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Risk Factors We Can Prevent or Change
It is difficult to say which risk factor increases stroke risk more because many of them are interconnected. For example, overeating and a sedentary lifestyle can lead to harmful medical conditions such as hypertension, high levels of bad cholesterol and obesity – all of which are linked to stroke.
Many of the risk factors for stroke are also major risk factors for heart attack. There is a direct correlation between cardiovascular disease and cerebrovascular disease.
Diet and Nutrition: A high level of “bad” cholesterol in the bloodstream is a major risk factor for stroke. The primary way that cholesterol enters our bodies is through fats in the food we consume, which is why a sensible, balanced diet is so important. Studies also link high levels of sodium (salt) in the diet, which increases blood pressure, to an increased risk of stroke.
Physical Activity: Regular physical activity helps control many of the risk factors associated with stroke. By improving blood circulation, exercise enhances the body’s ability to use oxygen, which in turn helps to reduce blood pressure. Regular physical activity has been shown to increase “good” cholesterol levels, decrease triglyceride (fat) levels, and help manage body weight.
Smoking: Smoking is a risk factor for all types of stroke. A study published in the May 2003 issue of Stroke, a journal of the American Heart Association, shows that the risk of stroke increases incrementally depending on how many cigarettes a day you smoke. Nicotine, the addictive element in cigarettes, raises blood pressure and increases the risk of developing hypertension. Cigarette smoke contains more than 4,000 chemicals, including 43 known to cause cancer. It thickens the blood, making it more likely to clot. Even environmental tobacco smoke (ETS), or second hand smoke, has been linked to increased risk of stroke because it contains the same harmful chemicals that smokers inhale. ETS includes mainstream smoke (smoke that is drawn through the mouthpiece of a cigarette and exhaled into the air by the smoker) and sidestream smoke (comes from the burning tobacco in cigarettes).
Substance Abuse: The use of certain illegal or controlled substances has been shown to increase the risk of stroke, particularly hemorrhagic stroke. Cocaine (“crack” in its smoked form) causes a severe elevation of blood pressure that can rupture a blood vessel leading to or inside of the brain. Smoked amphetamines — such as crystal meth and ice — as well as any illicit drug injected into the bloodstream can also produce stroke.
Among adolescents and young adults, an increasing percentage of strokes occur in relation to drug use.
Alcohol Consumption: Heavy and regular use of alcohol can dramatically increase blood pressure. Studies suggest that heavy alcohol use, defined as two drinks or more a day, may increase the risk of suffering a subarachnoid hemorrhage (SAH) more than tenfold.
Medical Conditions & General Health
Obesity: Obesity increases the chances of developing hypertension, high blood cholesterol, and diabetes, all of which are significant factors in stroke. Some research suggests that even modest weight gain (20-40 pounds) over ideal body weight doubles the chances of suffering a stroke.
Cholesterol Levels: Although it gets a lot of bad press, the waxy, fatty substance called cholesterol is necessary for healthy cell membranes, among other things. We manufacture cholesterol naturally in our liver and we consume it through our diet.
There are different types of cholesterol. HDL (high-density lipoprotein) is considered “good” cholesterol while LDL (low-density lipoprotein) is considered "bad". Good cholesterol (HDL) carries bad cholesterol (LDL) away from the arteries. Bad cholesterol (LDL) can combine with other substances in the blood to form plaque, which can stick to the artery walls and potentially lead to clot formation and ischemic stroke.
Some people are genetically predisposed to bad-cholesterol build up. Their liver produces too much LDL. But in most cases, bad behaviors, such as smoking and lack of physical activity causes increased LDL. Diets high in saturated, polyunsaturated and/or hydrogenated fats (trans fatty acids) and/or low in monosaturated fats, appear to elevate bad cholesterol without affecting good cholesterol. Lifestyle modification can help maintain cholesterol levels within the normal range (less than 200 mg/dL). When that is not enough, physicians also can prescribe appropriate medications to control cholesterol levels.
