When a blood clot blocks an artery supplying the heart or the brain, the result is a heart attack or stroke. Most Americans are familiar with these two serious health threats. But theyre probably less familiar with the dangers of venous thromboembolism, or VTE — a clot that forms in a vein. A clot in the leg or arm, known as deep-vein thrombosis, can cause pain, swelling, and redness in the affected limb. But the real threat occurs if the clot breaks off and travels to the lungs, causing a pulmonary embolism. "Venous thromboembolism is the third most common cardiovascular cause of death," says cardiologist Dr. Gregory Piazza, assistant professor of medicine at Harvard Medical School. Most VTE fatalities are due to pulmonary embolisms.Shared risks Theres a growing recognition that the same things that make people prone to heart attacks and strokes also leave them vulnerable to venous clots, says Dr. Piazza. A recent study found that three factors that raise cardiovascular risk — older age, smoking, and being overweight or obese — are also strongly linked to a higher likelihood of VTE. But a number of other factors can trigger a VTE, which occurs in an estimated one in 1,000 people in the United States each year (see "What puts you at risk for VTE?"). If you have one of those factors, its known as a "provoked" VTE.What puts you at risk for VTE? Anyone can develop venous blood clots, but the following factors leave you more vulnerable: Family history. Certain inherited conditions make the blood more likely to clot; the most common is factor V Leiden, which affects about 5% of whites. - Age. The risk increases as people grow older. - Decreased blood flow. The underlying reason is usually inactivity due to extended bed rest, prolonged travel, paralysis, or stroke. - Hospitalization. Being hospitalized for any reason raises your risk. - Injury to a vein. This most often results from a broken bone, surgery, or a severe muscle injury. - Increased estrogen. Pregnancy or the use of birth control pills or hormone therapy increases risk. - Chronic medical conditions. These include obesity, cancer, lung disease, kidney disease, and inflammatory bowel disease.Source: American Society of Hematology.Treatment trends People with VTE usually receive injected anti-clotting medications for a few days, followed by pills known as direct oral anticoagulants; examples include apixaban (Eliquis), dabigatran (Pradaxa), and rivaroxaban (Xarelto). Normally, people take these drugs for at least three months. People who have an "unprovoked" VTE (meaning they had no obvious risk factors) have up to a 50% chance of having a second VTE over the following 10 years, says Dr. Piazza. Theyre usually advised to stay on anti-clotting drugs long-term, provided they have a low risk for bleeding, an uncommon but serious side effect from these drugs. That advice also might extend to some people with provoked VTEs, because certain provoking factors (such as inherited clotting disorders and obesity) dont go away, says Dr. Piazza.Take-home advice To lower your odds of VTE, habits that lower your risk of heart disease (such as not smoking, eating a healthy diet, and being active) will help. The vast majority of venous clots occur in people recently discharged from the hospital, says Dr. Piazza. During your recovery at home, dont sit on the couch all day; follow your doctors advice to be as active as you can, he says. And be sure to know the warning signs (see "Symptoms of venous thromboembolism").Symptoms of venous thromboembolism Deep-vein thrombosis The affected area may be - tender or painful, with no known cause and worsening over time - swollen, red, and warm to the touch. If these symptoms linger for more than a few hours, call your doctor for advice.Pulmonary embolism Symptoms may include - difficulty breathing that happens suddenly, without an explanation - a fast or irregular heartbeat - coughing up blood - chest pain or discomfort, which usually worsens with a deep breath or coughing - very low blood pressure - feeling lightheaded or faint. If you have these symptoms — especially if they worsen quickly over a period of hours or persist — call emergency right away.(Harvard Health Letter)