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158 PART IV Wires Technique
goal is to put the antegrade and retrograde gear in
communication, by means of antegrade balloon inflation and subsequent retrograde guidewire advancement into the compartment occupied by the antegrade
balloon. Under this perspective, reverse CART and
AFR are two sides of the same coins: in the former the
wire is advanced from retrograde to antegrade, while
with the latter the wire is advanced in an opposite
direction.
Procedural description of AFR
AFR is performed as follows (Figure 17.2): (1) a first
wire is advanced (either voluntarily or inadvertently)
distal to the distal cap of the occlusion in the extraplaque space; (2) a balloon, sized 1:1 with the artery is
advanced over this wire and left across the distal
cap;(3) the occlusion is rewired in a parallel fashion,
with a second, low-tipload, polymer-jacketed wire,
loaded on an antegrade microcatheter, placed just
proximal to the distal cap; (4) the balloon is inflated;
(5) upon balloon deflation, the second wire is quickly
advanced through the dissection tears into the distal
true lumen, while such fenestrations are wide open for
a few seconds before collapsing.
Critically, similar to Stingray-based ADR (and at
variance with STAR and LAST), re-entry with AFR is
targeted at the site of balloon dilatation, which leads
to shorter dissection planes, higher likelihood of preservation of side branches, and improved distal runoff,
compared with those older wire-based re-entry
techniques. Figure 17.3 presents AFR in the context of
other ADR techniques, as well as other crossing strategies when an extraplaque situation has been reached.
When is AFR indicated? Similar to other ADR
techniques, this approach should be used in the following scenarios: (1) CTO length >20 mm; (2)
adequate distal “landing zone”; (3) in case of proximal cap ambiguity, entry in the extra-plaque space
can be facilitated by move-the-cap techniques
(scratch-and-go or balloon-assisted subintimal
entry); (4) safe extraplaque navigation in the occluded
segment can be achieved by use of the knuckle wire
technique and to quickly reach the landing zone.
Figure 17.2 AFR – step-by-step description. Step 1: the occlusion is wired in an extraplaque fashion, beyond the distal cap.
Step 2: the microcatheter is trapped out, and the occlusion is rewired, in a parallel wiring fashion, with a second,
polymer-jacketed wire, loaded onto the microcatheter and advanced just proximal of the distal cap. This can be
facilitated by using a dual-lumen catheter. A balloon, sized 1:1 with the artery at the re-entry site, is advanced over the
first guidewire, and parked at the level of the distal cap. Step 3: the balloon is inflated. This creates transient
fenestrations between the extraplaque space and the true lumen. Step 4: upon balloon deflation, the polymer-jacketed
wire is advanced through these transient fenestrations into the distal true lumen.
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Figure 17.3 Approaches available when the wire has reached an extraplaque situation.
An AFR case example is presented in Figure 17.4
and Figure 17.5, and Table 17.1 shows key AFR concepts, and tips and tricks to master the technique.
Common AFR failure mechanisms of AFR are discussed next. A dual-lumen microcatheter can be utilized to perform parallel wiring in the initial steps of
the technique, should conventional wiring with a
microcatheter prove difficult. Balloon undersizing
can lead to inadequate fenestration, which underlines
how important it is to use a balloon sized 1:1 with the
artery. Failure to cross the fenestrations can result
from two mechanisms: (1) fibrocalcific tissue at the
re-entry site, which can be overcome using a higher
tip-load polymer-jacketed guidewire or cutting balloon dilatation; or (2) wrong guidewire tip shape,
which should be corrected creating a 2-mm, 45° bend
(Figure 17.6). Finally, in the presence of a large, compliant hematoma intravascular ultrasound interroga-
tion can help identify the optimal site for re-entry.
Alternatively, moving the “base of operations” more
distally is another possible solution to this problem.
AFR presents several strengths. First, it is inexpensive, being performed with wires, microcatheters, and
balloons which have possibly already been used earlier during the case. This aspect makes AFR particularly appealing in clinical practices with limited
budget. Second, no proctoring is required, as the technique can be easily learnt by watching case examples
and studying relevant literature. Third, AFR is safe: to
date, no complications (in particular, perforation)
have been ascribed to this technique. Fourth, even in
case of failure, AFR does not preclude alternative
techniques (e.g., the retrograde approach), as it
already represents the antegrade component of
reverse CART. Fifth, if AFR is used as a last resort during the case, and it is unsuccessful, it will represent an
160 PART IV Wires Technique
Figure 17.4 Case example of AFR. Right coronary artery CTO. (a, b) The occlusion has an ambiguous proximal cap, is
approximately 20 mm long, and has a diseased distal vessel, visualized by bridging and contralateral collaterals. ((C) [LAO
projection], (d) [RAO projection]) An UltimateBROS3 guidewire over a Corsair Pro microcatheter is extraplaque track at
the landing zone (arrowheads). (e) A Sion Black (arrowheads), is advanced in a parallel wire fashion, up to the distal cap.
