Ann Thorac Surg 2007;83:272-278
© 2007 The Society of Thoracic Surgeons
New Technology
Introduction to Thoracic Endografting: Imaging, Guidewires, Guiding Catheters, and Delivery Sheaths
Grayson H. Wheatley, III, MD*,
Robert McNutt, RT,
Edward B. Diethrich, MD
Department of Cardiovascular and Endovascular Surgery, Arizona Heart Institute, Phoenix, Arizona
Accepted for publication March 27, 2006.
* Address correspondence to Dr Wheatley, 2632 N 20th Street, Phoenix, AZ 85006 (Email: gwheatley{at}azheart.com).
Presented at Second Annual Meeting of The Society of Thoracic Surgeons Thoracic Endografting Symposium, Chicago, IL, Dec 10–11, 2005.
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Abstract
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PURPOSE: With the recent approval of the first thoracic endoprosthesis in the United States for the treatment of isolated descending thoracic aortic aneurysms, there has been a dramatic increase in the number of physicians interested in getting involved in this emerging technology. However, many of these physicians do not have extensive endovascular experience, are not familiar with the catheters and guidewires used for thoracic endografting procedures, or do not have access to a full complement of endovascular resources.
DESCRIPTION: We discuss the basics of catheters, guidewires, and balloons necessary to perform thoracic endovascular procedures.
EVALUATION: Adequate radiographic visualization of the thoracic aorta and access vessels is essential for all phases of the thoracic endografting procedure. In addition, a vast array of catheters, guidewires, balloons, and sheaths have been designed to assist with endovascular access and delivery of various therapeutic modalities.
CONCLUSIONS: Each of the different catheters and guidewires serve an important purpose in the conduct of thoracic endografting procedures, and it is important to have a full understanding of these devices to ensure the best results.
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Introduction
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The first percutaneous endovascular procedure was performed in 1964 by Dotter on an isolated superficial femoral artery lesion [1]. Since this pivotal event, a wealth of different endovascular techniques has been developed to treat vascular pathologies throughout the human body. A vast array of catheters, guidewires, and sheaths has been designed to assist with endovascular access and delivery of various therapeutic modalities. At present, the number of guidewire and catheter options is almost overwhelming, and there is significant overlap in function between the different devices. As a result, confusion sometimes exists concerning appropriate guidewire and catheter selection.
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Technology
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The first thoracic endoprosthesis was approved by the Food and Drug Administration for the treatment of descending thoracic aneurysms in 2005, causing a surge in the number of cardiothoracic surgeons, vascular surgeons, interventional radiologists, and cardiologists interested in becoming involved with this evolving technology. However, many of these physicians do not have extensive endovascular experience, are not familiar with the catheters and guidewires used for thoracic endografting procedures, or do not have access to a full complement of endovascular resources. Therefore, we believed that it was necessary to review the basics of thoracic endovascular procedures including information about imaging systems, vascular access techniques, and the specific catheters and guidewires used in thoracic endografting procedures.
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Techniques
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Endovascular Imaging
Adequate radiographic visualization of the thoracic aorta and access vessels is essential for all phases of the thoracic endografting procedure, including preoperative planning, intraoperative endografting and postoperative endograft surveillance. Appropriate imaging and correct use of a wide array of endovascular tools such as catheters, sheaths, and guidewires are critically essential in the success of any thoracic endografting procedure.
There are several imaging modalities available to visualize the thoracic aorta and associated vascular anatomy. In addition to computed tomography, diagnostic aortography is a preoperative imaging modality that can assist with determining whether a patient is a candidate for thoracic endografting [2]. The aortographic images are useful in appreciating iliac artery tortuosity and calcification. Great vessel origin can also be better appreciated in relation to the aortic pathology. Intravascular ultrasound is useful in obtaining accurate aortic diameter measurements and in determining appropriate proximal and distal landing zones. Mural thrombus is often underappreciated by computed tomographic scan, but intravascular ultrasound can accurately demonstrate areas of mural thrombus that would be important to avoid as a landing zone. Transesophageal echocardiographic imaging can also be useful in appreciating the complex pathology of the thoracic aorta.
