"Where we didn't see a difference was ischemia driven, target vessel revascularization," he added. "And part of that, I think, came down to COVID, because when we looked at the TVF rates before COVID, they were exactly where we expected. But during COVID, everything completely flattened, and it kind of makes sense because it was hard to get to the hospital. Patients were reluctant, there was lack of healthcare resources. So target vessel revascularization, which is a behavior, really became limited. And so patients didn't present with angina. They managed things at home. Things took a little bit longer, but probably the greatest take-home message for me was that stent thrombosis where a stent just clots off sporadically was much lower, 66% lower in the OCT guided arm." 

Ali said OCT offers high-resolution imaging inside the artery and can easily visualize tissue protrusion, malopposition of stent struts, untreated focal reference disease and dissection, all things he says angiography misses. 

"So by picking it up and treating it, we were able to eliminate those risks and found that that ultimately related to a long-term benefit in stent thrombosis. So the take home message really is that OCT guidance led to a safer procedure," Ali explained.  

Key findings of the ILUMIEN IV trial

The ILUMIEN IV trial was the largest global, multicenter, randomized, control trial ever conducted to assess the efficacy of OCT guidance compared to angiography guidance, with 2,487 patients. Ali discussed the key findings of the study:

   • Improved Stent Area: The study demonstrated that OCT guidance led to an increase in the minimal stent area during PCI, indicating better stent expansion and optimization of the procedure.

   • Reduced Complications: Ali highlighted the significant reduction in procedural complications when OCT was used. These complications included major dissection, malopposition, tissue protrusion, and untreated focal reference segment disease. 

   • Long-Term Benefit: The trial also examined outcomes at two years post-PCI. While there were no significant differences in target vessel failure between the OCT and angiography-guided groups, an intriguing revelation emerged. Ali explained that when examining-specific components of target vessel failure, there were substantial reductions (ranging from 20% to 40%) in cardiovascular death and target vessel myocardial infarction. These findings aligned with previous intravascular imaging studies.

   • Stent Thrombosis Reduction: One of the most striking outcomes was the substantial reduction in stent thrombosis, which is the sudden clotting of stents. In the OCT-guided arm, stent thrombosis rates were 66% lower than in the angiography-guided arm. This marked a significant improvement in patient safety.

The impact on OCT in clinical practice

An important question arising from the ILUMIEN IV trial results is whether it will impact the wider adoption of intravascular imaging techniques like OCT. Ali acknowledged that the adoption of OCT and intravascular ultrasound (IVUS) has been relatively slow. However, he remained optimistic, pointing out that there has been a 60% increase in the use of intravascular imaging from 2013 to 2019.

"Nothing in medicine happens overnight. Even statins took 10 years to really be integrated. So these things are slowly being integrated into practice, and I think the totality of evidence is now getting towards the point at which this should get to the guidelines at a level one evidence, and then hopefully that'll swing the pendulum. The one thing to remember about this is an adjunctive technology, and so whenever you have an adjunctive technology, it's easy to say, I can get away around it. But now with ILUMIEN IV, along with the other late-breaking trials presented at ESC, the totality of evidence is really overwhelming," Ali said.