Achieving a longitudinal overlap of the antegrade and retrograde guidewires is the first step of conventional reverse CART. The conventional wiring in both an antegrade and a retrograde fashion is easier to make an overlap with unambiguous course of the CTO segment. With vessel course ambiguity, severe tortuosity or heavy calcification within the CTO segment, conventional wiring is not only cumbersome but also carries the risk of vessel perforation. This warrants more efficient and safer knuckle wiring with low (Fielder XT; Asahi Intecc) to intermediate penetration force polymer-jacketed (Pilot 200; Abbott Vascular, Santa Clara, CA, USA) guidewires. The appropriate low (Fielder XTA; Asahi Intecc) to intermediate penetration force wire (Gaia second/third; Asahi Intecc) is navigated across the distal cap to lie in subintimal space. This wire, with or without a knuckle (an umbrella-type bend or loop), is advanced via the microcatheter through CTO body within the subintimal space to establish retrograde base of operation. An antegrade base of operation is established by placing a short microcatheter at proximal cap using a workhorse wire which is then is exchanged with a low to intermediate penetration force wire to breach the proximal cap to enter subintimal space. After creating an antegrade and retrograde overlap zone, an antegrade balloon sized based on angiography is negotiated into the CTO segment to the point of guidewire overlap and inflated. The balloon dilatation makes or enlarges intimal/subintimal dissection and creates a connection between the spaces, known as CSS within which both guidewires are lying.4)12) In the conventional reverse CART technique, a large size antegrade balloon (Table 4) is selected to maximize the chance of CSS formation (Figure 3). Usually, a low to intermediate penetration force wire is used as the retrograde wire to track the created connection. However, in case of subintimal position of antegrade wire and intimal position of the retrograde wire, a high penetration force wire (Gaia Third, Conquest 12; Asahi Intecc), Hornet 14 (Boston Scientific, Marlborough, MA, USA), may be required to advance through the intimal plaque into the subintimal space.12)

If after few tissue ablations, there is failure of retrograde guidewire navigation into the antegrade guide, a guide-extension catheter (Guideliner; Vascular Solutions, Minneapolis, MN, USA), Guidezilla (Boston Scientific) can be delivered into the subintimal space to facilitate the process (mother-child reverse CART). Alternative strategies include IVUS assisted reverse CART, use of larger balloon to achieve greater tissue ablation, the use of smaller balloons with retrograde navigation of Gaia series of wires (contemporary reverse CART), deployment of stent in antegrade subintimal space for successful retrograde navigation of wire (stent assisted reverse CART) (Figure 4), or movement of base of operation overlap zone to a different location (shifting reverse CART).4)

The unwarranted intentional intimal/subintimal dilatation with a large balloon in the conventional reverse CART technique may lead to distal propagation of the subintimal hematoma and vessel perforation. Some reports indicate that the CART and conventional reverse CART techniques could be associated with subsequent coronary artery aneurysm formation and increased risk for target vessel revascularization due to longer stent length.19)20) Moreover, excessive manipulation of the retrograde guidewire or use of a knuckle wire technique to achieve guidewire overlap can create a large space around the retrograde guidewire, that may be an obstacle for the precise directional control of the same guidewire. Although this challenge may be overcome by dilatation with a larger antegrade balloon and tracking with low to intermediate penetration force guidewires, it is often cumbersome and time consuming.

The contemporary reverse CART technique has been introduced5) to minimize trauma to the vessel wall and to make the procedure more efficient through a precise directional control by efficient use of deflection mechanisms of the retrograde guidewire (Gaia series). The key steps of this technique are the: 1) antegrade preparation; 2) use of a small antegrade balloon as a target for the retrograde wire; and 3) retrograde intentional vessel tracking using a guidewire with high torque control (Figures 6 and 7).

This technique commences with simultaneous dual contrast injection from the antegrade and retrograde guiding catheters and navigation of an antegrade guidewire through the occlusion with the support of a microcatheter to within 5 to 10 mm of the distal cap. It is taken care not to advance the antegrade guidewire beyond the CTO segment to minimize the risk of formation of distal hematoma. Next, the microcatheter is exchanged for a small balloon (2.0 mm diameter in most cases) which is advanced towards the tip of the guidewire. Except for an ambiguous proximal cap or uncertainty of CC crossing, antegrade preparation first is preferable as it reduces donor artery risk and ischemic time of the CTO territory, and encourages going directly to reverse CART after retrograde CC crossing.

