Guide catheters, guide extenders, guidewires, balloons, and stents

Key points

Guiding catheter selection remains one of the essential pieces enabling a successful coronary intervention procedure in the cath lab.
Alternatives, such as using sheathless guides and guide catheter extensions, are now available to facilitate interventional procedures.
Numerous coronary guidewires are available today for operators to choose from, including several workhorse wires, hydrophilic coated wires, and specialty wires that have niche applications.
Coronary balloon catheters range from compliant to noncompliant and specialty balloons, and each has a specific role during a specific interventional procedure.
Currently available stents include bare metal stents, drug-eluting stents, and covered stents, with present-day procedures almost always employing the deployment of third- and fourth-generation drug-eluting stents.

Introduction

Guide catheters, guidewires, balloons, and stents represent the foundation upon which all percutaneous coronary interventions (PCIs) are built. For many of us, we became familiar with these tools during fellowship and have not “expanded our horizons” since, using the same “go-to” guide catheters and guidewires whenever possible. Each of these devices undergo continuous refinements and adaptations that have made PCI easier, safer, and applicable to more patients. In this chapter, we cannot extensively discuss the engineering and details of all these tools for use in the lab; instead, we have tried to put together a general overview. Recognizing that new products are introduced frequently for clinical practice, we have focused on the “theory” that defines and differentiates the equipment rather than the specific brand names.

Guide catheters

One of the most vital steps in performing a successful PCI is choosing an appropriate guide catheter. Without adequate guide support, device delivery and PCI can be very challenging and even dangerous. There are many characteristics that should be considered when selecting a guide catheter. Size, backup support, coaxial engagement, and trackability are several of the characteristics one should have in mind when choosing a guide catheter ( Fig. 4.1 ).

Construction

Guide catheters generally have three layers:

1.
The outer layer is usually nylon and contributes to the stiffness of the catheter.
2.
The middle layer is a braided wire mesh layer, which gives the torque control and radiopacity to a catheter. It also helps to provide the required stiffness to the catheter while preserving a larger inner diameter compared with a similar sized diagnostic catheter.
3.
The inner layer is hydrophilic coated to allow smooth passage for device delivery.

Choosing the optimal guide catheter

Operators typically have default guide catheters for left and right coronary interventions and internal mammary artery (IMA) and graft interventions based on personal experience and training. Nevertheless, on occasion, one needs to select an alternate guide catheter shape because of anatomic considerations, particular device-related concerns, or inventory supply issues. Support, size, length, presence of ostial disease, access site (right/left transradial or transfemoral), need to access bypass grafts versus native arteries, anomalous origins, and aortic root size are some of the important factors in choosing a guide catheter.

Backup support

When discussing guide support (backup) we mainly refer to two types of support: active and passive backup. Active backup uses the aortic root to assist in the development of a desired guide catheter shape and requires more manipulation. With the transradial approach, active support of the guiding catheter plays a more important role than with the femoral approach. Deep-seating the guide beyond the ostium of the vessel for easier deliverability of devices is an example of active support. On the other hand, passive backup is related to the catheter’s shape, size, and shaft length. This support relies on the composition and thickness of the walls of the guide shaft and tip of the catheter to engage the coronary ostium in a coaxial manner. This is inherent to the physical characteristics of the guide. In general, larger diameter guides provide more support. As one can imagine, active and passive approaches are used in combination.

Size

The majority of coronary diagnostic and interventional procedures can be performed with 6F guiding catheters ( Fig. 4.2 ). Nevertheless, certain techniques and rare devices require large-diameter guiding catheters. Appropriate case planning includes anticipating such considerations. Larger French catheters provide better support and better visualization at the risk of vascular complications, a longer recovery period, and increased contrast use. Thus current recommendations encourage the use of the smallest possible system that can provide the desired therapy for that individual patient. Catheter diameters or gauge are measured in French (F) sizes. (F size is calculated by multiplying the diameter in millimeters by 3; to calculate the diameter of a catheter in millimeters, multiply the F size by 0.33.)

Length

The standard length of a guiding catheter is 100 cm, although a length of greater than 100 cm can be used for a tortuous aorta or a very tall person. For distal lesion sites (saphenous vein graft, tortuous internal mammary artery) or chronic total occlusion cases where a retrograde approach is used, an operator may select a shorter length guide catheter (e.g., 90 cm) to allow devices to reach the intended target.

Side holes

Side hole–guiding catheters have been used in the presence of ostial lesions, which lead to changes in pressure waveforms (dampened waveforms or “ventricularization”) during engagement. This suggests that the catheter is occluding the entire effective orifice of the coronary ostia. With the ostia occluded with the catheter, coronary perfusion may be impeded; furthermore, powerful injection may result in coronary dissection. Side holes may allow blood flow through the catheter tip to perfuse the artery. Although the presence of side holes will yield a normal-appearing waveform, it is unclear that it decreases adverse patient outcomes. Catheters with side holes have their own disadvantages. There is an increase in contrast use from catheters with side holes because contrast is extruded from the side holes in addition to the main lumen. There may also be a false sense of security because the aortic pressure rather than the coronary pressure is being monitored that operators should be mindful of during a procedure with one of these guides.

Influence of access site

Transradial (TR) intervention has several advantages compared with transfemoral (TF) intervention. The TR route is more convenient for patients because the period of immobilization is less, the risk for bleeding is lower, and the overall hospital stay is shorter. Nevertheless, TR intervention has taken time to become adopted in the US because of misconceptions surrounding backup support from traditional TF guide catheters. Clinical trials have consistently demonstrated similar PCI success rates regardless of the access site.

In terms of guide catheter support, investigators have suggested that the angle between the primary curve of the guide catheter and the contralateral wall of the aorta helps to determine the amount of “support” a guide catheter can provide. In theory, these investigators suggest that slightly different catheter sizes would provide improve support for radial procedures compared with traditional TF guides; however, many radial operators use the same guiding catheter shapes regardless of access site. Given the relatively small caliber of the radial artery compared with the femoral artery, catheter size is generally limited to up to 7F with the advent of thin-walled sheaths.

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