Volume 43, Issue 2, Supplement , Pages A53-A61, February 2006
Intraprocedural imaging: Thoracic aortography techniques, intravascular ultrasound, and special equipment
Article Outline
Introduction
Appropriate preprocedure patient selection is a prerequisite for determining the optimal intraprocedural imaging techniques. Assessment of aortoiliac morphology before intervention, based on thin-cut contrast computed tomography (CT) reconstructions with center line aortic images, allows maximum utilization of total x-ray exposure and contrast agents in the interrogation of patient-specific anatomic variations. A delay in addressing the patient’s anatomy and device selection until the time of the procedure in the interventional suite precludes efficient, minimal-risk assessment for access and device delivery.
Organization of interventional suite
Organization of ancillary supplies and equipment for convenience and rapid access in the interventional suite enables efficient and precise procedures. Desirable facilities have a sterile, operating room-compatible environment equipped to accommodate procedures using local anesthesia as well as operative interventions that require general anesthesia and automated patient support. Interventional tables that enable unobstructed, thoracoabdominal fluoroscopic imaging are desirable, with the interventional room organized so that all procedural participants have unobstructed views of high-quality images displayed on moveable panels. Adequate floor space to accommodate ancillary equipment such as power injectors and intravascular ultrasound (IVUS) units increases organization and efficiency (Fig 1).
Fig 1.
Organization of the interventional suite provides all key personnel with an unobstructed view of procedural images. A, B, C are Primary Interventionalist Assistants H is; an Xray Technician.
Equipment
Thoracoabdominal endoluminal procedures should be performed in a facility that has efficiently organized ancillary equipment to expedite procedures and maintain patient safety. The Table includes a list of suggested ancillary equipment that can be supplemented with specific items preferred by the interventionalist(s). Specific items described in this chapter are identified by the order number and manufacturer in the Table.
Table I. Ancillary supplies for endoluminal thoracic intervention
| Inventory for thoracic endograft procedures | ||
|---|---|---|
| Description | Order no | |
| Misc | ||
 Boston Scientific/Medi-tech | ||
| FloSwitch HP (Luer-Lock) | 44-201 | |
| Boston Scientific/Medi-tech | ||
| Arterial Entry Needle | 44-166 | |
| 18 gauge 2.75 inch | ||
| Boston Scientific/Medi-tech | ||
| Terumo Torque Device | 6-653 | |
| Sheaths | ||
| Boston Scientific/Medi-tech | ||
| 10F × 10-cm Pinnacle Sheath | 15-726 | |
| Cook, Inc. | ||
| 22F × 25-cm extra large Check-Flo Sheath | G12831 | |
| Cook, Inc. | ||
| 20F × 65-cm Keller-Timmerman Sheath | G27051 | |
| 22F × 65-cm Keller-Timmerman Sheath | G09790 | |
| 24F × 65-cm Keller-Timmerman Sheath | G09791 | |
| Dilator Set | ||
| Cook, Inc. | ||
| 20F-24F Endovascular Dilator Set | 13218 | |
| Guidewires | ||
| Boston Scientific/Medi-tech | ||
| 0.035-in × 180-cm Bentson | 49-147 | |
| Boston Scientific/Medi-tech | ||
| 0.035-in × 180-cm Glidewire | 46-152 | |
| Boston Scientific/Medi-tech | ||
| 0.025-in × 260-cm Platinum Plus ST Guidewire | 46-611 | |
| Boston Scientific/Medi-tech | ||
| 0.035-in × 260-cm Amplatz Super Stiff Guidewire | 46-526 | |
| 6-cm tip length | ||
| Boston Scientific/Medi-tech | ||
| 0.035-in × 260-cm Meier Guidewire | 30-602 | |
| 10-cm tip length | ||
| Cook, Inc. | ||
