Endovascular 101
Authors:
Sebouh Bazikian - MS4 at Keck School of Medicine of University of Southern California
Sukgu Han - Associate Professor of Surgery at the University of Southern California. Co-director of Comprehensive Aortic Center at Keck Hospital of USC. Program Director of the Integrated Vascular Surgery Residency and Vascular Fellowship
Editor: Yasong Yu
Reviewers: Matt Chia and Kirthi Bellamkonda
Core Resources:
· Rutherford's Vascular and Endovascular Therapy 10th Edition Chapter#26-28
Additional Resources:
· Relevant Audible Bleeding episodes
o Holding Pressure Case Prep - AKA/BKA
o Journal Review in Vascular Surgery: Introduction to Endovascular Surgery – A Prime
· Closure devices:
o Mynx
o Proglide
Endovascular procedures are minimally invasive techniques used to treat conditions affecting blood vessels, such as aneurysms, stenosis, or occlusions, by accessing the affected vessels through an incision in a peripheral artery and using imaging guidance to navigate catheters and devices through the blood vessels to the treatment site.
Endovascular procedures can be broken down into 4 key steps
1. Establishing arterial access
2. Navigating to target treatment zone or vessel
3. Treating the lesion
4. Closure
Basic definition of wire, sheaths, and catheters
· Wires are thin, flexible metal devices used to navigate through blood vessels and to guide other devices, such as catheters or sheaths, to the target location. They are measured in thousands of an inch
· A 0.018 wire is 0.018 inch in diameter
o There are two categories of wires: Flexible and support
Flexible wires are soft and hydrophilic. They are considered the “workhorses” because they are useful for navigating through vessels.
· A common type of wire is called the Glidewire which is slippery and useful in traveling across tortuous vascular anatomy.
§ Support wire are generally a lot stiffer and not hydrophilic. For that reason they are used to deliver and deploy devices
· A common type of support wire is called the Lunderquist which is used for the deployment of stent grafts in endovascular aortic repair
· Catheters are flexible hollow tubes used in conjunction with wires to navigate vascular anatomy
o Various characteristics include the degree and shape of the taper, the lengths, and the stiffness.
o They are inserted inside the sheath
· Sheaths are hollow tubes of various diameters that are inserted into a blood vessel to provide a pathway for catheters or wires.
o They have a one way valve to prevent backflow of arterial blood and a side port that permits aspiration and administration of fluids.
o They also come with a dedicated dilator which is used to fill the lumen of the sheath and allows the surgeon to insert the sheath safely into the vessel.
· If the wire is the rail and the catheter is the train, the sheath is the ground.
Sheaths and catheters sizing
· Both are measured in French
o 1 French equals 0.33 mm. French size divided by 3 equals the approximate diameter in millimeters.
o Another way to think about Fr is roughly the circumference in mm. Divide by 3 instead of 3.14 to get the diameter
o Sheaths are defined by their inner diameter (ID)
o Catheters are defined by their outer diameter (OD)
o This is because catheters go inside the sheath, so the size of a catheter must be smaller or equal to the size of the sheath for it to fit inside.For example, a 5 Fr sheath can accommodate 5 Fr catheter/devices
o Of note, the hole in the artery will roughly be 2-4Fr larger than the sheath size. This is important when considering the type of closure that will be used at the end of the procedure.
Step One: Establishing Arterial Access
· Preop preparation:
o During physical exam, make sure there’s a palpable femoral pulse to rule out iliofemoral disease
o Review the CT if available for high femoral bifurcation or presence of vessel disease
· Patient positioning on the angio table, depends on the access site of choice.
o Typical position (for retrograde femoral artery access) is supine, arms tucked.
o Alternative access sites (ie. radial, brachial, carotid) may require arms to be out and prepped.
· How do you choose arterial access, location?
o Depends on location of lesion you are trying to treat and complexity of the path from the access site
o Size of the access vessel and device size must be considered when deciding on the access site
o The most common is retrograde femoral artery access
o When would other access points be used?
§ Radial artery, brachial, antegrade femoral access. The goal, target location, and path complexity defines the access point.
