We reported successful revascularization for long CTO lesions with very poor run-off target vessels using the EXCAVATOR technique, which brings the IVUS as far distal as possible to the BTK CTO and uses parallel wiring to allow antegrade guidewire passage to the distal true lumen under IVUS guidance. We previously reported the feasibility of EVT for FP CTO using the AnteOwl IVUS-guided approach and described the method used to perform AnteOwl IVUS-guided intraplaque wiring in FP CTO (Hayakawa et al. 2021). We converted IVUS images into angiographic images to navigate the second guidewire through an intraplaque route under IVUS observation from the subintimal space using the bias between asymmetrical structures of the IVUS transducer and IVUS guidewire. Using this technique, the target true lumen on either side of the IVUS catheter could be converted on the angiographic image, and if the guidewire was advanced in that direction, the guidewire could pass through the true lumen. However, to the best of our knowledge, this is the first report of the use of AnteOwl IVUS in BTK CTO intervention.
The primary strategy for BTK CTO is generally to use antegrade wiring; however, a previous clinical studies reported a relatively high rate of antegrade guidewire crossing failure (Kokkinidis et al. 2020; Tan et al. 2021). Various retrograde approaches have improved the success rate of the procedure in BTK CTO; however, lesions with poor distal target vessels are extremely difficult to treat with retrograde approaches (Schmidt et al. 2017). In the two cases experienced, distal target vessels were scarce, making it difficult to use the retrograde approach.
To overcome these issues associated with treating complex BTK CTO lesions, we devised a novel antegrade AnteOwl IVUS-guided wiring technique called the EXCAVATOR. AnteOwl is a novel IVUS with an asymmetrical structure of the proximal transducer and IVUS wire, facilitating the reflection of IVUS findings onto angiographic images to allow accurate navigation of the second guidewire into the intraplaque route. AnteOwl has a small profile and crossable catheter, durable hydrophilic coating, and high-resolution imaging.
The steps of IVUS-guided parallel wiring are as follows. The guidewire is first advanced as far distally as possible in an antegrade fashion. Next, we advance the microcatheter as far distally as possible and use the bougie effect, a method to dilate a stenosis by passing a microcatheter through, to insert the AnteOwl (Fig. 4 A). When the first guidewire is in the subintimal space, we manipulate the second guidewire into the intraplaque route under IVUS guidance (Fig. 4B). The IVUS catheter can be observed up to the point where it has been advanced within the CTO, and a second guidewire can be advanced to an intraplaque route by IVUS-guided parallel wiring. When the guidewire is advanced to the area that cannot be observed by IVUS, we step down to a floppy or intermediate type of guidewire and advance this guidewire under angiographic guidance. By repeating this process and proceeding along the intraplaque route, the guidewire can finally be passed through the distal lumen (Fig. 4 C, D). This IVUS-guided parallel wiring allows the passage of all intraluminal guidewires. The first guidewire is advanced as far as possible distal to the CTO, even if it is subintimal, and eventually the second guidewire is advanced into the true lumen guided by IVUS.
In recent years, IVUS has been used to determine the appropriate vessel diameter for BTK lesions, and clinically, it has accelerated improvements in wound care (Fujihara et al. 2020; Soga et al. 2021). In addition to the evaluation of the appropriate vessel diameter, the AnteOwl may also allow guidewire passage in difficult cases and reduce the incidence of distal puncture.
This AnteOwl-guided guidewire crossing has limitations because severe calcification may not enable the passage of the IVUS, or it may be poorly observed by IVUS. The presence of severe calcification makes it difficult to see on IVUS and prevents penetration of the guidewire. Case 2 was considerably more difficult than case 1, in part because of the presence of severe calcification, which required longer procedural time. Another limitation is that it is an antegrade intraluminal approach, which may require longer procedural time. In both cases, the retrograde approach was difficult to perform, especially in Case 2, where a very long occlusion from the SFA to the distal part of the peroneal artery was treated in a single term, but which still required a very long procedure time. Longer procedure time means increased radiation exposure for the patient and the operator. Case 2 required a longer procedure time and higher radiation dose than Case 1. Although these values were acceptable when compared with a previous report of the radiation dose for coronary angiography and intervention (Nakamura et al. 2016), the increased procedure time and radiation dose should be noted. In cases where a retrograde approach can be performed easily, we advise shortening the procedure time by shifting to a retrograde approach as soon as possible. A much larger study is required to confirm the efficacy of AnteOwl IVUS-guided EVT for BTK CTO.