C H A P T E R 1
`
`General principles of endovascular
`therapy
`
`Imran Mohiuddin, Panagiotis Kougias, Ross Milner
`
`Cardiovascular disease remains a major cause of mortality in the developed
`world since the beginning of the twenty-first century. Although surgical revas-
`cularization has played a predominant role in the management of patients with
`vascular disease, the modern treatment paradigms have evolved significantly
`with increased emphasis of catheter-based percutaneous interventions over
`the past two decades. The increasing role of this minimally invasive vascular
`intervention is fueled by various factors, including rapid advances in imaging
`technology, reduced morbidity, and mortality in endovascular interventions,
`as well as faster convalescence following percutaneous therapy when com-
`pared to traditional operations. There is little doubt that with continued device
`development and refined image-guided technology, endovascular interven-
`tion will provide improved clinical outcomes and play an even greater role in
`the treatment of vascular disease. In this chapter, a framework is provided for
`a brief history of endovascular therapy along with an overview of commonly
`used endovascular devices. The fundamental techniques of percutaneous
`access is also discussed.
`
`Brief history of endovascular therapy
`
`Evolution of diagnostic imaging
`The discovery of the X-ray imaging system by Charles Röentgen in 1895,
`marked one of the most remarkable milestones in the history of medicine.
`Within months after its discovery, X-rays were used by battlefield surgeons to
`locate and remove bullet fragments.1 This imaging modality quickly gained
`acceptance from physicians around the world in providing valuable diagnostic
`information in the care of their patients. As a natural evolution of this discovery,
`X-rays were soon adapted to evaluate the vascular system in conjunction with
`the use of a contrast material. In 1910, Frank performed the first venography
`in rabbits and dogs by injecting a solution of bismuth and oil intravenously
`and following its flow fluoroscopically.2 Heuser is credited (in 1919) for per-
`forming the first contrast study in humans by injecting a solution of potassium
`iodide into the dorsal vein of a child and following the flow of the substance
`to the heart.3 The use of such materials was initially quite toxic. This led to the
`
`1
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`development of safe contrast media, for example water soluble iodine-based
`organic contrast called Selectran-Neutral by Binz in 1929.4 Concurrently, newer
`injection methods were also being developed. In 1927, Moniz was the first to
`perform direct arterial injections, and he used this technique to inject sodium
`iodide into the internal carotid arteries.5 This direct approach was initially
`used to image the heart and thoracic aorta but was soon abandoned due to its
`hazards.
`Castellanos used an indirect method of injection whereby a contrast agent
`was injected into a vein in the arm and, after a delay, the aorta was visualized.6
`Due to dilution of the agent in the heart and lungs, the aorta could be visualized
`only 75% of the time. For a better study of these vessels, Werner Forssmann,
`a resident surgeon in Berlin in 1929, ran a urethral catheter through his own
`basilic vein to visualize his right ventricle. This earned him the Nobel prize
`in 1956.7 Also in 1929, dos Santos et al. described a technique of visualiz-
`ing the aorta using a direct puncture technique by translumbar injection of a
`contrast medium directly into the abdominal aorta.8 The modern aortogram
`via a femoral approach was first performed by Farinas in 1941,9 a technique
`that was quickly adapted by physicians around the world. With the advent
`of guidewires in the early 1950s, selective angiography with catheter-directed
`injection was developed further. In 1962, Guzman and colleagues reported a
`large series of patients who underwent coronary angiography using selective
`coronary catheterizations.10 Since then, the application of guidewires, cathet-
`ers, and introducer sheaths has become a standard approach when performing
`diagnostic angiography.
