Contemporary Interventional Bifurcation Treatment
Operators contemplating a bifurcation lesion intervention need to determine if the side branch in question is important and needs to be protected. This will in large part depend on its diameter. However, other factors also need to be considered such as the patient's overall condition, whether there is diffuse coronary atherosclerosis or not, and which angulation of the side branch is encountered before and after rewiring. In general, side branches with a diameter 2 mm should be protected. Stent implantation in the main vessel may lead to side branch compromise or occlusion due to plaque shift or other mechanisms. Long-term results have been improved with the use of DES compared with bare metal stents (BMS).1 However, even in the DES era it may be very difficult to rewire the side branch once it has been occluded, in particular if the DES in the main branch has a diameter <3 mm and is not well-suited for a wire to re-cross the stent struts. Open-cell or helical stent design will generally allow for a better re-crossing profile compared with a closed-cell design.7
The predominant technique used for bifurcation interventions employs provisional side branch stenting.8,9 The main branch is treated by implantation of a DES. The side branch is rewired (through the stent struts of the DES) and dilatation with a non-compliant balloon is performed. Side branch stent implantation only follows if deemed necessary due to dissection, plaque shift or other forms of severe side branch compromise. The geometry of the main vessel stent is protected either by a kissing balloon approach or by balloon inflation in the main branch after completion of side branch treatment. If a second stent needs to be implanted in the side branch, final kissing balloon inflation is usually performed.9 These basic principles are generally also adopted if dedicated bifurcation devices are employed. Such devices offer the promise of better side branch protection, as they usually allow for facilitated side branch access.
Kissing balloon inflation frequently poses the question of which balloon diameter to choose in order to allow for adequate stent expansion in the main branch without damaging the stent or even the main vessel itself. Morino et al. have proposed a formula to calculate the in vivo diameter of two balloons inflated in parallel in the main vessel:
R2 = D12 + D22
where R is the mean diameter of the two balloons in the main vessel and D1 and D2 are the diameters of the balloons in the main vessel and side branch, respectively.10 For example, using a 3.5 mm balloon in the main vessel and a 2.5 mm balloon in the side branch will result in a theoretical overall balloon diameter in the main vessel of 4.3 mm.
Role of Bioresorbable Vascular Scaffolds
The increased adverse event rate generally observed in bifurcation lesion treatment relates to diverse mechanisms such as incomplete stent coverage of parts of the lesion, several layers of stent struts at other parts, flow-limiting struts across the side branch ostium, or incomplete stent apposition. The Absorb™ Bioresorbable Vascular Scaffold (BVS) is made of poly-L-lactide acid (PLLA), with a strut thickness of 157 micrometres (µm) constructed as in-phase hoops with straight links, eluting everolimus.11 With regard to bifurcation lesions, it may offer several advantages. In particular, there is no long-term risk of stent thrombosis related to uncovered struts. Also, it is more flexible compared with a DES. It will not straighten the vessel and thus is not expected to change the native shear stress distribution. Over the course of 12-24 months, endothelial-dependent vasomotion appears to be restored,12 potentially further reducing the risk of late adverse events. Bioresorbable struts covering the ostium of the side branch have been observed to develop into a neointimal bridge, leaving a smooth ostial contour of the side branch.13,14