About 87 percent of all strokes are ischemic. These strokes most often occur when an artery bringing blood to the brain becomes blocked, stopping blood flow. Less frequently, a severe drop in blood pressure causes an ischemic stroke.
Brain cells (neurons) rely on a constant stream of blood supplying oxygen and nutrients to operate normally. When blood flow is interrupted for more than a few seconds, the neurons begin to malfunction. If blood flow is not restored quickly, the neurons begin to die. This is why immediate medical evaluation and treatment is absolutely essential for people who are experiencing symptoms of a stroke.
There are two types of ischemic strokes:
Sometimes a clot that develops elsewhere in the body—typically the heart, aorta, or carotid arteries in the neck—breaks off and travels in the bloodstream to the brain. This type of clot is called an embolus. When an embolus lodges in a brain artery, stopping blood flow, it produces an embolism that causes an embolic stroke. In addition to a blood clot, an embolus can be an air bubble or piece of debris.
When a clot (thrombus) develops in a narrowed part of an artery—typically from fatty buildup in the arteries (atherosclerosis) of the brain or neck—the result is a thrombotic stroke. This type of stroke comprises about 50 percent of all strokes. A thrombotic stroke is further differentiated as a large-vessel or small-vessel thrombosis, depending on the size of the artery in which the thrombus occurs. A small-vessel thrombotic stroke deep within the brain is also called a lacunar stroke.
Ischemic strokes are categorized according to the severity and duration of symptoms:
- Transient ischemic attack (TIA). A TIA is a sudden, transient episode of neurological dysfunction caused by lack of blood flow to part of the brain. A TIA is sometimes called a mini stroke, but it is actually a transient stroke, because it passes without causing permanent damage to the brain. TIAs typically last no more than 20 minutes or so. Since it is difficult to tell the difference between a stroke and a TIA until the TIA resolves, it’s wisest to treat a TIA as a medical emergency by calling 911.
- Progressing or evolving stroke. This is a stroke in the process of occurring. The sooner you get to an emergency department for stabilization and treatment, the better your outcome will be.
- Completed stroke. This is a cerebral infarction, and it means the stroke was severe enough and lasted long enough to kill a portion of brain tissue. Irreversible deficit, disability or death is likely.
Treatments for Ischemic Stroke
Emergency treatment for ischemic stroke is a powerful clot-busting medication called tPA. It must be given within 4½ hours after symptoms begin, keeping in mind that the earlier it is administered within that time period, the better the chances of a favorable outcome.
For patients diagnosed with ischemic stroke after the treatment window has passed, no medication to restore blood flow has been proven effective. However, some patients may benefit from mechanical clot removal up to six hours after stroke onset with a technique called thrombectomy.
Four different devices can be used to remove a clot:
The MERCI Retriever is inserted in an artery, where it can be maneuvered directly to a clot that is blocking blood flow, capture it and remove it. (MERCI stands for Mechanical Embolus Removal in Cerebral Ischemia.) The device is a nitinol wire that spontaneously assumes a corkscrew shape as it moves toward the clot. The first few loops of the spiral are deployed beyond the clot, and the last loops are deployed within the clot to ensnare it.
Two clot-removing devices use retrievable stents to extract blood clots: the Solitaire Flow Restoration Device and the Trevo Retriever. A stent is a small mesh tube that can be used to open a narrowed artery. The Solitaire and Trevo devices consist of a stent on the end of a thin catheter, which is threaded through an artery to the location of the blood clot. The clot is trapped in the stent, which is then removed. This restores blood flow through the artery.
Studies comparing use of the retrievable stents with use of the Merci Retriever have favored the retrievable stents.
A mechanical device called the Penumbra System removes blood clots by aspiration. The technique involves delivering a catheter into the clot and using continuous suction to remove the clot.
The extent of your disability (if any) will be determined after the stroke has ended and your condition has been stabilized. The length of time you will need to recover from a stroke will depend on its severity. Fortunately, about 50 to 70 percent of stroke survivors are able to regain functional independence. Others are permanently disabled to various degrees.
Ischemic stroke can be fatal. About nine percent of patients aged 65 to 74, 13 percent of patients aged 74 to 84, and 23 percent of patients age 84 and older die within 30 days.