Cholesterol Medications: The most prominent cholesterol drugs are in the statin family. They work by interfering with the cholesterol-producing mechanisms of the liver and by increasing the capacity of the liver to remove cholesterol from circulating blood (by producing more HDL). They include lovastatin (Mevacor®), fluvastatin (Lescol®), pravastatin (Pravachol®), simvastatin (Zocor®), atorvastatin (Lipitor®) and rosuvastatin (Crestor®).
Other Drug Treatments Include:
Nicotinic acid (niacin), which lowers LDL levels and raises HDL , must be given in large doses and can potentially be toxic. Questran (cholestyramine) and Colestid (colestipol) increases HDL levels and therefore the liver’s uptake of cholesterol from the bloodstream. Fibric acid derivatives, such as Lopid (gemfibrozil) and Tricor (fenofibrate), which can also increase HDL levels. Aspirin can thin the blood and reduce the possibility of clot formation.
Diabetes: People with diabetes are 2 to 4 times more likely to suffer strokes. Diabetes impedes the body’s ability to produce or properly use insulin, a hormone that allows our cells to absorb glucose (blood sugar). Glucose, the body’s main source of fuel, is created naturally during the digestive process. The pancreas is supposed to produce the right amount of insulin automatically to allow our bodies to use the glucose. In diabetics, the pancreas produces little or no insulin, so glucose builds up to high levels in the blood.
The disease falls into two main categories: type 1, which usually occurs during childhood or adolescence; and type 2, the most common form that generally occurs after age 45. There is also gestational diabetes, which can occur during pregnancy.
Diabetes can seriously harm blood vessels throughout the body, including those in the brain. High blood glucose levels can harden the arteries (atherosclerosis), thicken capillary walls, and make blood stickier — all significant risk factors for ischemic stroke. It can also cause small vessels to leak, reducing blood flow to the body tissue.
If blood sugar levels are high at the time of a stroke, brain damage can be more severe and extensive. This occurs because the body breaks down glucose differently when the brain is deprived of oxygen. The products of this breakdown are in and around the area of dead tissue (infarction) and are, themselves, toxic to the brain tissue. If blood circulation is restored to the area, these products will break down even further and result in an increase in the size of the infarction.
Treating diabetes can delay or prevent the onset of complications that increase the risk of stroke. Healthy eating, physical activity, and insulin via injection or an insulin pump are the basic therapies for type 1 diabetes.
Healthy eating, physical activity, and blood glucose testing are the basic management tools for type 2 diabetes. In addition, many people with type 2 diabetes require oral medication, insulin injection, or both to control their blood glucose levels.
Hardening of the Arteries (Atherosclerosis/Arteriosclerosis): Atherosclerosis and arteriosclerosis involve the buildup of deposits on the insides of the artery walls, which causes thickening and hardening (sclerosis) of the arteries. In atherosclerosis, the deposits consist of fatty substances. In arteriosclerosis, the deposits are composed largely of calcium.
The narrowing of the artery caused by the buildup of hardened plaque is called “stenosis.” The narrowing is measured as a percentage of the artery diameter that is blocked. For example, 70 percent stenosis means the artery is 70 percent blocked.
Atherosclerosis typically occurs in the carotid artery leading to the brain, resulting in a condition called carotid stenosis. This is a leading cause of ischemic stroke. Early warning signs of carotid stenosis include carotid bruits, which can be detected by a primary care physician during a physical exam. Carotid bruits are the noise made by the blood flowing past the blockage. The disturbed flow creates turbulence that can be heard by the physician listening to the artery with a stethoscope.
These narrowed vessels can be treated by “best medical management” or through surgical/endovascular procedure. Medical management would involve lifestyle modifications (diet, exercise, smoking cessation, etc) and medications including cholesterol medication and an antithrombotic agent. Procedures such as carotid endarterectomy or carotid stenting can also be done in appropriate patients to reduce the risk of stroke.
