OCT-measured plaque free wall angle is indicative for plaque burden: overcoming the main limitation of OCT?

The aim of this study was to investigate the relationship between the plaque free wall (PFW) measured by optical coherence tomography (OCT) and the plaque burden (PB) measured by intravascular ultrasound (IVUS). We hypothesize that measurement of the PFW could help to estimate the PB, thereby overcoming the limited ability of OCT to visualize the external elastic membrane in the presence of plaque. This could enable selection of the optimal stent-landing zone by OCT, which is traditionally defined by IVUS as a region with a PB < 40 %. PB (IVUS) and PFW angle (OCT and IVUS) were measured in 18 matched IVUS and OCT pullbacks acquired in the same coronary artery. We determined the relationship between OCT measured PFW (PFW(OCT)) and IVUS PB (PB(IVUS)) by non-linear regression analysis. An ROC-curve analysis was used to determine the optimal cut-off value of PFW angle for the detection of PB < 40 %. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated. There is a significant correlation between PFW(OCT) and PB(IVUS) (r(2) = 0.59). The optimal cut-off value of the PFW(OCT) for the prediction of a PB(IVUS) < 40 % is ≥220° with a PPV of 78 % and an NPV of 84 %. This study shows that PFW(OCT) can be considered as a surrogate marker for PB(IVUS), which is currently a common criterion to select an optimal stent-landing zone.