`
`Evolution of therapeutic interventions
`Ivar Seldinger, a Swedish radiologist, was the first physician to describe
`a unique method of establishing arterial access using a guidewire tech-
`nique in 1953, which heralded an evolution from diagnostic to therapeutic
`angiography.11 A decade later, Fogarty detailed the use of a balloon-tipped
`catheter to extract thrombus.12 Building on this, Dotter and Judkin in 1964
`described a method of dilating an arterial occlusion using a rigid Teflon cath-
`eter to improve the arterial circulation.13 In the field of venous intervention,
`catheter-based vena caval filters were introduced by Greenfield in 1973, and
`have revolutionized the current approach in the prevention of pulmonary
`embolism.14 The technique of balloon angioplasty was introduced by Gruntzig,
`who performed the first coronary artery intervention in 1974.15 To this day,
`this remains the most commonly performed endovascular procedure in clin-
`ical practice. The application of the balloon angioplasty catheter subsequently
`led to the development of the first intravascular balloon-expandable stent by
`Palmaz et al. in 1985.16 Several years later, Parodi, an Argentinean vascular sur-
`geon, combined both a Dacron graft and balloon-expandable stent technology
`to create a stent-graft, which was successfully used to exclude an abdominal
`aortic aneurysm from the systemic circulation.17 Technology in this field is
`rapidly evolving and more complex modular stents with thermal memory are
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`General Principles of Endovascular Therapy 3
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`in use today. There has also been an explosion in catheter-based technology,
`enabling access for the interventionalist to treat occlusive disease and increas-
`ingly, aneurysmal disease in nearly every vascular bed. Further development
`of this minimally invasive intervention is currently focused on combining a
`pharmacological agent with the current stent platform to create drug-eluting
`stents to improve the clinical outcome of endovascular therapy.
`
`Basic vascular access
`
`Percutaneous access can be achieved by a single- or double-wall puncture
`technique. In the former approach, a beveled needle is introduced, and a
`guidewire is passed after confirmation of arterial or venous access by visual
`inspection of back bleeding with or without the use of direct pressure meas-
`urement and inspection of arterial or venous waveforms. As a routine, we
`typically gain vascular access using a 21-gauge micropuncture needle and
`a 0.018-in. wire. The double-wall technique requires the use of a blunt needle
`with an inner cannula. The needle is inserted through the vessel, and then the
`inner cannula is removed, the introducer needle withdrawn until back bleed-
`ing is obtained, and a wire introduced. Although percutaneous access can be
`routinely achieved in nearly all patients, those with scarred access sites from
`prior interventions or patients with decreased pulses due to occlusive dis-
`ease represent a specially challenging subset that may benefit from ultrasound
`guidance with Doppler insonation or B-mode visualization of the target vessel.
`Indeed, access site needles have been developed with integrated Doppler
`probes.
`
`Retrograde femoral access
`Percutaneous retrograde femoral puncture is the most commonly used arter-
`ial access technique. Both groins are prepped and draped in a sterile fashion.
`Visualization of the femoral head using fluoroscopy is recommended. In the
`majority of patients, the common femoral artery can be found over the medial
`third of the head of the femur (Figure 1.1). Another advantage of access-
`ing the artery in this location is that the femoral head will serve as a hard
`surface to compress the artery against, after the completion of the proced-
`ure if manual compression is needed to achieve hemostasis. An 18-gauge
`◦
`angiographic needle is then advanced at a 45
`angle through the skin until
`pulsatile back bleeding is encountered. As with all needle access, the bevel of
`the needle should point upward. Going through and through the artery should
`be avoided, as this can lead to problematic bleeding. Depending upon the body
`habitus, the artery may lie anywhere from 2–5 cm below the level of the skin. If
`venous entry is noted, it is useful to remember that the artery lies lateral to the
`vein. It is also important to remember that there is approximately 3 cm of com-
`mon femoral artery that lies between the inferior ligament and the femoral
`bifurcation. Once brisk back bleeding is noted, a standard Bentson wire is
`passed through the needle into the artery for at least 20 cm. It is recommended
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`(a)
`
`(b)
`
`(c)
`
`Figure 1.1 Retrograde femoral artery access. (a) The common femoral artery can usually be
`found medially 2–3 cm below the inguinal ligament. (b) Once the needle enters the common
`femoral artery, brisk back bleeding is seen. (c) The Bentson guidewire is next advanced through
`the needle under fluoroscopic guidance to establish the arterial access.
