Subintimal

Subintimal refers to the space within a blood vessel wall that lies between the intima and the media. Under normal anatomy, the subintimal space is a potential space that remains collapsed, but during endovascular procedures it can be created or exposed when a dissection plane is formed by a guidewire or catheter. This subintimal space is most commonly discussed in the context of chronic total occlusion (CTO) interventions, where crossing the lesion intraluminally is not feasible.

In endovascular practice, a subintimal pathway can be used to bypass an occlusive plaque. The goal is to create a new lumen within the subintimal space that traverses the occlusion, followed by reentry into the true lumen distal to the lesion to restore antegrade blood flow. Techniques that utilize the subintimal approach include subintimal tracking and reentry (STAR) and controlled antegrade and retrograde subintimal tracking (CART), with variations such as reverse CART that combine antegrade and retrograde strategies to facilitate reentry. Reentry devices and specialized wires aid in reentering the true lumen after traversing the subintimal tract.

Risks and limitations associated with subintimal techniques include propagation of dissection, vessel perforation, or creation of a subintimal hematoma that can compress the true lumen. There is also a potential for occlusion of branch vessels, distal embolization, and restenosis. Imaging guidance with intravascular ultrasound (IVUS) or optical coherence tomography (OCT) is often used to plan, guide, and assess the strategy, as well as to verify lumen integrity after reentry. Overall, subintimal techniques can improve procedural success in complex CTOs but require careful consideration of risks and meticulous technique.