ABSTRACT Nearly 1 million percutaneous coronary interventions (PCIs) are performed each year in the US. Approximately 70% of these cases are considered complex and require the treatment of heavily calcified lesions, tortuous vessels, and multi-vessel disease, often with total or sub-totally occluded lesions. Many operators avoid these more complex cases, which are often not suitable for radial access approaches due to the limitations of smaller size guide catheters and lack of support required to effectively deliver coronary stents. To overcome this limitation, guide extension catheters (GEC) have been developed to help deliver stents in these challenging anatomies. GECs are currently utilized in nearly 18% of all coronary interventions. However, GECs have several key shortcomings that have prevented their usage other than as a bailout option. Specifically, current GECs are unable to access more distal tortuous lesions in 28% of cases resulting in the inability to deliver a stent in 56% of attempts. Blunt ended tubular GECs also have serious safety issues with coronary artery dissection and/or plaque or thrombus embolization. Given that GECs are used in 18% of all PCI cases, these data represent a significant volume of patients that are not treated effectively. Hence, CrossLiner Inc. has developed a novel multi-functional GEC that combines the requirement for deeper catheter intubation with a balloon microcatheter leading tip to allow crossing severe lesions in tortuous coronary vessels, followed by angioplasty to open the lesion for stenting. The combination of a GEC with a seamless transition from the outer to the inner microcatheter provides the capability for easier stent delivery which can unsheathed at the lesion as opposed to being delivered from a poorly supported proximal location. This approach enabled by the CrossLiner GEC could substantially enhance the ease of PCI in patients with complex lesions while reducing risks associated with procedural duration, radiation/contrast exposure, stent dislodgement, coronary dissection and perforation as shown with current GECs. Preliminary data support the utility of CrossLiner?s multi- functional GEC by demonstrating a significant 26% reduction in the force required to pass a 90 degree takeoff angulation and a 68% increase in intubation depth compared to the market leading GuideLiner GEC. These findings translated to a 62% reduction in the time to perform balloon pre-dilation and collectively support a likely significant increase in complex PCI success rates while simultaneously improving safety. The CrossLiner system is now ready for final refinement of performance features and process improvements which will be characterized first on bench (Aim 1) followed by in vivo assessment of safety and efficacy (Aim 2). Successful execution of these Phase I studies will appropriately position the Crossliner GEC system for full development, clinical studies, regulatory approval (future Phase II), and commercialization of this novel, highly innovative, and potentially ?game-changing? approach to improve the standard of care for complex PCI patients.