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Wanted: A Hybrid Peripheral CTO Algorithm
Peripheral and coronary CTOs differ; each requires its own tools and approaches.
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The comparison of peripheral chronic total occlusions and coronary CTOs is like comparing apples to oranges. There are many factors that differentiate the two, and merely using the same techniques and tools to revascularize peripheral CTOs as we do coronary CTOs will often lead to failure.
Instead, interventionalists who treat peripheral CTOs need to understand how the characteristics of peripheral CTOs and the tools available specifically for peripheral lesions can help us work toward developing a hybrid peripheral CTO algorithm — similar to, but distinct from, the hybrid coronary CTO algorithm.
Major Differences
There are many reasons why peripheral CTOs are not comparable to coronary CTOs (see Table on page 26). One is the morphology of the disease. Most coronary CTOs have intimal calcification, but peripheral CTOs usually combine intimal and medial calcification. That is a significant point, because coronary CTO wires tend to fail miserably when confronted with medial calcification. Peripheral CTOs not only have a greater percentage of calcium deposits than coronary CTOs, but due to the calcium combining with fibrin and thrombus, they also tend to have a very hard surface.
Coronary CTOs are usually short, whereas peripheral CTOs are usually long. The location of peripheral CTOs away from the sheath of the guiding catheter makes it very difficult to maneuver crossing modalities through the CTO cap and the CTO itself.
Another aspect to consider is that, in relation to the vessel diameter, the cap thickness of the coronary CTO is significantly smaller than the cap thickness of the peripheral CTO.
The majority of coronary CTO lesions are eccentric in shape, while in the peripheral arteries they tend to be a mix of eccentric and concentric above the knee and mainly concentric below the knee. Also consider that when peripheral CTOs rupture, they tend to confer a greater thrombus burden than when coronary CTOs rupture. So, proper wire catheters for these lesions must be well-utilized and well-understood, or else the procedure will be a troubled one.
A common complication during crossing of the peripheral CTO is deflection of the crossing tool by the CTO cap. The convex component of the peripheral CTO cap pushes the CTO crossing tool to the side of the CTO cap and the tool can end up in a corner between the vessel wall and the CTO cap. As operators push more, two things almost always happen: No. 1, we go deep into the intimal space, and No. 2, we perforate and exit the arterial wall.
Specific Tools Needed
Coronary wires and catheters do not work as well in peripheral vascular disease. Our group was the first to perform a trial of the CrossBoss coronary wire (Boston Scientific) in patients with peripheral vascular disease, and that catheter failed miserably. It was completely redesigned based on the feedback we gave the company, and now the peripheral version of the wire is commonly used in practice.
Wires developed for peripheral vasculature should be used in peripheral vascular interventions because they are made to support the peripheral CTOs. In particular, the tip of the peripheral wire is built completely differently from the tip of the coronary wire. The coronary wire tip is made for safety, to prevent perforations and dissections, whereas the peripheral wire is made with additional support to penetrate hard and complex caps.
Fortunately, low-profile balloons work very well in both coronary and peripheral CTOs.
A Hybrid Peripheral Algorithm
The coronary CTO is somewhat predictable in terms of location, morphology and lesion length, and it is easy to base a plan of attack on what the operator sees. If I asked 10 experts how to treat a focal lesion in the left anterior descending artery, all or nearly all would give the same answer. But if I asked how to treat a lesion in the periphery, I would probably get 10 different answers. Put another way, clinicians who treat CAD share a large common knowledge base, while within peripheral vascular disease, there is a large difference in basic common knowledge and fundamental approaches to the disease state. These are some of the reasons why we have been able to implement a coronary CTO crossing algorithm, but not one for peripheral CTOs.
However, there are things we can incorporate from the coronary CTO world into a peripheral CTO crossing algorithm. Coronary technical skills can easily be implemented in the peripheral arteries. Troubleshooting and planning methods for CTO crossing are similar in both areas, although telescoping methods are used much more often in peripheral vascular intervention. Operators for both procedures must have knowledge of the different catheter-wire combinations and their technical outcomes. Alternative access sites are becoming more common in both procedures, as is the antegrade/retrograde combination approach. And there are many commonalties between the two areas in post-procedural care, including dual antiplatelet therapy and lipid-lowering therapy.
We can also apply the knowledge we have gained from techniques we have adopted because of the challenging cap morphologies of peripheral CTOs. The proximal and distal portions of the long peripheral CTOs are almost always different. Often, the proximal portion might be antegrade convex but retrograde concave, and the distal portion might be retrograde convex but antegrade concave. Based on the basic laws of physics, it makes sense to approach the CTO in a hybrid manner by going after the distal CTO from a retrograde approach; the concave component of the CTO makes it much easier to cross. From there, you can venture the retrograde wire, and then reverse the access, and finish the therapy from the antegrade access that you already have. This is one method that has worked successfully in complex long CTOs.
The hybrid approach may be necessary even in short lesions in a single segment, because if they are calcified and chronic, they may not be able to be crossed in a conventional fashion. We have seen significant success in crossing within 2 minutes from the retrograde approach after we tried for 30 minutes to cross from the conventional antegrade approach.
‘Change Our Mindset’
Operators need to start thinking of peripheral CTOs in a completely different fashion than coronary CTOs. Compared with peripheral CTOs, coronary CTOs tend to be proximal and shorter, with thinner caps and less complex cap morphologies, and they are less likely to have side branches involved. Coronary CTOs tend to reconstitute in an area within 20 mm to 30 mm from the proximal to the distal cap, whereas peripheral CTOs tend to start distal from the origin of the operator’s catheter, which confers significant complexity. Peripheral CTOs are much more difficult to cross than coronary ones, and the wires and catheters made for coronary CTO crossing are useless when it comes to crossing complex long peripheral CTOs.
To be more successful in peripheral CTO crossing, we need to change our mindset and stop equating coronary and peripheral CTOs in terms of pathophysiology. We need tools such as catheters and wires to be designed specifically for peripheral applications; these tools must have more durability and pushability than their coronary counterparts to achieve the same success. Until these things are achieved, we are going to continue to struggle to treat peripheral CTOs.
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- J.A. Mustapha, MD, FACC, FSCAI, is director of cardiovascular research at Metro Health – University of Michigan Health in Wyoming, Michigan. He can be reached at jihad.mustapha@metrogr.org.
Disclosure: Mustapha reports he consults for Abbott Vascular, Bard Peripheral Vascular, Boston Scientific, Cardiovascular Systems Inc., Cook Medical, Medtronic, Spectranetics and Terumo.