Addendum: newer reports say that Hillary Clinton has a cerebral venous sinus thrombosis, a very different condition than described below, one requiring an entirely new post.
According to reports this evening, U.S. Secretary of State Hillary Clinton is being treated for a blood clot. I have no other information than what is in the news reports, but with what little information we have, her story seems typical and frightening.
Venous thromboemboic disease (VTE) is a disease where blood clots—usually in the legs—can break off and lodge in the lungs, causing a life-threatening emergency. Somewhere around 100,000 people die from these clots in the US every year. To understand why, we need a little anatomy lesson.
When blood leaves the heart’s left ventricle, it enters the aorta, the body’s largest artery, and from there is distributed throughout the body. After reaching the capillaries where oxygen and carbon dioxide are exchanged, the venous system takes over. Like the arterial system in reverse, blood courses from veins of increasing size until it returns to the heart at the right atrium.
The heart is a powerful pump, and provides the force needed to pump the blood throughout the body. The return trip isn’t quite as simple. Gravity fights blood flow back from the legs to the heart, and the pumping of the heart has lost much of it’s power. The legs, though, provide an assist. When you use your legs, for example to walk, the muscles help pump blood back up toward your heart, providing enough extra kick to get the job done.
That’s the first bit you need to know, and only half the story. There is another half to the circulatory system, one that runs between the heart and the lungs. To compete the cycle of gas exchange, blood must pass through the lungs where carbon dioxide is again exchanged for oxygen. Low-oxygen blood from the body reaches the right side of the heart and is shot through the pulmonary arteries into the lungs. After passing through capillary beds where the work is done, it returns to the left side of the heart full of oxygen to be pumped again from the left heart to the aorta and the rest of the body.
For the sake of this example, we’ll invent a patient much like Secretary Clinton. She had a recent fall and concussion that led her to take some rest. Presumably she was more immobile than usual. She’s also a person who spends a lot of time traveling, which also involves a lot of sitting still. Since the pumping of the legs isn’t returning blood to the heart as well, blood flow in the legs slows down, and the low flow can lead to blood clotting in the veins. (There’s actually a whole lot of anatomy, physiology, and biochemistry I’m skipping over for the sake of a clear explanation. We can get into that some other time.)
When a blood clot forms in one of the large, deep veins in the leg (deep vein thrombosis, “DVT”) a few things can happen. A person might notice pain and swelling in the calf or thigh. Or they might not. The blood clot may organize and stabilize, or may simply dissolve away. Or it might not.
In the worst case scenario, a blood clot breaks free of the vein wall and shoots up toward the heart. Once it enters the right side of the heart, the pump shoots it directly into the lungs (or the brain in certain circumstances). If the clot is very small, you may not notice it at all. If it’s very large you may drop dead on the spot.
When the clot lodges in the lungs (pulmonary embolism, “PE”), the heart keeps trying to pump blood out through the pulmonary artery. Since the arterial tree is blocked downstream, the pressure inside the pump rises, and new blood stops flowing from the lungs into the left heart. The entire circulatory system can collapse instantly, killing the patient.
Not every dies of a pulmonary embolism. As stated above symptoms range from none to sudden death. In between these extremes are chest pain, shortness of breath, even fainting (which makes me wonder if in Clinton’s case, the clot may have come earlier than her concussion).
DVTs and PEs require rapid diagnosis and treatment. Sometimes, in serious enough cases, drugs that actually dissolve the clot are used, but more often patients are given drugs that prevent further clotting while their bodies do the rest.
Hillary Clinton will likely get the best care science has to offer, and will hopefully recover quickly, but her’s is a common story. Immobilization, whether from illness or other reasons, is a risk factor for VTE, and while we may do everything we can to prevent it (moving around, preventative medication) sometime we just get unlucky.