The current retrospective study comparing OCT-guided to IVUS-guided PCI in patients presenting with ACS showed no statistically significant difference between both modalities in terms of post-PCI MSA. OCT-guided PCI was also associated with a significantly higher percent stent expansion compared to IVUS-guided PCI, with lower rates of no-reflow and dissections in OCT-guided PCI group. The higher resolution of OCT compared to IVUS enables for better detection of post-procedural tissue prolapses and thrombus [32]. This was evident in the current report.
Because post-PCI MSA is the most important independent predictor for long-term freedom of early and late post-procedural MACE [33], obtaining similar post-PCI MSA with OCT-guided compared to IVUS-guided techniques as we showed is clinically relevant. This is reassuring, in that the higher image resolution advantage of OCT is not negated by a lower post-PCI MSA. Adding to the robustness of the difference in post-PCI MSA finding, it should be noted that the pre-PCI MLA of the lesions was significantly lower in the OCT-guided group.
Recently, the ILUMIEN III: OPTIMIZE PCI randomized study concluded that OCT guided PCI (using a specific reference segment external elastic lamina-based stent optimization strategy) was safe and resulted in similar MSA to that of IVUS-guided PCI. However, it included a relatively heterogenous group of patients i.e., both elective PVI and PCI in the setting of ACS [34]. The current study, albeit non-randomized, focused exclusively on patients presenting acutely with ACS
Another study compared the ability of OCT-guided PCI to angiographic guidance alone in improving post-procedural fractional flow reserve (FFR) in NSTEMI patients. It showed that OCT-guided PCI resulted in a significantly higher post-procedural FFR [16]. Importantly, post-PCI MSA in this study set out to be the best predictor of satisfactory post-PCI fractional flow reserve (more than 0.90) with receiver operator characteristic analysis.
We also explored the difference between both intravascular imaging modalities on six-months clinical outcomes (MACEs). Although the study was not powered for such an endpoint, the incidence of MACEs at 6 months was significantly higher in IVUS arm, which is not in line with a somewhat more powered multicenter randomized study (the OPINION trial) that showed similar rates of target vessel failure at 12 months between IVUS- and OCT-guided PCI strategies, but in the OPINION TRIAL, the main focus was target vessel failure and not composite MACE outcome [18].
Our finding, albeit hypothesis-generating, that OCT strategy was associated with significantly less radiation dose and a shorter radiation time is noteworthy here. In the recently published iSIGHT trial, Radiation time was numerically longer in OCT group with no statistical significance [35].
Adding to the validity of the current study’s findings, and in a stepwise multivariate logistic regression model, using either IVUS or OCT for guidance of PCI among our patient’s population turned out not to be a significant independent predictor for the occurrence of no-reflow or dissection (both are important surrogate endpoints for future MACEs) [36].
The current study is not without limitations. First, this was a non-randomized comparison of both imaging strategies; therefore, selection bias cannot be excluded. Second, the lack of an angiography-guided PCI arm is a concern. Third, the study was not powered to detect differences in clinical outcomes, and thus any differences in this domain remain hypothesis generating. Larger randomized studies with longer follow-up periods are needed to answer this clinical question.
Despite these limitations, we believe our data add to the body of evidence supporting the use of OCT-guided PCI to optimize procedural outcomes in different PCI scenarios. That’s because, as we showed, OCT seems to provide higher resolution that translates into better detection of post-procedural tissue prolapses and thrombi, and this is accomplished without sacrificing post-PCI MSA or clinical outcomes.