An ischemic stroke occurs when the blood supply to a region of the brain is blocked resulting in tissue death. It is the cause of 80% of all strokes. The causes of the ischemia are variable but atherosclerosis (plaque build up in the arteries) is a major contributor. It is important to identify the causes of a stroke in order to appropriately manage the current incident and to prevent recurrence.
In an ischemic stroke blood flow to the brain is compromised. There are many potential causes but the most common subtypes include thrombotic, embolic and hypoperfusion. Thrombotic strokes can result when a thrombus or clot forms with an artery, blocking blood flow. An embolic stroke can occur when a small clot travels from a distant location and finally lodges in a small artery blocking blood flow. Finally hypoperfusion occurs when there is a traumatic event to the body that prevents blood from being pumped to the brain. If blood flow is not restored within minutes, neurologic injury will occur. Examples of hypoperfusion events include cardiac arrest, hypovolemic shock from large blood loss, cardiac arrhythmia and a large pulmonary embolus.
In a thrombotic or embolic stroke, an artery is blocked diminishing or completely obstructing blood supply to a region of the brain. The tissue becomes pale and after several hours to days the tissue becomes congested with dilated blood vessels and there are small areas of minute bleeding. If the blood flow is restored because of clot migration or lysis then the returned blood flow can leak into the brain tissue causing a larger hemorrhage and greater problems.
Thrombotic strokes can occur in large or small vessels. Arteriosclerosis, arterial dissection, arteritis and fibromuscular dysplasia are conditions that increases the likelihood of this occurring. Small vessels can also undergo vasoconstriction producing diminished blood supply. Individuals with conditions that make them more likely to clot are also at greater risk. Conditions such as Factor V Leiden, Protein S and Protein C deficiencies are examples. Other conditions such as Sickle Cell Anemia and Polycythemia vera also predisposes to clotting. Small vessel strokes can also occur in the setting of hypertension or with age. The tissue affected is in small areas of the brain and the symptoms can go un-noticed until there is a accumulation of damage. These are called lacunar infarcts.
Embolic stroke occurs because of a problem in other areas of the body. A small clot peels away from its source traveling to the brain to obstruct an artery there. The emboli can come from plaque formation in the aorta or carotid artery or they can come from emboli forming on the heart valves. In some cases the source is never found. Common conditions that can form emboli include myocardial infarction, a defect heart valve, a mechanical heart valve, an infected heart valve, atrial fibrillation, cardiomyopathy, and a carotid artery or aortic plaque.
Ischemic strokes are a major cause of death and disability, especially in the elderly. Early intervention is the key to survival and understanding the risk factors can aide in prevention. Seek care immediately if you or someone you know are experiencing the symptoms of a stroke.
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