Fresh data from the VIRTUS feasibility study presented at the Vascular Interventional Advances (VIVA) annual conference 2016 (18–22 September, Las Vegas, USA) suggest that venography may underestimate the severity of venous lesions and that intravascular ultrasound (IVUS) may be a more accurate method for assessing lesion severity and proper venous stent size.
The results were presented by Stephen Black, Guy’s and St Thomas’ Hospital, London, UK, who told delegates that the VIRTUS comparison of IVUS and venography is consistent with that previously seen in the VIDIO study, in which IVUS detected nearly twice as many iliac/common femoral vein obstructions than multiplanar venography in patients with advanced venous insufficiency.
“The current analysis we are looking at is in the context of the increasing importance of venous stenting and the undeniable binary nature of venous disease outcomes, in that treatment either works or it does not. We need to predicate venous stenting on two requirements,” Black explained. “The first is the identification of a suitable target lesion and the second is precise deployment of an appropriately-sized stent. We know that the majority of our investigations have been based on venography in the past and certainly this is still the gold standard, but more recent data have suggested that IVUS may play a role in defining lesion severity with more accuracy, and help with stent placement.”
The VIRTUS study was designed to assess the performance of the Vici venous stent system (Veniti) in achieving patency of target venous lesions up to 12 months post-stent placement. It is a prospective, multicentre, single-arm non-randomised trial, enrolling 200 patients at up to 45 sites worldwide. The patients enrolled all had clinically-significant chronic, non-malignant obstruction of the iliofemoral venous segment, with the first 30 involved in the feasibility study.
Black continued, “The current analysis was designed to evaluate the relative value of venography and IVUS in identifying venous lesions, quantifying severity, and sizing stent to the reference vessel. In this regard, the VIRTUS feasibility cohort provides a small but well-studied series of patients on which to base this analysis.”
There was a predominance of female patients (24 female, six male) and majority of patients (63%) were post-thrombotic. The majority of the lesions treated (83%, n=25) were on the left side, and extended from the common iliac vein down to the common femoral vein in 37% (n=11) of the patients, requiring stent extension below the inguinal ligament. The trial specifically excludes patients with extensions into the inferior vena cava, and extension was not recommended below the level of the profunda and femoral vein confluence into any of the inflow vessels.
Venogram requires multiple angles and views to detect and characterise lesions, and the percentage of stenosis is more difficult to quantify than with IVUS, Black said, meaning that “identification and quantification of a lesion is sub-optimal when using venogram”.
While venogram can be used to calculate target lesion diameter by assessing reference vessel diameter, “IVUS has added a further dimension to this by not only being able to look at diameter reduction, but also looking at a difference in area, which may be more sensitive. This is an area which we are looking at as to whether this is more valuable in predicting which lesions need a stent,” Black explained.
Pre-procedure, venogram and IVUS measurements of minimum luminal diameter were highly correlated (r2=0.587). Black reported that, on average, venogram minimum luminal diameter measurements were very similar to IVUS measurements, with an average difference of 0.2±1.7mm, venogram measurements being slightly lower. Measurements of stenosis severity were also highly correlated (r2=0.533), and venogram percentage diameter stenosis was very similar to IVUS, with an average difference of 2.7±12.8% and venogram slightly underperforming IVUS.
The degree of stent oversizing was greater for venogram than for IVUS (mean of 18.1±22.9% [mean 1.8±3.4mm] for venogram vs. 12.5±16.6% [mean 1.5±1.6mm] for IVUS), which Black attributed to “a mild underestimation of reference vessel diameter by venography, which may be associated with post-procedural pain in some patients.”
The most important finding, Black suggested, was that post-stent restenosis percentage was not highly correlated between venography and IVUS (r2=0.199). “This relatively low correlation can be explained by several cases where moderate residual intra-stent stenoses were missed by venography,” Black said. Residual stenosis averaged 4±12% greater on IVUS. “This may have implications on long-term clinical outcomes in this patient group if a stent is left without post-dilation to appropriately expand the stent,” noted Black.
“In addition, I would add that IVUS is undoubtedly valuable in reducing radiation exposure in this patient group, and I think that this will become more important as we progress further in understanding this patient set.”