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Zivelonghi et al. Vessel Plus 2019;3:30 I http://dx.doi.org/10.20517/2574-1209.2019.06 Page 9 of 11

a guidewire placed in the subintimal space via the retrograde approach. The antegrade and the retrograde
systems meet each other in the subintimal space Multiple dilatations of the retrograde balloon create a
connection between the anterograde and the retrograde spaces so that the antegrade wire may regain the
[19]
true lumen distal to the occlusion . This technique is rarely used nowadays, mainly due to the complexity
of tracking a balloon through the retrograde way. The reverse CART technique is currently preferred.

Reverse CART technique
Another method to connect the proximal and the distal lumen is the reverse CART technique. This
method is the most commonly used. A microcatheter is placed across a collateral vessel into the subintimal
space of a CTO segment, over a guidewire (via retrograde approach). An antegrade wire is advanced into
the CTO segment alone or with a microcatheter or a balloon. The balloon is placed adjacent to retrograde
microcatheter and inflated. The balloon angioplasty creates a connection between the two spaces. The
[7]
retrograde wire can now be passed into the proximal vessel and wire externalization can be performed .

DISCUSSION
According to the hybrid algorithm, a first and key point is the performance of a proper dual injection to
optimally view the CTO lesion and estimate its length, the proximal cap characteristics and the quality
[23]
[9]
of the distal target vessel to choose the optimal initial strategy . According to Christopoulos et al. the
dual injection has been demonstrated crucial for achieving high success rates in CTO PCI. Indeed, the
hybrid algorithm improves the success rate in CTO PCI when applied by experienced operators. In the
[10]
RECHARGE the success rate was 86% with a low incidence of adverse events (2.6%). In the multicentre
US registry the success with the initial crossing strategy resulted 58%, but after adoption of additional
[9]
strategies a final technical success rate was 91% with a low incidence of adverse events (1.7%). The only
problem could be the interpretability of the angiographic characteristics, for example the proximal cap
ambiguity is subjective, and it depends on operator experience. In the RECHARGE, despite the high
degree of several negative angiographic characteristics, AWE was the most frequently used first technique
(77%). AWE was successful in 62% of the cases with low success rate in very difficult CTO PCI. This
problem could be potentially bypassed using intravascular ultrasound imaging which would help better
defining the proximal cap [10,20] . In the same registry the algorithm’s suggestion that lesion length ≥ 20 mm
should drive the strategy to dissection and re-entry techniques, was less followed than expected. In 50%
of cases the first strategy applied was still AWE. Two possible factors should be kept into consideration:
(1) lesion length is often not clear, even if the dual injection should reduce this risk of misinterpretation;
(2) operators still prefer to wire the softest tissue of the CTO with dedicated wires and new microcatheters
(lower crossing profiles), while shifting to a dissection/re-entry technique is always a possible strategy in
case of AWE failure. Importantly, the threshold to change strategy should be within 15 to 30 min of failure
mode, to reduce contrast and radiation exposure. Overall the availability of subsequent strategies and the
[10]
ability to shift between different ones is crucial to increase the success rate from 60% to 85%-90% . Indeed,
as shown in the US registry, an easy switch in strategies allowed for an increase of technical success
from 64% with the firstly adopted technique to a final 91%. An alternative algorithm, the minimalistic
hybrid approach, was described by Zivelonghi et al. . The authors developed it in order to minimize the
[24]
use of double access, large bore catheters and femoral approach, thus reducing patient’s discomfort and
procedural complications. In this sequence of steps all the techniques are included: antegrade, retrograde
as well as sub-intimal and intraluminal techniques. The focus of this algorithm is to perform all the
possible techniques of the hybrid algorithm minimizing the unnecessary “damage” to the patient (for
example, no second access if not needed, 6F guiding catheters instead of 7-8F in case of “a priori” belief
that the procedure can be performed with 6F guiding only, default radial access in case of 6F guiding).