Deep Venous Thrombosis

Venous Thrombosis

Blood clots can develop anywhere in the vascular system, and can cause devastating consequences. In order for blood to clot, any two of the following three conditions must be met:

• Slow blood flow (“stasis”), such as occurs with prolonged bedrest after surgery, or a long transcontinental flight.
• Injury to the vessel lining, such as after knee or hip or pelvic surgery.
• Altered clotting system (so-called “Hypercoaguable state,” usually due to medication or to a genetic defect).

Because blood flow normally is very brisk in the healthy arterial system, clots almost never form in the arteries. Arteries that become heavily diseased with atherosclerosis, however, can develop clots (see Peripheral Arterial Disease). In veins, blood flow is much slower. This in itself is not enough to lead to spontaneous blood clotting, but when slow blood flow is coupled with another factor, such as local injury to the vein or a genetic defect in the clotting system, the conditions are set for a “perfect storm,” and the blood can clot.

The Superficial and Deep Venous System

The venous system is divided into the Superficial Venous System and the Deep Venous System. The superficial veins, which are relatively small veins, are just under the skin and often can be seen with the naked eye. When blood clots form in the superficial veins, this is termed “superficial venous thrombosis,” or “superficial phlebitis.” Phlebitis refers to the fact that inflammation, in addition to clotting, of the vein is involved. (Greek “phlebo-“ for vein, and “-itis” for inflammation). Phlebitis typically does not occur in normal veins. Veins that have become varicose, however, are notably prone to developing phlebitis. Although phlebitis causes a painful lump under the skin, which can be very distressing and scary to the patient, superficial phlebitis generally is not a dangerous condition. It usually resolves on its own in a matter of days to weeks, as the body’s own enzymes gradually dissolve away the blood clot.Superficial thrombophlebitis does not lead to the dangerous type of blood clots that break off and travel to the lung. The typical treatment for superficial phlebitis is conservative and involves non-steroidal anti-inflammatory drugs, oral antibiotics, and warm compresses.

In contrast, the Deep Veins are larger and more important to the venous circulation. When clots develop in the deep veins, they can be dangerous. This condition is termed “Deep Venous Thrombosis (DVT).” The danger lies in the fact that, since the deep veins are large, the clots that develop within them have the potential to grow to a large size. If some of these clots break off, they can travel to the right side of the heart and to the lungs and occlude the important pulmonary arteries (This is known as “pulmonary embolus”). The larger size of these clots causes severe limitation of blood flow through the lung. This can be serious and even life-threatening. Blood clots that occur in the region from the thigh to the level of the knee are the ones that are notably dangerous. Blood clots below the knee are not quite as dangerous, as they are small and have a lower propensity to break off and travel to the lungs.

DVT typically causes pain and marked swelling in the thigh/leg, but can also occur without causing any symptoms. Making a definite diagnosis of a DVT requires a vein ultrasound.

The traditional treatment for DVT involves thinning the blood with medications such as intravenous heparin or oral warfarin. These medications do not actually dissolve the existing clot. They work by preventing any further clot formation. The existing clot is gradually dissolved by the body’s own clot-degrading enzymes. This is a slow process and takes on the order of weeks. Thus, blood thinners work well, but the significant length of time it takes for the healing process is an important limitation that has consequences.

Chronic Venous Insufficiency and Post Thrombotic Syndrome

The presence of the clot in the vein, and its slow healing process, causes permanent changes in the vein and its important valves. Scarring occurs and these one-way valves become damaged and “frozen,” such that they leak. Leaky valves allow blood to be pulled down by gravity and collect in the veins of the leg and ankle when an individual stands up. Over time, these veins progressively enlarge and become bulging and varicose. This results in a condition known as Chronic Venous Insufficiency (CVI).

The high hydrostatic pressure in the veins causes blood cells and water to leak out of capillaries and collect in the soft tissue of the legs and ankles, causing pigment changes (The pigment is actually hemoglobin from blood cells trapped and deposited in the tissue) and edema. The extensive soft tissue edema interferes with oxygen delivery to the skin. Portions of the skin begin to die and skin ulcers can form, typically at the ankle. This syndrome of edema, pigment changes, skin death, and ulceration, is called Post Thrombotic Syndrome (PTS).

A New Treatment for DVT: Targeted Thrombolysis

A new treatment has emerged that actually removes the clot during the acute phase, before damage to the valves occurs, thus preserving valve function and avoiding the debilitating consequences of PTS. The treatment involves inserting a catheter into the clotted vein. The catheter has side ports, which allow the infusion of clot-busting medicine, and a wire parallel to the catheter, which can rotate and spin around the catheter and break the clot into small pieces. Lastly, the catheter has a balloon on each end which can be inflated to prevent the strong clot-busting medicine—or any dislodged blood clots—from travelling to other parts of the body. After the clot is broken up, the debris and any left-over clot-busting medicine can be aspirated through the ports with a syringe. This technique has been shown to rapidly remove the clot, and has resulted in the resolution of edema and prevention of future PTS.