What will happen to a person if a blood clot is formed and it blocks the blood flow to the brain?

Created: November 5, 2013; Last Update: December 27, 2016; Next update: 2020.

When we injure ourselves and start to bleed, our bodies make sure that the bleeding soon stops by forming a clump of blood (a blood clot) that closes the wound. This reaction is very important, because it ensures that we lose as little blood as possible, stops germs from getting into the wound, and allows the wound to heal.

But sometimes blood clots form in the bloodstream even though there are no external injuries, and blood vessels may become blocked as a result. This can lead to dangerous complications such as a heart attack or stroke. These kinds of blood clots only occur very rarely in healthy people. But certain illnesses and genetic factors can increase the risk of blood clots forming. Many people who have this higher risk take anti-clotting medication as prevention.

When we injure ourselves and start to bleed, this is what happens:

1. Our blood vessels become narrower. This reduces the flow of blood to the injured tissue, limiting the loss of blood.

2. Blood platelets in the bloodstream, known as thrombocytes, attach to the damaged area of the blood vessel and clump together to reduce the bleeding.

3. The body then activates a number of substances in the blood and the tissue. These substances solidify the clump by forming a special protein and fix the clump at the wound. These substances are called clotting factors or coagulation factors. There are 13 clotting factors in human blood and tissues. Most of them are made in the liver. The liver needs vitamin K to make some of these clotting factors. Our bodies cannot make their own vitamin K, so people have to get it in their diet.

Blood clots can also form even if the person does not have any external injuries. For instance, if blood flows too slowly and it starts to build up, large numbers of blood platelets may group together and stick to each other, forming a blood clot. It is also not uncommon for them to form because the inner walls of blood vessels are damaged, for example in atherosclerosis. If clotting factors are stronger, that can also increase the risk of blood clots forming for no identifiable reason. There are a number of reasons that this can happen, including a genetic predisposition, a tumor, or because somebody is taking a particular kind of medication. The medical term for a blood clot is “thrombus”.

If a blood clot forms in a vein it is called venous thrombosis. Venous thrombosis usually affects the veins in the legs. The main reason people get this kind of thrombosis in the legs is because they do not get enough movement over a long period of time – perhaps because they have had major surgery, or have a serious illness or injury. A blood clot in the legs can become dangerous if part of the clot (called an embolus) breaks off and blocks a blood vessel in the lungs. The medical term for this condition is pulmonary embolism. Typical signs of pulmonary embolism include sudden breathing difficulties, coughing, coughing up blood, and chest pain.

If blood clots form in arteries, the tissues and organs that they usually supply no longer get enough blood, or might not get any blood at all. This kind of thrombus usually develops in the coronary (heart) arteries or inside the heart. If a thrombus blocks a coronary artery, it can cause a heart attack. Blood clots that develop in the heart itself could cause a stroke if they move to the brain and block blood vessels there.

People who have atrial fibrillation have a higher risk of blood clots in the heart. Atrial fibrillation is a particular type of irregular heartbeat, where two of the chambers (called atria) beat very fast and irregularly. This means that blood does not flow through the heart as quickly and steadily. Artificial heart valves also increase the risk of a thrombus: Their surface is not as smooth as that of natural valves, so blood platelets are more likely to attach to them and form a blood clot.

Particular medications or illnesses such as cancer or genetic coagulation disorders can also increase the risk of blood clots developing.

Sources

• Andreae S. Lexikon der Krankheiten und Untersuchungen. Stuttgart: Thieme; 2008.

• Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 18th ed; 2011.

• Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.

• IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

  Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

  Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

Clearing Blockages in the System

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Your blood is an amazing, multi-purpose substance. It flows continuously through the body, carrying oxygen and nutrients to your cells. But if you get a scrape or cut, some of this flowing liquid quickly turns to a protective clot.

Clots are tangles of molecules and blood cells that clump together. They help prevent blood loss when the skin breaks open. They also help stop infections from getting inside the body. But when clotting happens inside a blood vessel, it can be dangerous.

Clots can form on the blood vessel walls to help them heal if they get damaged. Afterward, the clots usually dissolve. But sometimes a clot doesn’t get broken down as it’s supposed to. Clots may also form when they’re not needed.

