Causes of Stroke
Strokes are classified as either ischemic or hemorrhagic, as described above, depending on the cause of the loss of blood to the brain. There are several factors that may cause each type, as well as existing physiological conditions that may put a person at significant risk for developing stroke.
A common type of ischemic stroke is thrombotic stroke, in which a blood clot (also called a thrombus), blocks an artery. These blood clots are typically attached to the inside of the blood vessel, often forming around the plaques associated with high blood cholesterol. If the blood contains too much "bad cholesterol" (low density lipoprotein, or LDL), it may undergo a chemical reaction with the oxygen in the blood called oxidation. This oxidized LDL can be damaging to the artery cell walls, so the immune system responds by sending in white blood cells to try to eliminate the damaging molecules. These recruited white blood cells include macrophages, which specifically function to "eat" whatever harmful things initiated the immune response. Macrophages are very good at ingesting and destroying pathogens, however they are unable to do anything to the oxidized LDL that they eat. Eventually the macrophages burst, releasing all the oxidized LDL they have eaten causing an even higher concentration of this damaging molecule at that spot in the artery. The body responds by once again calling for help from more macrophages, cycling the process once again, continuing to damage the artery. These phenomena lead to chronic inflammation of the arteries and the disease known as atherosclerosis.
Atherosclerosis differs from similar artery hardening or narrowing diseases (such as arteriosclerosis) in that distinctive accumulations called plaques (or atheromas) form in the artery walls. These are lesions in the arteries, mainly composed of macrophages that have taken up lots of oxidized LDL, as well as other white blood cells. These plaques gradually grow over time, also collecting fibrin (a blood clotting protein), collagen (a fibrous connective tissue protein), and elastin (another connective tissue protein). Plaque development can also begin to affect the structure of the surrounding blood vessels, inducing formation of calcium deposits which make them harder and less elastic. Plaques may also induced localized thickening and expansion of the blood vessel walls, causing a gradual constriction over the course of many years. Patients may not realize that they have developed atherosclerosis until one of these plaques ruptures potentially obstructs blood flow through the artery. The rupture of a plaque releases its contents into the artery, exposing all the cholesterol and tissue proteins. Collagen and other tissue proteins can activate blood clot formation, so their sudden release into the artery may cause a blood clot to form quickly around the plaque, blocking the artery, and causing a stroke.
An embolic stroke is a type of ischemic stroke that occurs when the blockage of the artery is caused by debris that is flowing through the bloodstream. If the debris reaches vasculature that it cannot pass through, it will become lodged in the artery and block blood flow past the blockage point. Embolic strokes are very frequently caused by blood clots, which may come from a variety of sources. Patients suffering from atrial fibrillations, for example, are at especially high risk for blood clots. Atrial fibrillations are abnormal heart rhythms in which the upper chambers of the heart beat irregularly causing poor blood flow to the rest of the body. Because the cycle of the heartbeat is not complete, the blood in the atria can begin to stagnate, increasing the possibility that a thrombus can form in the heart and potentially cause a stroke or heart attack. Any condition that significantly affects the proper function of the heart and healthy circulation of blood can increase the likelihood of clot formation and stroke.
Patients with endocarditis, an inflammation of a heart, may also be at risk for stroke. In addition to the complications caused by the inflammation, endocarditis is characterized by lesions that may be composed of platelets, fibrin, and inflammatory cells or perhaps bacteria. Should any of these lesions break lose into the bloodstream, there is a risk for arterial blockage. Embolic strokes may also be caused by clumps of fat released into the blood stream, as a possible complication of severe fractures. If bone marrow escapes into the blood stream, for example, it can create blockages and cause embolic stroke. Likewise, masses of cancer cells released into the blood stream.
