How to Choose Angiographic Guidewire?

2.1 Length

The selection of a guidewire with a correct length can be very relevant to adequately reach and treat the target vessel. For this decision, distance from the access to the vessel to be treated and the shaft length of the sheaths and catheters to be used (either if it is a diagnostic catheter, a balloon catheter, or a delivery device of a stent or a stent graft) needs to be considered. In fact, this apparently less relevant subject may threaten the entire procedure.

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Depending on the manufacturer, guidewires can range from 80 to 450 cm. Additionally, some guidewires may allow the connection of an extension during the procedure. This is particularly the case when a coronary guidewire is used as it is designed for rapid exchange devices.

There is a trick that can help in extreme circumstances and as bailout option only. During the removal of a catheter from inside the patient, it is possible to connect an inflation syringe device to the guidewire port of the catheter, just after losing the guidewire, and inflate inside the port, which will keep the guidewire in place. It is crucial to perform this maneuver under fluoroscopy as the guidewire may move forward and the external tip can even migrate and be lost inside the patient.

2.3 Stiffness

There is no clearly accepted nomenclature that can reproductively relate a word or a group of words to the stiffness of a guidewire. As so, it is possible to find several guidewires with the label stiff, extra stiff, super stiff, or even ultra-stiff, without any objective information of its real stiffness. Flexural modulus is an engineering parameter related to a wire's resistance to bending (Figure 2). This measure is rarely displayed on the guidewire packaging or within the catalog [1]. Yet, it represents an objective method to quantify the stiffness of a guidewire.

This property is more frequently used to describe the body of the guidewire, but its use in the description of the tip of the guidewire can be very useful too. The stiffer the body of a guidewire is, the more support it will allow to deliver the intended endovascular devices to the target vessel. On the other end, a higher stiffness of the body reduces the ability of the guidewire to track the vessel tree. Concerning the tip, a higher stiffness increases the penetration capacity, but also turns the tip more aggressive to vessel wall increasing the risk of dissection or perforation.

3.4 Coating

Most of contemporary guidewires have a thin hydrophilic or hydrophobic coating applied at the final manufacturing process (Figure 4). Hydrophilic coating (e.g., polyethylene oxide or polyvinyl pyrolidone) needs water to be activated and to become slippery, but once wet, it allows an extremely low coefficient of friction [4]. As a result, it makes vessels easier to track and stenoses simpler to cross but leads to a decreased tactile feel, increasing the risk of dissection or perforation. Paradoxically, if a guidewire with hydrophilic coating gets dry, it loses lubricity and can get stuck, for instance, inside a catheter. Conversely, hydrophobic coatings (e.g., polytetrafluoroethylene or silicones) do not require water for activation [4]. As their name indicates, they repel water and create a smooth, 'wax-like' surface [3]. Hydrophobic coating reduces friction but leads to a less slippery guidewire with enhanced tactile feel. Frequently, hydrophobic coatings are applied to guidewire bodies to facilitate movement inside plastic catheters [4]. Nevertheless, both coatings can coexist in a single guidewire, allowing their respective specific characteristics to be present either at the tip or throughout the body. In some configurations, even the tip can have both coatings, for instance, hydrophobic at the end for tactile feel and tip control purposes and hydrophilic intermediate segment for smooth crossing. Moreover, both hydrophilic and hydrophobic coatings may chafe or degrade with use [4]. This can account for the deterioration in wire performance at times noted during long procedures, particularly when wires are working through areas of severe tortuosity and friction or after numerous device exchanges [4]. This can even lead the guidewire to get fixed inside the catheter, forcing both devices to be removed as one piece, jeopardizing the therapy of the targeted vessel.

4.4 Shape, shapeability, and shape retention

Most of the 0.035' guidewires used in peripheral interventions come in a preshaped format from the manufacturer. The more common available shapes are straight, angled, and J-shaped. The latter is the least traumatic. As so, it can be the best guidewire to use to deliver the intended devices to a target vessel. It can also be quite useful in tracking throughout a previously placed patent stent because the tip will not get stuck in the struts of the stent, neither will go between the stent and the vessel wall. Straight tips are more adequate to cross occlusions and angled tips to track vessels and to cross stenoses.

