Types of Stroke: Ischemic Stroke

Where does an embolus come from?
An embolus is a moving clot that floats through the blood. If the embolus floats up to the brain and gets stuck in one of the arteries that feeds the brain, it can block the flow of blood and cause an embolic ischemic stroke. An embolus that goes to the brain almost always comes from the heart. Only in very rare cases can an embolus come to the brain from another part of the body.

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An embolus that goes to the brain almost always comes from the heart because of the way blood circulates through the body. On the right side of the heart, blood that needs fresh oxygen comes in from all parts of the body. The diagram at right shows the path the blood takes as it comes in from the body and moves through the right side of the heart [image 1].The blood is then pumped out of the right side of the heart and into the lungs. Blood that comes into the right side of the heart from all parts of the body can only go to the lungs.

On the left side of the heart, blood with fresh oxygen comes in from the lungs. In the second image at right, the white arrows show the path the blood takes as it comes in from the lungs and moves through the left side of the heart [image 2]. The blood is then pumped out of the left side of the heart to all parts of the body. Blood that comes into the left side of the heart from the lungs is pumped out to all parts of the body.

Blood that flows through the right side of the heart moves from all parts of the body to the lungs. Blood that flows through the left side of the heart moves from the lungs to all parts of the body. If an embolus comes into the right side of the heart from another part of the body (like the leg), that embolus could not go to the brain because blood on the right side of the heart only goes to the lungs. An embolus can only go to the brain if it comes from the left side of the heart, which pumps blood to all parts of the body. This is why an embolus that goes to the brain usually comes from the heart.

How does an embolus get from the heart to the brain?
The last diagram at the right shows a large clot in the left side of this heart [image 3]. If a piece of this large clot breaks off, it becomes an embolus, or floating blood clot. Because the embolus is floating in blood that is pumped from the left side of the heart to all parts of the body, it can travel to any part of the body. If this embolus floats to the brain and gets stuck in an artery there, an ischemic stroke can happen.

What makes an embolus form in the heart?
An embolus almost never comes from a healthy heart. As our hearts beat, the heart muscle and valves are constantly moving and pushing blood around. In a healthy heart, there is no place where blood could sit still long enough to form a clot. Some children have problems with their heart muscle or valves. Sometimes kids are born with these problems, and sometimes kids get heart problems from infections or other illnesses. If part of the the heart muscle or valves is not moving normally, there can be places where blood isn’t being pushed around so well. Blood that is not constantly pushed around can sometimes slow down enough to form a clot. If a piece of a clot in the heart breaks off, it can become an embolus, float to the brain, and cause a stroke.

When can an embolus get to the brain from another part of the body?
In a person with a normal heart, an embolus cannot get to the brain from another part of the body because blood follows different paths as it moves through the right and left sides of the heart. On the right side, blood moves from the rest of the body to the lungs. On the left side, blood moves from the lungs to the rest of the body. In a healthy heart, the blood on the right side of the heart cannot cross over to the left side. Some children are born with heart problems that allow blood to cross from one side of the heart to another.

In a healthy person, blood on the right side of the heart always moves from the body to the lungs. In some children with heart problems, blood on the right side of the heart can move in from the body, cross to the left side of the heart, and travel to another part of the body without ever going to the lungs. In the final diagram at right, the white arrows show how an embolus floating in the blood can move up from one part of the body (like the leg) into the right side of the heart, cross to the left side of the heart, and travel to another part of the the body (like the brain) [image 4]. This is how a clot can move from another part of the body to the brain and cause a stroke.

Can anything else cause an embolus to form?
In children, heart problems are by far the most common cause of embolic stroke. Most children with heart problems are born with them. A few children get heart problems from infections or other illnesses. A child who has a heart problem and “thick blood” might be at even higher risk of forming an embolus and having a stroke. Occasionally, kids can have an embolic stroke during surgery. Other causes of embolic stroke, like very severe infection or some injuries, are very rare. Your doctor will explain to you what was the most likely cause of your child’s stroke.

Next: Hemorrhagic stroke

Last Updated: June 13, 2005