`
`that this maneuver is performed under fluoroscopy to confirm that the wire is
`going into the aorta. Once the wire is in place, the introducer sheath with its
`dilator can be easily passed into the artery. If there is any doubt about the path
`of the wire, a small amount of contrast can be injected through the needle to
`delineate the needle location.
`Arterial entry higher than the level of the femoral head can prove to be dif-
`ficult in achieving hemostasis, and retroperitoneal hematoma often develops.
`Entry into the femoral artery far below the inguinal ligament can lead to
`entry into the superficial or profunda femoral arteries. Catheterization of
`either of these arteries can result in post-op hematoma and pseudoaneurysm
`development.
`
`Antegrade femoral access
`Antegrade femoral puncture is more challenging than retrograde but can be
`invaluable in problematic infrainguinal lesions. We recommend that the oper-
`ator stand on the side that permits forehand approach of the needle (Figure 1.2).
`◦
`The needle is advanced at an angle of 45
`to the skin until pulsatile back
`bleeding is noted. With this approach, it is even more important to avoid
`low punctures, as this would limit the working room to selectively catheterize
`the superficial femoral artery. With obese patients, it is often necessary to have
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`General Principles of Endovascular Therapy 5
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`Figure 1.2 Antegrade femoral artery access. The needle is inserted just below the inguinal
`ligament in the common femoral artery whereby the guidewire is inserted in the ipsilateral
`superficial femoral artery.
`
`an assistant retract the pannus cephalad out of the way. Once back bleeding is
`noted, the Bentson wire is placed, followed by a sheath. If there is little room
`between the site of entry of the wire and the femoral bifurcation, a sheath-
`less technique may need to be employed. In order to selectively catheterize
`the superficial femoral artery, an angled catheter may help in directing the
`wire down the correct artery. If the guidewire begins to buckle, it should be
`withdrawn and retried using a different angle.
`
`Difficult access
`There are several techniques that can be employed to access the pulseless yet
`patent femoral artery. The common femoral artery almost always passes over
`the medial head of the femur, and attempts in this area will prove to be the
`most successful. Accessing the femoral artery via the contralateral side and
`placing a catheter over the bifurcation can be used to inject contrast and visu-
`alize the ipsilateral artery. Many patients have vessels that are calcified. Using
`magnification views, these calcifications can be used as a guide to determine
`the location of the femoral artery to which the needle can be inserted. Finally,
`a handheld ultrasound device can be used to determine the location of the
`noncompressible femoral artery with respect to the compressible femoral vein.
`
`Crossing the aortic bifurcation
`Crossing over the aortic bifurcation to gain access to the contralateral iliac
`artery is an indispensable technique in ileofemoral arterial interventions.
`This selective catheterization technique produces angiograms of significantly
`improved quality because of localized contrast injection. The first task is to
`determine the location of the aortic bifurcation. This can be done by either per-
`forming an aortogram for use as a road map or by using the L4 vertebrate and
`the iliac crest as a landmark. Calcifications in the arteries can help in establish-
`ing orientation. The catheter type can prove to be decisive in gaining access
`across the aortic bifurcation. We routinely use the Contra catheter, as this saves
`a step when an aortogram is also performed. The catheter is parked near where
`the bifurcation is suspected, and a glidewire is advanced. If initial attempts are
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`Figure 1.3 Gaining access across the aortic
`bifurcation. A curved catheter is inserted in a
`retrograde fashion from a femoral artery
`approach and is positioned across the aortic
`bifurcation. A guidewire is next advanced over
`the catheter to gain access in the contralateral
`common iliac artery.
`
`unsuccessful, the catheter and wire can be rotated. Alternatively, the catheter
`can be advanced 1–2 cm up into the aorta, which helps the guidewire select the
`contralateral common iliac artery. Once the artery is selected, the catheter is
`pulled back down and securely positioned across the bifurcation (Figure 1.3).
`Alternative catheters for this approach may be the Cobra or C2 catheter. Once
`inside the contralateral iliac, the wire is advanced past the inguinal ligament in
`order to securely position the catheter in the iliofemoral arterial segment. Sub-
`sequently, catheters and sheaths can be advanced with ease. There are several
`specially shaped sheaths available that facilitate in crossing-over.