| 0.035-in × 260-cm TFE Coated Lunderquist Guidewire | TS-CMG-35-260-LES3 | |
| 15-cm tip | ||
| ev3, Inc. | ||
| 0.035-in × 260 -cm Nitrex | N352604 | |
| Cook, Inc. | ||
| 0.035-in × 180-cm Graduate Measuring Guidewire | G09508 | |
| Catheters | ||
| Boston Scientific/Medi-tech | ||
| 5F × 100-cm | BERN 31-406 | |
| Cook, Inc. | ||
| 5F × 90-cm Pigtail-Royal Flush Plus | G09408 | |
| Ultrasound catheters | ||
| Volcano | ||
| 8.2F × 90-cm Vision PV8.2 F 88900 | ||
| Snares | ||
| Medical Device Technologies | ||
| 27-45-mm EN Snare | 392007045 | |
| Balloons | ||
| Medtronic Vascular | ||
| 12F Reliant Stent Graft Balloon | AB46-US | |
| 46 mm max diameter | ||
| Cook, Inc. | ||
| 14F CODA Balloon Catheter | 281477 | |
| 40 mm max diameter | ||
| Boston Scientific/Medi-tech | ||
| Equilizer Balloon Catheter | 17-112 | |
| 40 mm max diameter | ||
| Boston Scientific/Medi-tech | ||
| 8-mm × 8-cm Ultrathin Diamond Balloon | 16-510 | |
| For brachial artery access | ||
| Cook, Inc. | ||
| 4F Micro-Puncture Introducer Set | G04636 | |
| MPIS-401 | ||
| Boston Scientific/Medi-tech | ||
| 4F × 10-cm Pinnacle Sheath | 15-710 | |
| Boston Scientific/ Medi-tech | ||
| 5F × 10-cm Pinnacle Sheath | 15-721 | |
| Boston Scientific/Medi-tech | ||
| 4F × 100-cm BERN Catheter | 31-606 | |
| Cook, Inc. | ||
| 4F × 90-cm Pigtail Catheter | G09407 | |
| For body floss | ||
| Boston Scientific/Microvasive | ||
| 0.035-in × 450-cm Glidewire | 5194 | |
| Cook, Inc. | ||
| 5F × 130-cm Straight Tacron | G27619 | |
| Autovac | ||
| Boehringer | ||
| Autovac (Intraoperative Autotransfustion System) | 7904 | |
| Manufacturers | Website address | Telephone |
| Cook, Inc. | www.cookgroup.com | 800-457-4500 |
| 750 Daniels Way, PO Box 489 | 800-225-3238 | |
| Bloomington, IN 47402 | 800-228-4728 | |
| Boston Scientific/Medi-tech/Microvasive | www.bostonscientific.com | 800-642-4945 |
| One Boston Scientific Place | 800-338-0440 | |
| Natick, MA 01760 | 800-716-6700 | |
| Volcano Corporation | www.volcanocorp.com | 800-228-4728 |
| 2870 Kilgore Road | ||
| Rancho Cordova, CA 95670 | ||
| Medtronic, Inc. | www.medtronic.com | 707-525-0111 |
| 710 Medtronic Parkway | ||
| Minneapolis, MN 55432 | ||
| Boehringer Laboratories, Inc. | www.boehringerlabs.com | 800-642-4945 |
| 500 East Washington Street | ||
| Norristown, PA 19401 | ||
| Medical Device Technologies | www.mdtech.com | 800-338-0440 |
| 3600 SW 47th Avenue | ||
| Gainesville, FL 32608 | ||
| ev3 | www.ev3.net | 800-716-6700 |
| 4600 Nathen Lane North | ||
| Plymouth, MN 55442 | ||
| W. L. Gore & Associates, Inc. | ||
| Medical Products Division | www.goremedical.com | 800-437-8181 |
| P.O. Box 2400 | ||
| Flagstaff, AZ 86003 | ||
An interventional table with a long back extension enables sterile preparation and passage of equipment and catheters that have been organized for easy access (Fig 2). A selection of short 5F to 14F hemostatic sheaths are useful in various scenarios, from cannulation of the right radial artery with a 5F sheath to hemostatic introduction of larger diameter balloons using 12F to 14F sheaths for the ileofemoral arteries. Larger diameter 16F to 24F hemostatic sheaths (ie, Cook Check-Flow sheaths) provide hemostatic access to the ileofemoral vessels at various stages during the procedure after larger diameter (18F to 24F) delivery systems have enlarged the access site. In addition, a selected range of hydrophilic dilators (16F to 24F) are useful in assessing the diameter of access vessels to accommodate passage of delivery catheters and expedite decisions regarding the need for ileofemoral conduits to safely deliver devices.
