Blood Clots What are blood clots?
Blood is a liquid that flows within blood vessels. It is constantly in motion as the heart pumps blood through arteries to the different organs and cells of the body. The blood is returned back to the heart by the veins. Veins are squeezed when muscles in the body contract and push the blood back to the heart.
Blood clotting is an important mechanism to help the body repair injured blood vessels. Blood consists of:
· red blood cells containing hemoglobin that carry oxygen to cells and remove carbon dioxide (the waste product of metabolism),
· white blood cells that fight infection,
· platelets that are part of the clotting process of the body, and
· blood plasma, which contains fluid, chemicals and proteins that are important for bodily functions.
Complex mechanisms exist in the bloodstream to form clots where they are needed. If the lining of the blood vessels becomes damaged, platelets are recruited to the injured area to form an initial plug. These activated platelets release chemicals that start the clotting cascade, using a series of clotting factors produced by the body. Ultimately, fibrin is formed, the protein that crosslinks with itself to form a mesh that makes up the final blood clot.
The medical term for a blood clot is a thrombus (plural= thrombi). When a thrombus is formed as part of a normal repair process of the body, there is little consequence. Unfortunately, there are times when a thrombus (blood clot) will form when it is not needed, and this can have potentially significant consequences
Blood clot facts
· Blood clots form when blood fails to circulate adequately.
· Arterial thrombi form when a plaque ruptures and promotes an acute clot formation.
· Venous thrombosis occurs when prolonged immobilization allows blood to pool in an extremity and then clot.
· The diagnosis is suggested by the history and physical examination and often confirmed with a radiologic test.
· Treatment may require surgery, anti-coagulation medications, or a combination of the two.
· Prevention of blood clots involves attention to the risk factors for vascular disease.
· Serious complications can arise from blood clots, and individuals should seek medical care if they believe a blood clot exists.
What causes blood clots?
Comment on thisRead 39 CommentsHYPERLINK "http://www.medicinenet.com/script/main/submit-patient-comments.asp?questionid=1066"Share Your Story[->0]
Blood clots form when there is damage to the lining of a blood vessel, either an artery or a vein. The damage may be obvious, such as a laceration, or may occur on the microscopic level. As well, blood will begin to clot if it stops moving and becomes stagnant.
Venous thrombosis or blood clots in a vein occur when a person becomes immobilized and muscles are not contracting to push blood back to the heart. This stagnant blood begins to form small clots along the walls of the vein. This initial clot can gradually grow to partially or completely occlude or block the vein and prevent blood from returning to the heart. An analogy to this process is a slow moving river. Over time, weeds and algae start to accumulate along the banks of the river where the water flows more slowly. Gradually, as the weeds start to grow, they begin to invade the center of the river because they can withstand the pressure of the oncoming water flow.
Arterial thrombi (blood clots in an artery) occur by a different mechanism. For those with atherosclerotic disease, plaque deposits form along the lining of the artery and grow to cause narrowing of the vessel. This is the disease process that may causeheart attack[->1], stroke[->2], or peripheral artery disease[->3]. If a plaque ruptures, a blood clot can form at the site of that rupture and can completely or partially occlude the blood flow at that point.
Blood clots in the heart. Inatrial fibrillation[->4], the atrium or upper chamber of the heart does not beat in an organized manner. Instead, it jiggles, and blood tends to become stagnant along the walls of the atrium. Over time, this may cause small blood clots to form. Clots can also form in the ventricle after a heart attack when part of the heart muscle is injured and unable to contract normally. Since the damaged area doesn't contract with the rest of the heart, blood can start to pool or stagnate, leading to clot formation.
Blood leaking out of a blood vessel. Blood clots can form when blood leaks out of a blood vessel. This is very beneficial when a person gets acut or scrape wound[->5], because the clot helps stop further bleeding at the wound site. The clotting mechanism works well following trauma as well. Broken bones[->6], sprains and strains[->7], and nosebleeds[->8] all result in bleeding that is controlled by the body's clotting mechanism.
Blood clots causing other medical problems.Sometimes, normal blood clotting can cause medical problems because of its location. For example, if bleeding occurs in the urine[->9] from any of a variety of reasons (such as infection, trauma, or tumor) clots may form and prevent the bladder from emptying, causing urinary retention[->10]. Clot formation in the uterus may cause pain when the clots are passed through the cervix and can lead to vaginal bleeding, either as part of menstruation[->11] or as abnormal vaginal bleeding[->12] (menorrhagia, dysmenorrhea).
· What are the complications of blood clots?[->13]
How can blood clots be prevented?
Patient Comments: Blood Clots - Describe Your Experience
Patient Comments: Blood Clots - Causes
Blood Clots Glossary
Blood Clots Index
What are the risk factors for blood clots?