(f) A 2.0×15-mm semi-compliant balloon is advanced onto the UltimateBROS3 and inflated. (g) The balloon is deflated
and the Sion Black is quickly advanced into the distal true lumen, which is confirmed by contralateral injection
(arrowheads in h). (i, j) Final result after stenting.
Figure 17.5 (continuation) Intravascular ultrasound (IVUS) imaging after AFR (left panel) and after stent implantation
(right panel). (A) Proximal true lumen (arrowhead indicates side-branch ostium). (B) Entry point from true to false lumen
(wire in false lumen). (C) Wire in the extraplaque space (arrowhead indicates side-branch ostium). (D) Wire in the
extraplaque space (arrowhead indicates collapsed true lumen). (E, F) Wire in distal true lumen (arrowheads indicate ostia
of side-branches). (A’, C’, E’, F’) Final result corresponding to the sites indicated in (A, C, E, F). Arrowheads indicate
side-branches. The extraplaque track measures 21 mm (barely longer than the occlusion).
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Table 17.1 Antegrade fenestration and re-entry (AFR): tips and tricks.
1. Balloon-to-arty ratio should be 1:1: balloon undersizing is the most common failure mechanism as it leads to
expansion of the extraplaque space, without effectively creating fenestrations.
2. The correct tip shape for the re-entry guidewire is a 45° 2-mm curve (Figure 17.6). Lesser angle will not be
effective in achieving crossing through the fenestrations, and excessive curves (e.g., knuckle) will extend the
dissection distally.
3. Re-entry guidewire: it should be a polymer-jacketed wire (its lubricity will increase the likelihood of successfully
crossing through the dissection plane). We recommend low tipload wires to start (Fielder family, Sion Black). If this
is not successful, a higher-tipload wire can be chosen (Pilot 200, Gladius, Gladius Mongo, Raider). The latter are
particularly suited when excessive separation between the two wires is noted or when the re-entry area is
fibrocalcified.
4. Like reverse CART, AFR is an iterative process: several attempts might be required before the re-entry guidewire
successfully crosses a fenestration into the true lumen. If, after several attempts, re-entry is not achieved,
subsequent balloon inflation (at the same or slightly different site) can be attempter to recreate the transient
fenestrations.
5. Re-entry into the true lumen is felt as an increase in the freedom of movement of the guidewire, and possibly wiring
distal side branches. While a contralateral angiography is usually sufficient to confirm true lumen re-entry, intravascular ultrasound can be used in dubious cases.
6. In case where re-entry failure is thought to be due to fibrocalcified tissue at the re-entry area, reattempt using a
cutting balloon can be contemplated. Cutting balloon angioplasty will create deep longitudinal fenestrations,
making subsequent re-entry attempts easier.
Figure 17.6 The correct tip shape for the re-entry guidewire is a 45° 2-mm curve.
162 PART IV Wires Technique
“investment procedure” (subintimal plaque modification), which might facilitate a staged new attempt.
Finally, AFR can successfully be performed as a bailout of any hybrid algorithm techniques, thus representing yet another option for the CTO operator.
Outcome data on AFR
In 2018, we published our first experience with AFR
on six patients [12]. Successful recanalization was
achieved in all cases, and no complications were
observed. AFR was subsequently disseminated by the
authors at several meetings. A group of CTO operators
(with varying degrees of expertise) from 9 centers
compiled the technique and published their experience with their very first AFR cases [13]. This multicenter registry included 41 patients. Mean J-CTO
score was 2.5±1.4. True lumen re-entry with AFR was
achieved in 65.9% of cases, and with the use of alterna-
tive techniques in failed cases the operators had a final
technical success rate of 85.4%. Importantly, no AFRrelated complications were observed. At one-year follow-up, target-lesion failure was observed in just 8.3%,
with no differences between successful and failed AFR
cases.
AFR in the hybrid algorithm
Numerous hybrid operators (including those from the
multicenter AFR experience [13]) have incorporated
AFR in their interpretation of the hybrid algorithm.