Fig 2.
Long back table extension of the interventional table for preparation and passage of equipment and devices. Inset demonstrates the hemostatic valve and tapered tip that are recommended for large-diameter Check-Flow sheaths compared with the adjacent Keller-Timmerman sheath on the table (arrow).
A selection of guidewires beyond conventional short starter wires includes 260-cm-long stiffer wires (Nitrex, Meier, Amplatz, and Lunderquist) for delivery of the longer length, larger diameter delivery systems. We prefer guidewires with atraumatic radiopaque tips that are easily visualized in the ascending and transverse aortic arch. When, in selected instances, “body-floss” support is needed, 380- to 450-cm-long, 0.035-inch guidewires or comparable softer wires are useful for continuous transit of support from radial artery access through the entire length of the thoracoabdominal aorta to a femoral artery catheter. In most cases, we prefer the least stiff wire required for device delivery and believe this affords less traumatic passage, unless stiffer wire support is mandatory for delivery of the prosthesis.
Longer length, 80- to 100-cm-long, 4F to 6F angiographic catheters are desirable for thoracic procedures. Selected angled catheters and complex curves in longer lengths may be required. Many interventionalists also prefer marker catheters, and some use straight angiographic catheters in preference to the pigtail configuration if a catheter is to remain positioned outside of a device after deployment to enhance atraumatic removal following device delivery.
Noncompliant angioplasty balloon catheters in a range of sizes (6 to 20 mm) are also desirable. Recently, several different large diameter (40 to 46 mm) compliant balloons have become available for low-pressure atraumatic aortic occlusion and expansion of thoracic devices. These range from the novel Trilobe Gore Thoracic Aortic Graft (TAG) balloon to other larger compliant balloons that are available from Boston-Scientific (Equalizer), Cook (Coda), and Medtronic (Reliant). Each of these offers variations to suit interventionalist preference and require varying size introducer sheaths (8F to 12F) (Fig 3).
Fig 3.
Large-diameter (40 to 46 mm) compliant balloons: (a) Gore Trilobe, (b) Boston-Scientific Equalizer, (c) Cook Coda, and (d) Medtronic Reliant.
Imaging
Fluoroscopic imaging
Fluoroscopic imaging during the procedure should be performed with the goals of providing optimal precision for access to the vascular system and delivery of the device to the chosen anatomic position, conserving the total fluoroscopic exposure time to both patients and staff, and limiting the contrast volume. This can be accomplished by carefully positioning the patient to maximize localization of the anatomy being visualized. Positioning the x-ray column close to the patient’s body, centered over the anatomic areas of interest, reduces “scatter” of x-rays and helps eliminate parallax.
Careful planning of the procedure includes consideration of potential access routes and the potential need for additional equipment and maneuvers to quickly access alternative sites to cannulate and occlude arteries for hemostatic control. Selection of the appropriate arm for a radial artery catheter is predicated on whether access or imaging for the brachiocephalic vessels is anticipated, whether coverage of the left subclavian artery would obstruct pressure readings in the left arm, or both.
The establishment of a radial catheter in the right arm by using a micropuncture set provides continuous arterial monitoring and offers the ability to convert this site to 5F sheath access and concomitant 4F pigtail visualization of the origin of the right innominate artery as well as the ascending aorta and brachiocephalic vasculature (Fig 4). This approach can frequently be used for imaging during deployment of devices in the high ascending and transverse arch, where exact positioning of the prosthesis over or near the origin of brachiocephalic arteries is needed.
Fig 4.
Pigtail catheter (black arrow) inserted via right radial artery for visualization of the origin of the brachiocephalic arteries from the aortic arch during the procedure. The white arrow points to an intravascular ultrasound probe positioned at the origin of the left carotid artery from the bovine innominate.
The location of the origins of the innominate, left carotid, and subclavian arteries can be determined by contrast injections through this catheter. Visualization of the origin of the left subclavian artery can also be accomplished by placement of a wire or catheter through radial access in the left arm (Fig 5). During the procedure, arterial pressure monitoring can initially be done by using the radial artery catheter and then be converted to side arms on additional sheaths through other access arteries as access routes are alternated during various stages of the procedure.
Fig 5.
