Transient Ischemic Attack (TIA), Stroke

Definition and Causes:

Refers to transient stroke symptoms that occur due to temporary blockage of blood flow to the brain. This is most often due to a blood clot. Symptoms of a stroke develop abruptly and persist for a brief period of time, while the blood vessel is blocked and disappears when the clot dissolves and blood flow resumes.

Causes:

Temporary obstruction of blood flow due to a blood clot within an artery supplying the brain, is the most common cause of Transient ischemic attack. Arteries can become hard with aging and sometimes have plaque buildup (or atherosclerosis) within the vessel walls (think of it as rust within a pipe). Plaques within the arteries can cause the formation of blood clots. During a TIA blood clots may either form directly within the arteries inside the brain, or sometimes blood clots form along the arteries in the neck (two carotids arteries at the front and 2 vertebral arteries, which then dislodges (breaks off) and travel into the brain to block an artery causing a TIA. In other circumstances, clots may form within the heart itself (often associated with an irregular heartbeat called atrial fibrillation), and then travel throughout the heart within the arteries to the brain. When it blocks a blood vessel in the brain, symptoms of stroke would appear and as the clot dissolves, it relieves obstruction and symptoms resolve.

Symptoms:

Symptoms begin abruptly, last from a few minutes to a few hours, and disappear completely within 24 hours.

Symptoms depend upon the area of the brain which is deprived of the blood supply and may include

• Sudden weakness or numbness in any part of the body
• Loss of balance/ difficulty in walking
• Loss of sensation like touch, pain, temperature, hearing, or taste
• Difficulty swallowing
• Problems with writing and reading
• Vision problems i.e. complete loss of vision
• Speech problems (slurring or loss of speech)
• Vertigo or dizziness in combination with other symptoms that are mentioned above

For the diagnosis of TIA, the symptoms should be temporary and for a brief period of time and should resolve completely within 24 hours. TIA is a warning sign for the occurrence of stroke, and patients who have TIA are at increased risk of stroke.

Investigations and Treatment:

TIA needs to be properly and rapidly investigated in order to determine the cause, and treatment should be initiated urgently to decrease the risk of stroke.

A detailed history of the event is obtained together with a neurological exam

Labs

TIA is the warning sign for a stroke. Laboratory investigations and imaging should be performed within 24-72 hours (in most cases).

Investigations include:

• Blood work

• Electrocardiogram (ECG)

• Computed tomography (CT) scan of the brain: Used to visualize the brain and exclude bleeding or other conditions (e.g. tumors). This device uses x-rays. Patients will lie on a table with the head placed inside of the scanner (resembles a large donut). Computer analysis of X-ray images produces detailed images of the brain. The scanning time is usually very rapid (less than 1 minute). The scan is done to exclude hemorrhages and other conditions (e.g. tumor) that might be causing the patient’s symptoms. Note: Most CT scans of the brain, completed in the first 2-4 hours following an ischemic stroke, would appear normal

• Magnetic resonance imaging (MRI): MRI uses magnetic waves to produce images. The device looks like a long cylindrical tube. The patient lies on a table that slides into a hollow tube. Computer analysis generates images of the internal structures of the body, including the brain. MRI shows the normal structures, as well as any area that is affected by the lack of blood supply. The procedure takes 30-60 min. In some circumstances, a dye may be injected into the veins (enhanced MRI) just before the scan to help improve the detection of abnormalities. Patients who complain of claustrophobia or discomfort may be given a mild sedative to help relax prior to MRI scanning

• CT-angiogram (CTA) and MR-angiogram (MRA): Imaging techniques in which a dye is injected into the vein and a CT scan or MRI is performed while the dye is flowing in the blood vessels. Detailed images of the blood vessels are produced by computer analysis. In TIA patients, CTA or MRA is used to assess blood vessels in the neck and brain. CTA and MRA can show narrowing, blockages, dissections (a tear) within the vessels and aneurysms (pouches) on blood vessels

• Carotid and vertebral artery Doppler: Ultrasound imaging of the neck, helpful in assessing blood flow and plaque build-up in neck vessels

• Holter monitor: A small portable device that can be fixed on the chest and records the electrical activity of the heart. Used to monitor heart rate for 24-72 hours

• Cardiac ECHO: Imaging technique that uses sound waves to create an image of the heart; helpful in assessing the function of all chambers individually

• Transcranial Doppler: Ultrasound imaging on the skull that can be used to monitor blood flow within the blood vessels of the brain

TREATMENT:

The risk of stroke increases after TIA (~5-8% in the first 1-4 weeks and up to 12-15% at 90 days). This risk can be decreased with urgent investigations and early treatment.

Medicines used in TIA for prevention of stroke:

Antiplatelets:

• Antiplatelet agents are medicines used to prevent stroke recurrence by decreasing the formation of blood clots within the blood vessels. Examples include aspirin, Plavix (clopidogrel), Aggrenox, Ticlid (ticlopidine). Patients who have had TIA are often prescribed antiplatelet drugs (usually aspirin)

Anticoagulants:

• These drugs can prevent the formation of blood clots. While they are often referred to as “blood thinners”, they do not really “thin” the blood, but they do interfere with the body’s ability to form clots. Anticoagulants are used in situations where there might be a tendency to form blood clots. One such example is the heart condition called atrial fibrillation (AF). This condition becomes more prevalent with aging and associated with high blood pressure, previous heart attack, overactive thyroid, excessive alcohol consumption. In AF the top chambers of the heart (the atria) do not beat in a regular fashion, but instead quivers or “fibrillates”. This causes the blood within the atria to pool and clot. These clots then drop into the lower chambers (the ventricles) and are pumped out of the heart. The circulating clots are called emboli. If they get pumped into the brain, they may block a blood vessel and cause a TIA or stroke