The risk factors for arterial clots are those that are common to all diseases that cause narrowing of blood vessels, cholesterol plaque formation, and plaque rupture.
· High blood pressure[->14]
High cholesterol levels
Diabetes
Smoking
Family history
What are the symptoms of blood clots?
Comment on thisShare Your Story[->15]
Venous clots do not allow blood to return to the heart and symptoms occur because of this damming effect. Most often occurring in the legs or the arms, symptoms include:
· swelling,
· warmth,
· redness, and
· pain.
Arterial clots do not allow blood get to the affected area. Body tissue that is deprived of blood and oxygen begins to die and becomes ischemic (isch=to restrain + emia = blood)
· Pain is the initial symptom of the ischemia, or oxygen deprivation due to loss of blood supply.
· Other symptoms depend upon the location of the clot, and often the effect will be a loss of function. Heart attack and stroke are self-explanatory.
· In an arm or leg, in addition to pain, the limb may appear white, and weakness[->16], loss of sensation, or paralysis[->17] may occur.
· If the blood supply is lost to an area of the bowel, in addition to intense pain, there may be bloody diarrhea[->18].
How are blood clots diagnosed?
The initial step in making the diagnosis of a blood clot is obtaining a patient history. The blood clot itself does not cause a problem. It's the location of the blood clot and its effect on blood flow that causes symptoms and signs. If a blood clot or thrombus is a consideration, the history may expand to explore risk factors or situations that might put the patient at risk for forming a clot.
Venous blood clots often develop slowly with a gradual onset of swelling, pain, and discoloration. Symptoms of a venous thrombus will often progress over hours.
Arterial thrombi occur as an acute event. Tissues need oxygen immediately, and the loss of blood supply creates a situation in which symptoms begin immediately.
There may be symptoms that precede the acute artery blockage, that may be warning signs of the potential future complete occlusion of the blood vessel.
· Patients with an acute heart attack[->19] (myocardial infarction) may experience angina[->20] in the days and weeks prior to the heart attack.
· Patients with peripheral artery disease may have pain with walking (claudication[->21]), and a TIA[->22] (transient ischemia attack, mini-stroke) may precede a stroke.
Physical examination can assist in providing additional information that may increase the suspicion for a blood clot.
· Venous thrombi may cause swelling of an extremity. It may be red, warm, and tender; sometimes the appearance is difficult to distinguish from cellulitis[->23] or an infection of the extremity. If there is concern about a pulmonary embolus, the clinician may examine the lungs, listening for abnormal sounds caused by an area of inflamed lung tissue.
· Arterial thrombus symptoms are much more dramatic. If a leg or arm is involved, the tissue may be white because of the lack of blood supply. As well, it may be cool to touch and there may be loss of sensation and movement. The patient may be writhing in pain.
Arterial thrombus is also the cause of heart attack (myocardial infarction) and stroke (cerebrovascular accident) and their associated symptoms.
Testing for venous blood clots
Venous blood clots may be detected in a variety of ways, though ultrasound[->24] is most commonly used. Occasionally, the patient's size and shape limit the ability for ultrasound to provide a definitive answer.
Venography is an alternative test to look for a clot. In this test, a radiologist injects contrast dye into a small vein in the hand or foot and using fluoroscopy[->25] (video X-ray), watches the dye fill the veins in the extremity as it travels back to the heart. The area of clot or obstruction can thus be visualized.
Sometimes, a blood test is used to screen for blood clots. D-Dimer[->26] is a breakdown product of a blood clot, and its levels in the bloodstream may be measured. Blood clots are not stagnant; the body tries to dissolve them at the same time as new clot is being formed. D-Dimer is not specific for a blood clot in a given area and cannot distinguish a "good” or needed blood clot, one that forms after surgery or due to bruising from a fall, from one that is causing medical problems. It is used as a screening test with hopes that the result will be negative and show that there is no need to look further for blood clots.
The D-dimer blood test is usually ordered with the expectation that it will be negative. It is a useful test in patients who have a low probability of having a blood clot, and the health care practitioner usually counsels the patient that a positive blood test will likely require additional tests being ordered.
Should a blood clot embolize to the lung, this may be a medical emergency. There are a variety of tests to look for pulmonary emboli. A plain chest X-ray[->27] will not show blood clots, but it may be done to look for other conditions that can cause chest pain[->28] and shortness of breath[->29], which are the symptoms of a pulmonary embolus. An electrocardiogram[->30] (EKG) may show abnormalities suggestive of a pulmonary embolus and also may reveal other causes of chest pain.
