New insight to estimate under-expansion after stent implantation on bifurcation lesions using optical coherence tomography.

Optical coherence tomography (OCT) allows full volumetric segmentation of the lumen. However, for the estimation of stent under-expansion we still rely on the conventional method (CM) of single cross-sectional narrowing compared with reference vessel, likely masking true lesion significance, especially for bifurcations and tapered vessels. We, therefore, suggest a novel concept of volumetric metrics that take into account vessel tapering and major side branches and is capable of obtaining ideal lumen area for every frame of the stent by OCT. Forty-four patients with bifurcation lesions were enrolled. In volumetric metrics, expansion index was calculated as [(actual lumen area/ideal lumen area) × 100] in all frames. While minimum expansion index (MEI) was often located in the proximal segment to the major side branch, minimum stent area (MSA) by CM was frequently located in the distal segment (p < 0.001). Furthermore, the frequency of the under-expansion was significantly greater in newly metrics compared with CM [21 (47.7%) and 11 (25.0%), p = 0.045]. New metrics changed the presence of the under-expansion in 40.9% (18/44) of patients and the locations of MEI and MSA were different in 72.7% (32/44) of cases. Volumetric assessment enables to more accurately assess stent under-expansion.