Heart Disease (Cardiovascular Disease): One in five Americans has some form of treatable cardiovascular disease, such as heart valve disorders, heart muscle disease (cardiomyopathy), coronary artery disease, and hearth rhythm disorders(arrhythmias) in which the heart does not beat normally. People with coronary heart disease or heart failure have a higher risk of stroke than those with hearts that work normally. Certain types of congenital heart defects also raise the risk of stroke.
Atrial fibrillation, an arrhythmia that some patients describe as a “fluttering” in their chest, is a common risk factor for ischemic stroke and is most common in the elderly. The heart's upper chambers quiver instead of beat, which allows blood to pool and lead to clot formation. The clot can then break away, enter the bloodstream, lodge in an artery leading to or inside the brain, and result in an ischemic stroke.
Treating Atrial Fibrillation
Medications are used to slow down the rapid heart rate seen in atrial fibrillation. These may include drugs such as amiodarone, beta blockers, calcium antagonists, digoxin, disopyramide, flecainide, procainamide, propafenone, quinidine and sotalol.
Electrical cardioversion may be used to restore normal heart rhythm with an electric shock. Radiofrequency ablation may also be used to restore normal heart rhythm. This involves inserting a thin, flexible catheter into an artery and threading it to the heart muscle where a burst of radiofrequency energy is delivered through it to destroy tissue that triggers abnormal electrical signals or to block abnormal electrical pathways. Surgery (rarely used) also can be used to disrupt electrical pathways that generate atrial fibrillation. An atrial pacemaker can be implanted under the skin of the chest to regulate the heart rhythm.
High Blood Pressure (Hypertension): High blood pressure (generally considered over 120/80 mm Hg) is the most common and most serious of all the modifiable risk factors for stroke. People with uncontrolled high blood pressure are seven times more likely to have a stroke than those with controlled blood pressure.
When the heart beats and pumps blood into the arteries, it creates pressure in them and causes them to stretch. The degree of stretch depends on the health of the vessels (the more muscular and elastic, the more they can stretch) and how much pressure the blood exerts.
High blood pressure puts excess stress on the heart (which has to pump harder) and damages blood vessels. If there is a weak spot in a blood vessel wall in the brain, high blood pressure could eventually cause it to rupture.
High blood pressure can be cause by other conditions including kidney disease, pregnancy, hormonal disorders, or certain medications. The most common causes of hypertension appear to be family history, diet (high salt intake or obesity), or habits such as smoking and excessive alcohol intake.
Hypertension is often called the “silent killer”. It is not uncommon to have high blood pressure and not know it because symptoms are not always present. Thus it is very important for health care professionals to routinely check blood pressure. This condition can be managed through lifestyle changes (diet and exercise) and medications, of which there are many different types.
Transient Ischemic Attack (TIA): TIAs are "warning strokes" that produce stroke-like symptoms but no lasting damage. Recognizing and treating TIAs can reduce the risk of a major stroke.
Abnormal Blood Vessel Connections: Abnormalities within cerebral arteries and veins include arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs). AVMs and AVFs are abnormal connections between cerebral arteries (which carry blood to the brain) and veins (which take blood away from the brain).
AVMs are masses of arteries and veins without intervening capillaries. Arteries decrease in size the farther they are from the heart. Ultimately they become so small that they are called capillaries. Capillaries are large enough to allow only one or two red blood cells to flow through them at a time. The decrease in the size of arteries from the heart to the capillaries is accompanied by a large decrease in the pressure within them at these locations. Veins form where capillaries join together and they transport blood back to the heart under low pressure.
In AVMs, because there are no capillaries, high-pressure arterial blood empties directly into veins, which have thin walls capable of containing only low pressure. The stress of the pressure can cause a vein to rupture, resulting in hemorrhage. The other clinically significant consequence of arterial blood flowing directly into veins without intervening capillaries is that the tissues through which the blood flows cannot adequately extract oxygen and nutrients necessary for their functioning and survival. This can result in seizure or stroke.
