Sub-Intimal Tracking and Re-Entry and Investment Procedures: Current Applications and Future Directions

In seeking to improve upon chronic total occlusion (CTO) percutaneous coronary intervention success rates and minimize risk, CTO modification procedures (investment procedures) have been developed and utilized with increasing frequency. Two key techniques have emerged: subintimal tracking and re-entry (STAR) and subintimal plaque modification (SPM). Both require a staged approach with an index procedure for plaque modification and a second procedure weeks later for stenting. Both approaches require entry and wiring with a polymer-jacketed wire in the extra-plaque space, yet unlike SPM, which exclusively requires angioplasty of the extra-plaque space throughout the CTO segment, STAR also involves re-entry into the true luminal distal to the CTO before angioplasty. STAR and SPM, in many ways, represent a paradigm shift in our approach to CTO percutaneous coronary intervention from a 1-step to a 2-step approach in complex cases. In this review, we discuss the technical aspects of the procedures, and controversies and ongoing trials pointing to the future of these techniques. We also highlight non-device-based and intravascular ultrasound-based approaches to anterograde dissection and re-entry, which add to the CTO operator's toolkit for challenging cases.