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Blood Clots

What happens when a blood clot forms in the leg travels to the lung?

Blood clots may cause life-threatening medical conditions, and may be considered in the differential diagnosis of any symptoms or signs. Differential diagnosis is the list of potential causes of a patient's condition, which is considered by the health-care professional when caring for a patient and listening to them describe their signs and symptoms.

Deep venous thrombosis (DVT) and pulmonary embolism

Deep venous thrombosis (DVT) may lead to a pulmonary embolism.If there is a blood clot or thrombus in a deep vein of the leg or arm, it has the potential to break off (embolize) and flow through the veins toward the heart, and into the lung where it can become lodged in a pulmonary artery, which prevents the lung from functioning. Pulmonary embolism is a medical emergency and can cause serious illness or death.

An embolus is the medical term for a blood clot that has moved within the bloodstream to a different location. With pulmonary embolus (pulmonary embolism), two issues occur.

  1. The lungs' blood supply is comprised and the affected area of lung tissue may infarct, or die.
  2. Because of the blockage, the ability of the lung to provide oxygen to the body is decreased and hypoxia (decreased levels of oxygen in the blood and throughout the body) may occur.

Even if venous blood clots do not embolize, they may cause significant local problems with swelling and pain. Since blood cannot return to the heart if a vein is blocked by a clot, the limbs may chronically swell and have decreased function in a condition called chronic thrombophlebitis.

What happens when blood clots form and travel to the heart?

Arterial thrombus

An arterial thrombus stops the blood supply to the tissues beyond the blockage, depriving cells of oxygen and nutrients. This quickly leads to tissue death. Arterial thrombus is the mechanism that causes:

  • heart attack (when it occurs in the coronary arteries that supply blood to the heart)
  • stroke (when it occurs in arteries within the brain),
  • peripheral vascular disease (occurring in the arteries of the legs), or
  • ischemic bowel or mesenteric ischemia (when it occurs in the arteries that supply blood to the intestine)

Atrial fibrillation (AFib, AF)

In atrial fibrillation (AFib, AF), small clots may form along the walls of the atrium or the upper chambers of the heart. Should one of these clots break off, it may embolize, or travel in the bloodstream to the brain, blocking an artery and causing a stroke. Other arteries also may be involved when blood clots caused by the presence of AFib dislodge to stop blood flow (embolize), including those that supply blood to the bowel. This can cause bowel ischemia and tissue death (potential necrosis) of the intestine. Clots also can affect blood supply to the extremities (arms, fingers and toes).

Other types of blood clots

Blood should clot anytime it becomes stagnant. This also means that clots will form when blood leaks out of blood vessels.

Examples include some of the following:

  • With bleeding peptic ulcers, patients may vomit liquid blood mixed with clot.
  • Patients with rectal bleeding may also have clot mixed with the bloody stool if there has been time for the clot to form.
  • Sometimes patients with urinary tract or bladder infections develop associated bleeding in their urine, and small clots can form. On occasion these clots may be so big that they cannot be passed and block the urethra (the tube that empties the bladder), preventing urination and causing urinary retention.
  • Vaginal bleeding is a normal event for most women in the reproductive years and occasionally, blood can pool in the vagina and form clots before being expelled. If clots form in the uterus, they may cause significant pain and pressure as they pass through the cervix while being expelled.
Reviewed on 10/28/2016
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