National Clinical Trial Finds Certain Treatments for Blood Clots Not Effective

Stephan Moll, MD, professor of medicine and member of the UNC Hemophilia and Thrombosis Center, co-authored the results of a large-scale multicenter clinical trial focusing on catheter-directed thrombolysis and its effects.

National Clinical Trial Finds Certain Treatments for Blood Clots Not Effective click to enlarge Dr. Stephan Moll

Media Contact: Carleigh Gabryel, 919-864-0580,

December 7, 2017

CHAPEL HILL, NC – Deep vein thrombosis (DVT) – blood clots, usually in the legs – is commonly treated with either a blood thinner or by combining the use of blood thinners with a procedure called catheter-directed thrombolysis. In this procedure, doctors insert a catheter into the leg to administer so-called “clot-busting” drugs directly into the clot, breaking it up and allowing some of it to be sucked out of the vein through the catheter.

The findings of a clinical trial published in the New England Journal of Medicine show that such procedures are often unnecessary and can result in complications.

“Many clinics and hospitals rush into using the catheter-directed thrombolysis procedure as a first-line treatment to prevent the long-term complications of chronic swelling, pain and discomfort, called post-thrombotic syndrome,” said Stephan Moll, MD, professor of medicine and member of the UNC Hemophilia and Thrombosis Center at the UNC School of Medicine. “But we found that rush to be unwarranted.”

Moll was UNC’s principal investigator for the Acute Venous Thrombosis: Thrombus Removal with Adjunctive Catheter-Directed Thrombolysis (ATTRACT) study. ATTRACT was designed to determine whether performing the procedure as part of initial treatment for patients with DVT would reduce the number of people who develop post-thrombotic syndrome, a complication that can leave patients with chronic limb pain and swelling, and may lead to difficulty walking or carrying out their daily activities. The study involved 692 patients, randomly assigned to receive blood thinners alone or blood thinners and the procedure. Each patient was followed for two years. The study concluded that catheter-directed thrombolysis did not reduce the likelihood that patients would develop post-thrombotic syndrome.

“While intuitively it makes sense that early clot removal would decrease the long-term complications after a leg clot, this study showed that it doesn’t. This suggests that other mechanisms – such as inflammation of the blood vessels – may be predictors of bad outcomes and may have to be targeted in the future to decrease complications,” said Moll, cofounder of the UNC Blood Clot Education Program.

Moll added that the study did show a decrease in intensity of post-thrombotic syndrome symptoms in some of the patients who underwent the procedure: 24 percent of people on blood thinners alone experienced moderate to severe pain and swelling, but only 18 percent of people who were treated with blood thinners and the procedure did so. However, investigators could not determine why some patients experienced less severe pain and swelling than others.

“This is relevant and needs to be analyzed further – what characteristics in select patients make this procedure appropriate?” posed Moll.

Patients who undergo catheter-directed thrombolysis are also at risk of experiencing dangerous internal bleeding due to the powerful clot-busting drugs administered during the procedure.

“We are dealing with a very sharp double-edged sword here,” said principal investigator Suresh Vedantham, MD, a professor of radiology and of surgery at Washington University School of Medicine in St. Louis. “None of us was surprised to find that this treatment is riskier than blood-thinning drugs alone. To justify that extra risk, we would have had to show a dramatic improvement in long-term outcomes, and the study didn’t show that. We saw some improvement in disease severity but not enough to justify the risks for most patients.”

“This landmark study conducted at 56 clinical sites showed no benefits of catheter-directed thrombolysis as a first-line deep vein thrombosis treatment, enabling patients to avoid an unnecessary medical procedure,” said Andrei Kindzelski, MD, PhD, the NHLBI program officer for the ATTRACT trial.

For now, Moll and other researchers say the procedure should be reserved for use as a second-line treatment for some carefully selected patients who are experiencing severe limitations of leg function from DVT, and who are not responding to blood-thinners.

The ATTRACT study was led by researchers at Washington University; McMaster University in Ontario, Canada; Massachusetts General Hospital in Boston; and St. Luke’s Mid-America Heart Institute in Kansas City, Mo. UNC enrolled a large number of patients in the study, which Moll attributed to the comprehensive DVT care at Chapel Hill.

The ATTRACT Trial was supported by the National Heart, Lung and Blood Institute of the National Institutes of Health (NIH), grant numbers U01-088476 and U01-088118; Washington University’s Center for Translational Therapies in Thrombosis, grant number U54-HL112303; Washington University’s Institute of Clinical & Translational Sciences, which is supported by the National Center for the Advancement of Translational Sciences, grant number UL1-TR00044810; Boston Scientific; and Covidien (now Medtronic). Study drug and funding were provided by Genentech (a Roche Company). Compression stockings were donated by BSN Medical.

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