A major international clinical trial co-led by McMaster University has found that a minimally invasive procedure significantly improves symptoms and quality of life for people living with a painful and often disabling condition that can develop after deep vein thrombosis (DVT).
Researchers found that patients who received the procedure experienced less severe post-thrombotic syndrome (PTS) and significantly better quality of life six months after treatment compared with those who received standard care alone.
The trial is the largest randomized study to date to evaluate endovascular therapy — a procedure in which physicians use tiny tubes and stents inside blood vessels to clear chronic blockages caused by old blood clots.
PTS affects 20 to 50 per cent of people who have had a DVT — a serious condition where a blood clot forms in a deep vein, usually in the legs. PTS can cause chronic pain, swelling, heaviness and mobility limitations that interfere with daily life. Existing treatments — most commonly compression stockings — offer inconsistent relief and do not address the underlying cause of the disease. No medications have been proven to improve PTS severity in rigorous clinical trials.
The results, published April 13 in the New England Journal of Medicine, were simultaneously presented at the Society of Interventional Radiology (SIR) 2026 Annual Scientific Meeting in Toronto.
The trial was co-led by McMaster and Washington University School of Medicine in St. Louis, with McMaster’s Trials Research and Clinical Evidence (TRACE) clinical trial unit playing a key coordinating role.
“PTS can be life-altering, yet we’ve had very few effective treatment options,” says Sameer Parpia, senior author and data coordinating centre principal investigator of the study and an associate professor in the departments of Oncology and Health Research Methods, Evidence, & Impact at McMaster.
“This trial provides clear evidence that targeted endovascular therapy can make a meaningful difference for patients living with this condition.”
The multicentre trial enrolled 225 patients with moderate-to-severe PTS and imaging-confirmed iliac vein obstruction. Participants were randomly assigned to receive either endovascular therapy plus standard care or standard care alone.
Patients who received the minimally invasive procedure had significantly lower PTS severity at six months. Their disease-specific quality of life improved a clinically meaningful amount — and they also experienced important improvements in overall physical quality of life.
Because the procedure involves placing stents to reopen chronically blocked veins, patients require additional anti-clotting medication. This stepped-up blood-thinning approach is standard practice in endovascular care and was built into the study protocol. As a result, the trial found a higher rate of bleeding in the intervention group — an expected trade-off when more intensive anti-clotting therapy is used.
Importantly, most bleeding events were non-major and occurred more than 90 days after the procedure, rather than during or immediately after treatment.
“Our findings show that carefully performed endovascular therapy, supported by evidence-based medical management, can meaningfully reduce symptoms and improve daily functioning for patients with long-term blockages of important veins after a blood clot,” says Suresh Vedantham, professor of radiology and of surgery at WashU Medicine, the lead author the study and national principal investigator of the clinical trial.
“These results provide a strong foundation for clinicians as we work to deliver safe, effective, and durable treatment options for people living with the long-term consequences of deep vein thrombosis,” adds Vedantham.
The researchers acknowledge the contributions of the late Clive Kearon, a renowned McMaster thrombosis expert who helped design the study and secure early funding before his passing in 2020.
“This work reflects years of collaboration and dedication from clinicians, scientists, research staff and patients across North America,” adds Parpia.
The trial was funded by the U.S. National Institutes of Health’s National Heart, Lung, and Blood Institute.