Figure 17.7 shows a proposed role of AFR in the contemporary hybrid algorithm. When ADR is indicated
and the distal landing zone has been reached, Stingraycapable operators can attempt Stingray-based re-entry.
If this fails, or in case of Stingray unavailability, AFR
can be attempted. If this is also unsuccessful (despite
the troubleshooting maneuvers outlined above), the
Figure 17.7 Role of AFR in the hybrid algorithm.
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operator can switch to the retrograde approach. If this
is not feasible or too high-risk, the procedure will be
stopped. At this point, multiple balloon dilatations
throughout the occlusion (as part of AFR) have already
represented an “investment procedure,” which can
facilitate a staged reattempt. Of note, we have also utilized AFR as a bail out of a failed retrograde approach
(e.g., in case of difficult reverse CART), or combined
with the latter (“facilitated AFR,” see below).
AFR: Further developments and
future
Intravascular ultrasound can assist in the identification
of the optimal re-entry site (the area where the true
lumen is least compressed by hematoma and is not surrounded by fibrocalcific components) (Figure 17.8).
AFR can also facilitate antegrade crossing of the
CTO after a wire has reached the distal vessel with the
retrograde approach (similar to the “kissing wires”
technique). This “facilitated AFR” (Figure 17.9 and
Figure 17.10) can quickly convert a retrograde procedure to an antegrade one, thus avoiding the extra costs
(externalization wire), time and risks (e.g., donor vessel injury) associated with externalization. This facilitated AFR can be attempted either before resorting to
reverse CART (in case of failure), or, vice versa, as a
bailout of the latter.
At the moment of writing this chapter, multiple
inventors are developing dedicated AFR devices,
which have the potential to greatly streamline the procedure, further facilitating its adoption among less
experienced operators. Galassi et al. [14] have recently
published their experience with a dual-guidewire
Figure 17.8 Application of intravascular ultrasound (IVUS) in AFR troubleshooting. (a) Distal circumflex CTO. The asterisk
highlights, throughout the figure, a large second obtuse marginal (OM2) branch. (b) After antegrade wire escalation and
(c) predilatation, the OM2 branch is lost (dotted line in the insert). (a-d) IVUS interrogation shows (a) true lumen
situation distally, (b and c) a long extraplaque track compromising (c) the ostium of the OM2 branch, and again (d) true
lumen situation more proximally. IVUS measurement of the reference vessel diameter at the OM2 takeoff was ~3 mm. (d)
Accordingly, a 3.0 mm balloon was used to fenestrate at the OM2 ostium level, and re-entry into the OM2 branch was
performed with a Fielder XT wire. (e) Result after predilatation at the circumflex/OM2 bifurcation. (f) Final result after
implantation of two long stents from the OM2 branch to the proximal circumflex.
164 PART IV Wires Technique
Figure 17.9 Facilitated AFR. (A) Proximal right coronary artery CTO with (B) septal and epicardial collaterals from the left
anterior descending. (C) Antegrade wiring was attempted first, but the wire was extraplaque at the distal cap. (D) Failed
Stingray-based re-entry. (E) The retrograde approach was then performed via the first septal branch, (F) reaching the
posterolateral branch.
Figure 17.10 (continuation) AFR was performed using the retrograde system as a marker, with a 2.5×20 mm balloon on
the antegrade wire. (a) Upon balloon deflation, the antegrade Gaia Third was advanced into the distal true lumen using
the retrograde system as a marker. (b) Intravascular ultrasound showed an intraplaque track in the proximal part of the
occlusion, a short extraplaque segment, and then again intraplaque track again distal to AFR site. (c) Contralateral
injection confirmed true lumen position of the antegrade Gaia Third in the posterior descending artery. (D) Final result
after implantation of three drug-eluting stents. Asterisk indicates true lumen. Abbreviations: MSA, minimal stent area.
CHAPTER 17 Antegrade Fenestration and Re-entry 165
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balloon for AFR demonstrating a success rate of 71%
and no device-related complications.
Furthermore, AFR can also be employed to bail out
acute vessel closure in non-CTO PCI. Merella et al. [15]
report a case where the operator had lost wire control of
the distal vessel in a patient presenting with ST-elevation
myocardial infarction. The vessel re-occluded due to
dissection. AFR was successfully performed as a bailout
to achieve distal true lumen re-entry and led to recanalization of this iatrogenic acute vessel closure.
