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ATTRACT trial concludes clot-busting drugs do not prevent long-term blood clot complications for most patients

Team Representative:
Suresh Vedanthem, MD
Professor of Radiology
Mallinckrodgt Institute of Radiology, Washington University School of Medicine
Phone: 314-362-2900

Media Contact:
Joni Westerhouse
Phone: 314-286-0120

Summary of findings in laymen's terms:

About 300,000 Americans each year are diagnosed with a blood clot (deep vein thrombosis, DVT) for the first time. When standard treatment (blood-thinning drugs) is used, nearly half of patients develop a long-term complication called post-thrombotic syndrome (PTS). PTS causes daily pain and swelling of the leg, and sometimes progresses to major disability that prevents patients from walking, working, or conducting their normal daily activities.

Pharmacomechanical catheter-directed thrombolysis is a “clot-busting treatment” in which doctors remove blood clots through a tiny incision using specific drugs and devices. Actively removing blood clots may quickly restore blood flow, prevent permanent injury to the veins, and prevent PTS. ATTRACT, the most rigorously performed study of clot-busting DVT treatment to date, evaluated 692 DVT patients in 56 hospitals who were randomly assigned to receive, or not receive, clot-busting treatment.

Key Findings of the ATTRACT Trial

  • The clot-busting treatment a) did not reduce the development of PTS; b) did cause more bleeding; c) did not reduce the number of new clotting episodes; and d) did not significantly affect patients’ quality of life, over 2 years. For these reasons, it should not be routinely offered to patients with DVT.
  • The treatment did appear to reduce patients’ leg pain and swelling during the first month after study entry, and also reduced the severity of PTS. These findings will catalyze new research to learn which patients may benefit. 
  • This study will advance patient care by providing high-quality evidence that enables most DVT patients to avoid an unnecessary medical procedure. The study suggests that patient comfort during initial DVT care may be improved and late disability reduced through more targeted use of clot-busting treatment in specific groups. These advances will enable patients to make better choices for their care. 

Specific biological innovation of the study: 

  ATTRACT is the first multicenter randomized controlled trial to assess pharmacomechanical catheter-directed thrombolysis (PCDT), an innovative, image-guided therapy. PCDT was shown to achieve rapid clot removal with safety that compared favorably to past thrombolytic methods, and to enable a reduction in the severity of the post-thrombotic syndrome (PTS) in some patients. PCDT did not prevent PTS and should not be routinely used as first-line DVT therapy. Since ATTRACT is 3 times larger than any past trial of a catheter-based DVT treatment and had more rigorous protections against bias, these data will influence the care of many thousands of patients worldwide.

The study addressed a key directional controversy in DVT care; namely, the validity of the “open vein hypothesis” that posits that rapid restoration of an open vein will result in improved patient health. The surprising finding of ATTRACT was that PCDT reduced PTS severity without reducing its frequency, suggesting that the biological factors that drive initial development of PTS are different from those that define progression to severe PTS (the latter may be influenced by clot removal). These findings challenge fundamental dogma on this disease process, and will enable NIH to confidently re-focus research investments.

The study included comprehensive assessments of PTS and venous physiology using multiple patient-reported, physician-adjudicated, and imaging-based assessments. The correlations between the measurement scales and patient outcomes will enable substantial refinement of DVT research methodology, as well as greater insight into the mechanisms of PTS development and progression.
Finally, studies comparing medical versus procedure-based therapies are challenging - tremendous creativity and persistence were required to enroll the target sample in ATTRACT. The study benefited from innovative trial implementation practices and an unprecedented degree of interdisciplinary collaboration that harnessed expertise in medical DVT therapy, endovascular intervention, thrombosis trial methodology, and participant recruitment science.  

Potential impact on patient care and/or how the findings contributed to an improved understanding:

In his 2008 Call to Action on Deep Vein Thrombosis (DVT), the U.S. Surgeon General highlighted the patient disability caused by post-thrombotic syndrome (PTS), stressed the need to study clot-removal therapy as a key research priority, and provided a compelling public endorsement of the ATTRACT Trial. The completed study will exert an immense influence on DVT care and research:

  • Patient Safety and Healthcare Costs – The study found that the benefits of routine, first-line use of clot-removal therapy do not outweigh the risks (increased bleeding). This finding will save many thousands of patients from incurring the risks, discomfort, and inconvenience of an unnecessary medical procedure. Thee healthcare system will save many millions of dollars.
  • Personalization of Care – The study found that patients > 65 years old were more likely to bleed and less likely to benefit from clot removal therapy. On the other hand, clot removal reduced presenting leg pain and swelling, and also reduced the severity of PTS over two years, with a suggestion of greater benefit among patients with the most extensive DVT. The study data will empower patients to make the best decisions for their own care. 
  • Research Directions and Methods – The study clarified that while the open vein hypothesis is probably relevant to the progression of a DVT patient to more severe PTS, other mechanisms define the development of incident PTS. This fundamental disease insight will inform future NIH research investments. ATTRACT’s methodology for endovascular clinical trial patient recruitment and PTS evaluation have set a new standard for other investigators.
  • Collaboration – ATTRACT catalyzed a modern environment in which medical and endovascular physicians work collaboratively on DVT patient care and research, including new NIH initiatives that study image-guided interventions for DVT and pulmonary embolism, with greater cross-fertilization on guidelines panels and educational meetings. 

Journal citation:

Vedantham S, Goldhaber SZ, Julian JA, Kahn SR, Jaff MR, Cohen DJ, Magnuson E, Razavi MK, Comerota AJ, Gornik HL, Murphy TP, Lewis L, Duncan JR, Nieters P, Derfler MC, Filion M, Gu CS,Kee S, Schneider J, Saad N, Blinder M, Moll S, Sacks D, Lin J, Rundback J, Garcia M, Razdan R, VanderWoude E, Marques V, Kearon C; ATTRACT Trial Investigators.

Pharmacomechanical Catheter-Directed Thrombolysis for Deep-Vein Thrombosis.

N Engl J Med. 2017 Dec 7; 377(23):2240-2252. [PMID: 29211671]