Stroke And Cerebrovascular Disease
Cerebrovascular disease is a group of brain dysfunctions related to disease of the blood vessels supplying the brain. Hypertension is the most
important cause; it damages the blood vessel lining, endothelium, exposing the underlying collagen where platelets aggregate to initiate a
repairing process which is not always complete and perfect. Sustained hypertension permanently changes the architecture of the blood vessels
making them narrow, stiff, deformed, uneven and more vulnerable to fluctuations in blood pressure.
A fall in blood pressure during sleep can then lead to a marked reduction in blood flow in the narrowed blood vessels causing ischemic stroke
in the morning. Conversely, a sudden rise in blood pressure due to excitation during the daytime can cause tearing of the blood vessels resulting
in intracranial hemorrhage. Cerebrovascular disease primarily affects people who are elderly or have a history of diabetes, smoking, or ischemic
heart disease. The results of cerebrovascular disease can include a stroke, or occasionally a hemorrhagic stroke. Ischemia or other blood vessel
dysfunctions can affect the person during a cerebrovascular accident.
A stroke, or cerebrovascular accident (CVA), is the rapid loss of brain function due to disturbance in the blood supply to the brain. This can be
due to ischemia (lack of blood flow) caused by blockage (thrombosis, arterial embolism), or a hemorrhage. As a result, the affected area of the brain
cannot function, which might result in an inability to move one or more limbs on one side of the body, inability to understand or formulate speech,
or an inability to see one side of the visual field.
A stroke is a medical emergency and can cause permanent neurological damage and death. Risk factors for stroke include old age,high blood pressure,
previous stroke or transient ischemic attack (TIA), diabetes, high cholesterol, tobacco smoking and atrial fibrillation. High blood pressure is the
most important modifiable risk factor of stroke. It is the second leading cause of death worldwide.
An ischemic stroke is occasionally treated in a hospital with thrombolysis (also known as a “clot buster”), and some hemorrhagic strokes benefit from
neurosurgery. Treatment to recover any lost function is termed stroke rehabilitation, ideally in a stroke unit and involving health professions such
as speech and language therapy, physical therapy and occupational therapy. Prevention of recurrence may involve the administration of antiplatelet
drugs such as aspirin and dipyridamole, control and reduction of high blood pressure, and the use of statins. Selected patients may benefit from
carotid endarterectomy and the use of anticoagulants.
The most important modifiable risk factors for stroke are high blood pressure and atrial fibrillation (although magnitude of this effect is small: the evidence from the Medical Research Council trials is that 833 patients have to be treated for 1 year to prevent one stroke. Other modifiable risk factors include high blood cholesterol levels, diabetes, cigarette smoking active and passive), heavy alcohol consumption and drug use, lack of physical activity, obesity, processed red meat consumption[and unhealthy diet.Alcohol use could predispose to ischemic stroke, and intracerebral and subarachnoid hemorrhage via multiple mechanisms (for example via hypertension, atrial fibrillation, rebound thrombocytosis and platelet aggregation and clotting disturbances).The drugs most commonly associated with stroke are cocaine, amphetamines causing hemorrhagic stroke, but also over-the-counter cough and cold drugs containing sympathomimetics.
No high quality studies have shown the effectiveness of interventions aimed at weight reduction, promotion of regular exercise, reducing alcohol consumption or smoking cessation. Nonetheless, given the large body of circumstantial evidence, best medical management for stroke includes advice on diet, exercise, smoking and alcohol use. Medication or drug therapy is the most common method of stroke prevention; carotid endarterectomy can be a useful surgical method of preventing stroke.
Hypertension (high blood pressure) accounts for 35-50% of stroke risk. Blood pressure reduction of 10 mmHg systolic or 5 mmHg diastolic reduces the risk of stroke by ~40%. Lowering blood pressure has been conclusively shown to prevent both ischemic and hemorrhagic strokes. It is equally important in secondary prevention.Even patients older than 80 years and those with isolated systolic hypertension benefit from antihypertensive therapy.The available evidence does not show large differences in stroke prevention between antihypertensive drugs —therefore, other factors such as protection against other forms of cardiovascular disease should be considered and cost.