The retrograde approach is then commenced with CC crossing by guidewire and microcatheter. The retrograde CTO segment wiring is performed using a guidewire with good torque control and high penetration efficiency (Gaia series). The retrograde guidewire should be navigated without excessive torqueing and directed towards the antegrade balloon so that the shaft of the antegrade balloon and the retrograde wire are as coaxial as possible at the point of puncture. The retrograde puncture should aim towards the end of the balloon first (end balloon wiring technique) and, if this fails, towards the lateral side of the balloon. Fluoroscopy in two orthogonal projections is recommended to confirm the positional relationship between the retrograde guidewire and the antegrade balloon. After gently pushing the retrograde guidewire, the antegrade balloon is deflated, allowing the retrograde guidewire to puncture into the space created by the antegrade balloon. In case of failure, retrograde guidewire is still controllable because of smaller dissection plane created by smaller antegrade balloon. This technique does not usually warrant IVUS guidance as the retrograde wire is intentionally directed towards and then into the space created by the antegrade balloon under fluoroscopic guidance. However, if there is difficulty in achieving a connection, it is recommended to embark on IVUS assisted reverse CART.4)12)

The initial procedural strategy for CTO PCI is crafted based on anatomy such as proximal cap ambiguity, length of occlusion, distal vessel, interventional CCs. It is important to exploit the situation of conditional probability and attempts to use the procedure that is most likely to be successful, and in case of failures, endorses rapid change to alternative strategies.21) Once the decision to perform reverse CART is considered, it is recommended to adopt contemporary subtype because of its efficiency and safety. This technique could be employed as a primary approach or as an investment procedure when the antegrade approach is unsuccessful. The contemporary reverse CART is considered unsuitable in CTO cases with ambiguous proximal cap and/or CTO course, severe tortuosity, and heavy calcification because this technique requires antegrade preparation before embarking on retrograde CTO segment wiring, and the knuckle wire technique cannot be contemplated to advance the antegrade or retrograde guidewire as it is likely to create large spaces around the guidewires resulting in reduced retrograde wire control (Table 4). Also, short segment (<15 mm) CTOs are not suitable for the contemporary reverse CART, because of difficulty in embarking on antegrade preparation without propagating the hematoma beyond the distal cap.12) Short CTOs are best dealt with antegrade or retrograde wire escalation. Similarly, the contemporary reverse CART may not be possible with poor torque control of the retrograde guidewire due to tortuosity of CCs or strong cardiac motion.12)22) The length alone is not predictive of failure to cross the CTO body with traditional wiring techniques. However, traditional wiring is likely to fail in case of a long CTO accompanied by tortuosity or calcification or ambiguity. This situation warrants intentional subintimal wiring.22) The ideal method of intentional subintimal wiring from the retrograde side is knuckle wiring which should be followed by use of a large balloon intended for conventional reverse CART.

In the shifting (extended) reverse CART technique the inflation of antegrade balloon is undertaken outside the CTO segment (either proximal or distal) and the intimal/subintimal dissection is shifted beyond the beyond the CTO segment (Figure 8). This is followed by navigation of retrograde guidewire through the connection created between the proximal true lumen and the retrograde intimal/subintimal space. It is critical to identify the ideal point with diffuse plaque and to determine an appropriate balloon size in order to create an intimal/subintimal dissection efficiently with antegrade balloon. This technique may be applied if there is failure of retrograde penetration of a calcified distal cap or if the retrograde microcatheter cannot pass severe calcification. In such scenarios, the antegrade guidewire can be placed in the subintimal space beyond the distal cap. This follows inflation of antegrade balloon and retrograde navigation of a high penetration into the dilated subintimal space. Shifting reverse CART technique is useful in cases where antegrade preparation or retrograde cap penetration is not possible and where there are no significant side branches close to the site of the reverse CART technique.12)