Thrombus occurs when a a blood clot remains and circulates in the vascular system. It may reach vital organs, and prevent blood vessels from functioning correctly.
A thrombus is more likely to occur in people who are immobile, and who are genetically predisposed to blood clotting. A thrombus can also form if an artery, vein, or surrounding tissue is damaged.
In this article, we look at blood clots and the different types of thrombi that can occur. The article also looks at the symptoms, diagnosis, and treatment of thrombi.
Contents of this article:
Blood clots and thrombus types
A blood clot is usually a healthy physical response to injury. It quickly forms a plug that can reduce or even prevent bleeding.
A bit of blood clot that breaks free from the thrombus site and circulates in the bloodstream is called an embolus. An embolus moves through the vascular system until it eventually becomes lodged.
An embolus is a dangerous and potentially fatal complication of thrombosis, especially if the embolus reaches the heart, lungs, or brain. When this happens, the person is said to be experiencing an embolism.
A thrombus is a problem because it impedes the function of a blood vessel.
The effect of a thrombus on the body depends on its location. When a thrombus forms in an artery, such as in the heart or brain, it is called an arterial thrombosis. When a thrombus occurs in a vein, it is called a venous thrombosis. When this happens in the deep veins of the leg, it is called deep vein thrombosis (DVT).
Smoking tobacco may increase the risk of developing a thrombus.
Clotting is caused by chemical reactions between blood cells (platelets) and proteins (clotting factors). A healthy body regulates the clotting process as the body needs it.
When any of the following factors are present, a clot can form more easily within a blood vessel:
- tobacco smoking
- high cholesterol
- being obese or overweight
- diabetes mellitus
- not exercising (sedentary lifestyle)
Some of these factors also increase the risk of atherosclerosis, a condition where the blood vessels become clogged with fatty plaque deposits. Atherosclerosis increases the risk of blood clots blocking the arteries, as well as the veins.
Arterial and venous thrombosis can reduce or totally prevent blood flow. This can lead to severe and even life-threatening complications, depending on where the thrombus forms.
A thrombus does not usually cause any symptoms until it blocks or heavily restricts the flow of blood. Symptoms and complications of each type of thrombus are described below.
A thrombus in an artery can cause:
- unstable angina, a type of chest pain
- heart attack
- ischemic stroke
- peripheral arterial limb ischemia, where blood flow to the limbs is significantly reduced
These conditions all require prompt medical attention. People should seek emergency treatment if they experience any of the following symptoms:
- chest pain
- shortness of breath
- the lower half of the face droops down on one side
- sudden loss of strength in one arm or leg
- a limb that has become cold, pale, and painful
A thrombus in a vein, usually a deep vein in the leg, can cause the following symptoms:
- pain, swelling, and tenderness, usually in the calf
- an ache and warm sensation on the skin in the affected area
- red skin, particularly at the back of the leg below the knee
People who experience any of these symptoms should see a doctor. A DVT can be a life-threatening condition; blood clots can break off and travel through the bloodstream before coming to block arteries higher up in the body.
Doctors use several different methods to diagnose the effects or presence of thrombus formation.
- Duplex ultrasound is the most common test for diagnosing DVT. This method uses sound waves to create pictures of blood flowing through the arteries and veins.
- A D-dimer test measures a substance in the blood that results when a blood clot breaks down. If the test shows high levels of the substance, then a DVT or any other type of blood clot may be present, but this is not certain. If the test result is normal and few risk factors are present, DVT is considered unlikely.
- Venography involves a dye injected into a vein in the affected leg. This dye makes the vein visible on some types of X-ray, such as a fluoroscopy. If this shows blood flowing slower than usual in the vein, it may indicate the presence of a thrombus.
- Magnetic resonance imaging (MRI) and CT scanning create pictures of organs and tissues and can also be used to look at blood vessels.
- A VQ scan is a nuclear imaging study that shows the flow of air and blood within the lungs.
- Blood tests may be used to check for an inherited blood clotting disorder. This may be necessary in cases of repeated, but unexplained blood clots. Thrombi found in the liver, kidney, or brain also may be due to an inherited clotting disorder.
The aim of thrombus treatment is to quickly and effectively:
- control symptoms
- restore blood flow
- reduce and remove the thrombus
The following treatments are typically used to deal with the effects of thrombi:
Surgery for the effects of thrombosis will always be a medical emergency. It can involve directly accessing and unblocking an affected artery. In other cases, blood flow will be diverted or will completely bypass the blocked artery.
Inferior vena cava filters (IVC)
IVC filters are small mesh devices put in the inferior vena cava, which is a large vein, usually under local anesthetic. The IVC filter traps blood clot fragments and can stop them reaching the heart and lungs.
An IVC filter can be permanent and are typically combined with anticoagulation medication therapy when possible. However, doctors may remove the IVC filter after the risk of a blood clot has reduced.
Anticoagulants are often referred to as blood thinners. This name is misleading, however, because they do not thin the blood. Instead, they can reduce the likelihood of the blood forming clots, and this can reduce the size of thrombi.
If anticoagulants do not work, or if the person taking them is intolerant to them, then doctors will consider other treatments.
Compression stockings may be recommended alongside other treatments, to help manage the risk of complications occurring.
Doctors may recommend that people wear compression stockings while taking anticoagulant therapy for DVTs.
The stockings help prevent calf pain and swelling, and they reduce the risk of complications.
A person should wear compression stockings during the day for as long as their doctor recommends.
Raising the affected leg
Along with compression stockings, it is good to keep the legs affected by thrombi raised at night so that the foot is higher than the hip. This relieves pressure in the veins, improves blood circulation, and can help avoid complications.
Once a doctor has prescribed compression stockings, they will usually advise people to stimulate blood circulation by walking or exercising more frequently.
It is not always possible to prevent a thrombus from forming. However, there are steps that people can take to reduce their risk:
- avoiding or quitting smoking tobacco products
- maintaining a healthful weight
- following a healthful diet
- exercising regularly
It is particularly important for people to get up and move around whenever possible after a surgical procedure or during long-distance travel.
Those who are known to be at an increased risk of developing a blood clot may also be given anticoagulant therapy, as well as medications to reduce blood pressure and cholesterol levels in the blood.
If a person gets the right treatment at the right time, then even potentially fatal medical emergencies associated with thrombosis can be successfully treated.
Aftercare is of particular importance because complications can develop months or even years after the thrombus first formed, even after successful treatment.
Post-thrombotic syndrome is one of the potential complications of a DVT. This refers to the damage to surrounding tissue caused by the DVT formation, such as increase of pressure in the vein when blood flow is blocked, ulcerations, and pain. This can result in permanent damage, and under rare circumstances, the limb may even need to be removed.
Recovery depends on the location of the clot, as well as how much and for how long the blood flow was disrupted. The sooner the condition is dealt with, the less likely it is that long-term damage or complications will develop.