Finally, AFR has also been successfully adopted in
peripheral intervention, as shown by Del Giudice and
Gandini, who published a series of patients treated
with AFR by the dual-guidewire balloon described
above [16]. In fact, the straight course and absence of
side branches of the peripheral arteries in the legs
(e.g., the superficial femoral artery) make AFR particularly appealing.
Conclusions
AFR is a novel, targeted, safe, effective, and inexpensive ADR technique which can be used to achieve
CTO recanalization, either as a first-line strategy or
to bail out any other technique. Its adoption by several international operators with varying degree of
expertise and its promising initial multicenter experience confirm the reproducibility and teachability of
the technique. Further improvement of AFR, including the incorporation of intravascular ultrasoundderived information, combination with the retrograde
approach (facilitated AFR), and the development of a
dedicated device, will further facilitate the adoption
and increase the success rate of this novel technique.
References
1 Azzalini L, Carlino M, Brilakis ES et al. Subadventitial
techniques for chronic total occlusion percutaneous coronary intervention: the concept of “vessel architecture”.
Catheter Cardiovasc Interv 2018; 91(4): 725–734. doi:
10.1002/ccd.27025.
2 Colombo A, Mikhail GW, Michev I et al. Treating
chronic total occlusions using subintimal tracking and
reentry: the STAR technique. Catheter Cardiovasc Interv
2005; 64(4): 407–411. doi: 10.1002/ccd.20307.
3 Azzalini L, Dautov R, Brilakis ES et al. Procedural and
longer-term outcomes of wire- versus device-based antegrade dissection and re-entry techniques for the percutaneous revascularization of coronary chronic total
occlusions. Int J Cardiol 2017; 231: 78–83. doi: 10.1016/j.
ijcard.2016.11.273.
4 Azzalini L, Uretsky B, Brilakis ES, Colombo A, Carlino
M. Contrast modulation in chronic total occlusion per-
cutaneous coronary intervention. Catheter Cardiovasc
Interv 2019; 93(1). doi: 10.1002/ccd.27869.
Carlino M, Godino C, Latib A, Moses JW, Colombo A.
5
Subintimal tracking and re-entry technique with contrast guidance: a safer approach. Catheter Cardiovasc
Interv 2008; 72(6): 790–796. doi: 10.1002/ccd.21699.
6
Danek BA, Karatasakis A, Karmpaliotis D et al. Use of
antegrade dissection re-entry in coronary chronic total
occlusion percutaneous coronary intervention in a contemporary multicenter registry. Int J Cardiol 2016; 214:
428–437.
7
Maeremans J, Dens J, Spratt JC et al. Antegrade dissection
and reentry as part of the hybrid chronic total occlusion
revascularization strategy: a subanalysis of the RECHARGE
Registry (Registry of CrossBoss and Hybrid Procedures in
France, the Netherlands, Belgium and United Kingdom).
Circ Cardiovasc Interv 2017; 10(6): e004791. doi: 10.1161/
CIRCINTERVENTIONS.116. 004791.
Azzalini L, Dautov R, Brilakis ES et al. Impact of crossing
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strategy on mid-term outcomes following percutaneous
revascularisation of coronary chronic total occlusions.
EuroIntervention 2017; 13: 978–985.
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Harding SA, Wu EB, Lo S et al. A new algorithm for
crossing chronic total occlusions from the Asia-Pacific
Chronic Total Occlusion Club. JACC Cardiovasc Interv
2017; 10(21): 2135–2143.
Tanaka H, Tsuchikane E, Muramatsu T et al. A novel
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algorithm for treating chronic total coronary artery
occlusion. J Am Coll Cardiol 2019; 74(19): 2392–2404.
doi: 10.1016/j.jacc.2019.08.1049.
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Alkhouli M, Cole M, Ling FS. Coronary artery fenestra-
tion prior to stenting in spontaneous coronary artery dissection. Catheter Cardiovasc Interv 2016; 88(1): E23–E27.
doi: 10.1002/ccd.26161.
12
Carlino M, Azzalini L, Mitomo S, Colombo A. Antegrade
fenestration and re-entry: a new controlled subintimal
technique for chronic total occlusion recanalization.
Catheter Cardiovasc Interv 2018; 92(3): 497–504.
13 Azzalini L, Alaswad K, Uretsky BF et al. Multicenter
experience with the antegrade fenestration and reentry
technique for chronic total occlusion recanalization.
