6. Retrograde channel selection.
Operators should gain septal channel crossing experience before trying arterialised channels as septal channel rupture rarely causes tamponade. Careful review of angiogram with frame by frame assessment is essential for septal channel selection. Straight septal channels tend to be the easiest ones to cross and therefore straightness of channel should be considered more important than size. If multiple channels are available, 3 or 4 best channels should be selected and tried in order of likelihood of success.

Atrial channels are epicardial channels and rupture will cause tamponade. Familiarity with suction, coils, and other emboli material should be gained before attempting these channels. Size is the most important predictor of safe crossing in arterial channels and therefore the largest channel should be chosen unless it has severe tortuousity.

7. Retrograde wire selection.
Retrograde wiring of CTO requires less penetration power when compared to antegrade wiring as the distal cap is softer. The retrograde channel is often tortuous and therefore the torque control is poorer in the retrograde wire when compared with antegrade wire. The selection of retrograde wire is influenced by the CTO characteristics. In short soft CTOs where single retrograde wire crossing is considered, XT or XTA wire can be used. XT family of wires are also very good when the CTO is very long or when there is ambiguity of vessel course. The XT can be used to wire retrogradely as far as possible and when it is stuck, the XT can be used as a knuckle wire to show us the vessel course.

However, in most CTOs, there is no vessel course ambiguity and the planned approach is direct reverse CART. Therefore, Gaia Second wire is excellent for its torque control and the operator can often direct the retrograde Gaia Second very close to the antegrade wire allowing reverse CART to be completed with a small size balloon (contemporary reverse CART). Higher penetration wires (e.g. Conquest 9,12, Gaia 3rd) should only be used when vessel course is clear. Higher penetration wires are often needed to complete reverse CART (see IVUS guide reverse CART section below). In conclusion, for most cases, wires with good torque control (Gaia wires) should be used with reverse CART, but the exception to this is when the CTO is very short or very long or there is vessel course ambiguity, where XT type wires should be used.