Thoracic Endovascular Aortic Repair (TEVAR) Catheters

Introduction

“Diagnostic” catheters allow the endoluminal practitioner to assess areas of the vascular system and to evaluate for a possible intervention; additionally, they assist in performing an intervention. This often involves the delivery of radiographic contrast for opacification of the vessel lumen in radiographic studies. This can involve visualization of a specific branch vessel using a selective catheter, or visualization of a significant portion of the arterial arborization using a nonselective catheter. Additionally, we find the use of intravascular ultrasound catheters to be a powerful imaging adjunct, essential in the endovascular repair of aneurysms or dissections.

Materials

Catheters are constructed of a variety of materials, including polyethylene, polyurethane, Teflon (tetrafluoroethylene), and nylon. To a large extent, the physical properties of catheters reflect the materials of which they are constructed:

Polyethylene has traditionally been the most commonly used material in catheters, because it combines reasonable torquing ability with fairly low frictional resistance, while still remaining pliable. Nylon has a low coefficient of friction and has been a popular substrate for high-flow catheters; the stiffer material can withstand higher infusion pressures. The trend in recent years towards smaller catheter size to accomplish tasks traditionally performed with larger sizes has made nylon the most frequent material currently used in all diagnostic catheters. Catheters made of flexible polyurethane are stiffened by incorporating stainless steel mesh into their walls, and antifriction coating is applied to the outer and/or inner surfaces. Polyurethane is also used in the “eel-like” Terumo Glidewires, composed of a nitinol core covered with an antifriction-coated polyurethane jacket. Teflon’s stiffness makes an impractical material for most catheters, but its ease of control and extremely low coefficient of friction make it an excellent material for sheaths and dilators. Pebax (manufactured by Arkema Inc.), a newer material, is a polyether block amide that is useful for catheter production and can be manufactured to possess a wide range of physical properties. Most catheters manufactured today are composites, with a stiffer material for the main catheter body and a more flexible material for the soft tip.

Nonselective (Flush) Catheters

Nonselective catheters are usually constructed of nylon and are designed to rapidly infuse large volumes of contrast agent without injuring the vessel. In order to accomplish this, the distal portion of these catheters contains multiple side-holes, in addition to the standard end-hole. This distal portion is preformed into a shape that assists in dispersion of the contrast; e.g. Omniflush, Grollman, pigtail, straight, tennis racket, multipurpose. For aortography, a pigtail catheter is the standard choice (e.g. Royal Flush Plus Pigtail; Cook, Inc.). This catheter can distribute contrast over the large endoluminal area of the aorta; it also features radiopaque 1 cm markings that aid in measuring vessel segments or lesions. Nonselective catheters are generally used only in large diameter vessels (aorta or its primary branches).

Selective Catheters

Selective catheters, with a single end-hole, are designed for the selective catheterization and contrast injection of specific branch vessels. An abundant selection of preformed distal ends is available to assist in the catheterization of the various anatomic branch points of the vascular system. For primary aortic access from a retrograde femoral artery approach, we prefer a Berenstein-tipped catheter (Imager II Selective BERN; Boston Scientific Corp.), which is shaped similar to a hockey stick. When it is necessary to cross tight stenoses, an alternate angled tip hydrophilic-coated catheter may be useful (Glidecath; Terumo Medical Corp. or Slip-cath; Cook, Inc.). Some practitioners may instead favor a Judkins Right/ JR4 shape in their primary access catheter.

For selective catheterization of aortic arch branches, common catheter shapes include Berenstein or vertebral, JR4, Simmons, headhunter, and Vitek. For catheterization of renal or mesenteric arteries, popular shapes are cobra, renal double curve, Simmons, and Shepherd hook/Omni SOS. Catheter shapes commonly used for access to the contralateral iliac artery include cobra, Simmons, and pigtail. Catheters with curved distal ends are usually introduced over a guidewire with a floppy tip (e.g. Bentson), so that they may assume their preformed shape when the guidewire is withdrawn with its distal tip inside the catheter. In catheterization of branch vessels with an acute angulation from the direction of approach, a catheter with a secondary curve is helpful. These catheters, such as Simmons, Vitek, and SOS Omni, are first advanced past the target branch vessel. Then the catheter tip is made to cannulate the vessel while withdrawing the catheter back towards the access site. Catheters of this type also require manual reshaping to their preformed shape in the aorta proximal to the area of interest. To reshape, the catheter is advanced until the tip and primary curve are no longer supported by the guidewire. Then, with the tip engaged in a side branch, the main body of the catheter is either advanced or rotated, reforming the catheter into its native shape. Alternatively, a catheter may be reformed by reflection off the aortic valve or using a suture pull.

Catheter Dimensions

Most diagnostic catheters have a diameter of 4-6F, with 5F catheters being by far the most common. Regularly available catheter lengths range from 65-125 cm. Shorter lengths (< 80 cm) are generally used for procedures involving the abdominal aorta or proximal contralateral lower extremity (from retrograde femoral artery access). Most endoluminal procedures require longer length catheters; 100 cm catheters are used in the large majority of cases.

IVUS

Intravascular ultrasound (IVUS) catheters are a valuable resource for a practitioner performing endoluminal procedures. The distal portion of the IVUS catheter incorporates a cylindrical ultrasound transducer which generates real-time cross-sectional images of vessels. IVUS is the most accurate modality for measuring the luminal diameter of vessels, and it can also be used to identify the position of branch vessels, inspect vessel wall morphology, evaluate for the presence of plaques or thrombi, and to select appropriate landing zones for endografts. A particularly important application of IVUS is the confirmation of the true vessel lumen in aortic dissection.

In procedures traditionally performed with only angiography and fluoroscopic imaging, use of IVUS can often significantly reduce contrast volume and fluoroscopy time. For evaluation of the larger-diameter thoracic and thoracoabdominal aorta, a low-frequency catheter is needed (Visions PV 8.2F; Volcano Corp.). Familiarity with the artifacts produced by guidewires and catheters in the arterial lumen is essential in using this technology. Catheters which track over a centrally-placed guidewire generally provide superior imaging to those with an eccentrically-placed wire (“monorail”-type delivery systems).

Conclusion

Like many endovascular tools, there exists a variety of different products available for every possible catheter use. Personal preference certainly plays a role in catheter selection, but adequate knowledge concerning which catheters will effectively accomplish intended tasks should continually be sought, with the patient’s best interests remaining paramount. Consideration should also be given to the attributes of the guidewire-catheter combination. For example, a Bentson wire-Berenstein catheter combination will incorporate the steerability of an angled-tip catheter with the flexibility/mobility of a floppy-tip guidewire. If questions or problems arise, consultation with an experienced interventional specialist or endovascular surgeon is recommended.

References

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