The primary imaging modality used during implantation of the thoracic endoluminal graft is fluoroscopic aortography. To acquire these images, a fixed fluoroscopic C-arm or a portable C-arm is used. Historically most facilities have used portable C-arms [3]. Recently, there has been a trend among leading facilities to be outfitted with fixed imaging systems. However this can present a challenge and may require the clinician to learn a new method for these procedures; with a fixed C-arm, the patient becomes mobile and the C-arm becomes somewhat static. Another option is the hybrid C-arm, the Fischer SPX (Fischer, Denver, CO). It is a ceiling-mounted C-arm that pans around a fixed pedestal-type bed. This allows the physician to focus on one site, instead of having to follow the operative sight as it moves. In addition, the instrument table and anesthesia setup are more conveniently available to the operator. The fixed procedure table is radiolucent and has a full range of motions including Trendelenberg, reverse Trendelenberg, side-to-side tilt capabilities and variable height adjustments. The fluoroscopic equipment is used in conjunction with a contrast pressure injector. The combination of these produces angiographic and digitally subtracted angiographic images. These images are used to determine and mark the desired landing zones. To acquire these images, the tube is angled (using the predetermined ideal tube angle which is calculated from the preoperative CT scan) for proximal grafts. However, an anterior-posterior projection, with no tube angulation is used when the graft is being delivered near the celiac artery, because the column of contrast in the celiac artery will highlight the ostium in the anterior-posterior projection due to the added density.
Fluoroscopy provides real-time imaging during catheter and guidewire manipulation; continuous fluoroscopy is used when optimal image quality is required (ie, selective catheterization). Pulsed fluoroscopy is used when less detail is required, such as is positioning an OmniFlush (Angiodynamics, Queensbury, NY) or pigtail catheter. Most systems today also have a second monitor to transfer a reference image used for guidance "roadmapping." Another imaging technique is digital subtraction arteriography. Using this technique, a mask is acquired and then subsequently subtracted from the following images, with the contrast being injected in the only portion that is viewed, and there is no background image. It is imperative that both the image intensifier and the object are held in a constant position as motion artifact is detrimental to the accuracy of digital images.
Contrast injectors are very useful during fluoroscopy and digitally subtracted angiographic imaging. The main considerations include the total volume of contrast to be delivered and the injection rate (mL/sec); together these determine the duration of the bolus. Also important are the maximum pressure in pounds per square inch, which is the peak pressure the pump will generate during injection, and the pressure rate rise, which is the time to peak pressure. In practice, the latter is generally 0.4 seconds. Other features that some contrast injectors also offer are inject delays and roentgenogram delays. The former delays the injection of contrast to allow mask images to be acquired, whereas the latter delays roentgenogram exposure, preventing unnecessary images prior to the contrast arriving at the area of interest. This feature can be very useful when contrast is injected into the aorta for imaging at a distal location such as the feet.
Endovascular Access and Intervention
For thoracic endografting, we commonly perform a femoral cut-down on one common femoral artery. This is because the delivery sheath for the endoprosthesis is usually at least a 20-French size, and there is no safe way to repair this sized defect in the common femoral artery using a percutaneous approach. The contralateral common femoral artery is then accessed percutaneously. Occasionally, brachial access is needed to assist with delivery of the device or to perform coil embolization of the left subclavian artery. In preparation for this possibility, we place bilateral radial arterial lines in all of our thoracic endografting patients. We then have the anesthesiologist inject contrast in the appropriate arm through the radial arterial line and, using fluoroscopy, we puncture the brachial artery with the access needle as the contrast highlights the artery.
Guidewires
There are many types of guidewires that are available for a vast array of uses. Conventional guidewire construction (Fig 1) uses a core component and ribbon that are encased in coil with a tapered distal end. It is often difficult to deliver the thoracic endograft to the intended area of deployment due to angulation and tortuosity of the thoracic aorta. The extra support guidewire is an essential component of thoracic endografting, and is used to assist with tortuous anatomy and for traversing long distances with large devices. The most common extra-stiff guidewires include the Nitrex nitinol (EV3, Plymouth, MN), the Meier wire (Boston Scientific, Natick MA), the Amplatz (Boston Scientific), and the Lunderquist by Cook Inc (Bloomington, IN) (Table 1). The Lunderquist extra stiff guidewires (Cook Inc) are often used for aortic interventional procedures because they have excellent laser-weld transition, a high degree of shaft stiffness, a Teflon coating, a stainless steel mandrel, and tips that are available both straight and curved. The Lunderquist extra stiff 3 (Cook Inc) is the preferred wire for thoracic endografting, because the floppy tip is curved and designed to sit above the aortic valve in a nontraumatic fashion and will not wander into the coronary arteries or the brachiocephalic vessels.