`
`Brachial puncture
`Occasionally when the distal aorta or bilateral ileofemoral axis are inaccessible,
`the brachial artery becomes a very useful access site. The left brachial artery is
`the preferred upper extremity access of choice, as this avoids the origin of the
`carotid artery and thus reduces the chance of a cerebrovascular accident due
`to catheter-related thrombus embolization. The arm is abducted and prepared
`on a radiolucent arm board. The most common location for puncture is just
`proximal to the antecubital crease, and this location reduces the incidence of
`nerve injuries (Figure 1.4). Once sterility has been established, a micropuncture
`kit is used to access the artery. The micropuncture sheath can then be exchanged
`for a 6 Frsheath. Once at the aortic arch, an angled catheter can be used to
`deflect the wire down the aorta.
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`General Principles of Endovascular Therapy 7
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`Figure 1.4 Brachial artery approach. A Seldinger needle is inserted in a retrograde fashion in the
`brachial artery just above the antecubital fossa, whereby the guidewire is next inserted in the
`brachial artery.
`
`Table 1.1 Comparison of mobile C-arm and fixed angiosuite imaging system.
`
`Imaging system
`
`Mobile C-arm unit
`
`Fixed angiosuite unit
`
`Reliability
`
`Adequate
`
`Radiation exposure
`
`More
`
`Superior
`
`Less
`
`Availability
`
`Can be moved to different
`locations because of its
`portability
`
`Restricted to one
`location
`
`Likelihood to overheat
`with prolonged usage
`
`High
`
`Special construction
`
`None
`
`Low
`
`Needed
`
`Cost
`
`up to $20,000 US
`
`up to $2 million US
`
`Image-guided endovascular intervention
`
`Choosing an imaging system
`Excellent imaging is the key to endovascular therapies regardless of whether
`the intervention is performed in an imaging suite or an operating room. Fluoro-
`scopy is the modality used for digital subtraction angiography. Fluoroscopy
`functions via an image intensifier that receives, concentrates, and brightens
`an X-ray image to produce an electronic image that can be displayed on a
`screen. The larger size of an image intensifier usually allows for better qual-
`ity imaging. A standard imaging suite image intensifier is 15 in. in diameter,
`whereas a standard image intensifier on a portable C-arm is 12 in. in dia-
`meter. Both of these systems allow control of the irradiation by the use of a
`foot pedal. The advantages and disadvantages of each system are highlighted
`in Table 1.1. Although the versatility and durability of an angiosuite are bet-
`ter than a mobile C-arm unit, both are adequate for performing the majority
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`of endovascular procedures. For most surgeons, performing an endovascular
`intervention in the operating room using a mobile C-arm unit is a common
`strategy to build an endovascular practice. The portability of a C-arm unit
`enables surgeons to perform catheter-based interventions in any operating
`room, an environment that is intimately familiar to most surgeons in con-
`trast to an angiosuite in the radiology or cardiology service. Moreover, the
`cost of a C-arm unit is only a fraction of the price of an angiosuite, which is
`easier to acquire in hospitals with budgetary constraints. There are however
`several limitations, however, associated with a C-arm fluoroscopic equip-
`ment. Despite the significant technical improvements in the current model
`of C-arm systems, the image quality remains slightly inferior to that obtained
`from the angiosuite. This is due to several factors including higher focal spot
`size, fixed distance between the X-ray tube, and the power output of a C-arm
`image intensifier.18,19. A common concern about the mobile C-arm unit is its
`propensity to overheat. When this happens, the unit must be shut down and
`allowed to cool, which can be severely limiting. In contrast to a mobile flu-
`oroscopic unit, an angiosuite is typically more robust with less likelihood of
`overheating. In addition, all the necessary imaging equipments, such as image
`intensifier, fluoroscopic table, and power injector are typically electronically
`integrated in an angiosuite. Consequently, activating the image intensifier dims
`the room lights, initiates the imaging sequence, and times the injector activ-
`ation. Another benefit of the angiosuite is that most are directly linked to a
`hospital picture archiving and communication system (PACS), which facilit-
`ates viewing. Lastly, images captured from an angiosuite can be used to create
`rotational angiography or three-dimensional reconstruction for further image
`analysis.
