Coronary bifurcation lesion (CBL) is a narrowing of coronary artery adjacent to, and/or involving the origin of, a significant side branch. CBLs encompass a wide variety of anatomic subsets and clinical scenarios, from left-main bifurcation with a significant amount of myocardium at risk to a small branching lateral branch with a negligible amount of myocardium at risk. CBLs account for approximately 15% to 20% of all cases requiring percutaneous coronary intervention (PCI).[1] Catheter-based therapies can be technically challenging in terms of adapting available devices and strategies to the anatomy to restore vessel patency while preserving the fractal geometry of the bifurcation itself. Often, PCI of a CBL is associated with a lower prevalence of procedural success and higher prevalence of complications, thrombosis, and restenosis, than PCI of a non-bifurcation. Thus, safe and efficacious treatment strategies for CBLs are important. Considerable progress has been made in CBL treatment thanks to rapid development of stenting strategies/technologies, a new generation of antiplatelet agents, intravascular imaging and coronary physiology, as well as deeper understanding of the abnormal flow dynamics around bifurcated areas.[2,3] These developments have resulted in fewer adverse clinical outcomes. Here, we discuss techniques and evidence for PCI of CBLs. Stenting strategies for CBLs Several studies have demonstrated that a stepwise, layered, provisional stenting approach with bail-out side branch stenting is similar (or even superior) to the upfront 2-stent technique if treating a CBL. Recent studies have revealed comparable results with stepwise provisional and systematic dual-stenting in true left-main bifurcation lesions. Therefore, current guidelines and consensus statements recommend a provisional stenting strategy as first-line treatment for most CBLs except for those with complex anatomy and diffuse atherosclerotic involvement of the main vessel and side branch.[4] The provisional stenting strategy emphasizes the versatility of this approach, which allows adjustment of the treatment plan according to CBL complexity. This strategy starts with stent implantation in 1 branch and implantation of a second stent in the other branch only if indicated.[5] In a review article of this issue, Choo and Gurupparan[6] (Cardiac Vascular Sentral Kuala Lumpur, Malaysia) describe the key steps of the provisional stenting approach. However, release of the main-vessel stent often causes side branch occlusion because of shifting of the main-branch plaque or a change in the location of the carina, which leads to potentially fatal arrhythmias and perioperative myocardial infarction. Several innovative approaches have been reported as strategies for active protection of side branches: jailed wire, jailed balloon, balloon-stent kissing, and jailed Corsair. However, these approaches yield more frequent restenosis and repeat revascularization at the ostium of the side branch. Drug-coated balloons (DCBs) are a novel treatment strategy for coronary artery disease. They are based on the rapid and homogenous transfer of antiproliferative drugs into the vessel wall during inflation of a single balloon containing a lipophilic matrix without use of permanent implants.[7] Combined use of a provisional stenting technique and DCB to treat true CBLs is very attractive, and might improve clinical outcomes.[8,9] A provisional stenting strategy is the most common default strategy. Two-stent technique (eg, T-stenting, T and protrusion, crush technique, culotte, simultaneous kissing stents, V-stenting, and Y-stenting), which differ in the amount of metal protruding into the main branch, use of a first kissing balloon, and/or the choice of stenting the side branch as the first vessel, is preferred in certain subsets of complex CBLs. The goal of these 2-stent techniques is to provide maximal apposition to the vessel wall with effective drug delivery if drug-eluting stents are used. One of the most widely evaluated upfront 2-stent PCI technique for CBLs in recent times, the “double-kissing” (DK)-crush method, was found to elicit favorable results in a series of randomized clinical trials (DKCRUSH I to VII) upon comparison with provisional and other 2-stent technique for CBLs.[10] In a review article in this issue, Kwan and Lin[11] (Lenox Hill Hospital/Norwell Health, USA) evaluated all clinical trials and studies on DK crush. Specifically, DK crush was superior to classic crush (in the DKCRUSH-I trial) and to provisional stenting (in the DKCRUSH-II trial) in true non-left-main bifurcation lesions. DK crush was also superior to culotte (in the DKCRUSH-III trial) and provisional stenting (in the DKCRUSH-V trial) in unprotected left-main bifurcations. Moreover, DKCRUSH-IV, VI, and VII are trials investigating the functional results of DK crush. Even though PCI has evolved with different techniques for CBLs, optimal treatment in each individual case is controversial due to the high anatomic complexity and specific morphology of each CBL. A better algorithm for risk stratification and treatment based on DEFINITION criteria is available.[12] Intravascular imaging and coronary physiology of CBLs Angiographic ambiguity in visualization of lesions due to overlapping of the main vessel and side branch can lead to suboptimal stent deployment in complex CBLs.[13,14] Intravascular imaging, including intravascular ultrasound (IVUS) and optical coherence tomography (OCT), can provide essential information during procedure planning to ascertain anatomy and lesion preparation to check wire positions and lesion coverage after stent implantation, and to evaluate final expansion of the stent and vessel, which leads to improvement in clinical outcome. In a review article, Leesar et al[15] (University of Alabama, USA) summarized the role of IVUS and OCT for assessment of stenosis and stent optimization, and discussed new insights into the role of IVUS- and OCT-guided stenting in patients with CBLs. Studies have shown that IVUS-guided PCI of bifurcations might reduce major adverse cardiovascular events (MACEs). A multicenter study of bifurcation registries in South Korea showed, for the first time, that IVUS guidance during PCI of bifurcations might reduce 4-year mortality significantly compared with that using conventional angiography-guided PCI.