The impact of IVUS guidance in treating complex lesions; are all “complex” lesions the same?

The main reason for the application of intravascular ultrasound (IVUS) in guiding drug-eluting stent (DES) implantation is because of its clinical benefit that has been shown in previous meta-analyses which included more than 30,000 patients across all coronary lesion subsets (1). Complex coronary lesions represent a unique subset which are more susceptible to adverse clinical events such as restenosis and thrombosis following percutaneous coronary interventions (PCI) in the DES era and while IVUS guidance has been reported to be favorable in treating some classes of complex lesions (2-4), the lingering question remains: what is a complex lesion? Regarding chronic total occlusions (CTOs) for instance, they have been graded in their own complexity according to: long vs. short occluded segment, extent of calcification, etc. Thus, a very short and non-calcified lesion may not be as complex as a long and severely calcified one. Likewise, bifurcation lesions could be either true bifurcations or just simply involve the ostium of the side branch. These two scenarios pose different challenges that could be resolved via imaging, but eventually their long-term outcome will be greatly defined by the extension of the pre-existing disease. Additionally, the degree of shear stress, low flow velocity and presence of multiple layers of stent struts make bifurcation lesions vulnerable to stent thrombosis (ST) and thus surrogates of their complexity (5).