Data presented at the Charing Cross Symposium (24–27 April, London, UK) indicate that a rounder post-stent lumen shape has a positive correlation to 12-month patient improvement, placing emphasis on the change of lumen shape from pre- to post-stent and its effect on outcome. The data were presented by Lowell Kabnick (New York, USA).
With the emergence of dedicated venous stents understanding the role of individual design elements (cell architecture, radial strength, flexibility) in the performance of the stent and, more importantly, how this therapy improves patient outcomes is critical in continuing the treatment pathway and continued improvement of stents.
Kabnick maintained that stent design matters because while area is important, for a given perimeter, lumen shape impacts area, flow and pressure, and aspect ratio is a better predictor of stent performance and patient outcomes.ith the emergence of dedicated venous stents understanding the role of individual design elements (cell architecture, radial strength, flexibility) in the performance of the stent and, more importantly, how this therapy improves patient outcomes is critical in continuing the treatment pathway and continued improvement of stents.
He solidified his point by referring to a study published in the Korean Journal of Radiology in 2015 (Stent compression in iliac vein compression syndrome associated with acute ilio-femoral deep vein thrombosis) which demonstrated that better patency is associated with rounder lumen. The study included 48 patients with iliac compression and acute deep vein thrombosis followed for an average of 20 months. Follow-up was performed with CT (computed tomography) venography and stent compression was considered significant if lumen compression was greater than 50% (aspect ratio 1:2). The study found that significant stent compression was inversely correlated with stent patency (p<0.001).
“What we are trying to determine is whether shape influences better patient outcomes. We have found that healthy veins are highly compliant and change shape dynamically when pressure and flow change. The VIRTUS study provides a rich database of patient imaging studies and outcomes. We went through it and came up with the following question: Is change in post-stenting vessel shape a predictor of patient outcomes?” he said.
Kabnick reported what he found from taking a “deeper dive” into the VIRTUS feasibility cohort with an early look at lumen shape and 12-month patient outcomes. Intravascular ultrasound (IVUS) measurements were used pre- and post-stenting to get maximum and minimum diameters and calculate aspect ratio (maximum diameter [major axis]/minimum diameter [minor axis]). He found that the median pre-stent area was 43cm vs. a median post-stent area of 130cm, a 74% increase. But the aspect ratio went from a median of 2.8 pre-stent (an ellipsoid) to a median of 1.3 post-stent (a circle), a -45% change. Increased area meant a significantly rounder shape.
“Is the area important? Sure it is, however, the question is whether the aspect ratio is a better predictor of patient outcomes. We used the VCSS [Venous Clinical Severity Score] to look at the impact and found that the mean VCSS change (pre-stent to 12 months) was 5 (p<0.001). When we looked at the relationship between post-stent vessel change and 12-month patient outcome, there was no clear pattern for area change, while change in aspect ratio is clearer,” Kabnick said.
He further noted that aspect ratio showed a linear pattern with a moderately positive relationship between decreased ellipticity and clinical improvement. “Patients with the greatest lumen change oval to round most likely exhibit clinical improvement,” Kabnick explained.
He concluded that changes to pre-stenting lumen shape may be more important than area as rounder post-stent lumen shape has a positive correlation to 12-month patient improvement as measured by VCSS.