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Page 4 of 11 Zivelonghi et al. Vessel Plus 2019;3:30 I http://dx.doi.org/10.20517/2574-1209.2019.06

The aim of our review is to highlight the most recent scientific evidence about the use of hybrid algorithm
for the treatment of CTO.

OUTCOMES OF THE HYBRID ALGORITHM
Multicenter US registry
An important Multicenter registry from the USA examined the procedural technique and outcomes of
1036 consecutive CTO PCI using the hybrid algorithm between 2012 and 2015 in 11 US centers. Technical
success was achieved in 91% and a major procedural complication occurred in 1.7% of the cases. The initial
crossing strategy was successful in 58% of the lesions, whereas 39% required an additional approach. In this
registry, the application of the hybrid approach resulted in high procedural success and low complication
[9]
rate, supporting its expanding use in CTO PCI . It is important to notice that the physicians participating
in this registry were extremely experienced CTO operators with already years of expertise in CTO
techniques, thus the external validity of the results of this registry in a group of physicians with less CTO
expertise is debatable.

The RECHARGE registry
A solid source of data was also provided by the REgistry of Crossboss and Hybrid procedures in FrAnce,
[10]
the NetheRlands, BelGium and UnitEd Kingdom (RECHARGE) , which described the procedural and
clinical outcome of the adoption of the hybrid algorithm in Europe in a group of physicians with definitely
less expertise (during the registry) than the American doctors involved in the Multicenter US registry. In
this prospective, multicenter registry, patients treated electively for CTO PCI were prospectively included
from 17 centers between January 2014 and October 2015. A total of 1253 CTO PCI were performed. The
average J-CTO score was 2 ± 1 and was higher in the failure group (2.6 ± 0.6 vs. 1.9 ± 1, P < 0.001). Overall
procedural success was 86% and major in-hospital complications rate was 2.6%. The primary strategy was
successful in 60% of cases; a switch to a second-line strategy (as suggested by the principle of the algorithm)
occurred in 34% of cases, resulting highly successful (74%). Median procedural time was 90 min (IQR 60-
120 min) and median fluoroscopy time was 35 min (IQR 21-55 min), median contrast volume was 250 mL
(IQR 180-340 mL). High technical success rates combined with a low event rate supported further use of
this algorithm. Four techniques were mainly applied: antegrade wire excalation (AWE) was the primary
strategy in 77% of patients, followed by a retrograde technique in 17% and antegrade dissection reentry in
7%. The primary strategy was successful in 91% of easy procedures (J-CTO score 0), 80% of intermediate
(J-CTO score 1), 62% of difficult (J-CTO score 2) and 43% of very difficult lesions (J-CTO > 2). Second,
third or more bailout crossing strategies were used in 34% of cases and were successful in 74% of the
procedures, leading to an overall technical success rate of 86%.

Of note, a sub-analysis of the RECHARGE study was focused on investigating the feasibility and efficacy of
the radial approach in CTO PCI. The authors analyzed the 1253 patients undergoing CTO PCI according
to the hybrid algorithm and divided the population into two groups: a fully trans-radial approach (fTRA,
single o bi-radial accesses) vs. transfemoral approach (TFA, defined as single femoral, bi-femoral or
combined femoral/radial). A fTRA was applied in 306 (24%) cases, while 947 patients (76%) were treated in
the TFA group. Technical success was achieved in 259 of 306 patients (85%) in the fTRA group and 816 of
947 patients (86%) in the TFA group, and these similar success rates was also confirmed after propensity
score matching and stratification for J-CTO score. This was one of the first studies supporting the efficacy
of the radial approach as a valid alternative to the conventional trans-femoral one in CTO PCI .
[11]

The four angiographic characteristics of the hybrid algorithm
1. Proximal cap ambiguity: this refers to the possibility to clearly identify and define the entry point of the
CTO lesion and to engage it.