`Both portable C-arm and an angiosuite imaging unit have specialized func-
`tions that are commonly used during interventions. Magnified views are
`obtained when focusing on a limited area such as the aortic bifurcation for
`kissing stent deployment. Another feature is the road map technique. This
`allows for a representation of the arterial tree by contrast angiography on one
`digital screen with real-time fluoroscopy on another. Fluoroscopic images can
`be adjusted in different oblique angles to enhance the accuracy of visualizing
`certain vascular anatomy, such as the internal iliac arteries or the aortic arch.
`The most commonly used fluoroscopic angle is anteroposterior (AP) projection.
`In contrast, examples of the oblique views include the right anterior oblique
`(RAO) and left anterior oblique (LAO) angles. When visualizing the internal
`iliac arteries, for example, an oblique angle allows the origin of this vessel to be
`visualized so that it does not overlap with the common iliac artery. This is espe-
`cially important with iliac arterial interventions to prevent stenting across the
`origin of the internal iliac artery. Additional views such as craniocaudal correc-
`tion can also be obtained. This is particularly useful for correcting angulation in
`difficult aortic necks during endovascular aneurysm repair. Commonly used
`orientations of the image intensifier in diagnostic angiography are listed in
`Table 1.2.
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`General Principles of Endovascular Therapy 9
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`Table 1.2 Commonly used image intensifier orientations in arterial angiography and its
`contrast injection rates and volume.
`
`Procedure
`
`Orientation
`
`Abdominal aortogram
`
`Arch aortogram
`
`Descending thoracic
`aortogram
`
`Selective carotid angiogram
`
`Cerebral angiogram
`
`Mesenteric or renal
`angiogram
`
`Renal selective angiogram
`
`AP
`LAO 30–50◦
`Chin up
`Shoulders down
`LAO 15–30◦
`
`AP and lateral
`Face rotated to opposite side
`AP @10◦ craniocaudal,
`lateral
`
`Full lateral, pig catheter in
`aorta
`10–20◦ oblique to ipsilateral
`side
`
`Selective run off via CIA
`
`AP
`
`Dual run off via aorta
`
`AP
`Contralateral 20◦ AO
`iliac bifurcation
`Common femoral angiogram Ipsilateral 20◦ AO
`
`Subclavian angiogram
`
`Inferior vena cavagram
`
`Common femoral venogram
`
`Superior vena cavagram
`
`AP
`
`AP
`
`AP
`
`AP
`
`Injection
`rate
`(cc/s)
`
`Injection
`volume
`(cc)
`
`20
`
`30
`
`30
`
`4
`
`4
`
`20
`
`7
`
`8
`
`10
`
`–
`
`–
`
`7
`
`20
`
`8
`
`10
`
`30
`
`50
`
`50
`
`8
`
`8
`
`30
`
`12
`
`40
`
`60
`
`–
`
`–
`
`25
`
`30
`
`25
`
`30
`
`Imaging table
`The imaging table is an integral part of the endovascular suite. Although it is
`possible to perform an endovascular procedure in an operating room using
`a conventional operating room table, there are many drawbacks: variability
`in the cushioning and underlying metals provides for a nonuniform path for
`the radiation. For endovascular procedures, the primary requirement of the
`imaging table is that it must be radiolucent. In general, there are two types
`of radiolucent tables; fixed and movable. Fixed tables are constructed of a
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`nonmetallic carbon-fiber supported usually at only one end. This allows for
`unobstructed access for the C-arm because there are no structural elements
`underneath the table. These tables are relatively fragile and do not support
`patients in excess of 300 lbs. Movable tables allow for versatile positioning of
`the patient in the horizontal plane. They come with a set of bedside controls
`that also permit selection of the radiographic settings including gantry rotation,
`image intensifier location, collimation, and table height.
