PCI of CTOs is challenging. It is associated with low success rates, increased restenosis and reocclusion. CTOs of arteries are more challenging lesions to treat with angioplasty and stenting as compared to stenotic vessels primarily on account of the difficulty in guiding the wire across the lesion. Angiography alone cannot differentiate between the occluded lumen and the vessel wall and to characterize the content of the occlusion. Angiography provides a two-dimensional image of contrast-filled lumen, and does not allow an accurate assessment of the plaque.

OCT is a high resolution imaging technique that can improve the understanding of the vascular response after stenting of chronically occluded vessels. OCT correctly identifies tissue composition within the CTO, such as the presence of collagen and calcium and can identify intraluminal microchannels. OCT imaging of CTO anatomy and tissue characteristics can possibly result in significant improvements in PCI interventions by providing novel guiding capabilities.

In the ACE-CTO study, OCT was performed 8-months post stenting. High rates of stent strut malapposition and incomplete stent strut coverage were observed after CTO PCI using EES. The study highlighted unique challenges associated with stent implantation in CTOs.

The PRISON-IV trial showed inferior outcome in patients with CTOs treated with the ultrathin-struts (60 μm for stent diameter ≤ 3 mm, 81 μm >3 mm) hybrid-sirolimus eluting stents (SES) compared with everolimus eluting stents (EES, 81 μm). A recent study evaluated if the use of smaller stents (≤3 mm) was responsible for the inferior outcome reported in the trial. The study population was divided according to the different size of stents implanted in those receiving only stents with diameter ≤3 mm (Group-A, 178 patients), only stents >3 mm (Group-B, 59 patients), and those receiving stents of both sizes (Group-C, 93 patients). OCT was performed in 60 patients at follow-up, and documented a mild trend toward lower values of minimum in stent area in Hybrid-SES arm of Group A (4.4 ± 1.02 mm2 vs 5.0 ± 1.28 mm², respectively, P = 0.16).

OCT can thus provide significant information in CTOs.