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It is probably not something one thinks about often, but there are certain people that are predisposed to DVT. For example, Dan Quayle reportedly acquired his from prolonged immobilization in an airplane while campaigning for a second term. Patients confined to bed in the hospital are also immobilized and are at increased risk for DVT. A long cross-country drive without moving or taking breaks puts you at greater risk. Many women and some men have varicose veins which increases the chance of blood clotting of the lower extremities partially due to stasis. Cancer of any kind, but especially brain cancer is a major risk factor for developing DVT. Patients about to undergo hip and knee replacement operations have one of the highest known incidence of DVT, and paralyzed victims from any cause (spinal cord injury, stroke) have a great risk of blood clotting, especially during the first months after the onset of paraplegia.

If DVT occurs so commonly and has such significant sequela, you may be asking yourself why the media hasn’t made a big deal about it. The answer I suspect is that DVT and its sequela have been shrouded in mystery even to this day. It has been difficult to determine who exactly has it and who can be conclusively proved to have died as a result of it. Studying this disease has proven to be controversial, contradictory, laborious and not universally accepted. Still we know many facts about DVT and its prevention that deserve your attention. So pervasive and concerning is this disease, the American College of Chest Physicians have completed their Fourth Consensus Conference in 1995 to give recommendations to all physicians and surgeons to help prevent this illness. In the following pages I hope to give you a flavor of DVT and an appreciation, not only of how and why it occurs and what its consequences are, but also the extraordinary work that has gone into preventing this most common disease.

Venous thromboembolism is recognized in approximately 260,000 patients per year in the United States. Since less than half of them have symptoms, the number of people involved is over 500,000. You may be asking yourself since over half of the people with this disease don’t have symptoms, what is the harm of having a DVT? If the blood clot is confined to the calf region, approximately one-quarter of these patients will develop the so-called post-thrombotic syndrome, which can manifest itself as swelling of the leg or legs, discoloration of the skin, non-healing ulcers near the ankles, varicose veins with the potential for breakthrough bleeding, pain, infection or inflammation and a host of other physical findings. But the most feared danger is that this blood clot might progress toward the thigh and potentially a portion might break off and travel to the heart on its way to lodging in the lungs. This is called a pulmonary embolism (PE). It can be fatal or can lead to severe respiratory difficulties or it can cause no apparent problem at all. If the blood clot involves the thigh, the post-thrombotic syndrome is much more common, seen in up to 90% of patients and the chance of a PE is much higher as well.

Why do people get DVTs? In the 1860’s Dr. Virchow recognized three important risk factors. His postulates have remained unchallenged to this day. They are: (1) stasis; (2) hypercoagulability, and (3) vessel wall damage. Stasis means that the blood is moving slowly, or not at all, in the veins which may be due to immobility (such as former Vice-President Dan Quail sitting for a protracted period on an airplane) or it might be seen in someone who has suffered a stroke and is confined to bed, or because he or she was paralyzed in the early post-stroke period. Hypercoagulability means that the blood has a propensity to clot. This is seen in some patients who have abnormally high levels of clotting factor(s) in their blood or it can be a consequence of stasis causing these clotting factors to be in contact with each other in greater concentration and for a greater time than normal. Pregnancy, for example, causes an increase in several clotting factors and decrease in the blood’s natural tendency to break up small clots once formed. Last, vessel wall damage does not have to be due to direct trauma such as a fracture of the lower extremities or to a stab wound of a major vein, both of which could cause a deep venous thrombosis—it can be a simple matter of age. For example, patients over 40-years-old have decreased support structures in their vessel wall, making them weaker and therefore predisposes them to damage from stretching.

It turns out that it is now thought that all three of these risk factors must be present for somebody to develop a deep venous thrombosis. In the typical situation, a vein is overstretched (for a myriad of reasons) causing micro-tears of the inner surface of the vessel. There are regions of the vein that are structurally weaker such as where the vein branches and valves are located. This is where these tears are most likely to occur. Platelets in the blood then aggregate in the regions of the tears and then a whole cascade of events are set into motion that can lead to an eventual blood clot. People with varicose veins for instance, of which there are millions, have increased pressure in their superficial veins. If this is caused by high pressure in the deep veins of the lower extremity, eventually the pressure can lead to over-stretching and possible DVT. That is one reason why varicose veins are a risk factor for developing deep venous thrombosis. Just about any operation one undergoes causes a transient augmentation of blood clotting and the fact that patients are asleep and immobile during the peri-operative period, heightens the possibility of deep venous thrombosis. Because the veins in the calf region see the highest venous pressures and are structurally the weakest, most DVTs begin in the calf. About 1 in 5 of calf vein thromboses will propagate to the thigh, but about 50% of those will have a pulmonary embolus. Fortunately only a small fraction of these pulmonary emboli will be fatal. The pulmonary emboli may be so small that it is not even noticed by the patient or physician. Some investigators believe that we all have many small pulmonary emboli a day that do us no harm because our lungs have the extraordinary ability to break down the clot before any lung damage occurs if the clot is small.

leg illustration There are several drugs and mechanical devices that have been developed and used to prevent deep venous thromboses and to treat it should it occur. Unfortunately, depending upon your personal risk factors, the kind of operation you are going to have, or what medical or surgical problems you have will dictate what your treatment is.

If you are about to undergo a knee replacement procedure, the prophylactic drug of choice is going to be different than if you came to the hospital with congestive heart failure or a stroke because it has been found that the optimal regimen for one situation may not be optimal in the other, although it is unclear why this should be the case. Your vascular medicine or surgical specialist is an expert in this field and can give you the best information on your specific situation.

 

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Gregory Hines Interview

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