Endovascular crossing of Chronic Total Occlusions using impact force: An explorative design-study

Background: Chronic Total Occlusions (CTOs) are the most challenging lesions of Percutaneous Coronary Intervention (PCI). The most common failure mode is the inability to cross the lesion with a guidewire. Crossing is complicated by the lack of guidewire stiffness and the high penetration force of the fibrous proximal cap of the CTO, often causing guidewire buckling during penetration attempts. Therefore, the goal of this study was to explore a novel method to puncture the proximal cap of the CTO. Methods: Theoretical analysis and modelling of the clinical case and crossing action resulted in the selection of the "impact method", comprising the application of impact force onto the CTO that potentially causes fracture of the proximal cap without (large) environmental disturbance through an inelastic collision. This method was transformed into a functional prototype design, which was subsequently evaluated on its mechanical performance and puncture effectiveness, by means of High Speed Video (HSV) analysis, peak force measurements, and tests with different developed CTO models, representing variable CTO material characteristics. Results: The developed prototype (O 2 mm) uses a distal spring-loaded indenter (of different shapes) with a novel reload mechanism to exert impact force onto the CTO. The maximum indenter momentum and mean peak force, at 1 mm object distance and with maximized spring force, were experimentally determined at 1.3 mNs (mass 0.39 grams, mean velocity 3.4 m/s (n = 5)) and 19 N (n = 10), respectively. The puncture effectiveness of the indenter strike was found to be dependent on material characteristics of the targeted CTO model and the indenter tip shape. Proximal cap models with hard and brittle characteristics were fractured most effectively; on average in less than three indenter strikes with non-pointed indenter tip shapes. Conclusions: The impact method and prototype have shown potential to fracture fibrocalcific cap models. However, to draw final conclusions on potential (safe) endovascular crossing of CTOs, and the most optimal design (parameters) of the instrument, more knowledge on biomechanical properties of CTOs, or an in-vivo experiment, is needed. Nevertheless, it is believed that continued research and development of the method may, in time, improve the endovascular treatment possibilities of coronary CTOs.