On the other hand, the vast majority of the 0.014' and 0.018' guidewires available for peripheral purposes comes in a straight shape and needs to be shaped. As so, shapeability characterizes the capacity of the guidewire tip to be angulated and shaped by the interventionist and shape retention represents its ability to maintain the intended shape over time [3]. These properties depend on the tip design and materials. Accordingly, a core-to-tip design with a core made of stainless steel is particularly easy and accurate to be shaped, but almost impossible to be reshaped. Conversely, nitinol core makes the tip more difficult to be shaped because it tends to return to its original form (memory) but is more reshapeable.

The tip of the GW can be shaped using the puncture needle (for moderately angulated curves), with the non-cutting edge of the blade (for sharp angulations) or with the inserter (for both) (Videos 1 and 2, https://bit.ly/3jPF7aj).

The desired shape depends on the primary purpose the guidewire will be used (Figure 10). Moderately angled continuous curves are very useful to track throughout the artery tree or to select a target vessel (Figure 10A). Several sharp angulations may help in selecting arteries with an acute takeoff such as the anterior tibial artery (Figure 10B). A very short sharply angled curve (usually no more than 1 mm) is intended to perform forceful and well-controllable drilling (Figure 10C).

5.1 Basic rules for guidewire manipulation

One of the best friends of a vascular interventionist is the torquer (Figure 11). It is the most proper manner to control the orientation of the guidewire tip. Therefore, its utilization is of utmost relevance in tracking difficult anatomies or in crossing challenging lesions (for instance, if the drilling technique is to be employed).

After having crossed the target lesion, the guidewire should be advanced very smoothly to the distal segment of the vessel. Confirmation through contrast injection that the true lumen has been reached after crossing the lesion is a basic but essential step. If a guidewire with a very aggressive tip was used to cross the lesion, it should be replaced by a much safer guidewire with good body stiffness for support (frequently the initial workhorse guidewire is adequate for this intent), sometimes after having shaped the tip as a loop (J-shaped like). During the delivery of the intended devices to the target lesion, it is of paramount importance to avoid inadvertent retraction of the guidewire, particularly after a complex crossing step and to prevent back and forth or shaking motion of the guidewire. That is why the tip of the guidewire should be on sight at almost all times. In summary, the two goals are: to secure the access to the target vessel and lesion; to avoid any trauma to the distal intact vessels.

5.2 Crossing the target lesion

The opening 'workhorse' guidewire can be used in an initial attempt to cross the target lesion. Nevertheless, in many circumstances, a more dedicated guidewire will be required.

5.2.1 Crossing a stenosis

To cross a stenosis, it is perceptibly fundamental to stay intraluminal. For that purpose, the guidewire does not need to have increased stiffness, pushability, or penetration capacity. The tip should probably be hydrophilic as tactile feel is less relevant in those situations, and this can also improve the crossability of the guidewire. The tip is typically shaped in soft curve (Figure 10A), to be directed to the opposite direction of the stenosis. Specifically in tibial vessels, a 0.014' guidewire can be preferable as in the case showed in Figure 1.

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5.2.2 Crossing a chronic total occlusion

A chronic total occlusion is generally defined as an occluded artery of 3 months duration or longer [5]. When the vascular interventionist faces a chronic total occlusion, the best guidewire is obviously the one that successfully crosses the lesion. Nevertheless, there are several issues to consider in an attempt to cross a chronic total occlusion:

• The target artery. In fact, some arteries can be quite challenging to recanalize. For instance, an occlusion of the anterior tibial artery from its origin is, most of the times, very challenging to cross anterogradely because of the difficulty to engage the ostium. In those circumstances, adjuvant retrograde approach can be very helpful.

• The length of the occlusion. Longer occlusions are more difficult to cross and involve additional struggle to keep the guidewire in an intraluminal track. Moreover, the guidewire should have a stiffer body to support the crossing of a balloon or a support catheter, and it can also frequently require segmental pre-dilatations.

