by Frank C. Lynch, MD FSIR
Deep vein thrombosis (DVT) is the medical term that describes the condition where blood clots form in the main veins of the extremities. Most commonly, it refers to blood clots in the legs. There are three major factors that lead to DVT: slow blood flow, inflammation and anything that may make the blood more likely to coagulate. DVT causes extremity pain and swelling, and over time can lead to discoloration of the skin or even breakdown of the skin that leads to ulcer formation. Although DVT can result in these major health problems, it can also result in a more serious life-threatening condition, pulmonary embolism.
Pulmonary embolism (PE) results when blood clots in the extremities migrate through the heart and into the blood vessels of the lung. Once there, the blood clots block the flow of blood from the heart to the lungs. These blockages prevent oxygenation of the blood, prevent the release of carbon dioxide and produce tremendous strain on the heart as it tries to pump blood past the obstruction. Pulmonary embolism causes chest pain, shortness of breath and even sudden death.
As described above, DVT and PE are often thought of as two separate disease processes. However, since DVT leads to PE, it is more appropriate to think of DVT and PE as stages of a single disease process known as venous thromboembolic disease (VTED). VTED begins as DVT in the veins of the calf and if left untreated has a high likelihood of extending to involve the veins of the thigh and pelvis. If DVT remains untreated, it has a high likelihood of resulting in PE, which is often fatal.
The preferred method of prevention and treatment of VTED is blood thinners. Blood thinners prevent the initial formation of a blood clot. If a blood clot is already present, blood thinners prevent its growth, allowing the body’s own mechanisms to dissolve the existing blood clot. Blood thinners are inexpensive, safe and effective in the prevention and treatment of VTED. However, not everyone can receive blood thinners.
Patients who have recently had surgery or were involved in an accident cannot receive blood thinners because they may clause bleeding from the recent incisions or wounds. Patients who are already bleeding from their bowels, bladder or lungs cannot receive blood thinners because they may make the bleeding worse. Patients with stroke are also at high risk of bleeding into their brain, so blood thinners are often avoided in these patients. Finally, patients who may be at risk of falling are poor candidates for blood thinners because the usually minor trauma associated with a fall can be much more serious if the blood’s ability to clot is compromised. In all of these patients, a different method of preventing PE is called for.
All of the blood from both legs and both sides of the pelvis drain into a single blood vessel, the inferior vena cava (IVC). The IVC is the common pathway that all clots must travel on their way to the lungs. Thus, by placing a barrier in the IVC that traps the blood clot, the blood clot will never reach the lungs and PE is prevented. The purpose of an IVC filter is to do just that — capture the blood clot and prevent it from traveling to the lungs.
There are over 600,000 cases of PE in the United States annually, and over 200,000 deaths are attributed to PE in the United States each year. The problem with VTED is that it can be silent right up to the time that PE occurs, and when PE occurs it is fatal up to 10% of the time in the first hour alone. Although the DVT of VTED may cause leg swelling, a large number of patients who are found to have PE never knew that they had a blood clot in their legs. They did not have any signs that a physician could detect during a physical exam that might suggest that DVT was present. Complicating matters further is that the symptoms of PE — chest pain and shortness of breath — are caused by many other medical conditions. Because of this, the diagnosis of PE may not be made right away. If left undiagnosed and treatment is never initiated, PE is fatal 30% of the time.
These factors are important to keep in mind, since actively preventing VTED is a far more effective strategy than waiting to make the difficult diagnosis after the often fatal disease has occurred. Patients hospitalized for other causes are often at high risk for VTED, and VTED is now considered a preventable complication of hospitalization. The onus is now on health care providers to identify patients who are at high risk for VTED and institute preventive measures. These measures usually mean placing high-risk patients on blood thinners, and in some cases it may mean placing an IVC filter even in patients not known to have DVT.