Those with atrial fibrillation have a 5% a year risk of stroke, and this risk is higher in those with valvular atrial fibrillation.Depending on the stroke risk, anticoagulation with medications such as warfarin or aspirin is warranted for stroke prevention.
High cholesterol levels have been inconsistently associated with (ischemic) stroke.Statins have been shown to reduce the risk of stroke by about 15%.Since earlier meta-analyses of other lipid-lowering drugs did not show a decreased risk,[statins might exert their effect through mechanisms other than their lipid-lowering effects.
Diabetes mellitus increases the risk of stroke by 2 to 3 times. While intensive control of blood sugar has been shown to reduce microvascular complications such as nephropathyand retinopathy it has not been shown to reduce macrovascular complications such as stroke.
Oral anticoagulants such as warfarin have been the mainstay of stroke prevention for over 50 years. However, several studies have shown that aspirin and antiplatelet drugs are highly effective in secondary prevention after a stroke or transient ischemic attack. Low doses of aspirin (for example 75–150 mg) are as effective as high doses but have fewer side effects; the lowest effective dose remains unknown.Thienopyridines (clopidogrel, ticlopidine) "might be slightly more effective" than aspirin and have a decreased risk ofgastrointestinal bleeding, but they are more expensive.Their exact role remains controversial. Ticlopidine has more skin rash, diarrhea, neutropenia and thrombotic thrombocytopenic purpura. Dipyridamole can be added to aspirin therapy to provide a small additional benefit, even though headache is a common side effect.Low-dose aspirin is also effective for stroke prevention after sustaining a myocardial infarction. Except for in atrial fibrillation, oral anticoagulants are not advised for stroke prevention —any benefit is offset by bleeding risk.
In primary prevention however, antiplatelet drugs did not reduce the risk of ischemic stroke while increasing the risk of major bleeding. Further studies are needed to investigate a possible protective effect of aspirin against ischemic stroke in women.
Carotid endarterectomy or carotid angioplasty can be used to remove atherosclerotic narrowing (stenosis) of the carotid artery. There is evidence supporting this procedure in selected cases. Endarterectomy for a significant stenosis has been shown to be useful in the secondary prevention after a previous stroke.
Carotid artery stenting has not been shown to be equally useful. Patients are selected for surgery based on age, gender, degree of stenosis, time since symptoms and patients' preferences. Surgery is most efficient when not delayed too long —the risk of recurrent stroke in a patient who has a 50% or greater stenosis is up to 20% after 5 years, but endarterectomy reduces this risk to around 5%. The number of procedures needed to cure one patient was 5 for early surgery (within two weeks after the initial stroke), but 125 if delayed longer than 12 weeks.
Screening for carotid artery narrowing has not been shown to be a useful screening test in the general population. Studies of surgical intervention for carotid artery stenosis without symptoms have shown only a small decrease in the risk of stroke.To be beneficial, the complication rate of the surgery should be kept below 4%.
Even then, for 100 surgeries, 5 patients will benefit by avoiding stroke, 3 will develop stroke despite surgery, 3 will develop stroke or die due to the surgery itself, and 89 will remain stroke-free but would also have done so without intervention.
Nutrition, specifically the Mediterranean-style diet, has the potential for decreasing the risk of having a stroke by more than half. It does not appear that lowering levels ofhomocysteine with folic acid affects the risk of stroke.
Secondary prevention of ischemic stroke
Anticoagulation can prevent recurrent stroke. Among patients with nonvalvular atrial fibrillation, anticoagulation can reduce stroke by 60% while antiplatelet agents can reduce stroke by 20%.However, a recent meta-analysis suggests harm from anti-coagulation started early after an embolic stroke. Stroke prevention treatment for atrial fibrillation is determined according to the CHADS/CHADS2 system. The CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non-rheumaticatrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. It is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy,The most widely used anticoagulant to prevent thromboembolic stroke in patients with nonvalvular atrial fibrillation is the oral agentWarfarin while dabigatran is a new alternative which does not require prothrombin time monitoring.
