Drug eluting stents (DESs) have been shown to reduce the rate of restenosis considerably, and have widely expanded treatments for various types of severe lesions and indications of percutaneous coronary intervention (PCI) [1, 2]. However, coronary bifurcation lesions, which account for 15–20 % of all PCIs, still represent a challenging lesion subset for interventional cardiologists [3, 4]. Several studies have reported that a two-stent (complex stent) strategy does not offer any advantage over a single-stent (simple stent) strategy in bifurcation lesions [5, 6]. Therefore, single-stent implantation might be the first line strategy in bifurcation lesions. Although coronary artery bypass graft surgery (CABG) has been considered the standard method for treating unprotected left main coronary artery (ULMCA) bifurcation disease according to the current guidelines [7, 8], DESs have been used with increasing frequency for the PCI of ULMCA bifurcation diseases [9, 10]. A recent intravascular ultrasound (IVUS) study indicated that the presence of incomplete stent apposition (ISA), confirmed 8 months after DES implantation, was associated with a higher rate of myocardial infarction and very late stent thrombosis (VLST) at a 5-year follow-up. [11]. An optical coherence tomography (OCT) study of bifurcation lesions treated with a single DES showed that the frequency of thrombus attachment at side-branch orifices was lower with kissing balloon inflation (KBI) as compared to the frequency of thrombus attachment without KBI, possibly because of the reduction in jailed struts [12]. The Korean multicenter registry trial demonstrated that the single DES strategy with KBI was associated with a lower rate of major adverse cardiac events (MACE) and target lesion revascularization (TLR) than the single DES strategy without KBI [13]. Some reports suggested the importance of KBI from the in vitro and in vivo findings of the optimization of bifurcation treatments [14, 15]. However, little is known about the effects of the stent expansion method and stent platform design on the clinical outcome. We hypothesized that stent thrombosis after single DES stenting may occur even after KBI owing to residual stent struts protruding into the ostial side branch called “jailed strut” in bifurcation lesions. Here, we investigated the influences of stent implantation methods and stent platform design on the ISA area caused by jailed struts at the side-branch ostium, using a bifurcated elastic coronary artery model to gain insights into more sophisticated single stenting strategies.

The main findings of this study are as follows.

(1) The three-time KBI in single stenting was effective in reducing the ISA area caused by jailed struts at the LCx ostium, compared with the one-time KBI, for the two-link Nobori stent. (2) The two-link Nobori stent exhibited a distinctly lower ISA area caused by jailed struts at the LCx ostium than the three-link Xience stent, both with three-time KBI and one-time KBI.

Bifurcation treatment is recognized as a strong predictor of stent thrombosis [18]. ISA was defined as one or more struts clearly separated from the vessel wall with evidence of blood speckles behind the strut [19]. The ISA is recognized to pose certain risks for LST and VLST [20‐23]. Recent IVUS and OCT studies in patients with LST or VLST confirmed that the ISA is associated with LST and VLST [21, 23, 24]. Hariki et al. reported that the KBI significantly reduced the jailed struts at the side-branch ostium and the frequency of thrombus attachment, possibly because of the reduction in the number of jailed struts [12]. In this study, we demonstrated that three-time KBI with single stenting in LMT to the LAD at LM bifurcation was effective in reducing ISA area caused by jailed struts at the LCx ostium. Moreover, the two-link Nobori considerably reduced the ISA compared with the three-link Xience stent irrespective of one-time KBI or three-time KBI, indicating the importance of selecting the stent platform at LM bifurcations.

The bifurcation model remains motionless during the stenting procedure, whereas the in vivo coronary artery moves owing to cardiac contraction and relaxation. Therefore, data deviations resulting from the produce in this study may be underestimated compared with in vivo situations. Nevertheless, a sophisticated bench test system would help to gain an understanding of better stent implantation strategies at bifurcation lesions.

This bench study using a three-dimensional elastic bifurcated coronary artery model revealed that three-time KBI in single stenting is effective in reducing the ISA area caused by jailed struts at the LCx ostium in comparison with the general one-time KBI. Moreover, the choice of stent platform with a larger expansion capacity of stent cell has a considerable effect on the reduction of the ISA both with one-time KBI and three-time KBI. Our findings may help to improve the coronary bifurcation intervention for better clinical outcomes.