Computerized tomography[->31] (CT scan) is often the test of choice when suspicion of pulmonary embolus is high. Contrast material is injected intravenously, and the radiologist can determine whether a clot is present in the pulmonary vessels. The contrast material injected into the body can be irritating to the kidney(s) and should not be used in patients who have impaired kidney function. In older patients, screening blood tests (serum creatinine[->32]) to check kidney function may be required before a dye study is considered.
On occasion, a ventilation[->33] perfusion[->34] (V/Q) scan is performed to look for pulmonary emboli. This test uses labeled chemicals to identify inhaled air into the lungs and match it with blood flow in the arteries. If a mismatch occurs, meaning that there is lung tissue that has good air entry but no blood flow, it may be indicative of a pulmonary embolus. It is less accurate and more subjective than a CT scan, and requires the skill and experience of a radiologist to interpret. Two radiologist may interpret a VQ scan differently and come to different conclusions.
Testing for arterial blood clots
Arterial thrombosis is an emergency, since tissue cannot survive long without blood supply before there is irreversible damage. When this occurs in an arm or leg, often a surgeon is consulted on an emergency basis. Arteriography may be considered, a test in which contrast material is injected into the artery in question to look for blockage on imaging studies. Sometimes, if there is a large artery that is occluded, this test is done in the operating room with the presumption that a surgical procedure will be needed to open the vessel and restore blood flow.
For a heart attack (acute myocardial infarction, MI), the EKG may establish the diagnosis, although blood tests may be used to look for enzymes (troponin, myoglobin[->35], CPK) that leak into the bloodstream from irritated heart muscle. In an acute heart attack, the diagnostic and therapeutic procedure of choice is a heart catheterization[->36].
For an acute stroke (cerebrovascular accident, CVA), the test of choice is a computerized tomography (CT) scan of the head to look for bleeding or tumor as the cause of stroke symptoms. If the symptoms resolve, the diagnosis is a transient ischemic attack (TIA, mini-stroke), and further tests may include carotid ultrasound to look for blockages in the major arteries of the neck and echocardiography to look for blood clots in the heart that may embolize to the brain.
What are the complications of blood clots?
Comment on thisShare Your Story[->37]
Blood clots prevent proper circulation of blood.
Deep vein thrombosis[->38] of the leg or arm may cause permanent damage to the veins themselves and cause persistent swelling of the extremity. The life-threatening issue that may arise from deep venous clots is a clot that breaks off and embolizes to the lungs (pulmonary embolus), causing problems with lung function and oxygenation of the blood.
Arterial thrombus often is a life- or limb threatening event, since organs and cells do not get enough oxygen.
How can blood clots be prevented?
Prevention is key in thrombosis or clot formation.
Arterial thrombosis
· For arterial thrombosis, the most likely precipitating event is a plaque rupture with clot formation in the artery.
· Minimizing the risk of vascular disease requires life-long attention to the risk factors that lead to plaque buildup and "hardening" of the arteries.
· Blood pressure and cholesterol control, diabetes management, and refraining from smoking[->39] all minimize the risk of arterial disease.
· Although family history is an important risk factor, one needs to be even more vigilant about the other risk factors if there is a family history of early heart attack or stroke.
Deep vein thrombosis
The main risk factor for deep vein thrombosis risks is immobilization. It is important to move around routinely so that blood can circulate in the venous system. On long trips, it is recommended to get out of the car every couple of hours and in an airplane routinely get up and stretch.
Physicians and nurses work hard at getting people moving after surgery or while in the hospital for medical conditions. The low molecular weight heparin known as enoxaparin (Lovenox) can also be used in low doses to prevent clot formation. Patients are often given tight stockings to promote blood return from the legs and prevent pooling of blood.
In patients with atrial fibrillation, warfarin (Coumadin) was traditionally used to prevent clot formation and minimize the risk of embolus and stroke. Newer medications have been developed that prevent blood clot formation similar to warfarin and have been successfully used in patients with atrial fibrillation. These medications include dabigatran (Pradaxa), rivaroxaban (Xarelto), and apixaban (Eliquis). These newer drugs have advantages of reduced susceptibility to diet and drug interactions and convenience (lack of need for routine blood testing of the international normalized ratio or INR, as is required for warfarin therapy).
An important caution was issued by the FDA about the use of dabigatran because a clinical trial in Europe (the RE-ALIGN trial)1 was recently stopped because dabigatran users were more likely to experience strokes, heart attacks, and blood clots forming on the mechanical heart valves than were users of warfarin. There was also more bleeding after valve surgery with dabigatran use than with the use of warfarin. The FDA recommends that dabigatran not be used to prevent blood clots in patients with mechanical prosthetic heart valves.
