Venous Thromboembolism (Blood Clots, Deep Vein Thrombosis, Pulmonary Embolism)
Venous thromboembolism refers to a blood clot that forms in a vein. When a vein in the leg or arm is affected, it is known as deep vein thrombosis (DVT). If left untreated, some or the entire clot can break off and travel from the limb through the heart and to the arteries of the lung. This results in difficulty breathing, chest pain, and puts stress on the heart. If a large amount of thrombus (clot) lodges in the arteries to the lungs, death can result if not promptly treated. When the clot travels to the arteries in the lung, it is known as a pulmonary embolus (PE).
Deep Vein Thrombosis and Pulmonary Embolism Causes and Risk Factors
Generally, a combination of factors leads to venous thromboembolism, including an injury or trauma to a vein (e.g., surgery, motor vehicle accident), inactivity or stasis (e.g., prolonged travel, hospitalization, recovery from surgery), and a condition that predisposes to clotting (e.g., pregnancy, cancer, genetics). Tobacco use also increases the risk of a blood clot.
Patients may have different combinations of these risk factors leading to a "provoked," or explained, DVT or PE. In cases where no risk factor can be identified, the DVT or PE is considered "unprovoked." Evaluation by a physician familiar with DVT or PE is important to determine whether the blood clot is provoked or unprovoked, as this will affect treatment and prognosis.
For some people, anatomy may predispose to blood clots:
- May-Thurner syndrome: The left leg vein (common iliac vein) passes behind the right leg artery (common iliac artery) causing compression of the left leg common iliac vein. This may cause scarring and predispose to a blood clot in the left pelvis and thigh.
- Thoracic outlet syndrome (TOS): Compression of the arm vein (subclavian vein) by the space between the first rib and clavicle. Scar tissue from compression may form over time that predisposes to DVT. A sudden arm DVT in this setting usually occurs with sports activity (e.g., swimming) and is known as effort thrombosis or Paget-Schroetter's syndrome.
Deep Vein Thrombosis and Pulmonary Embolism Symptoms
Patients with DVT may develop sudden swelling and/or pain in the affected arm or leg. Redness of the skin may present. Dilated veins on the surface of the limb may develop, which can be a sign that a deeper vein is blocked.
PE may cause sudden shortness of breath and chest pain that worsens with deep breaths. Dizziness, fast or irregular heart rate, low blood pressure, low oxygen level, or fainting (syncope) are signs of a large PE that may be life threatening. These symptoms should prompt urgent evaluation in the nearest emergency room.
Deep Vein Thrombosis and Pulmonary Embolism Risk Factors
Reduction of risk factors that predispose to DVT and PE is the mainstay of prevention. Tobacco causes damage to blood vessels and increases clotting potential of the blood; abstinence is key. For patients with planned immobility related to surgery or hospitalization, prophylaxis with a preventative dose of blood thinning medication may be prescribed by your physician.
Diagnosing Deep Vein Thrombosis and Pulmonary Embolism
Based on the patient's complaints and appearance, the physician will decide to treat immediately or to evaluate further with blood work and imaging. All people with suspected DVT and PE should have vitals (blood pressure, pulse, oxygen level) taken and an electrocardiogram.
The gold standard for diagnosis is an imaging test that visualizes the blood clot in the limb (DVT) or lung (PE). Physicians evaluating a patient with suspected DVT or PE will determine which imaging test is best and how urgently the patient needs to be treated.
- Arm or leg ultrasound is a sonogram of the limb that evaluates the veins for the presence of a blood clot. This is a highly accurate, non-invasive and widely available test.
- Computed tomography angiography (CTA) is a detailed exam that generates three-dimensional (3D) pictures of the arteries of the lung with the use of contrast material that is injected through an IV. The exam is fast and is the gold standard for diagnosis of PE. Patients with severe kidney disease may not be eligible for this exam, due to kidney stress related to contrast material.
- Ventilation/perfusion scan (VQ scan) is a test that is less commonly utilized as the CT angiogram is more accurate. This is a nuclear medicine exam that compares the areas of the lung that are receiving blood to those that are receiving air. Areas that do not match up may suggest a blocked artery from PE. This test is only used in those patients that cannot undergo CTA.
Immediate treatment, before an imaging diagnosis is made, is indicated if there are urgent PE symptoms such as low blood pressure, fainting, heart strain, or low oxygen level. For patients with an identified PE, ancillary testing with transthoracic echocardiogram (heart ultrasound) and ultrasound of both legs may be pursued to better evaluate the strain on the heart and the burden of blood clot that remains in the legs, respectively.
