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2003;139(11):1409–1416.
6. Mimura H, Kanazawa S, Yasui K, et al. Percutaneous sclerotherapy for
venous malformations using polidocanol under fluoroscopy. Acta Med
Okayama. 2003;57(5):227–234.
7. Marrocco-Trischitta MM, Guerrini P, Abeni D, et al. Reversible cardiac
arrest after polidocanol sclerotherapy of peripheral venous
malformation. Dermatol Surg. 2002;28(2):153–155.
8. Woods JE. Extended use of sodium tetradecyl sulfate in treatment of
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1987;79(4):542–549.
T
Section E Catheters
12
Catheters and Catheterization Techniques
Susie J. Park • Gary P. Siskin
hroughout this textbook, there are several chapters that focus on the
embolic agents used for embolization and many more chapters
focusing on the clinical indications being treated with embolization
procedures. There is no doubt that these two broad areas of focus are
essential for these procedures to be successfully performed. However, there is
a third area of focus that requires attention as well: the catheters and the
catheterization techniques used today for embolization. Many times,
embolization procedures are either successful or unsuccessful based on the
choices made by individual physicians regarding the materials and techniques
used to deliver an agent to its intended target. This chapter will take a unique
look at embolization from this perspective.
CATHETERS USED FOR EMBOLIZATION
Almost every available angiographic catheter can be used to deliver one or
more of the many agents available today for embolization. Standard 4-Fr and
5-Fr angiographic catheters can be used to deliver coils, plugs, and particulate
embolic agents. However, the expanded indications for embolization into
smaller vessels that are increasingly located distally within a target vascular
bed are requiring the use of microcatheters. Microcatheter characteristics that
are favorable when it comes to the performance of embolization procedures
include trackability, flexibility, kink resistance, and radiopacity; radiopacity
is important to ensure that an embolic agent will be deployed exactly where
deployment is intended to be. Many microcatheters are being manufactured
with various tip configurations to facilitate catheterization of target vessels.
In addition, microcatheters are now available with various inner and outer
diameter sizes, so care must be taken to ensure that the microcatheter selected
is compatible with the agent being planned for embolization. Selective
catheterization in the setting of embolization can be challenging at times, and
almost nothing can be more frustrating for an interventionalist than to find
out that the microcatheter used cannot accommodate a particular coil or
microsphere after it has been positioned appropriately within the target
vasculature.
CATHETER AND EMBOLIC AGENT
COMPATIBILITY
Every embolic agent reviewed in the previous chapters requires a catheter for
delivery to the vascular bed being targeted for embolization. The actual
catheter selected for delivery will, of course, depend on the embolic agent
being used and the degree of selective catheterization required for the
condition being treated. It will also depend on the inner diameter of the
selected catheter because different agents either require or are more easily
delivered through appropriately sized catheters. There are some specific
issues surrounding catheter selection and the agent being used for
embolization.
Coils
When using coils for embolization, the delivery catheter must have an inner
diameter that constrains the coil as it is being delivered. If the inner diameter
of the catheter is too large relative to the size of the coil, then the potential
exists for the coil to begin forming within the catheter. This can result in the
coils getting stuck within the catheter, forcing the catheter to be removed. If
catheterization of the target vessel was technically challenging, then being
forced to remove the delivery catheter could have significant implications in
terms of the additional radiation dose, contrast volume, and physician time
required to repeat that portion of the procedure. This is particularly the case
with the use of microcatheters and newer detachable coils. For example, the
hydrogel coating of an AZUR detachable coil (AZUR Peripheral HydroCoil
Embolization System; Terumo Medical Corporation, Somerset, New Jersey)
may make it better placed with a microcatheter with a 0.027-in inner diameter
as compared with other coils that are easily placed through a microcatheter
with a 0.021-in inner diameter. Therefore, attention must be paid to catheter
selection to avoid this type of catheter–coil mismatch.
Coil passage through a catheter can be held up for other reasons as well.
It can occur with retrograde blood flow into the catheter with subsequent
thrombosis. This can be prevented with frequent flushing of the catheter or
even the use of a continuous infusion of saline through the catheter via a
Tuohy Borst adapter (Cook Incorporated, Bloomington, Indiana).1 In
addition, hydrophilic catheters can be softer than other catheters, which may
cause fibered coils to get stuck in the catheter near a curve or the tip.2 This
can result in a failure to deliver the coil to its target and the need to
prematurely remove the obstructed catheter.
Catheter stability is an important component of coil delivery to prevent
incorrect positioning of the coil as it is being deployed. The use of a guide
catheter or long sheath can assist with minimizing this potential technical
complication. In addition, before the use of any pushable coil, it is good
practice to test the stability of the delivery catheter by either injecting saline
through the catheter or by advancing the coil pusher to the tip of the catheter
before any coil is placed.
3
Plugs
It is important to understand that the available plugs typically require larger
catheters for delivery when compared with coils, and they cannot be
delivered with a microcatheter. For example, depending on the exact
configuration and size of an Amplatzer Vascular Plug (St. Jude Medical, Inc.,
St. Paul, Minnesota), either a 4-Fr to 5-Fr catheter or 4-Fr to 7-Fr guide
catheter/sheath would be required for delivery.4 Therefore, this
understandably requires that the target vessel can accommodate a catheter or
sheath of this size. It may or may not be possible for these catheters to track
over a guidewire to an area of arterial pathology if the vessels leading to the
pathology are small, tortuous, or diseased. This must be recognized before
settling on the use of a plug for embolization.
