Percutaneous coronary interventions (PCI) in chronic total occlusions (CTOs) have undergone tremendous advancements in techniques and success rates over the past 15 years. Expert hybrid operators are now able to achieve success rates in excess of 85-90% in very complex lesions. The main modalities of CTO failure in order of frequency are: (1) failure of guidewire crossing into the true distal lumen, (2) failure to cross with a balloon catheter and, least commonly, (3) failure of balloon inflation. Balloon uncrossable lesions occur in 6-9% of cases [ , ]. Using a variety of techniques, balloon crossing challenges can still be overcome in approximately 90% of cases [ ]. Not surprisingly, these cases require significantly longer procedure times, higher radiation exposure, and contrast use [ ].
There are two underlying principles to overcome the resistance preventing balloon crossing: increase guiding catheter support and/or plaque modification [ , ].
Increase guiding catheter support: This may be achieved by upsizing the guiding catheter or replacing with more supportive shapes (e.g., Amplatz). However, these exchanges can be very tricky if smaller (6F) sheaths are in place and often risk losing a hard-earned position of the CTO guidewire in the distal lumen. More commonly, guide-catheter extensions (e.g., GuideLiner, TrapLiner, Guidezilla) are the first approach. This can be supplemented by side-branch anchoring using small (1.5-2.0 mm diameter) balloons positioned proximal to the CTO. Very experienced operators (see below) may use subintimal distal anchoring [ ].
Plaque Modification: Lesion modification techniques may involve a variety of guidewires, microcatheters, and devices. The initial attempts are typically to either cross with a microcatheter or dilate with small (1.20-1.5 mm diameter) or long (≥ 20 mm) angioplasty balloon catheters. Longer balloons are more likely to penetrate deeper into the CTO lesion.
If conventional balloon inflations do not facilitate balloon crossing, a second guidewire (“buddy wire”) may be advanced through the CTO to attempt “wire cutting” or “see-saw wire-cutting” techniques [ ]. Another balloon-based technique is BAM (balloon assisted microdissection), also known as “grenadoplasty”, with reported success rates approaching 50% [ ]. A small diameter (1.20-1.5 mm diameter) balloon is advanced as far as possible and intentionally ruptured to produce microdissections and facilitate crossing. An alternative approach involves specialized crossing balloon catheters such as the Threader (Boston Scientific) or Glider balloon (Trireme Medical) [ ].
Specialty microcatheters, such as the Tornus catheter (Asahi Intecc), or more recent Turnpike (Teleflex) spiral or gold microcatheters (containing threads enabling a “screw-like” approach), are specifically designed for difficult crossing cases and may enlarge a channel through the CTO. More conventional microcatheters (e.g., Finecross, Corsair, Corsair Pro, Turnpike, Turnpike LP, SuperCross) may also work. If microcatheters cross the CTO but are still balloon non-crossable, the CTO guidewire in the distal lumen can be exchanged for a rotawire and rotational atherectomy ablation (or orbital atherectomy guidewire and catheter) can be used. In some cases where the original guidewire has crossed the CTO but the microcatheter remains stuck within the CTO, a rotawire can still be successfully advanced into the distal lumen, although this maneuver risks giving up guidewire position in true distal lumen. Where available, 0.9 mm excimer laser atherectomy over a conventional guidewire is also an option [ ].
When these methods fail, expert operators can utilize a subintimal crossing technique with advancing (typically by knuckling) a second guidewire subintimally distal to the CTO. Operators can then either inflate a subintimal balloon at the level of the CTO to alter the CTO plaque, or advance the balloon distal to the CTO, achieving a “subintimal distal anchor” and thereby facilitate balloon crossing over the true lumen guidewire. If these fail, a retrograde approach is yet another advanced strategy option. An interesting new technology is the SoundBite Crossing System (SoundBite Medical), which is a 0.018-inch wire that delivers acoustic shockwaves to the distal tip of a steerable guidewire [ ].
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Comments on Current Case
In this issue of Cardiovascular Revascularization Medicine , Synetos et al. described a successful procedure in a balloon-uncrossable CTO case requiring a combination of techniques that have previously been reported separately: proximal anchoring and distal trapping [ ]. It is interesting to note that the antegrade wire approach was attempted through a 6Fr guiding catheter. It has been common practice in CTO interventions to use larger guiding catheters, usually 7Fr or 8Fr. The size of these larger guiding catheters can accommodate all microcatheters, the crossboss/stingray components, and multiple guidewires/balloons. Finecross (Terumo), SuperCross FT (Teleflex) and Caravel (Asahi Intecc) microcatheters can all fit through a 6Fr guiding catheter and be exchanged by balloon trapping. Until recently, several commonly used CTO microcatheters, such as Corsair and Corsair Pro (Asahi Intecc) and the Turnpike family (Teleflex), have been challenging to use in 6Fr guiding catheters, due to insufficient room for microcatheter exchanges with a trapping balloon. However, the TrapLiner (Teleflex) has overcome this limitation in 6Fr guiders. Newer radial sheath designs, such as the 7F Glidesheath Slender (Terumo), have also greatly expanded the number of patients able to accept a 7F sheath.
The resourcefulness and expertise of these operators to execute these techniques concurrently in such a creative way is laudable. However, it should be appreciated that the requirement of accessing the left coronary artery through a septal collateral does pose additional risk, since a long segment of guidewire is advanced without microcatheter protection for the collateral, and the left anterior descending and left main coronary arteries. A potential concern in such a scenario is that a vigorous pulling movement could have a “cheese-cutter” effect on these vessels. The authors raised the possibility of exchanging for a rotablator wire through the caravel microcatheter and performing rotational atherectomy. Their reluctance to do so due to the presence of the coronary stent will not be shared by other operators who may prefer this approach and thus avoid the septal collateral to left main guiding catheter maneuver. In CTO lesions, the European expert consensus on rotational atherectomy recommends the use of smaller burr sizes than in non-CTO lesions [ ]. A single-center retrospective series of 75 CTO cases treated with rotational atherectomy for balloon-uncrossable and undilatable lesions was recently reported [ ]. By using burr sizes up to 0.5 vessel ratio, an overall 95% success rate was achieved, including 20% cases with dissections prior to rotational atherectomy, with very low complication rates.
The best technique is ultimately the technique that can be done successfully and safely, in a predictable fashion across all skill sets, and ideally low-cost. The proximal anchoring, distal trapping technique is extremely interesting but should be reserved for experts. Recently, we published a classification for CTO operators based on operator expertise and case volumes [ ]. This classification system recognizes that CTO PCI will not be limited to experts only, and guidance should be provided regarding which operators should be undertaking which type of CTO cases and the skill set that should be expected. Operators performing <10 CTOs cases per year should probably not be involved with CTO cases. “Level 1” (intermediate), operators have very good anterograde skills and are attempting at least 10 CTOs cases per year, typically J-CTO score ≤2, but lack the time or personal commitment to reach elite status. “Level 2” (expert), typically perform > 30 CTOs cases per year, have mastered the hybrid skill set, and can undertake any CTO case, irrespective of J-CTO score [ ]. Fig. 1 advances this notion as a classification of recommended techniques to overcome non-crossable balloon lesions according to the skill set and experience of the operator.