If large quantities of air or gas enter the bloodstream, an embolic stroke can also occur. Gas may enter the bloodstream through injection or trauma to the lung tissues. Scuba divers are at risk for gas embolisms if they ascend too quickly. At higher levels of pressure, the blood can absorb more gases, including oxygen. If the diver ascends to lower levels of pressure more quickly than their blood gases can adapt to the changes, gas bubbles can form in the blood and potentially travel through the arteries, get caught, and impede blood flow to the brain.
Cerebral venous sinus thrombosis is a rare type of stroke that occurs when a blood clot obstructs one of the veins that is responsible for draining blood from the brain. The blood pressure behind the obstruction can then build such that the blood vessels are damaged, causing hemorrhaging. The extensive leakage of blood can cause pressure on the brain, resulting in some of the usual symptoms of stroke, including weakness on one side the face and inability to move the limbs. Patients may also experience intense headaches, unexplained changes in their mental state, and seizures. The pressure on the brain, in addition to the compromised blood flow, can cause the patient to decline very rapidly.
A watershed stroke does not result from a blockage of the arteries, but from hypotension, or abnormally low blood pressure, which can result in a lack of adequate blood flow to the brain. Medically speaking, the watershed area refers to the parts of the body that receive blood through a path of vessels furthest from the heart. Circulation in some parts of the brain occurs through these very small end-point arteries, so as blood pressure decreases, these watershed areas will be the last to get blood. Oxygen starvation of these watershed areas of the brain due to this reduced circulation can ultimately be very damaging.
Congestive heart failure, in which the heart is no longer pumping efficiently enough to support the body's needs, is a common cause of watershed stroke. Advanced atherosclerosis of the carotid arteries, the main sources of blood to the head and neck, may also decrease blood flow to the brain making watershed stroke a concern.
Intracerebral hemorrhage, or bleeding within the brain tissue, is a very common cause of stroke. The brain relies on its complex network of arteries to keep all parts of it oxygenated and functioning well. If the arteries are compromised, the bleeding can prevent adequate oxygen delivery to downstream destinations. These hemorrhages can happen spontaneously in patients with hypertension, as the vascular systems in their brains are unable to cope with the high blood pressure, or in patients with bleeding disorders such as hemophilia. Patients with cerebral amyloid angiopathy, a blood vessel disorder in which the blood vessels in the brain are spotted with protein deposits, are also at greater risk for stroke due to intracerebral hemorrhage. Cocaine and amphetamine users also have significantly higher incidences of brain hemorrhages due to the physiological effects of these drugs on the heart, nervous system, and respiratory system.
Conventional Treatment of Stroke
Because of the prevalence of stroke as a complication of heart disease, there is much emphasis on stroke prevention through healthier heart habits. If a patient has atherosclerosis, atrial fibrillations, high blood pressure, high cholesterol, diabetes, or other diseases that may be putting them at risk for developing a stroke, the focus is on treating the specific condition that is introducing the risk.
If a TIA occurs, the immediate treatment is medicine that will help prevent blood clots. Aspirin, warfarin, clopidogrel, and dipyridamole are commonly prescribed. Because the a TIA is normally a warning that a stroke is a strong probability, further measures will be taken to treat whatever conditions are contributing to the risk of stroke. If the carotid arteries which supply blood to the brain are blocked, for example, surgery may be recommended to reopen them. One technique useful for widening carotid arteries is angioplasty, in which the surgeon inserts a balloon into the artery and enlarges it to expand the blocked artery. A metal coil called a stent can then be inserted to help keep the blood vessel open after the balloon has been removed.
If a stroke occurs, patients are normally admitted to a "stroke unit" within the hospital where they can be quickly evaluated by doctors that have extensive experience with stroke patients. The physicians assess the cause as rapidly as possible and perform a CT scan, a medical imaging technique, to see the brain and determine whether there has been hemorrhaging or whether the stroke is ischemic or hemorrhagic.