· Arterial puncture
o Femoral access:
§ Look for pulsatile vessel on the US (vein is medial, artery is lateral; “venous penis”)
§ Usually access at the level of femoral head for common femoral artery
o Seldinger technique is used to establish access to a vessel or cavity using needle, wire, catheters, and sheath.
o E.g. using the micropuncture kit:
§ contralateral arterial CFA access with s 21 gauge needle
§ .018” guidewire is passed through the needle
§ Needle is removed and a short 4 or 5 Fr microcatheter with an inner dilator is passed over the guidewire
§ The dilator and guidewire are removed leaving the catheter in place to maintain access
§ Bigger wire is inserted through the catheter, which is then removed over the wire
§ A sheath is inserted over the wire
· The overall purpose is to start with smaller arterial puncture and exchange to larger size to minimize complication should the access fail
· Often, percutaneous closure devices are preloaded at this step. We will discuss this later.
Step Two: Navigating to treatment zone or vessel
With sheath in place, a guidewire is inserted into the vessel under fluoroscopic guidance.
· Continuous fluoroscopy is taken with the C-arm during key steps to visualize wire movement
o The C-arm can be portable or built into the room
o X rays are emitted from the X-ray generator below the patient
o And the subsequent image is generated from the image intensifier above the patient
o Radiation safety:
§ wear protective gear which is made of lead. In addition, use the tableside lead shield whenever possible
§ minimize use of continuous fluoroscopy whenever possible
§ limit use of magnification, and digital subtraction angiography
§ keep the image intensifier as close to the patient as possible to minimize scattering
o The C-arm can rotate around the patient to get optimal viewing of the vessels
§ Frequently used terminology: 30 degrees RAO which stands for right anterior oblique, describing the relationship of image intensifier to the patient
Common projections used for lower extremity angiograms
· Iliacs: 20-30 degrees contralateral anterior oblique
· Femoralsl: 20-30 degrees ipsilateral anterior oblique
· Trifurcation and tibials: anatomic anterior-posterior or 20 degrees ipsilateral anterior oblique with feet in neutral supine position
· Thoracic aorta/distal aortic arch: 30~45 degree LAO
· Renals: AP
o maximizing image quality by limiting patient movement and with breath holding and collimating
· Contrast
o Two types of contrasts: Iodinated contrast vs carbon dioxide
§ Iodinated contrast has better resolution but patients can have allergic reactions and are at risk of contrast induced renal injury. Therefore, CO2 is preferred for patients with compromised renal function in which an image is created by transiently displacing blood. The downside is that it has lower image resolution than iodinated contrast, and rare but potentially serious complications of air locking.
o Power injection vs manual injection
§ When using power injection, you have control over pressure, the amount of contrast, timing, and rate or rise of injection. It allows for rapid filling of large arteries at high flow rates. Manual injection is more efficient for small vessels since you can control dilution and volume
· Types of Wires
o Characteristics: wire tip, stiffness, diameter, and length
o Guide wires
§ To assist in catheter placement, navigate different arteries, cross lesions, and deliver devices.
o The most common sizes used in vascular surgery
§ Large .035” - generally used for the aorta and iliac.
§ Small .014”/.018” - used for smaller branches like the SFA
o Length: from 120 to 360cm
§ Based on distance from access site to the lesion
§ Long enough to reach target lesions and beyond (inside pt) and deliver catheters (outside pt) but not too long that it’s falling off the table and slowing down exchange
o Flexible vs stiff/support wires
§ How do you decide which wire to use?
· Typically, you start with flexible wire inside an angle tip catheter to navigate to the target vessel. Once you reached and crossed the target vessel, the wire is exchanged to a stiff/support wire, which allows you to deliver
§ common brands and models used that every medical student should know and the settings they are used in?
· Example answer:
· Glidewire (Tumero): a floppy wire with a hydrophilic coating which is useful for navigating stenosis and tortuous vessels and is used in a variety of different vessels.
· Lunderquist (Cook): it is very stiff and used for endovascular repairs of AAAs
· Rosen wire: support wire with a J tip with intermediate stiffness. Less stiff than Lunderquist. Used to catheterize visceral and renal arteries.
· Bentson: starter wire, that’s short in length with a very long floppy tip that prevents vessel trauma.
· Types of Catheters
o Main purpose of the catheters
§ Allows to approach the target vessel based on the shape of the catheter
§ Allows wire exchange from flexible to stiff
o Sizes are based on Fr (4-5)
§ 5 Fr are the most common.
§ Microcatheters are for embolizations (2.5Fr)
o Nonselective (Angiographic catheter)
§ Common types are omni flush, pigtail, and straight
§ They have multiple side holes along the tip so they can inject high volume of contrast into large blood vessels like the aorta
o Selective catheters/Guide (shape) catheters
· Have an end hole only with no side holes so they can cannulate specific branch vessels
§ A variety of lengths and shapes depending on the curvature and tortuosity of the pathway to the target vessel.
