Be Aware of Risk in the Veins

Venous thromboembolism may be one of the most dangerous conditions you’ve never heard of, particularly for stroke survivors.

What is VTE?

Blood clots form when something slows or changes the flow of blood in the veins. A stationary blood clot that forms in one part of the body is a thrombus, then if it moves through the bloodstream until it lodges in a narrow vessel and blocks the flow of blood, is called an embolus. An embolus in a coronary artery can cause a heart attack, in a cerebral artery, it can cause a stroke.

When these blood clots occur in the veins it is called venous thromboembolism (VTE). There are two related, and potentially life-threatening, conditions that come under the category of VTE, deep vein thrombosis (DVT) and pulmonary embolism (PE). When they occur, they demand immediate medical attention.

DVT and PE

Deep vein thrombosis affects up to 2 million people in the U.S. and happens when a clot occurs in the larger veins deeper in the body, as opposed to a vein that runs close to the body’s surface. The risk of DVT in those who’ve had a stroke is higher than in those who haven’t. It occurs about twice as often after strokes caused by a bleed (hemorrhagic) than after those caused by a clot (ischemic).

DVT usually occurs in the leg, mainly affecting the large veins in the calf and thigh, usually on one side, not both. About half of people experiencing DVT don’t show outward signs or symptoms. When symptoms do occur, they show up in the leg that has a clot.

Pulmonary embolism occurs when a clot due to DVT breaks off and travels to the lungs, causing a blockage that can permanently injure the affected lung, lowering the blood’s oxygen level and potentially damaging other organs by starving them of oxygen. Blood clots that travel to the lungs are more likely to have formed and broken away in the thigh rather than in the lower leg or other parts of the body.

About half of people experiencing DVT or PE will not exhibit symptoms. When symptoms of DVT do show up, they may include:

  • Changes in skin color (redness)
  • Leg pain or tenderness, especially in the calf
  • Leg swelling (edema)
  • Skin that feels warm to the touch

Symptoms that may present for PE include unexplained shortness of breath, rapid breathing, chest pain (may be worse upon deep breath), rapid heart rate, lightheadedness/passing out or coughing up blood.

Get medical attention immediately if you have these signs or symptoms. DVT and PE are serious, potentially life-threatening conditions that demand treatment to prevent further complications.

The Centers for Disease Control and Prevention estimates that there are 300,000 to 600,000 VTE events annually in the United States.

Immobility and VTE

Immobility of the legs for long periods as can happen after surgery, long distance air travel or paralysis following a stroke is a major risk factor for VTE. When the legs don’t move for long periods, blood flow slows, and clots can form as a result. In fact, with stroke survivors this risk of VTE can be as high as 15 percent in the first few weeks after a stroke.

Dr. MingMing Ning

“When part of your body is paralyzed after a stroke, blood flow becomes more stagnant locally, and the nerves around the blood vessels don’t work well either,” said MingMing Ning, a neurologist specializing in ischemic stroke and co-director of the Cardio-Neurology Division at Massachusetts General Hospital.

“Normally, the nerves around the blood vessels keep blood flowing so clots do not form. When there is paralysis, that doesn’t happen,” Ning said. “Right after a stroke, in addition to being immobilized, your blood is more pro-inflammatory and pro-coagulable, that is, your blood actually turns thicker within the first couple of weeks. So during that time window, not only are you not moving, but you’re more likely to form clots — it’s a perfect storm for clot formation.”

Other Risk Factors

VTE is an equal opportunity condition and can affect people of either gender, all ages, races and ethnicities. But some risk factors for VTE are stronger than others. Increasing age (from 40 on) means increased risk. Experiencing surgery, major trauma, fractures of the hip or leg, carries strong risk. Other independent risk factors include:

  • active cancers and chemotherapy
  • prior superficial vein thrombosis
  • infection
  • varicose veins
  • kidney disease
  • inherited thrombophilia (a condition that tends to make the blood clot more easily)
  • prolonged immobility such as hospital or nursing home confinement or leg paralysis due to, for example, stroke or spinal cord injury

And among women:

  • use of oral contraceptives
  • pregnancy/postpartum period
  • hormone therapy

Any of the factors below in combination with stroke may justify preventive measures for VTE. A combination of two or more of them may have an effect on the length and type of treatment someone receives:

Prior VTE — People who have had a previous episode of VTE have a high risk of recurrence. In one study, patients with a history of VTE were eight times more likely to develop a new episode during a high-risk period, such as surgery or serious illness, than patients without such a history.

