The Hybrid Algorithm

Yes

No

Yes

No

Yes

No

Fail

Fail

Fail

Fail

Fail

Fail

 

Dual Injection

The first and most important step of CTO PCI is to perform dual coronary injection, in nearly all cases. Dual injection allows good visualization of the proximal and distal vessel and the collateral circulation, allowing selection of the most suitable initial crossing technique. Dual injection can also clarify the location of the guidewire(s) during crossing attempts. Angiographic review should be done for at least 15 minutes and focus on four parameters: (a) proximal cap; (b) lesion length; (c) quality of the distal vessel; and (d) presence of collaterals suitable for the retrograde approach (interventional collaterals).

Assessment of CTO characteristics

 

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 and to understand the course of the vessel in the CTO segment. 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 ostial occlusions, which require use of a primary retrograde approach.

 

2. Target coronary vessel beyond the distal cap

​Assessment of target vessel refers to the size of the lumen, calcification, presence of significant side branches, vessel disease at the reconstitution point, and ability to adequately angiographically visualize this segment.

 

3. Interventional collaterals

Size and suitability of collateral circulation for retrograde techniques. Optimal collateral vessels for retrograde CTO PCI:

  • Are sourced from a healthy (or repaired) donor vessel.

  • Can be easily accessed with wires and microcatheters.

  • Have minimal tortuosity.

  • 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)

  • Enter the CTO vessel well beyond the distal cap.

 

4. Lesion Length

​Lesions are dichotomized into those that are <20mm and ≥20mm long, and can only be accurately assessed by using dual injections (single injections often underestimate the length of the occlusion). When antegrade crossing is attempted, short CTOs (<20 mm) are usually approached with antegrade wiring, whereas in long (≥20 mm) CTOs, upfront use of a subintimal dissection/re-entry technique is preferred, because there is high probability that wire-based crossing attempts will result in subintimal wire entry.

 

Antegrade Wiring

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, 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.

 

Antegrade Dissection and Re-Entry

For long lesions approached in the antegrade direction, upfront use of a dissection/re-entry strategy is recommended. 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.  Re-entry is performed in most cases with the Stingray system.

 

Retrograde

The retrograde approach can be used either upfront (primary retrograde) or after a failed antegrade crossing attempt. Factors that favor a primary retrograde approach include an ambiguous proximal cap, distal cap at a bifurcation, or poor distal target vessel. Retrograde crossing of short (<20 mm in length) lesions is usually attempted by advancing the retrograde guidewire into the proximal true lumen (retrograde true lumen puncture, conceptually similar to antegrade wire escalation). Retrograde crossing of longer (≥20 mm in length) lesions is most commonly done with the reverse controlled antegrade and retrograde tracking and dissection (reverse CART) technique.

 

Change

Alternating between different CTO PCI techniques is at the heart of the “hybrid” algorithm. Every CTO is different and as a result may require different strategies for success. When one approach fails, something different should be attempted. Excessive persistence in the face of minimal progress increases the chances for procedural failure due to utilization of limited resources (radiation, contrast, time). Generally, no more than 5-10 minutes should be spent in a stagnant mode without minor (such as re-shaping the tip of wire, or changing to a wire with significantly different properties), or major (such as switching from an antegrade to a retrograde approach) technique adjustments being made. Effective strategy changes require high level of familiarity and comfort with all CTO crossing strategies.