In depth: Blood clots

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.

Human venous system

Human venous system

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.


  1. My great grandmother died as a result of a blood clot.
    At first, she felt a tingling in her leg, but the doctors dismissed it. Only later did they find it was a blood clot. By then, they had to amputate her lower leg.
    Bedridden, she lost the will to live, and died. “Mort d’usure,” is what they called it.
    I can’t help but harbor some resentment for those Millau doctors who failed to diagnose the clot in time. Maybe she could have had more years to enjoy chocolate and steak (her favorite meal; she wasn’t exactly conscious of the idea of nutrition) and watch Inspector Derrick. I miss her.

    • That sounds horrible. Im so sorry. It might have been an arterial rather than venous clot. Those can be deadly in a whole other way.

  2. Kara

     /  December 30, 2012

    34 years old, 6 months of progressive shortness of breath and feeling unwell …. mental illness runs in the family and no significant medical history or reasons for my sickness, so diagnosed as anxiety disorder and told “in the past we would have called this female hysteria. You should talke some ativan.” Old family doctor friend diagnosed me over the phone when I couldn’t even speak a whole sentence without huffing and puffing, and she escorted me to ER and demanded certain tests. A couple hours later: multiple bilateral pulmonary emboli. A couple of months later added idiopathic to the dx because no one could figure out why. Now followed by a hematologist. Happy to be alive, but very bitter to (multiple) a-hole docs who didn’t take my “I’m don’t feel right” seriously. Yes, I looked like a wreck and was nervous because I was FEELING like a wreck and nervous.

  3. Excellant explanation and graphic, I used to do case management for Kaiser with their members hospitalized in non-plan hospitals all over the world and it was always a concern with all the long travel inactivity.

    I am thinking that you may need to send this to John Boltan though because he seems to think the Ms.Clinton is making this up as a political ploy to avoid any more scrutiny re: Benghazi.

  4. Jefferson

     /  January 1, 2013

    I had a clot behind the knee that I initially assumed was a torn ligament – that’s how painful it was. The MD twisted my foot and the lack of pain puzzled him. Then it was obvious to me what it was and here’s why. I was diagnosed with factor V Leiden a year earlier but, being heterozygous, I wasn’t concerned. I would suggest that anyone with a previous clotting issues or has family members with clotting issues get tested. The bad: compression stockings and daily aspirin. The good: living and an excuse to get up every 45 minutes and take a walk.

  5. lumbercartel

     /  January 3, 2013

    More than forty years ago my father had a bilateral phelbectomy for severe varicose veins; it wasn’t for cosmetic reasons, but to improve lower leg circulation. Unfortunately, nobody mentioned to me what the early symptoms were so it wasn’t until ten years ago that I had my own veins stripped (including lots of arguing with insurance over “cosmetic procedures” despite the cumulative tissue damage, including a ruptured Achilles tendon.)

    Since then, I’ve been wearing medical compression stockings. Much as I hate the damned things (try to get ski versions!) the combination certainly made travel a lot better. Fortunately, no acute circulatory problems so far.

    Worth remembering that varicose veins are a risk, and worth using compression stockings when sitting for a long time is unavoidable.

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