Although AVFs can be congenital, more often they are caused by a trauma that damages an artery and vein that are adjacent in the brain. These blood vessel abnormalities can cause a host of neurological problems including seizures and bleeding (hemorrhage) into surrounding tissues.Two to four percent of all strokes are related to hemorrhage from cerebral arteriovenous abnormalities.
There are three general forms of treatment for AVMs/AVFs:
- Surgery: This is the longest-standing treatment for AVMs. It involves entering the skull and tying off or clipping the arterial vessels that feed the malformation, eliminating the draining veins, and removing or obliterating the nest (nidus) of the AVM.
- Endovascular Embolization: This involves closing off the vessels of the AVM or AVF by injecting an agent-- such as a special glue, tiny coil, or balloon-- into them to block blood flow through the abnormal connection. Embolization is often used before surgery to minimize blood loss, making the operation safer and shorter. It can also be performed before radiosurgery to make the AVM smaller and increase the chance that radiosurgery will be successful. In some cases, endovascular embolization alone can permanently cure an AVM.
- Radiosurgery: Despite its name, radiosurgery does not require any surgical instruments to be placed within the head. This procedure tightly focuses beams of radiation from outside the skull onto the abnormal vessels in order to injure and clog the AVM. The vessels gradually close off and are replaced with scar tissue. The results of radiosurgery can take from weeks to years to become fully effective. A danger of radiosurgery is damage to normal brain or spinal cord tissue around the AVM. Therefore, the procedure is usually reserved for AVMs that are relatively small (less than 3 cm in diameter), are situated so deep beneath important brain tissue that the surgical approach is hazardous, or involve so many vessels that embolization is not feasible.
Cerebral Aneurysm (Unruptured): A brain aneurysm is a weak bulging spot on the wall of a brain artery very much like a thin balloon or weak spot on an inner tube. Aneurysms form from wear and tear on the arteries, and sometimes from injury, infection or an inherited tendency. The primary problem a cerebral aneurysm poses is rupture and hemorrhagic stroke. Patients often experience no symptoms before a rupture occurs. In these cases, the aneurysm may be discovered incidentally, perhaps during an angiogram for carotid artery disease.
But sometimes, as an aneurysm grows, it compresses surrounding nerves and brain tissue, causing functional problems. In about 40 percent of cases, people with unruptured aneurysms experience some or all of the following symptoms:
- Peripheral vision deficits
- Thinking or processing problems
- Speech complications
- Perceptual problems
- Sudden changes in behavior
- Loss of balance and coordination
- Decreased concentration
- Short-term memory difficulty
Regardless of their size or whether they are producing symptoms, all aneurysms need prompt evaluation by a vascular neurologist. Appropriate treatment depends on the size and location of the aneurysm and the patient’s medical history. The risk of rupture increases with the size of the aneurysm and time. Evidence suggests that the risk of rupture for most unrepaired small aneurysms (less than 7 millimeters in size) is small. However, within the smaller sizes, some characteristics such as the shape of the aneurysm, location of the aneurysm and previous personal or family history of rupture can make the aneurysm a higher risk.
The most common treatment for both unruptured and ruptured aneurysms is coil embolization. A neurointerventional surgeon advances a small catheter through endovascular approach inside the aneurysm. The entry of a catheter in the blood vessel is either through the main blood vessel of the leg or the arm. This minimally invasive method allows the surgeon to approach the aneurysm from inside the blood vessels. Coils or glue-like material (Onyx) are then deposited within the aneurysm to seal the aneurysm. If the coils are used, they are usually made of complex metallic coats largely consisting of platinum that is inert and MRI friendly.
A more traditional way for treating aneurysm is an open surgical approach where the surgeon opens the cranium by drilling through the bone and blocks the blood flow into the aneurysm by applying a metal clip to its base (neck) where it connects to the blood vessel. This redirects the blood flow along its proper route.