Intraplaque therapies for facilitating percutaneous recanalization of chronic total occlusions

Chronic total occlusions (CTOs) are found in up to 30% of angiogramsperformed on patients with coronary disease. The technical difficulty ofperforming percutaneous coronary interventions (PCIs) in CTOs, primarilybecause of the inability to cross CTOs with a guide wire, is reflected inlow rates of PCI for CTO (approximately 9% of PCI procedures). Themain barrier to successful CTO crossing is the dense collagenous extracellularmatrix, particularly at the entrance, known as the 'proximal fibrouscap'. Current interventional strategies to overcome this barrier are basedprimarily on forceful penetration of the CTO plaque by the use of dedicatedCTO guide wires. These extra-stiff wires are designed to transfermaximal force to the tip to create a path within the plaque. However, thesewires can also cause vascular complications such as dissections; overallprocedural success rates remain modest. Several groups are working on newapproaches to actually alter the biology and structural characteristics of theCTO plaque to facilitate guide wire crossing. Preliminary data suggest thatplaque-directed therapies aimed at 'priming' it for wire crossing mayincrease PCI success in these challenging cases. New techniques for plaquemodification, either by 'softening' the collagenous matrix (collagenase) orby exposing and enlarging existing microvessels (intravascular thrombolysis, contrast injection) or by inducing new microvessels (angiogenic growthfactor[s]) are described in the present review.