Stroke

Stroke is one of the most common neurological conditions. Also called a cerebrovascular accident (CVA), it can have a devastating outcome. Just as you have a heart attack when the blood supply to the heart is compromised due to a clogged artery in the heart, stroke is similarly a brain attack and occurs when the blood supply to the brain gets compromised. The brain is richly supplied by blood vessels and does not tolerate ischemia (reduced blood supply) well.

There are different types of strokes and here I shall enumerate a few of them. Strokes can broadly be categorized under 2 headings:

1) Ischemic strokes ( when blood supply to the brain is compromised eg a clot in the artery supplying the brain shall cause an ischemic stroke).

2) Hemorrhagic strokes ( when a blood vessel in the brain ruptures, hemorrhage occurs into the surrounding brain structures causing a hemorrhagic stroke).

 

Ischemic strokes can be caused by several different kinds of disease processes and can be further classified either on the basis of the calibre of the blood vessel involved or on the basis of the pathogenic mechanism which caused the stroke.

On the basis of calibre of the blood vessel involved, strokes can be further classified as

1) Large vessel strokes: a big blood vessel in the brain gets blocked. Usually when the doctor refers to a large vessel stroke he means strokes involving large arteries such as the internal carotid artery (ICA), the middle cerebral artery (MCA), anterior cerebral artery (ACA) or the posterior cerebral artery (PCA).

 

2) Small vessel strokes: a small blood vessel in the brain gets blocked. Usually these are the penetrating arteries of the brain which supply the deeper parts of the brain.

Based on the mechanism/cause of ischemic strokes, we can classify strokes as:

1) Atherothrombotic : the stroke occurs due to atherothrombosis, the same mechanism which causes many of the heart attacks. The blood vessels of the brain become hardened and narrowed due to atherosclerosis: an inflammation of the arteries due to deposition of lipoproteins/fat and cholesterol . This deposition of lipoproteins give rise to what we commonly refer to as plaques. This most commonly occurs in people who have risk factors for both stroke and coronary artery disease namely diabetes, hypertension, high cholesterol, smokers etc.

2) Embolic: here a plaque may break off from its primary site such as the heart and travel up to the brain blocking off a brain vessel. Lots of things can embolize to the brain:

-cholesterol plaques

-fat embolism ( commonly seen after one has a long bone fracture. The long bones like tibia and femur are very rich in bone marrow which is rich in fat. When a fracture occurs rarely the fat may embolize via a blood vessel to the brain.

-air embolism ( strange though it may sound even a bubble of air can embolize to the brain and cause a stroke)

Embolic strokes can be of two types:

1) Cardioembolic : a clot embolizes from the heart to the brain.

2) Artery to artery embolic: a clot embolizes from a larger artery commonly the carotid artery in the neck to a small artery in the brain.

Hemorrhagic strokes: just as ischemic strokes, hemorrhagic strokes can also be of various types. Hemorrhagic strokes are usually classified on the basis of the compartment of the brain into which the bleeding occurs.

1) Bleeding can occur into the substance of the brain itself: this is called as primary intracranial hemorrhage (ICH)

2) Bleeding can occur in the subarachoid space of the brain: this is called sub-arachnoid hemorrhage (SAH). I shall be discussing this under a separate heading.

3) Bleeding can occur in either the epidural or subdural space: this is called epidural hematoma (EDH) and subdural hematoma (SDH) respectively.

 

Risk factors for stroke/ CVA

There are numerous risk factors for stroke. As both stroke and coronary artery disease involve blood vessels they share some common risk factors.

Risk factors can be divided into: modifiable and non-modifiable risk factors.

1) Non-modifiable risk factors include:

a) Age: strokes are more common in the older age groups. Strokes do occur in the young and even in children and infants but they have diffferent causes.

b) Sex: there is some sex difference in the incidence of strokes.

c) Race: hemorrhagic strokes are more commonly seen in Asians as compared to Caucasians.

d) Genetic causes: if you have a very strong family history of strokes or coronary artery disease ( example your father had a stroke, his father had a stroke and all at a relatively young age then you too have a high risk of having a stroke at some point in your life). Unfortunately the genes which impart this increased risk have still not been clearly delineated, so no one knows just how much is the risk. If bad cholesterol or high blood pressure and diabetes runs in your family and in you then your risk for strokes and heart attacks is increased.