• The associated calcification. Depending on its length, location (entry point of the occlusion and/or in its core), and whether it is concentric or eccentric, calcification can greatly complicate the crossing of an occlusion or the reentry after a subintimal path. It also increases the risk of complications such as perforations or ateroembolization. On another hand, medial calcification can occasionally help in defining the limits of the vessel and consequently can guide the interventionist to stay intraluminal.

• Visible run-off. As a rule, the end of the chronic total occlusion should be clearly defined. Nevertheless, in some instances, such as in tibial vessels with very poor collateralization, it may not be initially adequately outlined and only appears after having crossed the occlusion.

5.2.3 Sliding technique

This technique is particularly indicated for engaging softer chronic total occlusions with microchannels [6]. It is frequently the first approach. For that intent, the initial 'workhorse' guidewire with a soft hydrophilic tip and a body with some stiffness can be the option as reduced surface friction enhances passage through the chronic total occlusion core. The tip should initially be shaped in a single, long shallow bend (Figure 10A), and movement consists of simultaneous smooth tip rotation and gentle probing. But during the crossing, the interventionist should stay vigilant, as the guidewire has reduced tactile feel and typically advances with minimal resistance, frequently resulting in inadvertent entry to the subintimal space [7].

5.2.4 Drilling technique

If the sliding technique fails after a few attempts (one should not insist on this technique as it is easy to create several subintimal tracks that will jeopardize a desirable intra-luminal crossing), then the drilling technique should be tried. In this technique, a guidewire with a core-to-tip design with an uncovered tip should be preferred to enhance tactile feel. The tip is bended in a very short extension (Figure 10C) and clockwise and counterclockwise rotations of the guidewire are performed while the tip is pushed modestly against the chronic total occlusion (Figure 12). The important issue in this technique is that one does not push the guidewire very hard. Placing the balloon or the support catheter very close to the tip increases the penetration capacity. If the tip of the guidewire does not advance any more with gentle pushing, it is by far better to exchange for a stiffer tip and body guidewire, rather than continue pushing. If one pushes the wire hard, it will easily go into the subintimal space. Yet, when a stiffer guidewire is used, it may be difficult to perceive whether the tip has been engaged in the true or in a false lumen inside the chronic total occlusion. The movement of the tip may help in distinguishing one from the other. Typically, when the guidewire is in the subadventitial space, the tip budges markedly. Tactile feel from the guidewire during pullback can also aid as true lumen usually offers higher resistance. This technique has an increased risk of perforation, especially when using stiff tips guidewires [7].

5.2.5 Penetrating technique

The penetration technique comes next if the drilling technique does not succeed or when the interventionist has a chronic total occlusion with very calcified cap. In this technique, the preferred guidewires have a very aggressive tip (core to-tip design, uncovered tapered tip, with increased tip load, and a subsequent high penetration capacity) and a relatively stiff body. The tip shape is essentially straight, and a less rotational tip motion and a more direct forward probing is used in comparison to the drilling technique (Figure 13). Again, placing the balloon or the support catheter very close to the tip increases the penetration capacity and reduces the propensity of the tip to bend. Additionally, the distal target must be clearly identified and careful monitoring of the progressive guidewire advancement should be done. The guidewires employed in this technique should not be used to deliver the intended devices to the target lesion as the tip can easily damage the distally intact vessels. It is a technique with a particularly augmented risk of complications [7].