If studies show carotid stenosis, and the patient has residual function in the affected side, carotid endarterectomy (surgical removal of the stenosis) may decrease the risk of recurrence if performed rapidly after stroke.
Stroke is diagnosed through several techniques: a neurological examination (such as the NIHSS), CT scans (most often without contrast enhancements) or MRI scans, Doppler ultrasound, and arteriography. The diagnosis of stroke itself is clinical, with assistance from the imaging techniques. Imaging techniques also assist in determining the subtypes and cause of stroke.
Definitive therapy is aimed at removing the blockage by breaking the clot down (thrombolysis), or by removing it mechanically (thrombectomy). The more rapidly blood flow is restored to the brain, the fewer brain cells die.
Tight control of blood sugars in the first few hours does not improve outcomes and may cause harm. High blood pressure is also not typically lowered as this has not been found to be helpful.
Thrombolysis with recombinant tissue plasminogen activator (rtPA) in acute ischemic stroke, when given before three hours of symptom onset increases the risk of death in the short term but in the long term improves the rate of independence and late mortality; the increase in long term mortality is not significant. When broken down by time to treatment it increases the chance of being alive and living independently by 9% in those treated within three hours, however the benefit for those treated between three and six hours is not significant.
These benefits or lack of benefits occurred regardless of the age of the person treated. There is no realiable way to determine who will have an intracranial hemorrhage post treatment versus who will not.
It use is endorsed by the American Heart Association and the American Academy of Neurology as the recommended treatment for acute stroke within three hours of onset of symptoms as long as there are no other contraindications (such as abnormal lab values, high blood pressure, or recent surgery). This position for tPA is based upon the findings of two studies by one group of investigators which showed that tPA improves the chances for a good neurological outcome. When administered within the first three hours thrombolysis improves functional outcome without affecting mortality.
6.4% of people with large strokes developed substantial brain hemorrhage as a complication from being given tPA thus part of the reason for increased short term mortality. Additionally, it is the position of the American Academy of Emergency Medicine that objective evidence regarding the efficacy, safety, and applicability of tPA for acute ischemic stroke is insufficient to warrant its classification as standard of care. Intra-arterial fibrinolysis, where a catheter is passed up an artery into the brain and the medication is injected at the site of thrombosis, has been found to improve outcomes in people with acute ischemic stroke.
Removal of the clot may be attempted in those where it occurs within a large blood vessel and may be an option for those who either are not eligible for or do not improve with intravenous thrombolytics.Significant complications occur in about 7%. A randomized control trial of these procedures has not been done as of 2011.
Large territory strokes can cause significant edema of the brain with secondary brain injury in surrounding tissue. This phenomenon is mainly encountered in strokes of the middle cerebral artery territory, and is also called “malignant cerebral infaction” because it carries a dismal prognosis. Relief of the pressure may be attempted with medication, but some require hemicraniectomy, the temporary surgical removal of the skull on one side of the head. This decreases the risk of death, although some more people survive with disability who would otherwise have died.
People with intracerebral hemorrhage require neurosurgical evaluation to detect and treat the cause of the bleeding, although many may not need surgery. Anticoagulants and antithrombotics, key in treating ischemic stroke, can make bleeding worse. People are monitored for changes in the level of consciousness, and their blood pressure, blood sugar, and oxygenation are kept at optimum levels.[citation n
Ideally, people who have had a stroke are admitted to a “stroke unit”, a ward or dedicated area in hospital staffed by nurses and therapists with experience in stroke treatment. It has been shown that people admitted to a stroke unit have a higher chance of surviving than those admitted elsewhere in hospital, even if they are being cared for by doctors without experience in stroke.
When an acute stroke is suspected by history and physical examination, the goal of early assessment is to determine the cause. Treatment varies according to the underlying cause of the stroke, thromboembolic (ischemic) or hemorrhagic.