What is a stroke?
March 6, 2019
Stroke is one of the most devastating forms of cardiovascular disease. It is the fifth most common cause of death in the United States and the second worldwide. It is a major cause of disability. Strokes can leave people paralyzed, unable to speak, or unable to eat, making them a rightfully feared consequence of vascular disease. Fortunately, many strokes can be avoided with good preventative health care.
What is a stroke?
A stroke is damage to the brain that results from an alteration in blood flow. There are two major types:
- Ischemic – when blood flow to the brain is interrupted
- Hemorrhagic – when there is bleeding in the brain
Ischemic stroke
Ischemic strokes are the most common type. They usually occur due to a clot forming upstream of the brain (in the arteries of the neck, or less commonly in the heart) and flowing into the brain, blocking flow. Ischemic strokes can also occur due to a clot forming in the small vessels penetrating the brain. These are called lacunar strokes and usually occur because the vessels have been damaged over time by hypertension.
When the symptoms of an ischemic stroke last less than 24 hours, the event is known as a transient ischemic attack, or TIA – often called a “mini-stroke”.
Less commonly, ischemic stroke can be caused by a generalized decrease in blood flow to the brain, as can happen with a cardiac arrest or other catastrophic event.
Hemorrhagic stroke
There are two types of hemorrhagic stroke, intracerebral hemorrhages and subarachnoid hemorrhages.
Intracerebral hemorrhage occurs due to the rupture of a small artery within the brain. This results in a localized area of bleeding that causes dysfunction of that part of the brain. The size of the hemorrhage can enlarge, causing more and more symptoms.
The other type of hemorrhagic stroke is a subarachnoid hemorrhage, which usually occurs due to rupture of an aneurysm, or dilated blood vessel, on the surface of the brain. This results in bleeding into the fluid that surrounds the brain, and can rapidly result in coma or death. Aneurysms that cause subarachnoid hemorrhage can be hereditary, so it is important to know if anyone in your family has had such an event.
What are the signs of stroke?
Strokes can present with a number of different symptoms. The most common symptoms with ischemic strokes are what are called focal deficits, meaning a dysfunction of a specific part of the neurological system. This deficit could be weakness or numbness in one part of the body, slurring of words or inability to speak, loss of vision, facial droop on one side, or loss of balance.
Hemorrhagic strokes can often present with a headache. Classically, subarachnoid hemorrhages can cause a sudden, severe headache, like a “thunderclap”.
If you or anyone you know is having stroke-like symptoms, note the time when the symptoms began and seek treatment immediately. Rapid treatment is essential to limiting the damage from a stroke. Certain treatments cannot be given if the stroke has been going on for too long.
What causes strokes?
The main cause of ischemic strokes is disease of the carotid artery, which carries blood to the brain. This results in either obstruction of flow, or plaque breaking off and flowing downstream into the brain. The risk factors for carotid artery disease include high blood pressure, high cholesterol, diabetes, smoking, inactivity, and obesity. Sound familiar? These are the same risk factors for heart disease. This is not surprising since the arteries supplying the heart muscle are similar to the arteries supplying the brain.
Lacunar strokes and subarachnoid hemorrhages have high blood pressure as their major risk factor. Read about high blood pressure here and make sure yours is controlled!
If you are worried that you may be at risk for stroke, speak to your physician! You can also calculate your risk of a cardiovascular event (which includes stroke) here. Risk assessment is a crucial step in prevention. Based on your risk, you can assess whether you may benefit from a cholesterol medication according to the guidelines here.
Occasionally ischemic strokes can originate from a clot that forms in the heart. This is common in patients who have an irregular heart rhythm called atrial fibrillation.
Even less common is the possibility of a blood clot in a vein traveling through a hole in the heart (bypassing the lungs) and causing a stroke. This is called a paradoxical embolism, and although uncommon, can be investigated in younger stroke patients or patients without traditional risk factors.
Summary
Stroke is usually a consequence of vascular disease and is influenced by traditional risk factors such as hypertension, cholesterol, diabetes, and smoking. Preventative measures are important because strokes can be devastating. This includes lifestyle modifications and possibly medication. The various types of strokes are treated completely differently. If you or a family member have had a stroke, it is important to know what kind and what the cause was.