Understanding and Preventing Subsequent Strokes

Compared to advancements expected over the next few years, our understanding and treatment of strokes or cerebrovascular accidents today is relatively primitive. But tomorrow's improvements in treatments and efforts to prevent strokes depend on the research we do today.

We know that there are two main types of strokes: ischemic and hemorrhagic. Ischemic strokes comprise 85% of all strokes and occur when a blood clot causes a blockage in a brain artery. The blood clot then may cut off blood and oxygen flow to brain tissue, causing an area of brain death, called an infarct. Hemorrhagic strokes occur when leakage of blood or bleeding causes the damage to brain tissue. The bleeding in hemorrhagic stroke is caused by such things as a ruptured artery, aneurysm, or abnormal blood vessel in the brain.

Determining the exact type of stroke and its cause is the key to developing effective treatment and prevention efforts. For example, determining that a stroke happened in a certain area of the brain is not enough. Perhaps the blood clot that caused a stroke resulted from a heart defect. If the heart defect is not detected and treated, another stroke may be inevitable. This type of stroke -- when a blood clot travels from one area of the body to the brain -- is called an embolism. It is one of five types of ischemic strokes. The others are: a small vessel thrombotic stroke, in which a deposit from hardening of the arteries (arteriosclerosis) blocks a small blood vessel in the brain; a large vessel thrombotic stroke, in which a main supply artery, such as the carotid, is blocked by hardening of the arteries; strokes of miscellaneous or unusual causes, such as from migraines, trauma, or abnormal blood-clotting tendencies; and strokes of unknown causes, which make up nearly one-third of all ischemic strokes.

A battery of tests should be performed to determine, as precisely as possible, the cause of the stroke. If a physical defect is discovered, this can then be addressed. A heart problem may be treated with medication, abnormal blood vessels in the brain may be treated with surgery, or carotid arteries may need to be scraped of the plaque which caused the blockage.

Another stroke prevention strategy being studied is the use of angioplasty -- inflating tiny balloons -- to open clogged blood vessels in the brain and inserting stents to keep them open. A different study is testing cholesterol-lowering drugs to find out if they also reduce the rate of stroke recurrence. In most cases of ischemic stroke, patients will be given blood-thinning medications to help prevent blood clots from forming. Anti-platelet drugs, including aspirin, Ticlid, Plavix and Aggrenox, help stop platelets from starting a blood clot. Anti-coagulant drugs, such as warfarin (Coumadin), inhibit the body's blood-clotting proteins.

Besides inhibiting clots, risk factors that cause the arterial disease in the first place must be addressed. Well recognized stroke risk factors are high blood pressure, smoking, diabetes, high cholesterol and a heart beat irregularity called atrial fibrillation. These factors can be controlled to an extent with proper diet, medications and lifestyle modifications. Recent research has identified high levels of homocysteine in the blood as another high-risk factor for both heart attacks and strokes. A deficiency in Vitamin B may lead to elevated levels of homocysteine, and vitamin therapy may be beneficial.

Another line of research focuses on genetics and inflammation. Inflammation of blood vessels may cause strokes or make them more damaging, and an individual may inherit genes that control the body's inflammatory response mechanisms. For example, beyond simply a plumbing problem of a clot stopping blood flow, a stroke may be worsened by the chemical events causing inflammation at the microscopic level. Genes that affect inflammation may contribute to the long-term consequences that eventually result in a stroke. If the right genes are identified, stroke-prone individuals could be treated years before symptoms appear. Furthermore, current treatments like aspirin and cholesterol drugs may work by helping not only blood thinning and plaque build-up, but also because they have anti-inflammatory properties, too. We are currently conducting research at the Medical College that is testing one of the cholesterol-lowering "statins" in stroke patients to prevent recurrent strokes.

At present, the best treatments are about 30% effective in preventing subsequent strokes, and risk factor modification adds to that benefit. But research underway today will certainly provide more advances in stroke treatment and prevention for tomorrow. In the meantime, we must carefully identify strokes as they occur and address risk factors with the treatments we currently know best.