· Catheter with specific shapes can align your vector (the force you are exerting by pushing the wire forward at the access site) to the stenotic lesion.
§ Type of catheter that can be used to cross to the contralateral side at the aortic bifurcation – generally the omni.
· Types of sheaths
o Size range: 4-26Fr (larger available for endografts)
§ Size is decided by the device you have to deliver to the target lesion
§ Length is based on the support required from the procedure. The distance from the access site to the target site determines the length of the sheath required.
§ Common lengths range from 5 to 110cm
§ What are some of the common sheaths used and for which procedure?
· For endovascular aortic repairs, Dryseal sheaths range from 12Fr ~ 26Fr with lengths of 33cm to 65cm.
· For visceral and renal artery intervention, Ansil or Raabi sheaths range from 5Fr to 9Fr, with lengths of 45cm to 90cm.
· For lower extermity work, Ansil, Raabi, Balkin sheaths ranging from 4Fr to 7Fr with lengths of 45cm to 110cm.
· Steerable sheaths can actively articulate the shape of the sheath, allow you to navigate and treat more challenging anatomy.
Step Three: Treating the lesion
· The lesion has to be crossed with wire and catheters before treating the lesion. They may require the need to exchange sheath
· Stent and balloon sizing is measured by diameter in millimeters x length in centimeters
· Balloons
o Generally need to exchange wire to stiff support wire through the catheter, then the catheter is exchanged over the wire with the balloon mounted catheter
o Balloons have a wide variety of diameters and lengths
o Nominal vs Burst pressures
§ Nominal: pressure is where the balloon will inflate to the labeled diameter
§ Burst: pressure where 99.9% of tested balloons ruptured
§ Typically you inflate to nominal but can go higher depending on the type of lesion
o Compliant balloon vs a semi-compliant vs non-compliant balloon
§ Most of the time, we use a compliant balloon, but in certain situations where we need high pressure dilation, we use non-compliant balloon. This has to do with the nature of the lesion and risk of vessel rupture.
o Additional features
§ Cutting balloons have microblades on the wall. So the idea is to perform control rupture of calcified atherosclerotic lesions, so that the expansion happens more evenly.
§ Drug coated balloons are coated with paclitaxel to reduce the risk of neo-intimal hyperplasia So, it is sometimes used in peripheral cases where the surgeons feel that the lesions are more prone to developing neo-intimal hyperplasia or areas that have restenosed.
· Stents
o small mesh-like device made of metal that is used to prop open a blocked or narrow blood vessel. It is inserted through a catheter and deployed at the site of the blockage to improve blood flow and reduce the risk of future blockages.
o balloon expandable vs self-expanding stents
§ Balloon expandable
· Better radial force at the time of deployment
· More accurate deployment
· Mounted on balloons, so it is more difficult to track them across tight stenosis.
· May cause damage to the surrounding tissue due to balloon inflation.
§ Self-expanding
· Usually more flexible in tortuous vessels
· More resistant to kinking
· Higher risk of migration or dislodgement during deployment
· Post-dilation is often needed
o covered stents vs bare metal stents
§ Covered stents
· Covered by PTFE, polyurethane, or silicone
· May be more resistant to in-stent restenosis, compared to bare metal stents.
· useful in ruptured vessel
· EVAR/TEVAR/FEVAR devices are essentially fancy covered stents.
Step Four: Closure
· Hole in the artery is outer diameter of the sheath, and is bigger than the sheath size since sheath is measured by inner diameter
· Manual compression
o Direct pressure with fingertips
o Enough pressure without bleeding, but not too much that it cuts off circulation
o No peeking!
o Timing depends on sheath size, coagulation status, and vessel health.
· Closure devices
o Extravascular plug
§ Angio-seal: sandwiches the arteriotomy with a biodegradable anchor and collagen sponge. https://www.youtube.com/watch?v=XhgAs2SxNjA
§ Mynx: utilized a small balloon to create temporary hemostasis within the artery and covers the outside with a polyethylene glycol sealant. https://www.youtube.com/watch?v=_kcJM1lnQo8
o Suture-based
§ Sometimes placed at beginning of the case for large bore access
§ Proglide: https://www.youtube.com/watch?v=Wol22SlEpxE
· Complications
o What are the most common complications that you experience and how do you mitigate them?
§ Access site
· Hematoma, pseudoaneruysm, AV fistula, occlusion, infection
§ Navigation related
· Dissection, perforation, thromboembolism
§ Systemic
· Contrast induced AKI
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