In some cases, the physician may use blood work to decide whether an imaging test is needed. The D-dimer is a blood test that measures blood clotting and may be used to negate the possibility of a DVT or PE in patients with low suspicion for this condition.
Deep Vein Thrombosis and Pulmonary Embolism Treatments
The mainstay of therapy for a venous thromboembolism is blood thinning medication to stabilize the blood clot and prevent further PE. It is important to note that blood thinners do not break down the blood clot, but they stop further growth and instability that progress to PE. There are several blood thinners available today.
- Heparin agents are injectable blood thinners (enoxaparin) that are dosed two times daily by the patient or as continuous infusions (unfractionated heparin) that can be administered only in the hospital and require frequent blood testing.
- Warfarin is an oral blood thinning agent that has been available for more than 50 years. Each patient requires a unique dose to reach the ideal level of blood thinning, which is measured by a blood test known as the International Normalized Ratio (INR). At initiation of therapy, it may take several days to weeks to reach the correct blood level with warfarin dose adjustments. During this period, patients are "bridged," or treated with heparin so they are protected from the blood clot. Disadvantages to warfarin include multiple interactions with medications and common foods that may make the INR level fluctuate and put the patient at risk for bleeding (if too high) or blood clots (if too low).
- Novel oral anticoagulants are recently approved agents that act by blocking blood factors involved with clotting. Dosing varies: dabigatran and apixaban are dosed two times per day and rivaroxaban and edoxaban are once daily. The benefit of these newer drugs is patients achieve the appropriate level of blood thinning without any dose adjustment or need for blood monitoring. Disadvantages include the lack of a commercially available antidote should patients bleed due to blood thinning. In extreme cases, dialysis to remove the drug or blood transfusions to support the patient may be necessary.
Duration of therapy will depend on individual patient risk for recurrent blood clots (e.g., genetic predisposition) as well as the setting of the current blood clot (provoked versus unprovoked). At Mount Sinai, our vascular specialists are experts in the treatment and long-term management of patients with venous thromboembolism.
In cases where blood thinning medication is not an option, a device to protect the patient from PE may be considered. These are known as inferior vena cava (IVC) filters and are placed during a minimally invasive procedure that involves catheter placement in the groin veins or neck veins that is then fed into the IVC. The filter is deployed from inside the IVC in the abdomen. Filters may be removable or permanent; removable filters are generally retrieved several months after placement.
In cases where a life-threatening PE occurs, the physician may consider a clot-busting medication to breakdown the blood clot in the lung immediately; this is called thrombolysis. This may be performed by an injection in the vein (systemic thrombolysis) or by groin catheter delivery to the area of blood clot with suction (mechanical and catheter-directed thrombolysis). Rarely, surgery to manually remove the blood clot may be considered.
In cases of May-Thurner syndrome and TOS, catheter-directed thrombolysis to break down and clean out the blood clot is often pursued in addition to blood thinning medications. To correct the area of vein compression, TOS patients require surgery to remove the first rib and other offending structures. In some cases, people with TOS or May-Thurner syndrome may benefit from placement of a mesh tube (stent) inside the vein to keep the damaged vein open long-term. The stent is placed by a groin catheter.
Long-Term Effects of Deep Vein Thrombosis and Pulmonary Embolism
The long-term effects of DVT and PE depend on the severity of the blood clot as well as the individual patient. The major ones include:
- Venous insufficiency or "leaky veins" and post-thrombotic syndrome (PTS), which occurs due to damage to vein valves by the blood clot causing pooling of blood and fluid in the legs. Nearly 50 percent of people with a DVT may experience PTS. The symptoms include leg swelling, redness, varicose veins, and dark-stained skin. In more severe cases, non-healing ulcers may result. The best treatment is prevention; we recommend our patients with DVT where compression stockings (prescription grade) to prevent PTS.
- Chronic thromboembolic pulmonary hypertension (CTEPH) is the result of an old or recurrent PE that causes high blood pressure in the lungs and heart strain over time. Only a small number of people with PE develop CTEPH. Symptoms include shortness of breath, limited ability to exercise, dizziness, leg swelling, chest pain, and palpitations. Management should include care with a cardiologist. In advanced cases, surgery to debulk and remove the residual clot may be pursued.
Division of Vascular and Endovascular Surgery
Vascular Interventions – Cardiac Cath Lab
1190 Fifth Avenue, 1st Floor
New York, NY 10029