Background:It is believed that cutting balloon angioplasty (CBA) in treatment of in-stent restenosis (ISR) result predominantly in additional stent expansion and, to a minor extent, in a compression of neointimal tissue. However, longitudinal redistribution of tissue, which is a major mechanism for lumen expansion after balloon angioplasty or stenting, may also play a role for CBA in ISR. Method:The present study investigated the mechanism of lumen expansion by CBA. Intravascular ultrasound examination was performed before and after intervention in 40 lesions treated with CBA for ISR. We measured the vessel, lumen, and stent area at the site of minimum lumen area (MLA), as well as slices by 1mm intervals in segments that were 5mm proximal and distal to the MLA. We calculated plaque and neointima area. Result: Lumen and stent volume increased significantly along the entire segments, especially at MLA site (2.84짹1.24mm3 to 6.41짹1.87mm3, 7.39짹1.75mm3 to 8.82짹1.93mm3, respectively; p<0.0001). Neointima volume decreased along the entire segments, but reached significance only 2mm proximal and distal from the MLA site. The relative contributions of additional stent expansion and neointimal compression to lumen enlargement was 40.3% and 59.7%, respectively. Lumen expansion was correlated more strongly with neointimal compression at the distal segments (r=0.754 vs. 0.396), whereas more strongly with additional stent expansion at the proximal segments (r=0.735 vs. 0.558). Plaque volume decreased at the distal segments and increased at the proximal segments, but did not reached significance. Vessel volume increased along the entire segments and reached significance at the proximal segments. Conclusion:The mechanism of CBA is a combination of additional stent expansion and neointima compression. Contrary to deNovo lesions, neointima redistribution was not observed. However, plaque behind the stent redistributed proximally and resulted in vessel expansion.