Sheaths
Sheaths are essentially a tube conduit with a hemostatic valve that allows access into the vessel without loss of blood. Sheath measurements are based on the inner diameter, and there is a universal color coding system as follows: 4-French = red; 5- French = gray; 6-French = green; 7-French = orange; 8-French = blue; 9-French = black; 10-French = violet; 11-French = yellow. In addition to these standard sizes, there are also a number of large diameter sheaths (20-French to 24-French) that accommodate endoprostheses between 26 and 40 mm in diameter. Using large-diameter sheaths may be problematic in vessels that are small, tortuous, or calcified, or a combination of these.
Catheters
Catheter "talk" has a whole lingo of its own [4]. For example, the word track-ability describes the ability of the catheter to follow the guidewire through tortuous vessels and around corners without pulling the wire out of its intended location. Push-ability refers to the amount of force at the hub of the catheter that is needed to advance the tip of the catheter. Cross-ability is the term that describes the ease with which a catheter follows the guidewire across a lesion or through a diseased arterial segment. Steer-ability refers to the responsiveness of the catheter tip to handling maneuvers performed at the hub. As with sheaths, the French scale is used to size catheters (1-French = 0.33 mm); however, catheters are measured at their outer diameter.
Angiographic catheters are made from several different materials. Polyethylene catheters are pliable and have good shape memory. Polyurethane is even softer and more pliable and follows guidewires more easily than polyethylene, but has a higher degree of friction. Nylon catheters (such as those by AngioDynamics) are stiff and tolerate high flow rates; nylon is actually the most common material for catheters. Teflon is sometimes used as well, but is generally reserved for use in dilators and sheaths because it is much stiffer than the other material described.
In general, choosing the correct catheter size means picking the smallest diameter that supports the procedure. Catheters come in standard lengths that range from 65 cm to 110 cm in length. Their shape is associated with function and target area. For example, the H-1/Headhunter catheter is a cerebral catheter, but it can be used to cannulate the great vessels of the aortic arch. We summarize the catheters necessary for thoracic endografting procedures in Table 2.
Special catheter features include a variety of coatings that may improve pushability or other properties. Almost all catheters have radiopaque tips and some flush catheters have graduated measurement markers with optimal fluoroscopic resolution for taking vessel length measurements.
Among the types of catheters, there are two major types used in thoracic aortic procedures: (1) flush, and (2) selective catheters. Flush catheters are used in > 70% of all cases and allow large bolus injections of contrast in the aorta to visualize the main branches for road mapping. There are four different flush catheter shape formations, whereas selective catheters are available in literally hundreds of different shape formations, including those for visceral and cerebral interventions. We use the following catheters: Pigtail Marker (Angiodynamics), Pigtail/TR Flush (Boston Scientific), Bentson 2 (JB2) (Angiodynamics), Headhunter (Angiodynamics), straight arterial (Angiodynamics), internal mammary (Angiodynamics), and Glidecath (angled/straight) (Boston Scientific). Each of these catheters serve a unique purpose within the conduct of a thoracic endografting procedure. For example, the Bentson 2 catheter can be used to cannulate the left subclavian artery to assist with possible embolization for a type II endoleak.
Balloons
Balloons, like catheters, also have a descriptive lingo all their own. Compliance refers to how a material behaves under pressure. Compliant material is usually soft and stretches or deforms under pressure, which prevents the concentration of force from being focused at the stenosis and increases the risk of vessel dissection. The stiffer or more noncompliant the balloon material, the more dilating force it has, and the more uniformly it expands. Noncompliant balloons hold their shape despite added pressure, and exert more force against a hard lesion or metal stent to increase dilatation.
There are two types of ballooning: (1) profile and (2) therapeutic. Profiling refers to a gentle inflation of the compliant balloon to smooth out the contour of the artery or gently expand a deployed stent-graft and improve graft to wall apposition. Therapeutic ballooning refers to a forcible inflation of a semi-noncompliant balloon to dilate an arterial stenosis (such as an external iliac artery stenosis) to allow for graft delivery. The pressure needed to inflate the balloon to its manufactured diameter is measured in atmospheres and referred to as nominal pressure. Balloons are rated for burst, using a manufacturing threshold specifying that 1% of all balloons tested burst at this particular pressure. Most of the smaller balloons have a rated burst of between 10 and 15 atmospheres and large balloons between 3 and 6 atmospheres.
