Effective ways to prevent a stroke

A STROKE occurs when a blood vessel to the brain is either blocked by a clot or ruptures causing damage to the affected part of the brain. If you have sudden severe headache, dizziness, numbness or weakness in the face or limbs, difficulty in speaking, or difficulty in seeing, you may be having a stroke. The old adage "prevention is better than cure" is especially true for strokes. Understanding common causes of stroke will help you to take pre-emptive measures to prevent the onset of a stroke.

Fluttering heart

If you feel your heart "fluttering" away or have bouts of breathlessness, do not pass it off as anxiety or mere palpitations. It may be a harbinger of a potentially life threatening condition. Atrial fibrillation (AF), an abnormal heart rhythm which increases the risk of blood clot formation in the heart, is a major cause of stroke. For those over the age of 60 years, about 1 in 10 will develop AF. However, AF can also occur in younger people, especially those with excessively high thyroid hormones.

In AF, there is disorganised generation of electrical impulses from the left upper heart chamber (atrium), causing it to "quiver" at a heart rate of about 400 per minute instead of pumping at regular intervals. As a result, when blood from the lung vessels enter the left atrium, the blood flow slows down considerably as the left atrium hardly has any pumping action. This slow flow will increase the likelihood of blood clot formation in a part of the left atrium called the left atrial appendage, which is shaped like a windsock.

Stagnation of blood flow, with resultant blood clot formation in the left atrial appendage, may result in clot dislodgement. The clot can potentially travel up into the brain, thereby precipitating a stroke.

If you have AF, your doctor will try to convert the heart rhythm back to the normal rhythm by medication or procedures. If AF is persistent, doctors typically use a risk calculator to determine the risk score to find the optimal balance between benefiting from stroke prevention versus the risk of bleeding, before prescribing blood thinners.

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Hole in the heart

A less common cause of stroke resulting from a heart condition is the presence of small hole in the heart, termed patent foramen ovale (PFO). The foramen ovale is a hole between the left and right upper heart chambers that is present in the foetus which typically closes. If the foramen ovale remains open, it may allow blood to leak from the right atrium to the left atrium.

Typically, small blood clots form in the veins and are cleared when they pass from the right heart chambers to the lung circulation. Should some of these small blood clots pass from the right atrium across the PFO into the left atrium and eventually pass into the brain , it can cause a stroke.

This condition can be diagnosed with an ultrasound study of the heart (echocardiogram) and in some patients, a special device needs to be inserted through the leg vein into the PFO to seal it. Fortunately for most people with PFO, stroke does not happen and hence only a small minority of those with PFO need to undergo a procedure to close the PFO.

Blocked neck artery

Narrowing of the neck (carotid) artery accounts for 10 per cent to 15 per cent of all strokes. Most patients with blockage of the carotid arteries do not have symptoms and may only be aware of the condition when they get a stroke.

If you have multiple risk factors such as high blood pressure, high cholesterol, diabetes mellitus, or smoking, your doctor may advise you to do an ultrasound scan of your carotid arteries. If you have symptoms suggestive of a stroke, a computed tomography scan or magnetic resonance imaging (MRI) scan of your intracranial carotid or brain arteries may be performed

For stroke patients with more than 70 per cent narrowing, surgery to remove the obstruction (carotid endarterectomy or CEA), or insertion of a metallic cylindrical mesh to open up the neck artery occlusion via a small incision through the groin (carotid artery stenting or CAS), are the available options.

Compared to medication alone, CEA has been shown to be more beneficial in patients with more than 70 per cent carotid artery narrowing who have had recent non-disabling strokes.

However, both CEA and CAS are not low-risk procedures. In the International Carotid Stenting Study published in Lancet journal in 2010, the incidence of stroke, death, or heart attack was 8.5 per cent in the CAS group compared with 5.2 per cent in the CEA group. New strokes detected on MRI brain scans were significantly higher than clinically obvious strokes, with 50 per cent of patients in the CAS group and 17 per cent in the CEA group showing at least one new abnormal stroke finding detected on post-treatment MRI brain scans done in a median of one day after treatment.

Hence, given the risks of CAS and CEA, one should consider carefully before undergoing a procedure and should have a thorough discussion with one's doctors. If there are no symptoms, the stroke risk is low and optimal management of associated heart disease and optimal control of risk factors such as high blood pressure (BP), diabetes, high cholesterol and smoking cessation can give good outcomes.

Stroke in young patients

For young patients who develop stroke, 25 per cent are due to a tear of the inner lining of the carotid artery in the neck. Stroke occurs as a result of occlusion of the artery due to blood clot formation in the wall of the artery or more commonly, clot formation at the site of the tear which then becomes loose and travels to the brain. The small Cervical Artery Dissection in Stroke (CADISS) trial showed a 2 per cent stroke rate at three months by treating the patients with blood thinning medications. A carotid ultrasound should be a useful test in detecting this condition.

High blood pressure

While about 80-90 per cent of strokes are due to a blood clot, there is a small percentage of strokes where the artery to the brain ruptures, causing bleeding around or in the brain. This type of stroke, although less common , is deadlier and is usually related to high blood pressure. Most of such strokes can be prevented by good control of the blood pressure. Hence, keeping your blood pressure within the normal range is one of the most effective ways to prevent a stroke.

Key steps to stroke prevention

The best way to manage stroke is to prevent it by adhering to the following:

• Control risk factors such as high blood pressure, high cholesterol or diabetes mellitus, and stop smoking;
• Check for atrial fibrillation if you have palpitations;
• If you keep losing weight, or feel breathless, check for the presence of excessive thyroid hormones to avoid AF;

*If you have severe carotid artery occlusion, don't forget to check for heart disease as many people with severe carotid disease have significant heart disease.

As CAS and CEA are not low risk procedures, you will need to discuss the pros and cons of either procedure versus medication with your physician before making a decision:

1) If you require long term blood thinning medication, a discussion with the physician on the type of medication and measures to reduce the likelihood of bleeding is necessary;

2) If you have severe occlusion of brain or neck arteries, excessive lowering of BP may cause fainting attacks and even precipitate a stroke.

Lastly, if you have persistent severe headaches, you may require a scan of your brain vessels to detect uncommon vascular abnormalities that can cause life-threatening strokes such as arterial aneurysms or other vessel abnormalities.

Remember, the best treatment for stroke is prevention.

• This article is produced on alternate Saturdays in collaboration with MWH Heart, Stroke & Cancer Centre