Starter wire (single arrow) advanced from the left radial artery across the origin of the left subclavian artery from the aorta. Intravascular ultrasound (IVUS) probe (double arrows) demonstrates IVUS image from the aortic lumen (a) at the origin of the subclavian artery (s).
To appropriately image the aortic arch and brachiocephalic arteries, it is necessary to determine an appropriate gantry angle (the degree of right, left, caudal, and cranial angulation and left of the fluoroscopy) to identify precisely the origin of vessels and distances between pertinent landmarks perpendicular to the centerline of the transverse arch (Fig 6). Calculation of the gantry angles from the preintervention three-dimensional reconstructions expedites planning. This is accomplished by observing the degree of anterior-posterior angulations of the descending aorta relative to the transverse and ascending portion of the arch and calculating the rotational angle of the fluoroscopy unit that is required to display the anatomy parallel to the centerline of the transverse arch. Because of the anatomy of the aortic arch, this is usually accomplished with a left lateral rotation (left anterior oblique) of 30° to 40°, but may be more angled in patients with tortuous anatomy.
Fig 6.
Example of gantry angle correction after deployment of a Talent thoracic device, demonstrates (a) angulations between anterior (black line) and posterior (white line) ends of the stents on the proximal end of the device, and (b) additional 20° left anterior oblique angulations rotate the stents in the image that is rotated so anterior and posterior stents are aligned. This figure also demonstrates the utility of wires with radiopaque, atraumatic proximal tips to aid in identifying the wire in the ascending aorta.
Extensive imaging during procedures can be avoided by examining the preintervention images to assess the origins of the brachiocephalic arteries (ie, bovine arch); identify the origin, patency, and orientation of vertebral arteries; and assess the visceral arteries, particularly the celiac and superior mesenteric arteries (Fig 7). The preintervention studies are particularly useful for determining patency of ileofemoral access arteries and the potential need for conduits rather than determining need after failed or complicated access endeavors during the procedure.
Fig 7.
Angiographic assessment of the origin of a nearly occluded celiac artery origin (arrow) with a distal extension thoracic device having an open wire configuration positioned for deployment. The end of the cloth-covered portion of the device is identified by figure 8 markers. Double arrows point to patent superior mesenteric artery.
An important principal for accurate deployment of devices and localization of branch vessels is to perform contrast studies with the anatomic focus being positioned in the center of the fluoroscopic screen. This eliminates parallax that can adversely affect accurate identification and precise deployment. Placing a radiopaque ruler with large measurement gradations beneath the patient along the left psoas muscle before performing procedures can also be particularly useful in assuring accurate positioning of devices and providing a fixed landmark for identifying position without repeated fluoroscopic and contrast studies.
In the thoracoabdominal aorta, optimal imaging frequently requires contrast injection of 15 to 20 mL of contrast over an interval of 1 to 2 seconds. For this reason, repeated sequences can require large contrast volumes. The use of nonionic contrast agents and carefully planning imaging sequences can optimize utilization and limit total contrast volume. Careful planning of contrast sequences with storage of angiographic runs and a delay of several seconds to visualize runoff anatomy before and after deployment can be particularly valuable.
Intravascular ultrasound
IVUS is a critical technology that is particularly useful in the treatment of thoracoabdominal lesions. IVUS can be used to determine aortic wall morphology, enhance the selection of appropriate fixation sites, enable branch vessel origin location, and especially, to identify dissection entry and re-entry tears and observe continuity of the dissection membrane. After device deployment, IVUS is used to assess the accuracy of deployment, determine expansion of the device, and assess apposition of the prosthesis to the vascular wall. Maximizing the potential of nonionizing ultrasound imaging can significantly reduce x-ray exposure and contrast agent usage.
IVUS utilization and interpretation requires an understanding of the principals of ultrasound interpretation in vascular anatomy. Careful inspection of arterial wall morphology, branch vessel origins, and integrity of entry and re-entry sites relative to fixed anatomic landmarks can significantly enhance appropriate device selection and expedite accurate placement.
In the thoracoabdominal aorta, imaging of the larger diameter vessel walls requires low-frequency catheters (ie, 8 to 10 MHz). Catheter designs that enable delivery of the ultrasound elements without a monorail delivery wire eliminate wire artifact and enhance 360° views of the arterial anatomy. For this reason, coaxial phased array systems that produce images utilizing electronically rotating signals rather than mechanical rotating systems over eccentric wire delivery provide optimal imaging (Fig 8).