`
`Power injector
`There are two methods for delivering contrast: hand injection with a syringe
`and electronically calibrated precise power injection. For most small vessel
`and selective angiography, hand injection is adequate. However, for optimal
`opacification of high-flow blood vessels like the aorta, the use of a power
`injector is mandatory. Conversely, the power injector is also useful in small
`vessels when the contrast must be injected at a fixed slow rate. The power
`injector permits the operator to determine the rate of injection, total volume
`of injection, and pressure of the injection. Table 1.2 briefly outlines com-
`monly used injection rates and contrast volume for diagnostic arteriographic
`studies.
`
`Basics of radiation safety
`
`Radiation exposure
`Radiation safety is important in endovascular surgery not only because of
`regulations but also due to patient and personnel considerations. There are
`several federal, state, and local guidelines that are available for review. Sig-
`nificant levels of radiation exposure pose serious health hazards to medical
`personnel if standard safety guidelines are not followed. The general guid-
`ing philosophy is ALARA (as low as reasonably achievable).20 This protective
`philosophy mandates that all interventionalists must compare the benefits to
`the risks of radiation exposure. With regards to exposure, there are three key
`principles: monitoring time, scatter, and distance of exposure.
`With longer and more complex endovascular procedures, it becomes imper-
`ative to use the personal dosimeter device or badge. An external dosimeter
`badge must be placed over any radiation protective garments on the collar
`near the thyroid. A second badge is recommended to be worn underneath the
`protective garments at the waist level. This second badge becomes mandatory
`in pregnant women. The effective dose equivalent is then calculated from a
`weighted average of the two badges and is used to calculate exposure risk.
`The duration of exposure is directly proportional to the received radiation
`dose. In this way, personnel exposure is linked to patient exposure. Reduc-
`tion of personnel exposure can be effectively accomplished by reducing the
`“beam-on” time by judicious use of the exposure switch to ensure that radi-
`ation exposure is occurring only when the fluoroscopist is actively viewing the
`image and optimizing the number of images used in an exposure sequence.
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`General Principles of Endovascular Therapy 11
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`Road mapping, pulse-mode fluoroscopy, and image hold and transfer can also
`help limit the time of exposure. Use of a control booth whenever possible (as
`in lower extremity run off) will also help to minimize radiation exposure time.
`Another very important consideration is the scatter phenomenon. Although
`the majority of the radiation beam is absorbed by the patient, there is scatter
`radiation that is emitted from the patient in all directions. This scatter can be a
`major source of hazard for angiosuite personnel. Emission of radiation follows
`the inverse-square law whereby the radiation intensity decreases proportion-
`ately as the square of the distance from a point source.20 Because increasing
`the distance decreases the radiation field intensity, it is always prudent to back
`away from the source when proximity is not required. Keeping the image
`intensifier as close to the patient as possible helps to maintain low fluoroscopic
`beam intensity and also allows the image intensifier to serve as a scatter barrier
`between the patient and the operator. One final point is that use of magnifica-
`tion modes further increases beam intensity, scatter, and heat production and
`should be used judiciously.
`
`Radiation shielding
`Shielding involves the use of protective barriers. The best type of shielding
`protects the whole body of an individual. Barriers may be fixed, moveable,
`or worn by the individual. The control room is an example of a structurally
`fixed barrier. Mobile barriers may be rolled into position inside angiosuites
`to protect nurses and anesthesia personnel who do not need to be near the
`patient for extended periods of time. Alternatively, ceiling-mounted transpar-
`ent barriers may also be used to protect the upper body of the interventionalist.
`Flexible protective clothing such as aprons, skirts, and vests should always be
`used when working in an unprotected zone. The typical protective clothing
`consists of 0.50 mm lead impregnated rubber. Ninety-five percent of scatter is
`directed towards the head and neck, and the use of a thyroid shield is strongly
`recommended. In addition, leaded eyeglasses are available that can absorb
`70% of scatter exposure to the lens. Personnel who have frequent back expos-
`ure should wear wrap-around protective garments (others may wish to wear
`them for comfort).
