lodges in a cerebral artery. Most of these strokes are of cardiac origin (Cardioembolic).

  • Cardioembolic Stroke: the majority of embolic strokes originating in the heart are due to atrial fibrillation. In fact, about 16% of strokes are associated with atrial fibrillation, and the presence of atrial fibrillation increases stroke risk by about 5-11% per year, depending on other risk factors. [5]The relative stasis of blood in the left atrium leads to blood clot formation, and these clots can be expelled from the heart to enter the cerebral circulation.
  • Paradoxical embolism (Patent Foramen Ovale)

Systemic hypoperfusion (Watershed stroke)

Systemic hypoperfusion is the reduction of blood flow to all parts of the body. It is most commonly due to various types of shock. Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially "watershed" areas --- border zone regions supplied by the major cerebral arteries. Blood flow to these areas does not necessarily stop, but instead it may lessen to the point where brain damage can occur.

Hemorrhagic stroke

A hemorrhagic stroke, or cerebral hemorrhage, is a form of stroke that occurs when a blood vessel in the brain ruptures or bleeds. There are two types of hemorrhagic stroke: intracerebral hemorrhage, and subarachnoid hemorrhage.

Intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is bleeding directly into the brain tissue, forming a gradually enlarging hematoma (pool of blood). It generally occurs in small arteries or arterioles and is commonly due to hypertension, trauma, and vascular malformations. The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system. ICH has a mortality rate of 44 percent after 30 days, higher than ischemic stroke or even the very deadly subarachnoid hemorrhage.[6]

Subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is bleeding into the cerebrospinal fluid (CSF) surrounding the brain. The two most common causes of SAH are rupture of aneurysms and bleeding from vascular malformations. Bleeding into the CSF from a ruptured aneurysm occurs very quickly, causing rapidly increased intracranial pressure. The initial bleed can be brief, but rebleeding is common. Death or deep coma ensues if the bleeding continues. SAH has a 37-45% mortality for patients 45 and older.[7][8]

Signs and Symptoms

Diagnosis

Treatment

Risk Factors & Prevention

  • Atherosclerosis: many of the risk factors listed below are also risk factors for atherosclerosis.
  • Hypertension is the most powerful risk factor for ischemic stroke, and the primary risk factor for intracerebral hemorrhagic stroke. Keeping blood pressure below 120/80 reduces the risk of both primary and recurrent stroke.[9][10]
  • Smoking: cigarette smoking significantly increases stroke risk, and the risk is dependent on the amount of smoking. Risk decreases over significantly by about 2 years after quitting cigarettes.[11]
  • Transient Ischemic Attack: Occurrence of TIA is a strong risk factor for stroke. In one study, 5% of patients with TIA developed stroke within 2 days, 10% within 90 days.[12]
  • Atrial Fibrillation (AF) increases stroke risk by about five times. The average yearly risk for stroke in untreated AF is 5%.[13]
  • Diabetes mellitus
  • High Cholesterol: treatment of high cholesterol and other blood lipid disorders reduces the rate of first stroke and recurrent stroke. [14]
  • Age: the risk of stroke in adults increases significantly over the age of 55, and continues to increase thereafter.
  • Ethnicity: African Americans have twice the risk of a first stroke as whites.

References

  1. ↑ Centers for Disease Control and Prevention (CDC). Prevalence of disabilities and associated health conditions among adults: United States, 1999. MMWR Morb Mortal Wkly Rep. 2001; 50: 120–125
  2. ↑ Circulation. 2007;115:e69-e171.
  3. ↑ http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.106.179918
  4. ↑ Goldman: Cecil Textbook of Medicine, 22nd ed., Copyright © 2004 W. B. Saunders Company
  5. ↑ Robert G. Hart, MD Jonathan L. Halperin, MD. Atrial Fibrillation and Stroke Concepts and Controversies. Stroke. 2001;32:803.
  6. ↑ Caplan LR (1992). "Intracerebral hemorrhage". Lancet 339 (8794): 656-8. PMID 1347346.
  7. ↑ El-Saed A, Kuller LH, Newman AB, Lopez O, Costantino J, McTigue K, Cushman M, Kronmal R. Geographic variations in stroke incidence and mortality among older populations in four US communities. Stroke. 2006; 37: 1975–1979.
  8. ↑ Rosamond WD, Folsom AR, Chambless LE, Wang CH, McGovern PG, Howard G, Copper LS, Shahar E. Stroke incidence and survival among middle-aged adults: 9-year follow-up of the Atherosclerotic Risk in Communities (ARIC) Cohort. Stroke. 1999; 30: 736–743
  9. ↑ ALLHAT Officers and Coordinators for the ALLHAT Collaborative Research Group. The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial.Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic: The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT).JAMA. 288(23):2981-97, 2002 Dec 18.
  10. ↑ Seshadri S, Beiser A, Kelly-Hayes M, Kase CS, Au R, Kannel WB, Wolf PA. The lifetime risk of stroke: Estimates from the Framingham study. Stroke. 2006; 37: 345–350
  11. ↑ Wolf PA, D’Agostino RB, Kannel WB, Bonita R, Belanger AJ. Cigarette smoking as a risk factor for stroke: the Framingham study. JAMA. 1988; 259: 1025–1029
  12. ↑ Johnston SC, Gress DR, Browner WS, Sidney S. Short-term prognosis after emergency department diagnosis of TIA. JAMA. 2000; 284: 2901–2906
  13. ↑ Hylek E. M., Go A. S., Chang Y., Jensvold N. G., Henault L. E., Selby J. V., Singer D. E. N Engl J Med 2003; 349:1019-1026, Sep 11, 2003
  14. ↑ Stroke.Stroke, statins, and cholesterol. A meta-analysis of randomized, placebo-controlled, double-blind trials with HMG-CoA reductase inhibitors.Blauw GJ, Lagaay AM, Smelt AH, Westendorp RG.1997 May;28(5):946-50. PMID: 9158630

External Links

  1. http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.106.179918
  2. http://www.cdc.gov/stroke/
  3. http://www.strokeassociation.org/presenter.jhtml?identifier=1200037

Further Reading

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