Abstract
The hybrid algorithm for chronic total occlusion (CTO) percutaneous coronary intervention provides guidance on selection of the optimal CTO crossing strategy in a stepwise fashion. First, dual injection is performed. Second, four angiographic lesion characteristics are assessed—(1) proximal cap ambiguity, (2) quality of the distal vessel, (3) lesion length, and (4) presence of adequate collateral vessels—allowing adequate crossing strategy selection. Wire escalation is favored for <20 mm long lesions, whereas dissection and reentry is favored for >20 mm long lesions. The antegrade approach is favored when the proximal cap is clear, and the retrograde approach is favored for lesions with an ambiguous proximal cap when appropriate collateral vessels are present. Early change of crossing strategy is recommended if the initially selected crossing strategy is unsuccessful.
Keywords
Algorithm, Antegrade dissection and reentry, Antegrade wire escalation, Change, Chronic total occlusion, Retrograde, Technique
The optimal approach to chronic total occlusion (CTO) percutaneous coronary intervention (PCI) continues to evolve. Although various CTO crossing techniques have been developed (antegrade wire escalation; antegrade dissection/reentry; and retrograde, as described in Chapter 4 , Chapter 5 , Chapter 6 ), there are different schools of thought about the relative merits and priority of each of those approaches.
In January 2011 several high-volume CTO operators convened in a workshop that took place in Bellingham, Washington and created a consensus algorithmic approach about how to optimally approach CTO crossing. This approach, named the hybrid approach to CTO PCI ( Fig. 7.1 ), focuses on opening the occluded vessel, using all available techniques (antegrade, retrograde, true-to-true lumen crossing, or reentry), tailored to the specific case in the safest and most effective and efficient way.
The main principle behind the hybrid approach is that operators should master all of the skill sets of CTO PCI and be able to alternate between these techniques during the same CTO PCI procedure to recanalize the CTO. The goal has been to demystify the procedure by breaking down its various components and gaining in-depth understanding of the principles underlying each technique, making it reproducible and teachable, and thus available to the broader interventional community. The hybrid approach has been used in a large number of cases in both the United States and Europe with high success rates, and is also useful in learning CTO PCI in a stepwise fashion.
7.1
Description of the Hybrid Algorithm
The first and arguably most important step of CTO PCI is to perform dual coronary injection, in nearly all cases, as described in detail in Section 3.2 . Dual injection allows good visualization of both the proximal and distal vessel, as well as the collateral circulation, allowing selection of the most suitable initial crossing technique. It also clarifies the location of the guidewire(s) during crossing attempts. Routine performance of dual injection is the simplest and most important step to increase the success rate and safety of CTO PCI.
In-depth review of diagnostic angiographic images prior to PCI is critical. Most experienced CTO operators recommend against performing ad hoc CTO PCI, instead performing CTO PCI only after a well thought out procedural plan has been developed. Time spent studying the diagnostic film is an investment toward a successful CTO PCI procedure. Moreover, radiation and contrast can be reduced during PCI, since the anatomical information has already been obtained during prior diagnostic angiography. Sometimes, however, dual injection images may not be performed until the time of PCI.
Four angiographic parameters are assessed ( Chapter 3, Section 3.3 ): (1) the morphology of the proximal cap; (2) the length of the occlusion; (3) the vessel size and presence of bifurcations beyond the distal cap (i.e., landing zone); and (4) the location and suitability of collateral channels for retrograde access ( Fig. 7.2 ).
- 1.
Proximal cap location and morphology . This characteristic refers to the ability to unambiguously localize the entry point to the CTO lesion by angiography or intravascular ultrasonography (see Chapter 9 , Section 9.1 ) and to understand the course of the vessel in the CTO segment.
An ambiguous proximal cap increases the complexity of the procedure and decreases the likelihood of success. A favorable proximal cap is one that is tapered, as opposed to blunt, and has no bridging collaterals or major side branches that would make engagement of the CTO segment difficult using traditional wire escalation techniques. A particularly challenging anatomic subset is that of flush aorto-ostial occlusions, which require use of a primary retrograde approach (see Section 9.3 ).
