Low success rates with conventional antegrade wire-based approach even in very skillful and experienced hands have been reported. There is limited published data on the success of IS CTO PCI. Werner et al. reported a 70 % primary success in IS CTOs compared to 85 % in de novo lesions [3]. Abbas et al. reported 63 % procedural success in patients with CTOs due to IS restenosis [2]. These lower success rates occur despite the presence of previously placed stents serving as a “road map” of the course of the occluded artery as well as providing some protection against vessel perforation. Failure usually results from the inability to cross the lesion with a guidewire, with a hard proximal cap making lesion engagement and penetration difficult. It can also result in sub-stent wire tracking, particularly with stiff, penetrative wires, which prevents subsequent passage of balloons and stents even if distal true lumen is reached. As reported in several studies, IS CTOs are longer [1, 2], tissue is often harder, not due to calcifications but to fibrous and compact neo-intimal proliferation. An ostial location has also been found to predict procedural failure [2]. Moreover, presence of prior stents interfere with microcatheters, balloons and new stents. Obviously, stent-fractures, undersized stents, deformed and malapposed stents might increase the difficulty to cross with wires, balloons and stents.

The hybrid strategy has been shown to be effective for increasing success rates with IS CTOs, with technical and procedural success now similar in patients with CTOs due to ISR and de novo CTOs, (technical success 89.4 % vs. 92.5 %, P = 0.43; procedural success 86.0 % vs. 90.3 %, P = 0.31). In their multicenter study, Christopoulos et al. showed that the most common crossing approach was antegrade wire escalation (41.1 %), followed by the retrograde approach (31.4 %), and antegrade dissection and re-entry (27.4 %). The CrossBoss catheter was used in 54.4 % of cases (26.7 % of de novo CTO cases) [1].

Antegrade wire escalation has been historically used as a first approach, and is still the preferred technique for crossing in-stent CTOs for most operators, although the CrossBoss is now a very helpful tool to add for improved success (Fig. 10.2). Inability to cross the occlusion with a guidewire is the main mode of technical failure, whereas inability to advance or fully inflate a balloon catheter accounts for a minority of cases. As for de novo CTOs, there is no general rule of treatment, as lesion characteristics are highly variable and hardly predictable before a proper dual injection is performed. Soft tip tapered polymer-jacketed wires (such as the Fielder XT) can be first tried a few minutes to search for any central in-stent micro channel, but our experience with this wire in IS CTOs has been deceiving. These soft wires are less steerable and may also slip outside the stent structure, in the sub-intimal plane. Therefore, escalation goes quickly to stiffer polymer jacketed such the Pilot 200 with a special attention not to track the wire under the stent struts. But the most useful guidewire family in that situation are the high torque and hard tip wires like the Miracle 12 which provide a very acute control and torque of the tip to allow the wire to stay within the stent. Because the wire is non-tapered, it is less likely to exit through a stent strut. Several orthogonal views should be taken in order to visualize the wire track within the stent (Fig. 10.2). Hard and tapered wires can be interesting to puncture the proximal cap or go for a short distance trough very hard tissue. In our experience, the Confianza Pro 12 has very good torque control and should be preferred to polymer-jacketed stiff tapered tip like Progress 200 T which can easily slip under the struts. Nevertheless, the latter wire, due to its slippery characteristics, is interesting during cases of very fibrotic and hard restenotic tissue and could facilitate wire progression. Finally, the Gaia family wires have emerged as very efficient wires for in-stent occlusions. Given that the ambiguity of the vessel course is limited with IS CTO, the Gaia wires, especially the less tapered Gaia 3rd version, can be very effective; the wire is pushed up to deflection of its tip. Then, the wire is pulled and redirected away from the resistance. Several orthogonal views should be taken to confirm that the wire stays within the border of the occluded stents.

Although very useful in CTO PCI, knuckled wires should be avoided as a first strategy because of the absence of cleavage space within an IS CTO. Such knuckled wires can track under the stent struts or in the subintimal sub-stent space, resulting in crossing outside the stent structure. Although it has been described [7] with successful stenting in the sub-adventitial layer under the previous occluded stent, extreme caution should be applied for the following reasons: (1) although sub-intimal stenting appears to be safe in the majority of cases, stenting outside a previously deployed stent can lead to substantial overstretching of the adventitia, as a result of non-compressible in-stent tissue leading to potential perforation. (2) Distal re-entry can be laborious and (3) outcomes are unknown with this technique. The key point of a wire-based strategy is to enter the proximal cap in the “true lumen” and avoid to track underneath the stent struts. If the cap is blunt and hard, inflating an OTW balloon (adapted to the size of the proximal vessel) a few millimeter upstream to the in-stent CTO segment can help, as with the performance of an anchoring balloon technique. The back-up support for wire puncture is therefore stronger. Moreover, this technique allows a very good coaxial alignment of the wire in order to puncture the center of the proximal cap instead of the sub-stent space. The Venture catheter is a steerable and orientable micro-catheter that sometimes can be used successfully used with or without Stingray guidewire in that kind of situation [8]. Again, orthogonal angiographic views should be taken most of the time without contrast injection in order to confirm that the wire tracks within the stent borders. If the wire crosses into the distal true lumen but no microcatheter or balloon can cross the occlusion, several solutions could be sought. The first is the CrossBoss catheter that could cross as described later, even over the wire [9]. But in cases of very fibrous and hard tissues we recommend the use of the Tornus or the Corsair microcatheters that can be screwed into the lesion using counter-clockwise motion [10]. After crossing with the microcatheter, the crossing wire can be exchanged for a high support soft tip wire to complete the procedure. However, if the wire crossed outside the stent structure and re-entered more distally, it is wise not to pursue with Tornus or Corsair, as both can get entrapped within the stents struts. In such cases, sequential balloon dilation starting with a very small balloon is the preferred approach, leading to strut enlargement and ability to deliver subsequent new stents in the segment.