Comparative analysis method of permanent metallic stents (XIENCE) and bioresorbable poly-L-lactic (PLLA) scaffolds (Absorb) on optical coherence tomography at baseline and follow-up

Aims: Fully bioresorbable Absorb poly-L-lactic-acid (PLLA) scaffolds (Abbott Vascular, Santa Clara, CA, USA) are a novel approach for the treatment of coronary narrowing. Due to the translucency of the material (PLLA), the optical coherence tomography (OCT) measurement methods used in the ABSORB trials were unique but not applicable for permanent metallic stents. When the Absorb scaffold and metallic stents are compared in the context of randomised trials, it is challenging to compare the two devices using the conventional methods. The primary purpose of this report is to explain the biases in conventional methodologies applied for metallic stents and for PLLA scaffolds at baseline and follow-up, and to propose a new standard methodology that enables us to compare two different devices using an almost identical and methodological language. Methods and results: A consensus amongst multiple core labs and expert researchers of OCT was reached on a new standard OCT measurement methodology that enables us to compare these two different devices. In brief, the proposed OCT methods are summarised as follows. 1) Both endoluminal and abluminal scaffold/stent contours should be traced. 2) Consistently, endoluminal and abluminal incomplete stent apposition areas should be measured. 3) The area occupied by scaffold/stent struts should be quantified directly or virtually. 4) The strut area should be systematically excluded from the flow area as well as the neointimal area. 5) Additional information on the degree of embedment could be reported using the interpolated lumen contour. Interobserver variability of the proposed method was excellent (intraclass correlation 0.89-100). Conclusions: A standardised OCT measurement methodology is proposed. This should be implemented in ongoing and future trials comparing the Absorb scaffolds and metallic stents.