Fig 8.
Top, Monorail intravascular ultrasound (IVUS) catheter (left) with image artifact (right) produced by attenuation of the ultrasound energy by the wire (thick arrow) compared with attenuation of the signal by calcified arterial plaque (thin arrows). Bottom left, IVUS catheter with phase-array imaging elements positioned over a wire through the center of the catheter produces 360° vessel images. Right, Phase array image of the abdominal aorta at the origin of the left renal artery (L) with the renal vein (V) coursing over the superior aspect of the aorta.
Critical to intravascular ultrasound image interpretation is familiarity with artifacts produced by wires and catheters in the arterial lumen, attenuation of the ultrasound signal by calcification in the vessel wall, and the appearance of thrombus, dissection flaps, and enhancement by prosthetic graft materials, as well as the observation of pulsatility in true and false arterial lumens in a dissected artery (Fig 9).
Fig 9.
Intravascular ultrasound images of (a) transverse thoracic aorta with adjacent innominate vein and soft tissue in the mediastinum on the superior aspect; (b) soft plaque (double arrows) in an iliac artery with monorail wire artifact (a) disrupting the image of the normal appearing iliac artery wall (single arrow); (c) descending aortic dissection with septum (arrow) between the true and false lumens (f) with stagnation of flow in the false lumen; and (d) natural fenestration (re-entry) of flow at the origin of the superior mesenteric artery (arrow).
Imaging during vessel access
Imaging plays a critical role in successful vascular access. For percutaneous groin cannulations, imaging of access vessels by using fluoroscopy to identify the location of the common femoral artery adjacent to the femoral head is an invaluable maneuver that prevents complications related to high or low femoral artery access, or potential retroperitoneal bleeding associated with high arterial punctures, or both. Transcutaneous ultrasound gray-scale imaging units are useful for imaging the accuracy of percutaneous access, with the overall priority being to successfully cannulate the artery without encountering comorbid complications of arterial dissection, embolization, and bleeding. Careful observation of the initial passage of an atraumatic wire through the vascular anatomy, supplemented by IVUS inspection of the vessel wall continuity and location of the guidewire in the lumen, assures appropriate wire introduction.
For most percutaneous procedures, minimizing sheath profile is desirable for the obvious reasons, although larger profile sheaths are needed to accommodate larger catheters or balloons. The choice of percutaneous vs open access is influenced by the underlying vessel pathology, apparent from preprocedure physical examination, and by the potential need for rapid access and delivery of larger profile sheaths and catheters.
Two alternative methods for imaging vascular anatomy following the initial wire introduction are used. The most frequently used method is to substitute an atraumatic wire access for an angiographic catheter and to perform selected views to visualize the vascular anatomy. An appealing alternative for patients with contrast allergy or renal insufficiency, and a way to limit the total contrast volume, is to use the wire access to perform IVUS interrogation of the vascular anatomy and place a calibrated ruler beneath the patient, positioned parallel to the spine along the left psoas muscle, to identify branch vessels and pathologic lesions. In this manner, the location of branch vessels can be identified, dimensions of the vascular anatomy confirmed, and the length and location of vascular lesions and associated fixation sites identified. Appropriately planned in conjunction with preintervention CT images, the IVUS inspections can significantly expedite procedural planning and reduce fluoroscopic and contrast requirements. Total fluoroscopic exposure may also be minimized by using pulsed modes for many of the imaging sequences, as the location of the IVUS catheter relative to the ruler can be accomplished with less resolution.
Imaging during device deployment
Imaging of device deployment is obviously critical to accurate placement and successful exclusion of pathologic lesions. After guidewire access is established, visualizing the passage of the delivery catheters throughout the continuity of the vascular access is frequently advisable, particularly if there is any resistance to movement of the device. Observation of the initial passage may be compromised by the need to maintain fluoroscopic equipment in a fixed position relative to the lesion after roadmapping at the appropriate gantry angle.
