Changes in coronary bifurcations after stent placement in the main vessel and balloon opening of stent cells: theory and practical verification on a bench-test model

Objective To describe changes that occur in stent morphology and structure after its implantation in coronary bifurcation. Side branch (SB) compromise after stenting of main vessel in coronary bifurcation is a major intraprocedural problem and for the long term, as a place of restenosis. Methods We created an elastic wall model (parent vessel diameter 3.5mm, daughter branches 3.5mm and 2.75mm) with 30, 45 and 60 degree distal angulation between branches. After stent implantation, struts to the side branch were opened with 2.0mm and consequently 3.0mm diameter balloons. Subsequent balloon redilatations and kissing balloon inflations (KBI) were performed. All stages of the procedure were photographed with magnification up to 100 times. Results We found that the leading mechanism for side branch compromise was carina displacement, and discovered theoretical description for expected ostial stenosis severity. Based on our model we found that displacement of bifurcation flow divider cause SB stenosis with almost perfect coincidence with our theoretical predictions. Opening of stent cells through the proximal and distal stent struts always increased interstrut distance, but never achieved good apposition to the wall. Balloon diameter increase didn’t give proportional enlargement in stent cell diameters. KBI leads to some small better stent positioning, correcting main vessel strut dislodgment from wall, but never gave full strut-wall contact. Distance between struts and wall was minimal only when the stent cell perfectly faced ostium of SB. This was also our observation that the shape of ostium of SB becomed elliptically-bean shaped after stent implantation and generally kept that shape during consequent stages of experiment. Measured diameter and area stenosis were perfectly fitted and theoretically predicted from our concept. Conclusion We have described stent-wall deformations in stent-balloon technique for treatment of coronary bifurcation demonstrating carina displacement as possibly main mechanism of side branch compromise after main vessel stenting. We have shown that KBI could not give full strut-wall contact if there is no perfect facing of stent cell and SB ostium.