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For other articles and previous issues click here. July 11, 2005 Clear
Passage — Interventional Alternatives to Catheter-Directed
Thrombolysis for Treating DVT New interventional techniques that combine drugs with macerating devices are promising to greatly improve treatment for the extremely common and potentially dangerous blood-clotting condition, deep vein thrombosis (DVT). At the 30th annual scientific meeting of the Society of Interventional Radiology (SIR) in New Orleans in April, members presented three new pharmamechanical clot-busting techniques that are proving effective and also less costly and less time-consuming than conventional treatments. While the studies to date have been on small numbers of patients, “the new combination techniques seem to offer a significant advance in treating DVT,” says Suresh Vedantham, MD, an interventional radiologist at Washington University in St. Louis and one of the presenters. Vedantham also heads the DVT research committee on SIR’s venous taskforce. DVT is the formation of a blood clot or thrombus in the body’s deep veins. While deep vein clots can form in the major veins in the arms, pelvis, or elsewhere, most occur in the deep veins that pass through the center of the leg and are surrounded by muscle. DVT affects one or two people out of every 1,000. DVT occurs most often in people over the age of 40, those who are obese, and those who have already had a thrombus. Other risk factors include prolonged bed rest, long-distance travel, surgery involving the leg joints or pelvis, and hormone changes related to pregnancy and childbirth, replacement therapy, or oral contraceptives. DVT symptoms can include swelling of the leg or lower limb, tenderness of the leg or calf, warmth, redness, and pain that worsens when standing or walking. DVT can also have no symptoms. A deep vein clot that occurs below the knee typically only needs to be monitored carefully, says Mahmood Razavi, MD, another presenter and director of peripheral intervention at the Institute for Cardiovascular and Coronary Interventions at Sequoia Hospital in Redwood City, Calif. However, DVT that occurs at or above the knee can cause serious complications and should be treated, he says. Typically, patients with DVT are treated with anticoagulants or blood thinners. However, anticoagulants do not actively dissolve the clot; they just prevent new clots from forming. The clot can break off, travel through the bloodstream, and lodge in the lung. A clot that lodges in the lung is known as a pulmonary embolism, from which as many as 100,000 people die each year in the United States. While pulmonary embolism is the most feared consequence of DVT, untreated clots can also cause postthrombotic syndrome, a serious condition characterized by fatigue, chronic leg pain, and swelling. In severe cases, postthrombotic syndrome can cause skin ulcers. Postthrombotic syndrome is an under-recognized condition. It used to be considered an unusual, long-term aftereffect, Vedantham says, but long-term studies have shown that as many as 50% of patients suffer from postthrombotic syndrome within two years of developing DVT. Postthrombotic syndrome may develop months or years after the diagnosis of DVT. Eventually, the body will dissolve the clot on its own, but, in the meantime, the clot can cause irreversible damage to the vein. “Physicians need to know that by treating DVT, they should be not only trying to prevent a pulmonary embolism but also postthrombotic syndrome,” Vedantham says. Physicians have looked at treating DVT as they do clots elsewhere in the body—with surgery and clot-busting drugs delivered through an IV. But they have found that surgical thrombectomies and intravenous drugs are not a great solution. “Surgical thrombectomies offer better clinical outcomes in terms of the leg, but surgery has all the risks associated with an invasive procedure. It is technically challenging, and requires a long recovery period,” Vedantham says. That seems to be why surgical thrombectomy has really never been commonly adopted. In addition, clot-dissolving drugs can cause bleeding, which can lead to bleeding events. Approximately 10 years ago, interventional radiologists developed a nonsurgical procedure to treat DVT called catheter-directed thrombolysis (CDT). Performed under imaging guidance, the procedure delivers medications directly to the clot through a catheter inserted in the vein rather than through an IV in the arm. The procedure is usually performed under a sedative. A catheter is advanced through the blood vessels of the body to the vessel that has the clot—the site is determined with imaging. Once the catheter is in place, a special machine delivers the clot-busting medication—usually atleplase or urokinase—at a precise rate. Directly infusing the clot in this manner not only reduces the total dose of drugs needed but also the amount of drug that circulates through the body, minimizing potential systemic side effects. While the patient is on the table, any narrowing in the vein that might cause clots to form in the future is identified by venography, an imaging study of the veins, and treated with balloon angioplasty or stent placement. CDT effectively removes many clots, especially if performed within 10 days after symptoms begin. It provides almost immediate relief of pain and swelling and may reduce the likelihood of postthrombotic syndrome, while restoring blood flow in more than 85% of cases. The drawback—and it’s a serious one—is that CDT takes one to two days, sometimes more, in the hospital under the watchful eye of an interventional radiologist. “Part of the problem is that catheter-directed thrombolysis is somewhat user-unfriendly,” Vedantham says. “A patient needs to have a catheter placed and have a drug infused in his [or her] leg for about 48 hours and be watched in the intensive care unit of the hospital.” Such inpatient treatment not only adds to the expense and puts a strain on physician resources but also bucks the trend in medicine to treat people in short-procedure