• Consequently, if AF is identified in patients with TIA, they may be prescribed an anticoagulant to prevent the formation of these clots. The oral agent warfarin is an old drug that has been used for many years to help prevent strokes due to AF. However, it is somewhat difficult to get the blood levels (called INR) correct and so requires frequent blood work for monitoring. A number of different foods and medications also affect blood INR levels. The routine use of warfarin in patients with AF is gradually being replaced by the new anticoagulants including Pradaxa (dabigatran), Xarelto (rivaroxaban), Eliquis (apixaban) and Savaysa (edoxaban), which are just as good or better than warfarin and do not require any blood monitoring

Antihypertensives:

• Blood pressure reduction in hypertensive patients (those with high blood pressure) significantly reduces stroke risk. Patients with TIA are usually prescribed blood pressure lowering drugs if they have high blood pressure

Cholesterol-lowering drugs (Statins):

• High cholesterol has been linked to heart disease and stroke. Consequently, TIA patients with high cholesterol may be prescribed statin agents to lower their cholesterol levels

Some drugs that are used commonly in the treatment of TIA include:

Treatment of carotid artery stenosis (narrowing):

Carotid artery stenosis (or narrowing) is often due to plaque build-up from atherosclerosis (hardening) within the vessel. Blood clots can subsequently form on top of the plaque and can dislodge and go into the blood vessels within the brain, leading to stroke. Carotid Doppler studies as well as CTA and MRA (see above) can be used to assess the degree of narrowing. If the carotid artery is narrowed along the same side as the TIA, i.e. right or left brain, then opening the vessel either surgically (called carotid endarterectomy) or through balloon angioplasty might be an option. Procedures might be considered for patients with stroke symptoms who have moderate 50-69% or severe greater than 70% narrowing of the carotids. Patients are usually referred to a neurologist to discuss this and assist with deciding on whether the patient may be a good candidate to have the vessel opened and if so, which procedure would be the best option. For patients with TIA due to vessel narrowing, if opening the vessel is advised (based on location and size of TIA, and other medical factors), the procedure is often performed as soon as possible after the event and usually less than 4 weeks.

Sometimes the vertebral arteries in the posterior neck are narrowed and may be a cause of TIA at the back of the brain or deep brain areas (the brain stem). Surgery is not used in these areas but, angioplasty and stenting is sometimes an option.

Treatment of asymptomatic carotid artery stenosis:

If the narrowing of the carotid artery by greater than 60%, is detected on a carotid Doppler study and the patient does not have TIA/stroke symptoms, then the vessel is considered asymptomatic (no symptoms) and the annual risk of stroke is low ~2%. Surgically treating these asymptomatic carotid vessels, i.e to remove the plaque, lowers the annual stroke risk from 2% to 1%. Hence, given the very small 1% benefit of surgery, many patients are treated with medical management only. However, in selected cases, surgery might still be an option. This can be discussed with doctors (neurologists, neuro- or vascular surgeons) with expertise in TIA/stroke management.

Lifestyle modification/ changes:

Smoking cessation:

• The physician should discuss smoking cessation and propose options for discontinuation e.g. nicotine patch, Champix (varenicline)

Limit alcohol consumption:

• Excessive alcohol consumption may lead to atrial fibrillation (see above) which is a cause of stroke, as well as weakening the heart muscles (called cardiomyopathy), which can also potentially cause clot formation within the heart that can travel out of the heart to the brain and lead to TIA or stroke

Regular physical activity:

• Inactivity has been associated with stroke. Regular exercise leads to healthy heart and maintenance of good blood flow within the arteries

Weight control:

• Obesity has been linked to heart disease and stroke. Consequently, weight loss and maintenance of the ideal body weight is encouraged in patients who have incurred a TIA to help decreases the risk of stroke. A dietician should be consulted and a proper diet plan should be followed if necessary

Low salt/ Low fat diet:

• Low salt diet helps in reducing blood pressure towards normal values, while low-fat consumption may impact of overall lowering of cholesterol in the bloodstream

Risk Factors and Prevention:

Non-modifiable risk factors for TIA:

• Advancing age
• Family history of vascular disease (heart attack, stroke)
• Prior stroke or TIA

Modifiable risk factors:

• High blood pressure (hypertension)
• High blood cholesterol
• Atrial fibrillation (irregular heartbeat)
• Diabetes
• Overweight
• Excessive alcohol consumption
• Physical inactivity (sedentary lifestyle)
• Smoking
• Illicit drug use

Outcome:

TIA patient is at high risk of stroke occurrence, i.e. a TIA is a warning of an impending stroke and needs to be taken seriously. Patients should seek urgent medical attention. Some TIA symptoms are more ominous for impending stroke than others. Factors that have been associated with increased risk of stroke following a TIA include:

• Age greater than 60 year
• High blood pressure
• Weakness of face, arm or leg or speech difficulty during the event
• Duration of symptoms greater than 60 minutes more concerning than symptoms lasting less than 60 minutes
• If the patient has diabetes

The chances of stroke occurrence would depend partly on these factors as well as the urgency of the investigation and treatment. Stroke can be prevented in many patients who sustain a TIA.