Basic Wire-Handling Strategies for Chronic Total Occlusions

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3. Steering your Wire

a) Wire characteristics ~ which one to choose?

i) Basic characteristics of the different wires: Looking at those wires that are either already on the market or soon to come out, and leaving the Magnum Wire aside as a special case, wires designed for treating CTOs largely divide into two main groups, polymer coated wires and coil wires (Table 1). The polymer coated wires have a hydrophilic coating, which means they attract very little resistance when they come into contact with tissue in the lumen, and move quite easy through soft tissue. The operator feels little resistance. These wires offer good maneuverability in tortuous vessels, and compared to the coil wires can be steered more easily to the true lumen immediately after a sharp bend. On the other hand, one has to be careful as they can easily find their way down false lumina. These wires do not have the greatest torquability. As a rule, they are generally harder to steer than coil wires, and may not respond as well to attempts to get them to follow the precise path one has in mind. In contrast, the coil wires tend to encounter more resistance inside the lumen than polymer coated wires, but as these wires have been developed to have good torquability even inside a hard tight CTO, they do respond well to the minutest commands. They also tend not to slip very easily into the softer tissue of false lumina, and the operator can usually learn the feel of the guidewire tip. The harder the wire tip, the greater the torquability of the wire. The less resistance at the tip is felt by the operator, the easier it is to find a false lumen. To give an example, the tip of the Miracle 3g wire is not quite as hard as that of the ACS Standard wire, and resistance will be harder to detect if by mistake the latter wire ends up in a false lumen. Once again, the harder the tip of the wire, the more careful you have to be about false lumina when advancing it around a sharp bend. Another thing to bear in mind is that as the tip of the coil wires attracts a lot of resistance, it is more difficult for it to end up in or select very small channels. This means that it is more likely than the polymer coated wires to end up creating a false lumen. The recently introduced tapered wires (Conquest 0.014-0.009 in; Crossit 0.014-0.010 in), tend to slip into or select very narrow channels more easily than normal coil wires. These wires are also useful for penetrating the fibrous cap. With the Conquest and the Crossit XT 300-400 wires, the hard tip means that they do tend to end up in false lumina just after tight bends, and it is hard to feel resistance if they do so. These wires require the close attention of the operator, since they can also cause perforations in the vessel wall.

ii) Which wire to choose? When tackling CTOs, wire selection must be tailored to the specific characteristics of the lesion. Exchanges for more suitable wires must be made during the procedure, if circumstances demand it. This is because different wires offer different advantages. There is no one wire that fits all eventualities.

When the occlusion is no older than 6 months, and the CTO is relatively soft, an intermediate wire will usually be the first choice. When a wire with a hard tip is used in this kind of softer tissue, it is quite difficult to feel subtle changes in resistance and easy therefore to end up creating a false lumen. The Miracle3g with its superior torquability may sometimes be a good choice here, but again one has to be careful not to open up a false lumen. For a relatively hard taper CTO of between six to twelve months old, I tend to start off with the ACS Standard or Miracle 3g or 4.5g wires. When there is a recanalization channel or some other kind of channel, and one spots some kind of light bend in the channel, a polymer coated wire such as the Choice PT is a good initial wire, but change to a coil wire if there is any indication that the wire has started along a false channel. When dealing with a convex-type lesion with no dimpling, go for a hard wire like the Miracle 12g, or a tapered wire, such as the Conquest, the Cross It XT300-400. With less hard wires, there is the risk of creating a false lumen. In a really hard convex-type lesion, a heavy-duty wire like a Miracle 12g or up, or a Cross Wire 80g or up is best. In CTOs that are fairly short, or where one can predict the course of the lumen relatively easily, it should be possible to use a single hard-tipped wire all the way through, from penetrating the proximal fibrous cap, passing through the CTO and getting through the distal fibrous cap. In longer CTOs, however, especially if the course of the lumen is not obvious, if one tries to avoid making a false lumen by judging from the feel of the resistance at the wire-tip, he may end up pushing the wire into the media. If the same hard wire is then used to penetrate the CTO’s proximal fibrous cap, there is a higher risk of causing a perforation or making a false lumen. It is normally better, after the initial breakthrough into the CTO, to switch to a Miracle 4.5g or less, or on a case-by-case basis, to an intermediate wire. For similar reasons, a polymer-coated wire is less than ideal in these kinds of lesions. Once there is a false lumen, it may be desirable to switch back to a harder wire or a tapered wire to look for another channel, or break through the hard tissue in the middle of the CTO. Going back to a hard (Miracle 6g or 12g) or tapered wire to penetrate the distal fibrous cap can help to minimize the risk of false lumina. If because of tortuosity or tight bends, resistance is strong and handling difficult, the best thing might be to switch to a polymer coated wire when trying to find a channel through relatively soft CTO tissue.

As I state below, handling the wire is a delicate and painstaking task. You will also often find that the distal fibrous cap is thinner than the occlusion’s proximal fibrous cap, so it helps to be able to feel a channel that actually connects to the distal true lumen. A tapered wire may be useful for this. Once again though, once the wire goes along a false lumen in the distal fibrous cap, there may be no choice but to use that penetration point.

Figure 6

Figure 6: Shape of the wire-tips

b) Wire tip shapes

There are four different shapes for CTO wires, as is shown in Figure 6, and the most common, or basic shape has a 2-3mm 45° curve as in (a). When you are selecting a branch with the wire and then planning to cross it forward to the CTO, use a (d) type wire. Wire type (b) with its large curve is a good wire to use when you have created a large false lumen and need to pull out of that and locate the true lumen. One thing to bear in mind however is that big-curved tips have a tendency to find their way through the intima and as these can make existing false lumina even larger, you should try to use one with as small a curve as possible. With the (c) type wire, the core in the wire gets bent and this wire can quickly get worn out inside highly resistant hard CTOs. This kind of curve though is sensitive to resistance, and is a good one when you need very delicate and precise control of the wire tip. Because it does not withstand torque as well, it tends to make false lumina and may make previously created channels even larger.

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