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Page 2 of 11 Paraggio et al. Vessel Plus 2019;3:12 I http://dx.doi.org/10.20517/2574-1209.2018.72

Table 1. American Heart Association/American College of Cardiology lesion classification system
Anatomic risk groups
Low risk Moderate risk High risk
Discrete (length < 10 mm) Tubular (length 10-20 mm) Diffuse (length < 20 mm)
Concentric Eccentric Excessive tortuosity of proximal segment
Readily accessible Moderate tortuosity of proximal segment Extremely angulated segments > 90°
Nonangulated segment ( < 45°) Moderately angulated segment ( > 45°, < 90°) Total occlusions > 3 months old and/or bridging
Smooth contour Irregular contour collaterals
Little or no calcification Moderate or heavy calcification Inability to protect major side branches
Less than totally occlusive Total occlusions < 3 months old Degenerated vein grafts with friable lesions
Not ostial in location Ostial in location
No major side branch involvement Bifurcation lesions requiring double guidewires
Absence of thrombus Some thrombus present

[4]
light about CTO procedures demonstrating a clinical benefit in term of reduced angina symptoms ,
[6]
[5]
improved left ventricular ejection fraction and improved long term survival . However, when looking
to recent randomized clinical trials, there are still some concerns about effective clinical impact of CTO
revascuarization, showing conflicting results [7-10] .

Above all these clinical and prognostic considerations, only in the last few years, the developing of
new techniques and new devices and guidewires has raised the procedural success to near 90% [11-15] in
experienced centers. However, observational reports still showed that CTO procedural success rate is lower
[12]
in less skilled hands, reaching in some cases only 70% . Following technical advancement and procedural
increased success, interventional cardiologists have been recently more involved in CTO procedures. Hence,
it is now advisable for the interventional cardiologist to follow specific training programs and to consider on
site proctoring before starting to perform CTO procedures. Moreover, operators involved in such courses
and on-site CTO programs could improve their learning curve even in complex percutaneous coronary
interventions (PCI), bringing their experience about CTO devices and techniques to everyday practice.

Hence, in this review, we focus the attention on specific insights on CTO devices and techniques, which
could enhance interventional cardiologist capability to overcome many challenges and complications
encountered during daily PCI.

PLANNING THE PROCEDURE: WEIGH THE PROS AND CONS
Accurate angiographic review with complete quantification of possible hazard during the procedure remains
a cornerstone of successful CTO PCI. In this context, dual injection angiography should be performed in
all cases except in the complete absence of contralateral collaterals. A complete evaluation of CTO lesion
characteristic before the procedure is the key for the success.

A first extensive evaluation of anatomic predictors of PCI success was reported in AHA/ACC Guidelines
[16]
for Percutaneous Interventions [Table 1] . However, regarding CTO procedures, many scores have been
proposed, but the most commonly used for its simplicity in identifying main characteristics that may impact
[17]
procedural success is the “J-CTO” score . Patients with higher J-CTO score have significantly lower success
rate. The four angiographic parameters of this score are: (1) proximal cap location and morphology, with
a clearly defined and “tapered” proximal cap favoring antegrade approach; (2) lesion length, with a value
> 20 mm clearly more challenging to cross; (3) calcification; (4) bending > 45° within CTO lesions, which
lower procedural success.

[15]
[14]
More recently many other scores, such as RECHARGE CTO score and PROGRESS CTO score , have
demonstrated a similar predictive ability of CTO procedural success when compared with J-CTO score.