ILUMIEN II Raises Questions as to What OCT Offers Over IVUS

Optical coherence tomography (OCT) and intravascular ultrasound (IVUS) guidance each result in comparable levels of stent expansion, according to post-hoc analysis of 2 prospective studies dubbed ILUMIEN II.

On IVUS, “the strongest predictor of early stent thrombosis and restenosis is the absolute degree of stent expansion,” Gregg W. Stone, MD, of Columbia University Medical Center (New York, NY), and colleagues write in their paper published in the November 2015 issue of JACC: Cardiovascular Interventions.

Lloyd W. Klein, MD, of Rush Medical College (Chicago, IL), while crediting the researchers for “trying to find a way in which OCT could have an impact with clinical meaning,” emphasized to TCTMD that the results show no particular advantage either way for OCT vs IVUS.

The ILUMIEN II findings were presented earlier this year at EuroPCR in Paris, France.

Stone et al compared the relative degree of stent expansion—defined as the minimal stent area divided by the mean of the proximal and distal reference lumen areas—between 2 groups:

• Patients who underwent OCT-guided stenting in the ILUMIEN I study (n = 354)
• Those who had IVUS-guided stenting in the ADAPT-DES study (n = 586)

The researchers, having randomly chosen 1 lesion per patient for analysis, propensity-matched 286 pairs (n = 572 patients) based on reference vessel diameter, lesion length, calcification, and reference segment availability.

Median degree of stent expansion after PCI (primary endpoint) was comparable whether procedures had been done using OCT or IVUS guidance, as mean stent expansion.

Rates of “any” stent malapposition, tissue protrusion, and stent edge dissection were higher in OCT cases, but when restricted to “major” occurrences, these all were “infrequent and not significantly different between groups,” the paper notes. On QCA, in-segment diameter stenosis trended greater with OCT guidance than with IVUS (13.0% vs 12.3%; P = .07) and minimal lumen diameter at the stent edges was smaller (2.3 mm vs 2.4 mm; P < .0001).

Severe complications including no reflow, abrupt closure, and perforation were similarly rare in both groups.

In addition, multivariable analysis performed in the entire cohort of patients confirmed the similarity between OCT and IVUS apart from in-segment diameter stenosis being greater for OCT (13.3% vs 11.2%; adjusted P = .009).

Building the Case for OCT

Klein, who collaborated with others on the 2013 Society for Cardiovascular Angiography and Interventions consensus statement outlining best practices for intracoronary imaging and assessment, told TCTMD in an interview that intuitively OCT would seem to have an edge over IVUS.

“Most interventionalists have a bias that, because OCT makes better pictures—the images are better and more detailed—there ought to be some reason to be using it…, especially over IVUS,” he said, noting that there is “a little bit of an art to reading an IVUS image, whereas with OCT…it’s just so obvious what you’re seeing. That’s a cool thing.”

But based on the level of evidence available now, “it’s way too soon to actually say there’s an advantage to using this,” he stressed.

The ILUMIEN II researchers are trying to build the case for OCT, Klein commented. “And they have a very difficult problem ahead of them, which is that IVUS, although it’s not as pleasing to the eye, really gets to the things you’re supposed to see intravascularly.”

Yet according to Klein, it is still unknown how the morphological information obtained with either of the 2 modalities should be used. “If you have underexpansion or malapposition or a small tiny dissection that isn’t covered, the natural reaction is to try to fix it. But we actually don’t have any idea what this means long-term,” he stressed.

Stone described the ILUMIEN II data as “reassuring,” in that they show “OCT may lead to similar acute procedural outcomes as IVUS.

“However, there were some differences, and just how good these imaging modalities are compared to angiography and each other is being evaluated in the prospective randomized ILUMIEN III trial,” he wrote in an email to TCTMD. “In ILUMIEN III we are also using a dedicated new stent sizing protocol to see if we can get even better results with OCT. Finally, if this trial is positive, we expect to perform the ILUMIEN IV trial, which will be a randomized outcomes trial to see if intravascular imaging guidance leads to improved long-term clinical results compared to angiography alone.”

Note: Stone and several coauthors of ILUMIEN II are faculty members of the Cardiovascular Research Foundation, which owns and operates TCTMD.