Catheter Cardiovasc Interv 2020. doi: 10.1002/ccd.28941.
14 Galassi AR, Vadalà G, Testa G et al. Dual guidewire
balloon antegrade fenestration and reentry technique
for coronary chronic total occlusions percutaneous coronary interventions. Catheter Cardiovasc Interv 2022 May.
doi: 10.1002/ccd.30324.
15 Merella P, Lorenzoni G, Gasparini GL, Oreglia JA, Casu
G. Antegrade fenestration and re-entry for bailout
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doi: 10.1016/j.carrev.2018.08.014.
16 Del Giudice C, Gandini R. Subintimal crossing of chronic
total occlusions in peripheral arteries with a dual guidewire balloon catheter: the PRAESTO study. J Endovasc
Ther 2022 Jul 2;15266028221106308. doi: 10.1177/
15266028221106308.
18
CHAPTER 18
Retrograde CTO PCI: Step by Step
Michael Megaly1 & Ashish Pershad2,*
1
Willis Knighton Heart Institute, Shreveport, LA, USA
2
Department of Interventional Cardiology, Chandler Regional Medical Center, Gilbert, AZ, USA
*Corresponding author
Introduction
Retrograde PCI was first described in the 1990s.
Procedures were performed through saphenous vein
grafts (SVG) [1, 2]. In 2006, septal collateral crossing
was reported in Japan [3], which was then followed by
an evolution of the technique to include even epicardial collaterals. Retrograde techniques have contributed to the increased success rates of CTO-PCI [4, 5].
Retrograde CTO PCI is technically challenging and is
associated with higher complications rates [6, 7]. It
has however become a fundamental tool in contemporary CTO PCI and this chapter goes over the steps
of this complex procedure.
Indications of retrograde CTO PCI
Proximal cap ambiguity remains one of the most
important indications of the retrograde approach.
Attempts to resolve proximal cap ambiguity may
involve using pre-procedure CTA, or intra-procedure
IVUS, when suitable anatomy permits. In certain
geographies, the threshold for going retrograde may
be a lot lower based on local practice patterns, operator expertise and unavailability of specific devices to
perform dissection re-entry [8–12].Absolute indications of the retrograde approach in contemporary
practice include:
(1) Aorto-ostial occlusions: In these cases, it is often
impossible to seat a guiding catheter to get support for
the intervention and aggressive manipulation of wires
or the guide carries a high risk of aortic root dissection (EXAMPLE 1).
(2) Inability to engage the CTO vessel (e.g., anomalous origin of the CTO vessel (EXAMPLE 2).
(3) An ambiguous proximal cap which cannot be clarified by the techniques described earlier (CTA/IVUS).
Other relative indications for going retrograde include
(1) Diffusely diseased distal vessel deeming it unfavorable for reentry and available interventional retrograde collaterals.
(2) When the distal cap of the CTO is at a bifurcation
(when ADR techniques might lead to compromise of
one of the branches of the bifurcation).
Fundamentals of the retrograde
approach
The retrograde approach is a technically demanding
procedure. Proper set up helps improve the safety and
success of the procedure.
(1) Access:
Both radial and femoral access can be used for retrograde CTO PCI. Bi-radial access is feasible and associated with fewer vascular complications [13]. Left
radial access is ergonomically challenging for the
operator. Radial access in general offers less support
and its use in taller patients might require use of a
100-cm guide, which can make externalization of
wires challenging. Femoral access should be attained
with the standard of care “safe femoral” techniques
using ultrasound and fluoroscopy [14]. Preclosure
with a single perclose device (Abbott Vascular, US), is
helpful, especially with 8-Fr. Access.
(2) Guides:
Retrograde CTO PCI almost always requires two guiding catheters. In rare cases where collaterals are ipsilateral, a single 8-Fr. guide can be used. An alternative to
using a single guide for ipsilateral collaterals is having
another guide for externalization – the so-called PingPong technique. Retrograde guiding catheters should
be 90 cm in length to allow the microcatheters to reach
their targets and to facilitate externalization, especially
when collaterals are long and tortuous.
Chronic Total Occlusions: A Guide to Recanalization, Third Edition. Edited by Ron Waksman and Shigeru Saito.
© 2024 John Wiley & Sons, Ltd. Published 2024 by John Wiley & Sons, Ltd.