[16] Reassuringly, Chen et al[17] clarified that IVUS use following systematic 2-stent techniques for CBLs, from the data of a propensity score-matched population, was associated with a reduction in stent thrombosis (particularly a reduction in late stent thrombosis) and resulted in a significant reduction of ST-elevation myocardial infarction. In addition, a meta-analysis from 5 studies involving 7830 patients with CBLs showed that IVUS-guided revascularization could reduce the incidence of MACEs in early follow-up and cardiac death in late follow-up compared with that using an angiography-guided revascularization strategy. The ongoing randomized DKCRUSH VIII trial will evaluate differences in efficacy and safety between IVUS-guided and angiography-guided DK-crush stenting in patients with complex CBLs according to DEFINITION criteria, thereby providing IVUS-derived criteria to define optimal DK-crush stenting for CBLs of high complexity.[13] The advent of OCT has provided some unique advantages thanks to its very high resolution. OCT can generate automatically contoured luminal areas across the variable geometry of CBLs.[18] Thus, OCT is a promising guidance method for PCI of CBLs from planning the strategy, to guidance during PCI and, finally, checking the interventional result. Development of 3-dimensional (3D) OCT allows better evaluation of coronary anatomy (particularly of the side branch ostium that is difficult to visualize by 2D OCT) to further improve the value of this technique in guiding PCI in these patients.[19] European Trial on Optical Coherence Tomography Optimized Bifurcation Event Reduction (OCTOBER) is the first adequately powered clinical trial aimed to show if routine OCT-based guidance of stent implantation improves clinical outcomes compared with standard angiographic-guided implantation in CBLs.[20] The forthcoming results will provide more evidence for the role of OCT in complex CBLs. Knowledge of how to achieve optimal flow dynamics in CBLs is increasing. Fractional flow reserve (FFR) can guide treatment strategy, simplify the procedure, and reduce unnecessary complex interventions. In the DKCRUSH-IV trial, changes in side branch FFR were compared between patients undergoing DK crush versus provisional stenting for true CBLs.[21] The DKCRUSH-VI trial showed that angiographic guidance and FFR-based guidance of provisional stenting of true CBLs provided similar clinical outcomes at 1 year.[22] The DKCRUSH-VII trial found that a post-PCI FFR ≤0.88 predicted a higher incidence of target-vessel failure through 3-year clinical follow-up.[23] Taken together, a compelling body of evidence has shown that use of intravascular imaging and coronary physiology during PCI for bifurcations leads to optimal stenting results and improves clinical outcomes. Researchers and interventional cardiologists may engage with these technological advances to provide more robust data on identifying clinically important strategies. Dual antiplatelet therapy (DAPT) for PCI of bifurcations The optimal duration of DAPT (defined as aspirin plus a P2Y12 inhibitor) in the setting of PCI for bifurcations to maintain the subtle balance between ischemia and bleeding risk is a challenge for physicians. In the Combined Insights From the Unified RAIN and COBIS bifurcation registries (BIFURCAT) encompassing 5537 patients, extended DAPT (>12 months) was associated with a lower incidence of MACEs compared with that using standard DAPT (6–12 months), driven by a reduction of all-cause death in patients with acute coronary syndrome (ACS) but not in patients with chronic coronary syndrome (CCS) after a median follow-up of 2.1 years.[24] Similarly, MACEs occurred less frequently in the extended DAPT group as compared with those in the short-DAPT (<6 months) group and standard DAPT group in ACS patients and CCS patients in the Euro Bifurcation Club registry,[25] as well as in the Korean Multicenter Angioplasty Team (KOMATE) registry and Korean Coronary Bifurcation Stenting (COBIS) registry.[26] Most studies have advocated use of extended DAPT in such high-risk patients because it has been shown to reduce ischemic events compared with standard DAPT. With regard to the choice of P2Y12 inhibitor while treating a patient using PCI for bifurcations, use of potent inhibitors instead of clopidogrel could mitigate ischemia risks. However, the beneficial effect of extended DAPT and use of a potent P2Y12 inhibitor in reducing the risk of MACEs seems to be coupled with an increased risk of bleeding (especially in patients with a high risk of bleeding). Therefore, carrying out large randomized trials, targeting specifically patients undergoing PCI for bifurcations and comparing short-term versus long-term DAPT regimens as well as the use of potent P2Y12 inhibitors, seems necessary. CBLs remain fascinating and challenging subsets of lesions in interventional cardiology. In this issue, a clinical research article by Sheiban et al[3] (P. Pederzoli Hospital, Italy) and a meta-analysis by Kan et al[27] (Nanjing First Hospital, China) note that the broad anatomic spectrum and pathologic spectrum of CBLs are responsible for the complexity of these lesions. These articles reflect the discovery and advances in CBL intervention. PCI methods for bifurcations have evolved substantially in the last decade, thereby resulting in improvements in CBL management. Guidelines for clinical practice are crucial to improve the procedural quality and clinical outcome, and continue to evolve owing to the rapidly changing landscape of therapeutic options.[28] The Chinese Society of Cardiology have published the first guideline on percutaneous treatment for coronary left-main bifurcation lesions to optimize procedural outcomes in patients with CBLs in China.[29] However, treatment of CBLs is controversial, and multiple technical strategies have been proposed. Nevertheless, continuous refinement of stenting techniques and accumulation of related evidence of bifurcations represent a major clinical need. Tailoring a strategy based on CBL anatomy and patient characteristics will have a greater role in future routine clinical practice. Funding None. Conflicts of interest None. Editor note: Yaling Han is the Editor-in-Chief of Cardiology Discovery. The article was subject to the journal’s standard procedures, with peer review handled independently by this editor and her research groups.