- 2.
Lesion Length . Lesions are dichotomized into those that are <20 mm and ≥20 mm long. As noted earlier, in most cases this characteristic can be accurately assessed only by using dual injections.
In CTOs in which antegrade crossing is attempted, short CTOs (<20 mm) are usually best approached with antegrade wiring, whereas in long (≥20 mm) CTOs, up-front use of a subintimal dissection/reentry technique is preferred, because there is high probability that wire-based crossing attempts will result in subintimal wire entry. A lesion length <20 mm has been identified as a predictor of rapid CTO crossing in the Multicenter CTO Registry in Japan (J-CTO; Chapter 1 , Fig. 1.6 ). With the wide adoption of dual injection, it has become evident that the length of the occlusion is frequently shorter than the one estimated by single injections.
- 3.
Target coronary vessel beyond the distal cap . This refers to the size of the lumen, presence of significant side branches, vessel disease at the reconstitution point, and ability to adequately angiographically visualize this segment.
- 4.
Size and suitability of collateral circulation for retrograde techniques. Optimal collateral vessels for retrograde CTO PCI:
- a.
Are sourced from a healthy (or repaired) donor vessel.
- b.
Can be easily accessed with wires and microcatheters.
- c.
Have minimal tortuosity.
- d.
Are not the only source of flow to the CTO segment (which places the patient at risk for intraprocedural ischemia during crossing of the collateral).
- e.
Enter the CTO vessel well beyond the distal cap.
- a.
More favorable collateral circulation characteristics lower the barriers to utilizing retrograde techniques as an initial strategy or as an early crossover strategy.
What constitutes an interventional collateral (i.e., a collateral that can be wired during a retrograde approach) varies depending upon the experience and skills of the operator. In-depth understanding of the collateral circulation is also of paramount importance during antegrade crossing attempts, since dissection reentry techniques and the formation of subintimal hematomas may compromise ipsilateral or bridging collaterals, leading to poor visualization of the distal vessel at the reentry zone and occasionally ischemia. Degenerated or even recently occluded bypass grafts anastomosed to the target vessel distal to the CTO can be also used as retrograde conduits to facilitate PCI.
Assessment and utilization of these four angiographic characteristics is highly dependent on operator experience and skill set, and thus is constantly evolving.
Antegrade wire escalation refers to the use of guidewires of increasing stiffness to cross a CTO. In the past, a gradual escalation was performed: starting with a workhorse guidewire and then increasing in stiffness to a Miracle 3, 6, 9, and eventually a Confianza Pro 12 guidewire. Currently, however, a more rapid escalation is favored from a tapered-tip polymer-jacketed guidewire (Fielder XT or Fighter) to either a stiff polymer-jacketed wire (Pilot 200) when the course of the CTO is uncertain, or a stiff-tapered tip guidewire (Gaia 2nd or Confianza Pro 12) in cases where the course of the CTO is well understood ( Chapter 4 , Fig. 4.5 ). Streamlined use of a relatively small array of guidewires can simplify clinical decisions and inventory management and also leads to in-depth understanding of the properties of the different wires.
For long lesions approached in the antegrade direction, up-front use of a dissection/reentry strategy is recommended ( Fig. 7.3 ). Dissection can be achieved either by advancing a knuckle formed at the tip of a polymer-jacketed guidewire (such as the Fielder XT or the Pilot 200) or by using the CrossBoss catheter. Antegrade dissection minimizes the risk for perforation (by the blunt guidewire loop or by the CrossBoss catheter tip) and allows for rapid crossing of long occlusion segments. Reentry can be achieved using a stiff polymer-jacketed or tapered-tip guidewire with a sharp distal bend, or more consistently by using the Stingray system, as described in Chapter 5 .