Balloons are measured by their diameter and their length (eg, 8 x 4 balloon = 8 mm diameter x 4 cm length). The Equalizer (Boston Scientific) can be used in thoracic aortic interventions to profile the deployed stent-graft, and it comes in 20 to 40 mm sizes with a 7-French shaft and a 14-French sheath for introduction. It is a compliant latex balloon with radiopaque markers at its proximal and distal ends. The Cook Coda balloon (Cook Inc) has a 32 or 40 mm inflated diameter, a 10-French shaft and a 14-French sheath for introduction. It is made of polyurethane and is a semi-compliant balloon with radiopaque markers that deflate very quickly, which is a benefit when temporarily occluding the thoracic aorta. Finally, the Gore Tri-lobe balloon (WL Gore & Associates, Flagstaff, AZ), which is probably the most advanced of the balloons described in this article, has a 26 to 40 mm inflated diameter, and a 105-cm working length with a 20-French sheath for introduction and radiopaque markers 5 cm apart. Its silicone construction allows quick inflation and deflation and the tri-lobe design offers continuous flow and decreases the "wind sock" effect. This balloon is extremely useful in situations in which profile ballooning is required in a tenuous landing zone to minimize the likelihood of dislodging the graft with the ballooning process secondary to wind-socking. Table 3
summarizes our balloon selection.
Additional Tools
A variety of other tools may also be useful in thoracic aortic endografting procedures. Snares, such as the EV3 Gooseneck (EV3, Plymouth, MN) and INTER-V Ensnare device (INTER-V, Gainesville, FL), are intended for use in thoracic endografting procedures to retrieve and manipulate foreign objects and are useful when establishing brachial-femoral guidewire access to assist with delivery of the thoracic stent in cases of severely tortuous aortas. Embolization coils may also be needed to treat a type II endoleak by coiling the origin of the left subclavian artery or to deposit the coils in the sac. Peripheral vascular stents and covered stents may be important tools when addressing iliac artery stenoses to help with delivery of the sheath and thoracic endoprosthesis.
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Clinical Experience
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Between February 2000 and July 2004, 158 patients with diverse pathologies of the descending thoracic aorta were treated with endoluminal grafts as part of an institutional review board-approved single-center investigational device exemption protocol [5]. All grafts were delivered using basic catheter and wire techniques and imaging was performed with a ceiling-mounted C-arm. Indications for study enrollment were atherosclerotic aneurysm (n = 76), aortic dissection (n = 36), penetrating aortic ulcer (n = 15), contained rupture (n = 11), pseudoaneurysm (n = 10), traumatic aortic injury (n = 5), aortobronchial fistula (n = 4), and aortic coarctation (n = 1). One hundred fifty six of 158 patients (98.7%) were ultimately treated, with a mean patient age of 72 ± 12.1 years. One (0.6%) patient developed paraplegia. Only 12 patients required reintervention and 30-day mortality was 3.8% (6 of 156). Mean follow-up was 21.5 ± 18.8 months, and the overall mortality was 17.3% (27 of 156).
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Comment
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In conclusion, thoracic endografting is a complex procedure that requires the use of complex endovascular technologies. To obtain optimal results and ensure patient safety, physicians must have a thorough understanding of the imaging systems, catheters, guidewires, and delivery sheaths used for the conduct of these procedures. We have attempted to provide our recommendations and suggestions for a reasonable selection of devices and materials required for thoracic endografting procedures.
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Disclosures and Freedom of Investigation
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The authors have no disclosures relating to the completion of this study. No external funds were used to perform the evaluation and all of the tested technology was separately purchased to complete the study. In addition, they had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report.
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Footnotes
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Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.
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References
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- Dotter CT, Judkins MP. Transluminal treatment of arteriosclerotic obstructionDescription of a new technic and a preliminary report of its application. Circulation 1964;30:654-670.[Abstract/Free Full Text]
- Mitty HA. Advances in angiography and their impact on endovascular therapy Mt Sinai J Med 2003;70:359-363.[Medline]
- Sternbergh 3rd WC, Tierney WA, Money SR. Importance of access to fixed-imaging fluoroscopy: practice implications for the vascular surgeon J Endovasc Ther 2004;11:404-410.[Medline]
- Pukin L. Devices and techniques for endovascular surgery: catheters, stents, coated stents, and stented grafts Mt Sinai J Med 2003;70:386-392.[Medline]
- Wheatley 3rd GH, Gurbuz AT, Rodriguez-Lopez JA, et al. Midterm outcome in 158 consecutive Gore TAG thoracic endoprostheses: single center experience Ann Thorac Surg 2006;81:1570-1577.[Abstract/Free Full Text]
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Abstract
Introduction
