CIRSE 2019: New Data Show High Chronic Outward Force Causes Significantly More Restenosis

BIOFLEX-COF is the First In-Human Trial to Investigate the Influence of COF on Stent Patency

BARCELONA, Spain and BUELACH, Switzerland, September 11, 2019 – Twelve-month results of the BIOFLEX COF trial have demonstrated that the implantation of stents with low chronic outward force1 (COF) was associated with less neointimal hyperplasia2, consequently resulting in less restenosis. Patients treated with BIOTRONIK’s low COF, Pulsar® stent, showed significantly lower restenosis rates than patients treated with the high COF, LifeStent implant. Prof. Martin Funovics, Medical University of Vienna, Austria, presented the fullcohort primary endpoint data at the CIRSE annual conference in Barcelona.3

BIOFLEX-COF is the first randomized controlled trial (RCT) to investigate differences in clinical outcomes of nitinol stents with high versus low COF in de novo superficial femoral artery (SFA) occlusive arterial lesions. The low-COF Pulsar stent had a mean restenosis rate of 26%, while the high-COF LifeStent implant showed 35%, as measured on CT angiography (CTA) at one year (p<0.001, t-test & Mann-Whitney U test).

“We initiated the BIOFLEX COF trial to close the gap on how COF impacts the human neointima,” explained principal investigator Prof. Funovics. “These RCT data support our hypothesis that high COF leads to increased neointimal hyperplasia, which causes restenosis and increases the risk of repeat interventions for the patient. Our results suggest that COF impacts clinical outcomes and should therefore be an important factor in the choice of the stent.”

Self-expanding nitinol stents must be oversized by at least a minimal amount to ensure contact with the vessel wall and prevent migration. Once the stent is deployed, it exerts a continuous force upon the vascular wall, termed COF.4 While an animal study has found increased neointimal hyperplasia, inflammation and injury scores in vessels5 treated with high COF stents, human data were not available until now.

The investigator-initiated BIOFLEX-COF RCT enrolled 83 patients with symptomatic peripheral arterial lesions eligible for endovascular stent implantation. The patients were randomized 1:1 to either a high COF group or a low COF group. The trial’s primary endpoint is the amount of in-stent restenosis at one and two years as assessed by contrast-enhanced CTA.

“At BIOTRONIK, we develop our technologies to continuously improve patient outcomes,” commented Dr. Alexander Uhl, Senior Vice President of Corporate Marketing at BIOTRONIK. “With its unique design, Pulsar stent offers the benefits of a low COF stent and thin struts while resisting crush force: The optimal balance of radial forces keep the vessel open, increase blood flow and reduce stress to the vessel wall. This helps to decrease patients’ risk of restenosis and need for re-interventions.”


BIOTRONIK is a medical technology company that develops trusted and innovative cardiovascular and endovascular solutions. Driven by purpose and integrity, BIOTRONIK has partnered with hospitals and health systems for more than 50 years, helping to deliver care that saves and improves the lives of millions of patients with heart and blood vessel diseases. BIOTRONIK is headquartered in Berlin, Germany, and represented in over 100 countries.


  1. COF refers to the force exerted by a nitinol stent onto the vessel wall after pre- and post-dilatation.
  2. Neointimal hyperplasia refers to post-intervention vascular remodeling due to proliferation and migration of vascular smooth muscle cells in the tunica intima layer, resulting in vascular wall thickening and the gradual loss of luminal patency.
  3. Funovics M. Results of the BIOFLEX-COF RCT, comparing high vs low chronic outward force of nitinol stents in the SFA. Presented at: CIRSE 2019; September 8, 2019; Barcelona, Spain.
  4. Wressnegger A, Kaider A, Funovics MA. Self-expanding Nitinol Stents of High vs. Low Chronic Outward Force in De-novo Femoropopliteal Occlusive Arterial Lesions (BIOFLEX-COF). 2017 Dec 14;18(1):594.
  5. Funovics M. BIOFLEX-COF The Effect of Stent Radial Force. Presented at: CIRSE 2017; September 18 2017; Copenhagen, Denmark.
    Pulsar is a trademark or registered trademark of the BIOTRONIK Group of Companies.
    LifeStent is a trademark or registered trademark of Becton, Dickinson and Company or its affiliates.