Carina shift versus plaque shift for aggravation of side branch ostial stenosis in bifurcation lesions: volumetric intravascular ultrasound analysis of both branches.

BACKGROUND Although carina shift and plaque shift are suggested as mechanisms of side branch ostial (SBo) compromise after main vessel (MV) stenting in bifurcation lesions, there are few direct evidence. Our purpose was to confirm the mechanism of SBo compromise after MV stent implantation. METHODS AND RESULTS Intravascular ultrasound images of both MV and SB before procedure and immediately after MV stenting were evaluated in 44 bifurcation lesions. Three 5 mm segments of interest were volumetrically analyzed: the proximal MV, distal MV, and SBo. SBo compromise was defined as a lumen volume decrease, carina shift as a vessel volume decrease, and plaque shift as a plaque volume increase in the SBo segment after MV stenting. The vessel volume increased, and the plaque volume decreased significantly in the proximal MV and distal MV. In contrast, in the SBo, the vessel volume decreased (53.0±17.5 mm(3) versus 50.4±16.2 mm(3); P<0.001), with the accompanying small increase in plaque volume (23.0±9.8 mm(3) versus 23.4±9.8 mm(3); P<0.001). The SBo compromise was significantly correlated with the carina shift (r=0.941; P<0.001), but not with the plaque shift (r=-0.019, P=0.90). Distal MV lumen volume increase was significantly correlated with SBo compromise (r=0.555; P<0.001) and carina shift (r=0.557; P<0.001), but not plaque shift (r=-0.228; P=0.14). CONCLUSIONS Our study indicates that carina shift, not plaque shift, is the major mechanism of SBo compromise after MV stent implantation, and the carina shift is primarily influenced by distal MV lumen expansion.