Extension distance mismatch--an unrecognized factor for suboptimal side branch ostial coverage in bifurcation lesion stenting.

Background: The unsatisfactory side branch (SB) ostial strut coverage remains a problem in coronary bifurcation stenting. Both the surplus and lack of struts at SB ostium may be the causative mechanism. We propose that the inability of available stents to cover the "extension distance" of the bifurcation region is the cause of in-stent restenosis.
Methods: The extension distance (ED) is defined as the maximal distance at the carina tip, which must be covered by the stent struts to ensure optimal coverage of the main branch (MB) and SB openings. A mathematical model was created, representing the key factors that govern geometrical reconfigurations after stent implantation in bifurcations. There are two options--with and without bifurcation region deformation. The theoretical assumptions were tested on a bifurcation model (soft polyvinylchloride polymer tubes) permitting free wall deformations and the following parameters: Parent Vessel, MB, SB diameters of 3.5, 3.0, and 2.5 mm, respectively, with an angle of 45 degrees between the MB and SB. After stenting, final KBI with 3.5 mm and 3.0 mm balloons was performed up to 20 atm.
Results: After the carina displacement, the ED, which has to be covered, is considerably smaller if the suboptimal result (DS >50%) at the SB ostium is acceptable. The maximal EDs from the bench test measurements are: Vision, Abbott Vascular - 5.62 mm +/- 0.04; Liberte, Boston Scientific Corp. - 5.2 mm +/- 0.03; Chopin2, Balton - 4.58 mm +/- 0.05; Volo, Invatec - 4.41 mm +/- 0.04; Driver, Medtronics - 4.39 mm +/- 0.04; BxSonic, Cordis, J&J - 4.48 mm +/- 0.05. The theoretical maximal ED of the model is 6.91 mm-28-62% larger than actually observed with different stents.
Conclusions: The achievement of perfect ostial coverage of the SB is unsatisfactory with most of the currently available stents, especially when poststenting excessive dilation of the ostium of the SB is performed.