Sometimes, clots break off a vessel wall and travel through the blood to other parts of the body. They may cause a lot of damage, depending on where they block blood flow. Blood clots can potentially harm the brain, heart, lungs, or other organs.

But researchers have made great progress over the last few decades in managing blood clots. They continue to develop new ways to treat and prevent such blockages.

Clogs in the System

Three main things can lead to dangerous blood clots, explains Dr. Mitchell Elkind, an expert on stroke at Columbia University. “One is an abnormality in the blood that makes it more likely to clot. For example, geneticHaving to do with genes. Genes are stretches of DNA you inherit from your parents. They define features like your risk for certain diseases. causes, cancer, or damage from smoking,” he says. “The second is when blood doesn’t flow properly.” This can be a side effect of diseases and disorders of the heart or blood vessels.

The third is damage to the lining of blood vessels. One cause of such damage is cholesterol buildup in the blood. Cholesterol is a waxy, fat-like substance that can clump together to form plaques. If a plaque breaks apart, it can damage the blood vessel.

Blood clots can happen to anyone, at any age. But some people are at increased risk. These include older adults and those with certain heart conditions.

Major surgery or a serious injury also add risk. Obesity, being physically inactive, and some medications can boost the chance of a dangerous clot, too.

“And once you’ve had one blood clot, you’re at high risk of another one,” notes Dr. Nigel Key, an expert on blood disorders at the University of North Carolina.

Some infections may also increase the risk of blood clotting. Recent studies have shown that the virus that causes COVID-19, SARS-CoV-2, can cause blood clots in some people.

Symptoms of a Clot

Blood clots can occur anywhere in the body. That makes it difficult to find them before they cause a problem, Elkind explains. The symptoms of a blood clot depend on where they are.

A clot blocking blood flow to the brain can lead to a stroke. Strokes can cause sudden difficulty seeing, speaking, or walking. They can also make you feel weak, numb, dizzy, or confused.

A clot that blocks blood flow to the heart can cause a heart attack. The most common signs are crushing chest pain and difficulty breathing. Others range from cold sweats to arm or shoulder pain.

A clot in the lungs can cause shortness of breath, pain when breathing deeply, or even coughing up blood. A clot in a vein deep within the body is called a deep vein thrombosis, or DVT. Symptoms include swelling, pain, warmth, or red or discolored skin. These usually happen in your legs. Long periods of inactivity can increase your risk.

“Compared with a heart attack or stroke, there’s low awareness of the symptoms of deep vein thrombosis,” Key says. Many symptoms overlap with less dangerous conditions, such as a muscle sprain.

If you have symptoms of a blood clot, call your health care provider or 911 immediately. You may need to go to the hospital to have blood or imaging tests.

Busting Blockages

Treatment depends on where a clot is and how long you’ve had symptoms. Certain drugs can break up and dissolve some types of clots. But they have to be given within a few hours of when symptoms start.

A type of surgery called a thrombectomy can be used to remove clots in large blood vessels. It can be used even if people don’t get to the hospital in time to receive clot-busting drugs. “That’s been a huge benefit for patients,” says Dr. Waleed Brinjikji, an expert on stroke at the Mayo Clinic.

This technique has also let researchers study what clots are made of after they’re removed. “We’re starting to realize how different clots can be,” says Brinjikji.

Different types of clots might benefit from different removal techniques or drugs. So Brinjikji’s team is now testing ways to identify the type of clot before it’s removed. That way they can start to test which treatments work best.

Stopping a Clot

If you have a clot that’s forming, certain medications may help shrink it or stop it from growing. These drugs are called anticoagulants. They’re more commonly known as blood thinners.

Sometimes, people with certain heart conditions are given blood thinners to prevent blood clots from forming. But blood thinners can have side effects, including an increased risk of bleeding. So doctors don’t give them to everyone.

Elkind’s team has been researching which heart conditions may benefit from this type of preventive treatment.

Recent research has shown that blood thinners may help in COVID-19. They might reduce the risk of blood clots and organ damage in people hospitalized with COVID-19. More work is underway to figure out how best to prevent and treat blood clots for those with the disease.

This work will also help researchers better understand how other viruses can affect the blood, Elkind explains. “I think we’re going to learn a lot about how other infections also trigger clotting from studying COVID-19,” he says.

There are many things you can do to decrease your risk of harmful blood clots. See the Wise Choices box for tips.