Sub-intimal tracking and re-entry and investment procedures: current applications and future directions.

In seeking to improve upon CTO percutaneous coronary intervention (PCI) 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 (EPS), yet unlike SPM which exclusively requires angioplasty of the EPS throughout the CTO segment, STAR also involves re-entry into the true lumen distal to the CTO before angioplasty. STAR and SPM in many ways represent a paradigm shift in our approach to CTO PCI from a 1-step to 2-step approach in complex cases. In this review, we discuss the technical aspects of the procedures, as well as controversies and ongoing trials pointing to the future of these techniques. We also highlight non-device-based and intravascular ultrasound-based approaches to antegrade dissection and re-entry, which add to the CTO operator's toolkit for challenging cases.