Regardless of the accuracy of procedural imaging, the stiff components of endograft delivery systems will modify the vascular morphology in curved segments. Contrast injections through an imaging catheter are needed to acquire a final roadmap and identify vascular structures after positioning the device before deployment. The need for access via the contralateral groin or from the radial artery, as has been discussed previously, can be used in various combinations to enhance the visualization of associated structures either with the contrast imaging catheters or by placement of radiopaque wires to identify vessel origins.
During the release of endovascular devices in the thoracic aorta, particularly in the transverse and high descending aorta, lowering of the blood pressure or induction of temporary asystole using adenosine infusion, or both, is an important component of precise placement. One should also be aware that as the stiffer delivery catheter components are withdrawn and the flexible device is released, the reformation of native aortic curves and kinks will occur, potentially affecting the accuracy of device deployment. During the release of a device, additional imaging injections can be used to enhance precision and final placement.
After the device is deployed, it is necessary to carefully observe the removal of delivery catheter components without disturbing the position of the deployed device. Maintaining guidewire and catheter positions and repeated careful inspection of additional maneuvers, such as balloon dilation or passage of additional device components, are required to ensure that the security of the initial prosthesis is maintained.
Frequently during procedures in which multiple devices are being deployed, serial images to inspect components and determine the need for additional interventions can be accomplished through angiographic catheters, or by reinsertion of the IVUS to inspect the deployed device and to plan subsequent interventions. To accomplish this expeditiously and to limit blood loss, deployment catheters can be withdrawn and large-diameter hemostatic sheaths (ie, 16F to 24F Cook Check-Flow sheaths) can be positioned through the delivery site, enabling passage of IVUS catheters while maintaining hemostasis. An advantage of IVUS is an ability to map additional segments of the aorta either proximal or distal to the deployed device and to plan for placement of additional components relative to vascular anatomy. IVUS is particularly useful when combined with appropriate gantry angle of the fluoroscopy column to identify the origin of the visceral vessels, thus enhancing precise deployment (Fig 10).
Fig 10.
Intravascular ultrasound (IVUS) images acquired with the catheter lying in the true lumen demonstrating (a) transverse arch at the origin of the carotid artery (c), (b) origin of the subclavian artery (s), (c) chronic dissection with the IVUS probe in the true lumen (t), and (d) re-entry tear at the origin of the right renal artery (arrow).
A particularly useful application of IVUS is the identification of entry and re-entry tears in aortic dissections and the selection of patients for treatment with an endoluminal device for exclusion of the false lumen. IVUS can be used to identify the origin of branch vessels, determine the proximal point of fixation related to the brachiocephalic vessels, and determine the successful reperfusion of the true lumen by the deployed devices. It can identify the location of critical visceral vessels related to re-entry sites and assess pulsatility in the true and false lumen after deployment. IVUS enables observation of the false lumen after coverage of entry or re-entry sites by demonstrating the return of systolic pulsatile flow to the true lumen, as well as concomitant decrease and stagnation of flow in the false lumen (Fig 11).
Fig 11.
Intravascular ultrasound (IVUS) images before (left) and after (right) endograft deployment over the entry site of a type B descending thoracic aortic dissection (arrows). After device deployment, IVUS confirms enlargement and return of pulsatile flow to the true lumen with stagnation of flow in the false lumen (f). Both images were acquired from the same area in the descending aorta just above the origin of the celiac artery.
Observations of the perfusion patterns throughout the length of the thoracoabdominal aorta can easily be observed and complemented by contrast injections as needed. Pressure measurements acquired from sheaths in the femoral arteries are useful in assessing perfusion of the true lumen and, in many cases, obviate the need for fenestration of the dissection as frequently practiced in contrast-guided procedures.
After device deployment and successful completion of the endograft exclusion, observation of the access vessels during and after delivery sheath and component removal is particularly important. In patients with difficult access or during procedures where several device deliveries are required, unsuspected vessel injuries can easily be detected by serial imaging, thus avoiding further complications that are associated with identifying retroperitoneal bleeding and vessel disruption after sheath access has been removed. In addition, maintaining guidewire position for an interval following sheath removal assures rapid re-entry of exclusion devices if needed to prevent catastrophic hemorrhage.
Competition of interest: none.
PII: S0741-5214(05)01909-9
doi:10.1016/j.jvs.2005.11.003
© 2006 The Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.
Volume 43, Issue 2, Supplement , Pages A53-A61, February 2006
