The goal of any CTO PCI is to achieve revascularization for the patient. Thus, the procedure should be performed in a manner that is safe, results in a complete revascularization with restoration of flow to all distal branches and is performed in a manner that minimizes the patient’s exposure to radiation and contrast. It should be recognized and accepted that many lesions will be amenable to a successful procedure that employs any number of different strategies and approaches. Ideally, the safest and most efficient procedure should be performed that leads to a good procedural outcome. Based on the hybrid approach, anatomy should lead an operator towards this scenario and there are a number of features of the occlusion that predispose the lesion for an ADR based approach using the CrossBoss and Stingray system as described in the following chapter on the hybrid approach (Chap. 11) .

Lesions with tapered entries and defined proximal caps with a short course are generally amenable to antegrade wire escalation or a true-to-true approach (Chap. 5). Should this approach fail due to subintimal passage of antegrade equipment, then the lesion may be amenable to an ADR strategy as an immediate bailout. Those lesions that are most suited to ADR are occlusions with defined proximal cap anatomy (either angiographically or by intravascular ultrasound; IVUS), with longer courses (>20 mm, where wire based approaches are less likely to succeed) and where there is a good target vessel to attempt re-entry. When assessing the distal landing zone, areas with a good calibre and without severe calcification or disease are ideal. Most importantly, the landing zone should be remote from and proximal to major side branches and sites of bifurcation in the distal vessel. This factor is crucial to prevent the loss of significant territories after stent deployment. Finally, vessels that have donor arteries providing complex or non-interventional collaterals should also be strongly considered for ADR as a primary strategy.

When an ADR strategy is employed (either as an early bailout after a failed antegrade wire strategy or as a primary manoeuvre) there are a number of key principles that should be adhered to. Ideally, the CrossBoss should be advanced alone with no wire ahead of the device. This is achieved by rapid rotation of the device (Fig. 6.1a) after locking the handle at an appropriate distance from the Y-connector. On occasion, it is necessary to advance knuckled guidewires into the architecture of the occluded vessel. This is usually performed in order to define the anatomy within the CTO segment, particularly in the setting of anatomical ambiguity in the target vessel (Fig. 6.3a). However, knuckle wires will create substantial disruption in the subintimal space. Therefore, as soon as the anatomical course of the vessel is defined, the knuckle should be removed and the CrossBoss advanced alone by rapid rotation. This is particularly important at the landing zone in the distal vessel. “Finishing out” the final few centimeters of subintimal dissection with the CrossBoss will create considerably less disruption in the subintimal space. This will greatly lessen the risk of compressive intramural haematoma and loss of the landing zone and site for re-entry.

Another “golden rule” of ADR is that antegrade contrast injections into the occluded vessel should not be performed. There is a major risk that this will lead to hydraulic dissection in the artery. Again, haematoma in the distal subintimal space is likely to evolve and the landing zone can be lost. When the artery is supplied by auto-collaterals contrast injection from the guide can be avoided by directly injecting contrast into the collaterals or branches that provide them by sub-selecting and siting micro-catheters into these vessels.

The CrossBoss catheter is a stiff device that tends to pass in a straight direction (Fig. 6.3). Therefore, while it will frequently follow the main artery that is the target for recanalization, the device will also track side branches. It is imperative that operators are aware that this can occur during the procedure. Careful radiographic assessment is mandatory and it is advisable to check the position of the CrossBoss in 2 orthogonal views as it makes progress in the vessel. If the CrossBoss tracks a side branch over a short distance, it rarely causes any problems. However, if this situation has not been recognized and the CrossBoss is advanced very distally into a small vessel there is a risk of perforation and this must be avoided. When the CrossBoss has tracked off course into a branch, it should be withdrawn back to the main vessel and a “redirection” manoeuvre is then needed to allow it to track to the landing zone to facilitate Stingray based re-entry. This is usually achieved by advancing a guidewire ahead of the CrossBoss into the architecture of the main target vessel. However, this is done semi-blind and we suggest that the guidewire is advanced for only a short distance beyond the origin of the branch. Once this course is defined, the CrossBoss can be passed beyond the side branch, the wire withdrawn and the CrossBoss advanced on its own as usual.

After the CrossBoss has successfully created a track to the distal landing zone in an area beyond the distal cap of the CTO, but proximal to any significant side branches, then this device must be removed with the Stingray balloon sited in the same segment of the distal vessel. The commonest steps to achieve this exchange (using the trapping-balloon technique, see Chap. 4) of equipment are as follows: Firstly, an 8 F guiding catheter is recommended for the occluded vessel to facilitate the use of trapping balloons in the guide catheter. The CrossBoss is a long, over-the-wire (OTW) device. We usually place a strong hydrophobic wire with a stiff shaft at the tip of the CrossBoss, such as a Miracle Bros 12 (Asahi Intecc, Japan). Taking care not to allow the subintimal wire to drift forwards, the CrossBoss is removed from the artery and brought back inside the guide catheter. At this point, a trapping balloon (3 mm diameter in an 8 F system) is deployed to grip the wire inside the guide catheter and fix the wire’s distal position. The CrossBoss can then be removed. Leaving the trapping balloon in place and inflated, the Stingray balloon (also an OTW system) is then advanced into the guide catheter until it reaches the trapping balloon. No fluroroscopy is needed for this step. The operator can feel the Stingray balloon hitting the back of the trapping balloon. At this point the trapping balloon is deflated to allow the Stingray to be advanced into the artery.

Management of the Stingray is a crucial part of the procedure. The preparation and subsequent inflation of the Stingray need to be meticulously performed. The Stingray balloon should be prepared before it is advanced inside the artery while the CrossBoss is still in place, to avoid some unnecessary time during the exchange when blood flow could fill the subintimal space. We recommend the following manoeuvres: The central port (OTW segment) should be flushed with heparinized saline to promote easier balloon advancement. A 3-way-tap should be attached to the side port (balloon segment). A 10 ml Luer-lock syringe should be attached to the 3-way-tap and pulled to “full negative” to create a vacuum. The tap should be closed to the balloon, any air expelled from the syringe and then this manoeuvre should be repeated two or three times to create a substantial vacuum in the shaft of the Stingray balloon. A 2 ml Luer-lock syringe filled with neat contrast should then be attached to the 3-way-tap. All air should be expelled from the system before it is opened to the contrast syringe. Once the tap is opened contrast will be sucked into the Stingray creating a column of contrast from the distal side port to the balloon itself. During advancement of the balloon into the coronary, the small syringe can stay on the side port, while some further suction of contrast into the balloon wings will be achieved with more time. When the balloon is in place, the system should then be closed to the balloon again and an inflation device filled with neat contrast attached. Neat contrast is necessary in the inflation device to allow adequate visualization of the deployed Stingray. Finally, after all air is expelled the tap can be opened between the balloon and the inflation device to allow the balloon to be inflated.

When advancing the balloon, the distal tip of the stiff guidewire that the Stingray is advanced over should not be allowed to drift any further into the target vessel. This will risk disruption and haematoma at the landing zone as well as potentially leading to the unusual possibility of a distal perforation. The Stingray should then be advanced to the landing zone and deployed. The rated burst pressure of the Stingray balloon is 6 atmospheres and inflation to 4 atmospheres is recommended. It is crucial not to inflate the Stingray to high pressure. If the balloon bursts then the subintimal space will be severely disrupted and it is highly unlikely that the procedure will be successful.