`Every angiosuite should have a protocol in place to monitor the integrity
`of its protective garments. Folding and rolling of lead garments should be
`avoided, as this will lead to cracking. At the minimum, annual X-ray evaluation
`of the protective clothing should be practiced to evaluate for cracks. Drop off
`lead garments with shoulder and waist Velcro is available which allows for
`removal without breaking scrub.
`
`Common devices used in endovascular interventions
`
`Guidewires
`Guidewires are used to introduce, position, and exchange catheters.
`A guidewire generally has a flexible and stiff end. In general, only the flexible
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`end of the guidewire is placed in the vessel. All guidewires are composed of
`a stiff inner core and an outer tightly coiled spring, which allows a catheter to
`track over the guidewire. There are five essential characteristics of guidewires:
`size, length, stiffness, coating, and tip configuration.
`Guidewires come in different maximum transverse diameters ranging from
`0.011 to 0.038 in. For most aortoilliac procedures, a 0.035 wire is most commonly
`used while the smaller diameter wires are reserved for selective small vessel
`angiography such as infrageniculate or carotid lesions. The 0.035 Bentson wire
`is often used as the initial guidewire to obtain access to the groin vessels for
`most interventions.
`In addition to diameter size, guidewires come in varying lengths usually
`ranging from 180 to 260 cm in length. Increasing the length of the wire always
`makes it more difficult to handle and increases the risk of contamination. While
`performing a procedure, it is important to maintain the guidewire across the
`lesion until the arteriogram has been satisfactorily completed. A good rule of
`thumb to follow is that the guidewire should be twice the length of the longest
`catheter being used. This allows for easy catheter exchanges while maintaining
`the guidewire across the lesion.
`The stiffness of the guidewire is also an important characteristic. Stiff wires
`allow for passage of large aortic stent-graft devices without kinking. They
`are also useful when trying to perform sheath or catheter exchanges around
`a tortuous artery. An example of a stiff guidewire is the Amplatz wire. For
`initial access, standard guidewires are coated with a nonhydrophilic coat-
`ing composed of Teflon and heparin to lubricate the surface and reduce the
`thrombogenicity of the guidewire. The heparin coating lasts for about 10 min.
`Hydrophilic coated guidewires, such as the Glidewire, have become invalu-
`able tools for assisting in difficult catheterizations. The coating is primed by
`bathing the guidewire in saline solution. The slippery nature of this guidewire
`along with its torque capability significantly facilitate difficult catheterizations.
`There are several disadvantages of hydrophilic coated guidewires that need
`to be remembered. These wires must be constantly rewetted in order to main-
`tain their lubricated surface. Glidewires are often very slippery and difficult
`to handle with gloved hands, and one must be careful to monitor the tip of the
`wire while performing catheter exchanges.
`Guidewires come in various tip configurations. Most tips of guidewires are
`soft. Many angiographers use the J-tip wire as the initial access guidewire,
`as it is associated with the lowest risk of dissection. We use the Bentson
`wire, which has a soft floppy tip that is straight in its packaged form but
`forms a functional large J-tip when being advanced through a vessel. Angled
`tip wires like the angled Glidewire can be steered to manipulate a cath-
`eter across a tight stenosis or to select a specific branch of a vessel. The
`Rosen wire has a soft curled end that makes it ideal for renal artery stent-
`ing. The soft curl of this wire prevents it from perforating small renal branch
`vessels.
`
`LLBC: “chap1” — 2005/10/29 — 16:52 — page 12 — #12
`
`University of Maryland, Baltimore
`IPR2016-00208
`
`Exhibit 2011
`Page 12 of 19
`
`

`
`General Principles of Endovascular Therapy 13
`
`Catheters
`Catheters come in all different shapes and sizes and are sized according to
`their outer diameters. A plethora of catheters have been designed for specific
`arterial beds and designated by configuration, which are discussed in the last
`chapter of this book. Most catheters must be advanced over a wire to limit
`intimal injury. Catheters are generally differentiated based on whether they are
`nonselective or selective. An example of a nonselective catheter is the pigtail
`catheter. This type of catheter has multiple side and end holes that allow for
`a large cloud of contrast agent to be infused over a short period of time. They
`are most commonly used for viewing of high-flow vessels like the abdominal
`ao