Age — Patients older than 40 are at higher risk, and that risk doubles with each subsequent decade.

Cardiac or respiratory failure

Immobility — Prolonged immobility like on very long flights combined with other major risk factors increases the chances of VTE.

Oral contraceptives — Women who use estrogens for contraception or menopause and men receiving estrogen therapy for prostate cancer are at increased risk for VTE.

Some inherited or acquired blood conditions, such antiphospholipid antibody syndrome

Being pregnant, or having had a baby recently, puts a woman at greater risk of developing a blood clot. Her risks increase when the following also apply:

  • Has experienced previous blood clots
  • Genetic predisposition to blood clots
  • Obesity
  • Prolonged immobility, such as bedrest or long distance travel
  • Multiple births
  • Increased maternal age
  • Other illness, such as cancer and serious infection


Diagnosis is done by assessment — a healthcare professional gathers information about a person’s medical history, age, medications and specific lifestyle factors. A Doppler ultrasound may be performed on the legs and certain blood tests that detect a greater chance of blood clotting may be performed. Additional testing with CT angiography (a test used to see arteries and veins throughout the body) may be done if PE is suspected.


Survivors determined at risk of VTE based on medical assessment may receive treatment designed to prevent clots from forming. This treatment may include approaches such as:

  • Getting the patient to move around early on
  • Avoiding dehydration or other provoking factors such as smoking
  • Anti-clotting, blood-thinning medications
  • Though sometimes helpful for patients who have not had a stroke, wearing compression stockings has not proven effective for preventing VTE in those who’ve had a stroke, and also may increase the risk of skin complications.

The risk of a clot forming goes down over time, especially for those survivors who are able to move around. Patients who are wheelchair-bound should probably be on some form of blood thinner or aspirin to prevent clots from forming. “Most ischemic stroke survivors will be put on either a blood thinner or an antiplatelet such as aspirin,” Ning said. “So that treats both the risk of clotting from the stroke and the risk of clotting in the legs. But aspirin is less effective than blood thinners in preventing venous clots.”

Bleeding Stroke

Dr. Steven Greenberg

Hemorrhagic stroke survivors may also have VTE, and for them, blood thinners may be problematic. “Treatment of DVT in patients considered at high risk for intracerebral hemorrhage is challenging,” said Steven M. Greenberg, also of Massachusetts General and director of the Hemorrhagic Stroke Research Program. “It requires careful balancing of the risks of potentially catastrophic brain bleeding versus equally catastrophic pulmonary embolism.”

One option is to place a filter in the inferior vena cava, which carries blood from the lower body to the lungs, blocking most clots from reaching the lungs. This does not treat the actual clotting process in the legs. An option that addresses that is the new generation of novel oral anticoagulants. These medicines are FDA-approved for treatment of DVT, and each carries substantially lower risk of triggering intracerebral hemorrhage than the older standby agent, warfarin.

A Special Risk

VTE can also cause a stroke in people with a common condition called patent foramen ovale (PFO), a connection between the upper chambers of the heart. Normally blood from the lower body goes through the lungs, which filter any clots before they can get to the arteries of the brain. However, in those with a PFO, a clot in the leg can pass through this connection between the upper chambers and travel directly to the brain to cause an ischemic stroke. “PFO is common — found in up to one in four healthy adults, so it is often an under-diagnosed stroke risk for patients with venous clots,” Ning said. PFO has been recognized as a cause for stroke relatively recently, and is often only discovered after an otherwise unexplained stroke.

Before Travelling

Because car and airplane travel can mean being immobile for extended periods of time, it’s a good idea to talk with your healthcare provider about your trip and find out if they have specific recommendations for you to reduce your risk of VTE while travelling.


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