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Complex Lesion Subsets
9.1
Proximal Cap Ambiguity
Online Cases 2 , 5 , 16 , 30 , 32 , 33 , 34 , 45 , 47 , 49 , 51 , 55 , 56 , 69 , 80 , 88 , 93 , 104 .
Proximal cap ambiguity refers to the inability to determine the exact location of the proximal cap of the occlusion, due to the presence of obscuring side branches or overlapping branches that cannot be resolved despite multiple angiographic projections. It is encountered in approximately 31% of chronic total occlusion (CTO) percutaneous coronary interventions (PCIs) and is independently associated with technical failure. In the hybrid algorithm, proximal cap ambiguity is an indication for a primary retrograde approach ( Fig. 9.1 ); however, several antegrade options also exist ( Fig. 9.2 ).
9.1.1
Better Angiography
High-quality angiography, including dual injections and multiple, possibly steep, angiographic projections, may help resolve proximal cap ambiguity. Here are some examples :
- 1.
A Vieussens collateral (which is a collateral from the conus branch of the right coronary artery [RCA] to the left anterior descending artery [LAD]) may not fill with contrast if the RCA catheter is deeply engaged, or it may have a separate ostium instead of originating from the aorta. Contrast injections with the catheter less deeply engaged in the RCA can allow filling of the Vieussens collateral and help clarify proximal cap ambiguity ( Fig. 9.3 , Online Case 2 ).
- 2.
The origin of the CTO may overlap with the origin of a side branch. Various angiographic views with different angulation may help to separate the branches.
9.1.2
Computed Tomography Angiography
Computed tomography angiography (CTA) can help clarify the course of the occluded vessel ( Fig. 9.4 ), as well as provide information on the presence of calcification and tortuosity. CTA is particularly useful when the proximal lesion anatomy is unclear ( Section 3.3.6 ). There are ongoing efforts for coregistration of the coronary angiography and computed tomography images to facilitate crossing.
9.1.3
Intravascular Ultrasonography
Intravascular ultrasonography (IVUS) can help clarify the location of the proximal cap, especially when there is a side branch close to the occlusion ( Fig. 9.5 ). A short-tip, solid-state IVUS catheter is preferred as it can reach further down the vessel, allowing enhanced visualization. However, sometimes a smaller diameter rotational IVUS catheter can be used for smaller side branches that have a longer landing zone .
How?
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In ostial branch occlusions (e.g., ostial obtuse marginal CTO), inserting an IVUS in the main vessel can demonstrate the entry point into the occlusion (see Online Case 34 ) ( Fig. 9.5 ).
-
In main vessel occlusions, if there is a side branch adjacent to the occlusion (classic example is LAD CTO at the takeoff of a large diagonal branch, see Online Case 93 ), the IVUS is inserted into the side branch to identify the beginning of the CTO.
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IVUS guidance can be either (a) real-time (i.e., crossing attempts with simultaneous IVUS visualization), or (b) intermittent (i.e., imaging, followed by crossing attempts, followed by reimaging, etc.).
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Real-time guidance has several limitations:
- 1.
It requires 8 Fr guide catheters if the Corsair or Turnpike microcatheters are used, or 7 Fr guide catheters if lower profile microcatheters (such as the FineCross or Micro 14) are being used. Alternatively, a ping-pong guide catheter technique can be used.
- 2.
Intravascular position of the IVUS during crossing attempts may interfere with guidewire manipulation and hinder simultaneous contrast injection.
- 3.
The IVUS catheter may require constant repositioning due to movement during guidewire manipulation. Hence, live IVUS guidance is infrequently used for wiring through ambiguous proximal caps, and intermittent (serial imaging) is preferred instead.
- 1.
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In both scenarios, IVUS can be used to demonstrate the wire position during antegrade wire-crossing attempts. If the wire is in the intima or the subintimal space, but within the occlusion, a microcatheter can be advanced over the wire to provide additional support and facilitate crossing. If not, the wire is withdrawn and redirected.
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If a suitable sized artery is available, the short-tip solid-state IVUS catheter is preferred (Eagle Eye short tip, Volcano); it minimizes the extent of distal advancement, which is needed for distal imaging, and is also more deliverable.
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Increasing the diameter of the field of view can be useful in visualizing the occluded vessel, particularly as it traverses away from the IVUS catheter.
What Can Go Wrong?
- 1.
Injury (including perforation) of the side branch from advancing the IVUS catheter, hence the IVUS catheter should not be advanced through very small or tortuous vessels.
- 2.
Thrombosis, due to insertion of multiple equipment in the coronary artery.
9.1.4
Move-the-Cap
See Online Cases 32 , 45 , 82 , 83 , and 104 .
