exchange (Rx) use. Long (300 cm) wires have become almost obsolete since the technique of balloon trapping has gained wide application to remove or insert OTW balloons or microcatheters. The only limitation of this technique is its inapplicability in very small guiding catheters (5 Fr) or when a guide extension is present (except Trapliner). Anyway, almost all wires (Abbott, Asahi, Terumo) have wire extensions that can be fixed at the distal end to increase wire length. Most wires (Abbott, Asahi, Terumo) anyway allow fitting at the distal end a dedicated extension wire. Finally, maintaining pressure with an Indeflator connected to the central lumen of the OTW microcatheter or balloon catheter allows flushing it out keeping the wire in place (Nanto technique).
Guidewires consist of a central core of stainless steel or nitinol alloy that makes up the proximal section of the wire, approximately 145 cm long, and which tapers toward a distal section measuring 35–40 cm. This distal segment has a further outer covering of either a fine coil spring consisting of tungsten, platinum, or stainless steel, or a polymer coating loaded with a material such as tungsten to improve radiopacity. The tip often has a lubricious coating that is either hydrophobic or hydrophilic (Figure 5.7). Using stainless steel as the core material improves the steerability and torque control, but steel wires can be deformed by tortuosity and cannot be reshaped. A nitinol core also offers excellent torque control, but the wire retains its shape better and can be reshaped if deformed. Increasing the core diameter increases shaft support (Figure 5.8). There is often a short transition zone between the tapered distal segment whereas some wires have a very gradually tapering central core, which tends to track better around tortuous anatomies and prolapse less when there is extreme angulation (Figure 5.8). Features of the functional design of guidewires are listed in Table 5.4. Guidewires can be classified into general purpose or “workhorse” and dedicated wires (Table 5.5).
Figure 5.8 The components of a rapid exchange balloon catheter.
Table 5.4 The selection of a guidewire depends on the characteristics required to deal with lesion complexity or particular vessel characteristics. The characteristics of guidewires can be altered by modifying specific components during the production process.
| Flexibility | Flexible wires can better negotiate severe tortuosity or angulation without deformation. | Shaft core material (nitinol offers greater flexibility and shape retention), core thickness (thinner core = more flexible). |
| Support | Improved equipment delivery when hampered by angulation, tortuosity, lesion severity, calcification. | Shaft core material, core thickness. |
| Steerability is a function of: | ||
| Torque transmission | 1 : 1 transmission of torque to the tip is the ideal. | Core materials are chosen for having good torque transmission, which is also improved by a thicker core with more gradual distal taper. |
| tip shape ability | Importance increases as lesion complexity increases. | Nitinol is more difficult to shape, but can be reshaped; steel is easier to shape but can be ruined by being deformed. |
| Lubricity | Can ease wire passage in tight, calcified, severely tortuous lesions. | Tip or distal segment coating with silicon, hydrophilic coating, or polymer coating: “plastic jacketed” wires are the most lubricious but also the most dangerous; when combined with a stiff tip long dissections can be inadvertently created:hydrophilic requires water for activationhydrophobic does not require water for activation, allows feedback from distal tip so that excessive friction when creating a subintimal dissection or going below stent struts can be detected. |
| Tendency to prolapse | Can be important when negotiating angles >75° | A gradually tapering core with a smooth transition toward the tip improves support and tracking around bends; abrupt tapers and floppy cores are more likely to prolapse. |
| Visibility | The level of visibility becomes more important in obese patients or when angled working views are required. | Lubricious polymer‐coated nitinol wires can be difficult to see, platinum, steel, or tungsten markers at distal tip. |
| Tactile feedback | Provides the operator with essential nonvisual information, allows “palpation” of the lesion at the distal wire tip. | Hydrophylic wires provide poor tactile feedback; hydrophobic wires provide more feedback. |
| Tip stiffness | A soft gentle tip is essential for all “workhorse” wires; to reduce the risk of vessel trauma; stiffer tips are required for dedicated CTO wires. | More gradual distal taper, distal core material (e.g. high tensile steel). |
Table 5.5 Classification of guidewires.
| Product name | Core material | Rail support | Radiopaque tip length (cm) | Tip type | Tip style | Tip tapering | Tip stiffness | Tip load (g) | Tip coating type |
|---|---|---|---|---|---|---|---|---|---|
| Workhorse wires | |||||||||
| Hi‐Torque BMW Universal | Elastine Nitinol | Moderate | 3 | Polymer/ Spring coil | Shaping ribbon | Non‐tapered (0.014″) | Soft | 0.7 | Hydrophilic |
| ChoICE Floppy | Stainless steel | Light | 3 | Polymer/ Spring coil | Core‐to‐tip | Non‐tapered (0.014″) | Soft | 0.8 | Hybrid (distal 3 cm uncoated) |
| Runthrough NT | Stainless steel/ Nitinol | Light | 3 | Stainless steel coils | Shaping ribbon | Non‐tapered (0.014″) | Soft | ||