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Zivelonghi et al. Vessel Plus 2019;3:30 I http://dx.doi.org/10.20517/2574-1209.2019.06 Page 7 of 11

angiography, to be able to know adequately the anatomy and to choose properly the best primary
approach and the eventual following approaches. We suggest unfractionated heparin as the best form of
anticoagulation during CTO PCI, with an activated clotting time more than 350 s. Heparine is considered
the safest anticoagulation method because in case of complications it can be rapidly reversed with
protamine, if needed.

Antegrade wire escalation
It is the sequential use of guidewires with different characteristics from the proximal to the distal part of
the lesion in order to try and remain intraluminal during the whole trajectory and to achieve directly the
distal true lumen after the CTO. It is the most commonly used primary strategy in CTO PCI (around three
[10]
quarter of the cases) . Following the hybrid algorithm, you can choose AWE as primary strategy in case
of: (1) an unambiguous proximal cap; (2) < 20 mm occlusion length; and (3) good distal target vessel. Soft
tapered polymeric wires are the initial choice. These wires can cross the occlusion through small invisible
channels or by crossing the softest part of the lesion. After trying for a few minutes without progression,
it is better to rapidly step up to stiff spring coil tapered wires to overcome hard and fibrotic/calcified
[7]
segments, and then change again with a soft wire to complete the crossing of the CTO . Penetration force
[18]
and maneuverability of the wire should always be supported by a microcatheter . The CTO crossing wires
should be exchanged once they access the distal true lumen, with safer wires, to prevent distal small vessel
perforation. A possible AWE technique can be applied when the first wire is constantly directing into the
false lumen: the parallel wire technique. The first wire is left in the false lumen and a second wire is passed
parallel: by doing so, the first wire keeps the dissection channel closed and acts as marker for advancing
the second wire .
[19]
Anterograde dissection re-entry techniques
Antegrade dissection occurs when a guidewire or a microcatheter is advanced within the subintimal space.
This can be obtained with the CrossBoss catheter or a knuckle wire technique . In the latter approach,
[4,6]
which is also the first step of the STAR technique, a 360 degrees looped polymer jacketed wire (the knuckle
wire) is advanced in the direction of the distal cap of the CTO. It is important not to rotate the knuckle
wire to avoid entanglement. This approach is known to be much safer than advancing stiffer guidewires
without knuckle, as the knuckle tracks the vessel anatomy in the subintimal space without perforating
the vessel. The CrossBoss catheter has the advantage of creating a smaller sub adventitial space than the
knuckle wire, further it can facilitate the use of the Stingray system for final re-entry in the true lumen, as
it created a larger subintimal channel. After subintimal crossing there are two primary method to re-entry:
(1) LAST Method; (2) device-based (Stingray system).

The LAST Method
After gaining the sub-intimal space, the wire is advanced after the distal cap of the CTO, and the
microcatheter is positioned near the desired re-entry point. A dedicated guidewire (stiff polymer jacket or
[6]
stiff tapered) is selected and directed to the distal true-lumen in order to obtain a successful re-entry .
Stingray-based reentry
The Stingray balloon has a flat shape with two side-exit ports. Upon low-pressure (2-4 atm) inflation, one
[20]
exit port is automatically oriented toward the true lumen and the other one toward the vessel adventitia .
The delivery catheter shaft is 0.014” guidewire compatible. The Stingray guidewire is a stiff guidewire with
a 20 cm distal radiopaque segment, a 1.5 mm, 28º angle, distal bend, and a tapered tip with a 0.0035” distal
prong. The Stingray guidewire is advanced through one of the two side ports of the Stingray balloon under
fluoroscopic guidance to re-enter into the distal true lumen.

These techniques, specifically the Stingray-based approach, are less frequently adopted, and were often
considered as the last chance in the beginning. Indeed in the RECHARGE registry and also in the data