 

As you may realise the above risk factors are non-modifiable, meaning there is precious little you can do to change them. You cannot stop aging, change your race or sex or modify the genes that you were born with !!! Not at this juncture at least. Maybe in the future science shall advance to the extent that we can modify these bad genes.

 

Modifiable risk factors:

There are numerous modifiable risk factors for strokes and CAD. I shall list them out as follows:

1) Hypertension: hypertension or high blood pressure (BP) is the number one modifiable risk factor for both strokes and heart attacks.  Hypertension has rightly  been called the Silent Killer. It usually does not cause any overt symptoms and people are unaware that they have a high blood pressure. At times vague complaints of headache and fatigue may make them seek medical attention where a blood pressure evaluation shall disclose that they are hypertensive. (hypertensive meaning one who has high BP).

2) Diabetes mellitus: diabetes mellitus (DM) too increases the risk of strokes and CAD especially when the blood sugar is uncontrolled and constantly elevated. People who have DM may not know that they have diabetes for a long time as initial signs and symptoms may be subtle. In the setting of uncontrolled blood sugar they may have complaints of polyuria ( too much and too frequent urination), polyphagia ( hungry and always eating, most of the diabetics are obese) and polydipsia ( feeling thirsty all the time). As the disease advances complications of diabetes emerge namely poor wound healing, frequent urinary tract infections, heart attacks, strokes, eye-problems (cataracts and retinal problems leading to impaired vision), nerve problems ( neuropathy) and kidney problems ( renal insufficiency sometimes requiring dialysis).

3) Smoking: people who smoke have a much higher risk of getting a heart attack or a brain attack. The toxins in cigarette smoke damage the lining of the blood vessels in both the heart and the brain.  No amount of smoke is good for the heart or the brain. One should quit completely to lower this risk of heart and brain attacks.

4) Sedentary life-style/ lack of exercise:  a sedentary life-style also predisposes to strokes and heart attacks. People who are obese especially those with central obesity ( fat around the tummy) have higher risk of strokes and heart attacks.

5) Hypercoaguable states: certain people have factors in their blood which make their blood more coaguable, meaning the blood clots more readily. Examples include patients who have diseases like lupus, sickle cell anemia etc.

6) Dyslipidemia or bad cholesterol:  as many of you know there are many types of cholesterol found in our bodies. Not all cholesterol is bad. People who have more bad cholesterol (increased low density lipoproteins, increased very low density lipoproteins) and low levels of good cholesterol (high density lipoproteins) have higher risk of strokes and heart attacks.

 

Treatment of stroke: before I talk about the treatment of stroke, I rather talk a bit about stroke prevention. Prevention is always better than cure. Stroke prevention involves modification of the risk factors for stroke. Smoking cessation is the key as smoking is an important risk factor for stroke. Smokers get atherosclerosis at an earlier age than non-smokers (their arteries get hardened). Smoking cessation may involve behavioral therapy as well as use of nicotine patches and gums. People who have hypertension should ensure that their hypertension is adequately treated. Nowdays we recommed aiming for blood pressures of 120/70 mm Hg or even less. There are many drugs out there for the effective treatment of high blood pressure. The same is true for diabetics and euglycemia (getting blood sugar as close to normal) is the goal. This may be achieved either by pills (oral hypoglycemic drugs) or with insulin. Recommendations are to reduce Hb A1C (also called glycosylated hemoglobin to below 7). The importance of regular physical exercise cannot be overstated. I would recommned some cardio-vascular exercise like brisk walking or jogging. This is good both for the brain as well as the heart. Diet too plays an important role in stroke and dietary modifications may be one way to reduce your risk for strokes and heart attacks. Eating a diet rich in fish oils, poly unsaturated fatty acids, green leafy vegetables and fruits helps to naturally lower your cholesterol down. Recently the benefits of cooking in olive oil have been emphasised.

 

Management of an acute stroke:

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