If the stroke is ischemic, the focus is on dislodging the obstruction either by dissolving it or physically removing it. If the blood vessels are blocked by blood clots, then blood thinners are administered to help minimize additional blood clotting. Thrombolysis, or "clot busting," can also be done using a drug called tPA, though its use is somewhat controversial. If administered within the first few hours following stroke, tPA appears to improve the neurological outcome in stroke patients. Some patients given tPA develop brain hemorrhages after being given tPA, however, so the administration of tPA is not yet considered a standard for stroke treatment.
Physical removal of the blockage can also be performed through a mechanical thrombectomy procedure. A corkscrew-like device is inserted into the artery where it can physically grab on to the blood clot, allowing it to be pulled out of the vessel by the surgeon. This is a useful strategy for patients that cannot take thrombolytic or anticoagulant (blood thinning) drugs, however there are sometimes complications with bleeding.
Whereas anticoagulants and thrombolytic drugs are a mainstay in treating ischemic strokes, they are quite dangerous for patients with hemorrhagic strokes as they may cause more uncontrolled bleeding. As with ischemic strokes, the doctors will try to identify the source of the bleeding. If high blood pressure induced the hemorrhaging, blood pressure medication will be administered to help control the bleeding. Medications to control brain swelling and seizures may also be necessary. Depending on the case, brain surgery may be recommended to relieve pressure against the brain as the blood accumulates. If the hemorrhaging is the result of a broken blood vessel, it is also possible for surgeons to clip the artery closed to prevent continued blood loss.
Patients Medical's Stroke Prevention Therapies
Stroke is currently the third most common cause of death in the United States. Much can be done to prevent having a stroke by identifying the factors that put you at risk and making positive changes to your lifestyle to remove those risks. At Patients Medical, we can help you devise a healthy new life plan to revolutionize your health to increase your longevity and radically reduce your risk of having a stroke.
We will begin with a comprehensive interview to help you identify medical conditions or habits that may increase the probability of developing a stroke. High blood pressure and high cholesterol are two of the most common conditions that set the stage for a stroke to occur. We may perform blood tests, as well as a complete physical exam, so that we may begin to understand your state of vascular health. We will also analyze your dietary habit which may either contribute to existing medical conditions or put you at future risk for medical conditions that can enhance your chances of having a stroke. We can help you completely redesign your diet to promote greater overall health.
In outlining your new diet regimen, we will include foods that are rich in calcium, magnesium, and potassium to help reduce blood pressure and keep your electrolytes balanced to reduce the risk of stroke. People with diets rich in vegetables, fruits, and whole grains also have a lower incidence of stroke. Antioxidant rich foods, such as beans, spices, berries, and potatoes can also play a preventative role in the development of vascular disease. Antioxidants can help reduce the formation of oxidized LDL, the bad form of cholesterol that can cause plaque formation and lead to atherosclerosis. Omega-3 fatty acids, which are common in fish but also added as a supplement to a lot of foods these days, can also be incorporated into the diet, as it has been shown to reduce blood pressure, improve blood cholesterol levels, and reduce inflammation. Your nutritional program will be tailored to your current personal health conditions.
Stress can also contribute to the likelihood of having a stroke. By fostering a relaxed, positive lifestyle, we can not only reduce your likelihood of stroke, but enhance your overall feelings of health and well-being. Exercise can be a wonderful stress reliever and improve your cardiovascular health, so a physical fitness regimen may be part of your stroke prevention therapy. (Please also see our article on Stress Reduction to learn more about how Patients Medical can help you.)
Next Steps:
While you may find this medical information useful, as the next step we strongly recommend that you make an appointment to see one of our physicians to ensure that your health issues are properly addressed.
To schedule an appointment with our physicians, please call our patient coordinator at 1-347-269-4748, send the form below or an email to: info@patientsmedical.com. We are currently accepting new patients and look forward to being of assistance.
We are located at: Patients Medical PC, 800 Second Avenue, Suite 900 (Between 42nd & 43rd Street), Manhattan, New York, NY 10017.
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Date of Publication: 07/21/2009
Article Last Updated: 01/29/2010