Clotting is necessary to prevent blood loss when you are injured. However, if you have a blood clot in a deep vein that breaks away and travels to your lung, it can be dangerous.
Information about deep vein thrombosis and pulmonary embolism (blood clots)
Deep vein thrombosis explained
Sometimes the clotting process – known as coagulation – is triggered inappropriately, and a clot forms inside a vein when it is not needed to prevent blood loss. Well known risk factors for such unwanted coagulation include surgery, cancer, immobility, obesity, smoking and pregnancy.
A deep vein thrombosis (DVT) is a blood clot that has formed in one of the veins that lie deep inside the muscles of the leg. Most of the time, the ability of blood to clot is rather useful; it forms a plug that saves us from bleeding to death from a minor wound.
Whatever the cause, a DVT can become large enough to act as a dam in the affected vein, trapping blood and leading to the classic symptoms of swelling of the leg and pain. But this is not the worst of it. Some or all of the clot can break away from where it was formed and travel out into the lungs via the heart, leading to a pulmonary embolism. What this is and how it happens is explained on the next page.
How a deep vein thrombosis (DVT) can cause a pulmonary embolism (PE)
A pulmonary embolism (PE) is one of the most serious consequences of a deep vein thrombosis (DVT), although it is possible to have a pulmonary embolism without experiencing a prior DVT. When a PE occurs following a DVT it begins with either the whole clot, or more commonly part of the clot, breaking away from where it was formed in the leg vein and traveling onwards and upwards into the heart and then out into the lungs.
Most of this journey is through rather large blood vessels, but once in the lungs, where they capture oxygen, the blood vessels become smaller in size.
Eventually the clot reaches a blood vessel too small to pass through and blocks the vessel. This effectively turns off the oxygen supply from part of the lung and is then called a pulmonary embolism.
A pulmonary embolism can be fatal so it is very important that you are alert to the symptoms, which can include shortness of breath, chest pain, coughing up blood, and a racing heart.
This is also why it is so important that a DVT is treated quickly and effectively, and thereafter you receive adequate protection against any recurrence of either a DVT or PE.
Treatment is especially important if you have already had a PE in order to prevent recurrence. If you think that you are experiencing the symptoms of a PE you should contact your doctor immediately.
Treating deep vein thrombosis (DVT) / pulmonary embolism (PE) and preventing recurrence
The drugs used to treat blood clots are called anticoagulants – because they act on the coagulation (clotting) process. This is a complex series of steps that occurs in a specific sequence. Hence, by interrupting one or more of these steps it is possible to reduce the likelihood of a clot forming.
For many years the standard treatment of DVT and PE has been daily injections of one type of anticoagulant called a heparin, together with tablets of a second anticoagulant called a vitamin K antagonist, for the initial treatment period. Thereafter, a single treatment with warfarin. This standard treatment for DVT and PE is highly effective, but it does have a number of limitations. These include the need for injections, and the interaction of vitamin K antagonists (e.g warfarin) with a number of common foods and with other medicines.
For many years the standard treatment of DVT and PE has been daily injections of one type of anticoagulant called a heparin, together with tablets of a second anticoagulant called a vitamin K antagonist, for the initial treatment period. Thereafter, a single treatment with warfarin. This standard treatment for DVT and PE is highly effective, but it does have a number of limitations. These include the need for injections, and the interaction of vitamin K antagonists (such as warfarin) with a number of common foods and with other drugs.
Frequent blood tests are needed throughout the whole treatment period to find the appropriate dosage – a process known as monitoring.
Alternative oral medication
Goldhaber SZ, Morrsion RB. Pulmonary Embolism and Deep Vein Thrombosis. Circulation 2002;106: 1436–38 • Spencer FA, Emery C, Lessard D, et al. The Worcester Venous Thromboembolism study: a population-based study of the clinical epidemiology of venous thromboembolism. J Gen Intern Med. 2006; 21: 722–27 • Goldhaber SZ. Pulmonary Embolism. N Engl J Med 1998; 339: 93–104 • Prandoni P, Lensing AW, Cogo A, et al. The long-term clinical course of acute deep venous thrombosis. Ann Intern Med 1996; 125(1): 1–7