units whenever possible. That’s probably why, Vedantham says, few DVT patients undergo CDT. In the past few years, interventional radiologists have tried to improve the CDT so they could still use it to treat DVT but in less time and with fewer risks. They have since developed three new techniques, all of which combine the direct delivery of clot-busting drugs with devices that chew or dissolve the clot at the same time. One technique is the Power Pulse Spray, which injects a diluted clot-dissolving drug to the area of the clot at high force. The advantage of the spray is that it delivers the drug to more surface area throughout the clot. It takes roughly a half-hour for the clot to partially dissolve, and then the vein is sprayed again with powerful saline jets. The jets create a vacuum that draws the thrombus into the catheter, where it is removed from the body. The Power Pulse Spray technique is a new method of using the already existing AngioJet device, says Jacob Cynamon, MD, director of vascular and interventional radiology at the Montefiore Medical Center in the Bronx, N.Y. Cynamon reported on his experience with the method at the SIR meeting. “In all of the cases in which we used this technique,” he says, “no one had to be treated with the drug for more than 24 hours. We definitely improved the procedure from a 48- to 72-hour procedure to one that is less than 24 hours and, in many cases, patients could be treated in two to three hours.” A second technique uses the Trellis-8 Peripheral Infusion System, which uses an inflated balloon placed on both sides of the clot to prevent pieces of it from traveling to other parts of the body. The physician feeds a wire “filament” through the clot. The wire begins to whip around, chewing the clot into pieces, which are aspirated into the catheter and removed from the body. The FDA recently approved the Trellis as a drug infusion catheter for vascular clots. Razavi, of Sequoia Hospital, reported on his experience with the Trellis system at the meeting. By macerating the clot, the amount of time the patient had to be exposed to the drug was substantially reduced. Most patients needed just under two hours of exposure to the drug as opposed to overnight with the drug alone, Razavi says. Razavi says he didn’t have the data yet, but theoretically because the infusion system isolates the treatment area, less medication escapes into the circulatory system, which should result in less bleeding and thus fewer complications. The third technique is the Helix Clot Buster Thrombectomy Device in which a miniature impeller is housed in the distal end. The impeller creates a recirculating vortex that breaks the thrombus into pieces that can be flushed from the body. The HELIX is FDA-approved for dialysis graft clots and is used off-label for DVT. Small-scale studies have shown all three of the combination techniques to be highly effective. “The preliminary data looks extremely encouraging,” Vedantham says. “It gives patients the benefits of CDT in a shorter, safer, more user-friendly fashion.” Razavi says it’s hard to say which of the three combination techniques, if any, is the best. “The only way to know is to do a comparative analysis, and we’re now accumulating experience,” he says. Cynamon says he likes the Power Pulse Spray because he has found it to be the easiest way of removing the clot. The radiologists say all the techniques including CDT have the best results when the clot is fresh. “It is better to do it within two weeks of the clot formation,” Razavi says. “If you do it in the first two weeks, the efficacy is quite high. Longer than three weeks, and the efficacy of getting rid of the clot drops.” The procedure’s success is not necessarily affected by the size of the clot, Razavi says. The Trellis device can be used to treat up to 30-centimeter segments. “Theoretically, you should be able to treat a 30-centimeter segment the same as a 15-centimeter segment. You just use a longer device,” he says. “It works the same.” On the other hand, he says, the longer the segment, the longer it could take to clean out the clot. “The amount of clot could just mean you have to do it longer, so the procedure could take a little longer.” The pharmamechanical techniques are performed under conscious sedation, not general anesthesia. “Some patients sleep through it, but most are groggy and awake,” Vedantham says. The procedure is not particularly painful, he says. “There is a little bit of discomfort during the procedure. Afterward, the patients are sore, but it’s not bad, and the faster you can do the procedure the better for the patient’s comfort. When you have to have a catheter inserted for a couple of days, it does lead to more soreness.” Patients typically feel better immediately after the procedure. “With this form of treatment, you’re removing the clot and opening the flow in the vein, so you tend to see a lot faster symptom resolution,” Vedantham says. Patients still need to be treated with anticoagulation drugs to prevent pulmonary embolism and the clot from coming back. Pharmacomechanical CDT is an adjunct rather than a competitive therapy, Cynamon says. Further studies are needed to compare the combination techniques with conventional CDT as well as with standard anticoagulation therapy, the interventional radiologists agree. “SIR is working with other societies to develop pivotal multi-center randomized trials to compare the different CDT methods. It’s something I’m hoping will bear fruit over the next year or two,” Vedantham says. Even if the long-term results are the same, Vedantham
says, the combination techniques would be better because they are
less labor-intensive and have fewer complications. However, he adds, “interventional radiologists are clearly best suited to provide these treatments because of their vast experience in imaging the veins and in delivering targeted, catheter-based treatments to the veins.” — Beth W. Orenstein is a freelance health writer and based in Northampton, Pa. She is a regular contributor to Radiology Today. |
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