5.2.6 Subintimal technique

It is usually the last technique to be employed, even if it can be a first option in specific situations such as very long chronic total occlusions. For this technique, a guidewire with a stiff body and a soft short tip with hydrophilic coating is usually preferable. The short tip allows a short loop. After having created the loop, the guidewire is advanced to the end of the occlusion. To reenter into the true lumen, the loop has to be undone. Sometimes, the guidewire needed to be exchanged to a guidewire with a reduced diameter (if the initial guidewire was not a 0.014' guidewire), with an uncovered tip (to increase the tactile feel and reduce the tendency to stay in the subintimal space that a hydrophilic tips has), a good torqueability, and an angled shaped tip (to be able to direct this one to the true lumen). Sometimes moving the balloon or the support catheter and the guidewire as one can be very useful (Video 3, https://bit.ly/3jPF7aj and Figure 14). If the loop, during the crossing, becomes too large, it means that most certainly, a perforation has occurred. In these situations, the guidewire should be retracted and an another subintimal track should be pursued.

5.2.7 Retrograde access

When the antegrade approach is not successful, a retrograde puncture may be required. Retrograde puncture of the popliteal artery is usually not a big issue. However, at below-the-knee level, since arteries are quite small and fragile and frequently the tibial or peroneal artery to be punctured is the unique artery to the foot, extreme care must be the rule. As so, after having performed the puncture with a 21G needle (either guided by ultrasound or by X-ray), a guidewire is to be engaged inside the artery. To avoid additional injury to the artery, the devices introduced in it should be kept at the strict minimum. That why usually it is most preferable to initially advance only the guidewire without any catheter or sheath (Figure 15). Therefore, the guidewire to be chosen needs to have a hydrophilic stiff body due to the lack of a sheath, the relevance of having adequate torqueability to guide the tip and to perform the snaring of the guidewire, and a potential need for an additional catheter if the guidewire does not reach the true lumen or the same subintimal track made anterogradely. A 0.018' diameter guidewire is probably the best option as it is still a delicate guidewire, but with more support than a 0.014' guidewire. The tip should be soft and most probably hydrophilic to track easily the punctured vessel retrogradely. As no sheath should usually be introduced, hard push on the guidewire can lead to irreversible kinging of its body, which can jeopardize the intervention.

5.2.8 Pedal plantar loop technique

This technique consists in creating a loop with the guidewire from the anterior tibial artery to the posterior tibial artery, or the reverse, through the foot vessels [8, 9]. The most common pathway is through dorsalis pedis artery, deep plantar artery, deep plantar arterial arch, lateral plantar artery, and posterior tibial artery. Indications for this technique are similar to the retrograde access. However, it can be performed when no distal vessels are available for puncture, being also less invasive. Moreover, this technique can improve the outflow for tibial arteries.

However, complications related to foot vessels manipulation can precipitate a serious worsening of the ischemic condition. Taking this into account, the guidewire to be chosen to this technique needs to have a soft hydrophilic tip to easily track through tortuous foots vessels without damaging them. The body should also have reduced stiffness to track across the created loop, that's why usually a 0.014' guidewire is preferred.

Curriculum topic: Interventional cardiology

Percutaneous balloon dilatation, first described by Andreas Gruentzig in , was initially performed without the use of guidewires.1 The prototype balloon catheter was developed as a double lumen catheter (one lumen for pressure monitoring or distal perfusion, the other lumen for balloon inflation/deflation) with a short fixed and atraumatic guidewire at the tip. Indeed, initially the technique involved advancing a rather rigid balloon catheter freely without much torque control into a coronary artery. Bends, tortuosities, angulations, bifurcations, and eccentric lesions could hardly, if at all, be negotiated, resulting in a rather frustrating low procedural success rate whenever the initial limited indications (proximal, short, concentric, non-calcified) were negated.2 Luck was almost as important as expertise, not only for the operator, but also for the patient. It is to the merit of Simpson who, in , introduced the novelty of advancing the balloon catheter over a removable guidewire, which had first been advanced in the target vessel.3 This major technical improvement resulted overnight in a notable increase in the procedural success rate. Guidewires have since evolved into very sophisticated devices. Although they all may look alike from the outside, wires are widely different in their materials, internal structure and design, hence, their wide diversity in function.4 Wiring is of course only one, but not the least, of several steps in coronary intervention, yet the attention given to wire selection is often superficial.

This article is aimed at understanding the way wires are constructed, how this influences their specifications, and how to select them for a given purpose. We propose to cover '

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