166
CHAPTER 18 Retrograde CTO PCI: Step by Step 167
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(3) Donor vessel management:
There should be a safety wire placed in the donor
vessel to allow management of complications should
they occur. (e.g., proximal dissection of the donor
vessel). ACT should be maintained between 300–
350 seconds to avoid thrombosis of the donor vessel
and checked diligently during the case with the
responsibility preferably delegated to a specific
individual. If there are any angiographically
significant lesions in the donor vessel, they should
be treated first to prevent ischemia especially after
the diseased segment is crossed by a potentially
occlusive microcatheter.
Management of collaterals in
retrograde CTO PCI
(1) Choosing the collateral channel
Collateral channels size and morphology change
over time; therefore; a careful review of prior angiograms is fundamental when planning the retrograde approach [15]. When selecting a collateral
channel, multiple factors are considered. Angles of
entry and exit, presence of a major bifurcation at
the distal cap, distance from the distal cap are some
considerations. The most important factors predicting the success of retrograde crossing are the
size of the collateral [16] and tortuosity of the collateral [17]. SVGs are the safest collaterals to cross
because of their large size, lack of tortuosity, and
lack of side branches [18]. They can be crossed even
when occluded with a polymer jacketed wire and
MC and their traversal without dilatation does not
cause distal embolization into the native circulation.
Their use is limited by the acuteness of the angle of
the anastomosis which can sometimes make retrograde access challenging especially with hair pin
like angulations.
The most common retrograde collateral used are
septal collaterals. Large non-tortuous septal collaterals are commonly used [19] but even invisible
(Werner class 0) septal collaterals can be crossed
with surfing [20]. When traversal is stalled, they
can be dilated with a 1.5–2
any untoward consequence. Most perforations of
septal perforator branches are benign and require
no specific treatment. Epicardial collaterals are the
least preferred of all collaterals due to the lower
success rate of traversal and higher risk of perforation and tamponade, especially in prior bypass
patients [19, 21]. Internal mammary artery grafts
should rarely be used given the high risk of injury
and subsequent hemodynamic compromise [22]
(Figure 18.1).
mm balloon without
Crossing the collateral with a guidewire
(2)
The first step is to reach the collateral channel using a
workhorse guidewire inside a microcatheter. A double
bend on the wire may be required for entering the
septal collateral. Once the guidewire enters the collateral, it is followed by a microcatheter. Guidewire
choice depends on the type of collateral used and
operator expertise. A soft hydrophilic wire is used to
traverse any collateral channel (e.g., Sion, Suoh 03
(Asahi Intecc, Japan) A 1 mm bend is usually placed
on the guidewire tip. When attempting to cross
occluded SVGs, a stiffer polymer jacketed wire might
be helpful. This can be followed by a softer wire to
navigate to the distal cap.
In septal collaterals, crossing can be angiographyguided or blind with the so-called surfing technique.
The guidewire is advanced rapidly without simultaneous rotation until it either buckles or advances
into the distal target vessel. If the wire buckles, it is
withdrawn and redirected. Again, a soft hydrophilic
wire (Sion, Sion black, or Suoh 03 – in small or tortuous collaterals) is usually utilized. In epicardial
collaterals, an angiography-guided approach is
always utilized and tip injections in orthogonal
views are recommended to map out the course of the
vessel before crossing is attempted. A Suoh 03 and a
Sion Black are the preferred wires for epicardial collateral crossing.
(3) Crossing the collateral with a microcatheter
After confirming the guidewire position with a retrograde injection, the microcatheter should be advanced
to the distal cap through the collateral. The choice of
microcatheter depends on the channel used. A 150-cm
microcatheter is used, either torqueable (e.g.,
Corsair,
Asahi Intecc, Japan, or Turnpike LP, Teleflex, US)
or non-torqueable (Caravel, Asahi Intecc, Japan,
FineCross MC, Terumo, USA). Torqueable microcatheters are usually preferred, as they provide more
support to penetrate the distal cap and advance within
the CTO body. However, in certain circumstances
(e.g., tortuous epicardial collaterals, non-crossable
collaterals, etc.), the smaller profile non-torqueable
microcatheters can be useful (Caravel, FineCross
MC).
Multiple steps can be used to overcome difficulties when the microcatheter-does not cross the
collateral [23]. The first step is to increase support
by using a larger guide or to use guide extensions
catheters. This can be followed by either changing
to a 135 cm microcatheter, which can help transmit
torque better than a 150 cm catheter or use a different microcatheter (e.g., smaller profile, more
torqueable). Another technique is to use a small
balloon to dotter or dilate the collateral channel
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