The move-the-cap techniques use antegrade dissection/reentry to clarify the course of the occluded vessel and achieve crossing. There are three variations of this technique: the balloon-assisted subintimal entry (BASE) technique, the scratch-and-go technique, and the Carlino technique. Each allows the operator to decide on the site of proximal subintimal entry .
9.1.4.1
Balloon-Assisted Subintimal Entry ( Fig. 9.6 )
Step 1 Wire the Vessel Proximal to the Chronic Total Occlusion
Step 2 Advance Balloon Proximal to Proximal Cap
How?
-
Use a slightly oversized compliant balloon (1.1:1 or 1.2:1 balloon:vessel diameter ratio).
-
Check in orthogonal projections that the wire and balloon are actually within the intended segment.
What Can Go Wrong?
-
Balloon may not advance due to severely diseased proximal vessel and/or severe calcification. In such cases predilation with a smaller balloon or other lesion preparation (e.g., with atherectomy or laser) may need to be performed first. Alternatively, a larger or more supportive guide catheter (such as Amplatz 1 for the RCA) or other guide supporting techniques, such as side branch anchor or guide catheter extension ( Section 3.6 ) may need to be used.
Step 3 Balloon Inflation
Step 4 Contrast Injection
How?
-
Through the guide catheter to verify that proximal vessel dissection has indeed occurred.
What Can Go Wrong?
-
Propagation of the dissection either downstream (potentially compressing the distal true lumen) or upstream (causing aortocoronary dissection). This can be prevented by gentle injection under fluoroscopic or cineangiographic imaging. Side-hole guides, or partially disengaging the guide, can also reduce the contrast injection force.
Step 5 Delivery of Microcatheter Proximal to Proximal Cap
How?
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Over the workhorse guidewire that was used to deliver the angioplasty balloon.
What Can Go Wrong?
-
Inability to deliver microcatheter due to tortuosity or calcification (unlikely given prior balloon inflation). If it occurs, additional balloon dilations or increased guide catheter support may be needed.
Step 6 Insert Polymer-Jacketed Guidewire and Create Knuckle Into Dissection Plane
How?
-
Advance a polymer-jacketed guidewire (such as Fielder XT, Fighter, or Pilot 200) through the microcatheter. Wire is advanced by pushing, not turning, to minimize the risk for fracture
What Can Go Wrong?
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Perforation. Can be prevented by checking the wire course in orthogonal projections.
-
Inability to form a knuckle. The wire tip may be reshaped into an umbrella-handle or other configuration, ensuring that the wire is folding back on itself rather than dissecting forward, before reinserting.
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Guidewire entrapment in the vessel wall ( Fig. 9.7 ). This is a very infrequent complication. Potential solutions include advancing a second guidewire next to the entrapped wire and performing balloon inflations in an attempt to free the wire. If the guidewire fractures, IVUS can help ascertain that there is no wire unraveling into the proximal part of the vessel or into the aorta.
Step 7 Chronic Total Occlusion Crossing (as Described in Section 5.4 )
How?
-
Once a wire knuckle enters the subintimal space it can be advanced through the occluded segment with very low risk of causing perforation due to the distensibility of the subintimal space. Reentry can now be set up beyond the distal cap of the CTO, ideally proximal to the origin of any large branches.
Step 8 Reentry (as Described in Section 5.4 )
How?
-
In most cases reentry is achieved as close to the distal cap as possible, using the Stingray system, as described in Chapter 5 . High-end reentry approaches, such as the “double Stingray” (see Online Case 80 ) or use of the retrograde approach, may be needed if the distal cap is at the bifurcation of a large branch (e.g., right posterior descending and right posterolateral vessel).
9.1.4.2
Scratch-and-Go ( Fig. 9.8 )
See Online Cases 2 , 16 , 32 , 45 , 59 , and 61 .
Step 1 Wire the Vessel Proximal to the Chronic Total Occlusion
Step 2 Advance Microcatheter Proximal to Proximal Cap
How?
-
Use any standard microcatheter, such as the Corsair and Turnpike.
-
Check in orthogonal projections that the wire and microcatheter are actually within the intended segment.
What Can Go Wrong?
-
Microcatheter may not advance due to severely diseased proximal vessel and/or severe calcification. In such cases predilation with a small balloon may need to be performed first. Alternatively, a larger or more supportive guide catheter (such as Amplatz 1 for the RCA) or other guide-supporting techniques (such as side branch anchor, or guide catheter extensions; Section 3.6 ) may need to be used.
Step 3 Insert Stiff Guidewire Over Microcatheter and Advance Toward Vessel Wall
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