Liquid Agents
Cyanoacrylates are one example of a liquid adhesive used for embolization
procedures, and the main pathology treated with these agents are
arteriovenous malformations. Glue embolization is typically performed
through a microcatheter positioned as close as possible to the nidus.5 Because
polycarbonate can be destroyed by cyanoacrylate, polypropylene syringes
should be used for these procedures.
5,6
Although attention to the technical
details of administration is important to prevent catheter adhesion to
intraluminal glue (e.g., dilution, catheter position, etc.), there is no specific
microcatheter that is recommended for use with cyanoacrylates.
This is not the case with Onyx (Covidien, Irvine, California), which is
another liquid embolic agent. Onyx is an ethylene vinyl alcohol copolymer
used in conjunction with dimethyl sulfoxide (DMSO). Onyx is nonadhesive,
which means that the delivery catheter is unlikely to become adhered to it
after delivery. DMSO is necessary during Onyx administration because it
inhibits the polymerization of Onyx, which begins after the diffusion of
DMSO in the presence of aqueous media such as blood.7 The problem is that
DMSO can also potentially erode a delivery catheter. As a result, the
microcatheters used in association with DMSO administration must be
DMSO compatible, indicating that the catheter manufacturer has done the
appropriate testing to ensure that the catheter will maintain its integrity
during DMSO and Onyx administration. The manufacturer of Onyx has done
their own internal testing leading to specific recommendations for which
catheters should be used with DMSO. The testing they perform is extensive,
including detachment force testing (to determine the amount of force required
to detach a catheter from Onyx), dynamic pressure testing (to determine the
required pressure to push Onyx through a patent catheter), precipitated Onyx
testing (to determine the pressure required to dislodge precipitated Onyx
from both sides of the catheter), fuse joint segment burst testing (to determine
the pressure required to burst each catheter-fused joint segment and the distal
segment with marker band[s]), and others including catheter tensile strength
testing, static burst testing, pressure profile testing, and collapsed lumen
(kink) testing (Covidien, Laci Costa, written personal communication). As a
result of this testing, recommended catheters include the Apollo, Marathon,
UltraFlow, Echelon, and Rebar catheters, all of which are manufactured by
Covidien (Irvine, California). There are other manufacturers claiming DMSO
compatibility with their microcatheters as well, but the manufacturer of Onyx
has not tested these catheters.
Particles
Particulate polyvinyl alcohol (PVA) particles have historically been
associated with microcatheter clogging. This is most likely due to particulate
aggregation, making the effective size of the PVA particles larger than their
actual size.8 Selecting a catheter with an appropriate inner diameter is
essential to ensure that catheters do not become occluded while using PVA
particles. Although 4-Fr and 5-Fr catheters can certainly be used to
administer PVA particles, it is more common practice for microcatheters to
be used for this purpose. This is due to the vascular beds or tumors and other
pathology that are typically targeted with PVA particles. In general,
microcatheters with inner diameters of 0.027 to 0.028 in are more appropriate
and easier to use in association with particulate embolization than smaller
inner diameter catheters. Although it is possible to use microcatheters with
smaller inner diameters, more injection force and more frequent flushing are
required to avoid catheter occlusion. From a delivery perspective, the
development of spherical embolic agents in recent years, including bland and
drug-eluting microspheres, has resulted in easier administration and a lower
incidence of microcatheter occlusion due to the fact that these microspheres
do not aggregate.
Gelfoam
Gelatin sponge particles are commonly used for embolization.
Interventionalists often prepare these particles at the time of the embolization
procedure with the use of a cutting method or pumping method.9 Although
gelfoam is most easily administered through a 4-Fr to 5-Fr angiographic
catheter, it can be administered through a microcatheter as well.
Administering gelfoam through a microcatheter can be done with the use of
smaller syringes and higher injection pressures. However, concern has been
raised that this can result in fragmentation of the gelfoam, leading to smaller
particles being administered. Katsumori and Kashara10 as well as Osuga et
al.11 have shown that this is not the case and that gelfoam can be safely
delivered intact through a microcatheter.
CONSIDERATIONS FOR CATHETERIZATION
DURING EMBOLOTHERAPY
Vascular Anatomy
During all embolization techniques, a thorough knowledge of vascular
anatomy is required before embolization. Understanding the tissues and
organs being supplied by individual vessels allows the interventionalist to
increase the level of certainty that the target organ is being embolized and to
gauge the risk of nontarget embolization. In addition, it is well established
that there are various branching patterns of vessel origins all falling under the
heading of “normal anatomy.” Without understanding where anomalous
vessels to particular organs may arise, it would be impossible to be certain
that all of the vessels responsible for the arterial supply are accounted for and
embolized as necessary. For example, it has been well established that
branches of the internal mammary artery can supply lung parenchyma in a
patient with hemoptysis, that branches of the ovarian artery can supply the
uterus in a patient with uterine fibroids, and that branches of the superior
mesenteric artery can supply the liver in a patient with hepatocellular
carcinoma. Having this knowledge can enable the interventionalist to study
all possible sources of arterial supply to a target organ before concluding that
the procedure has been successfully completed.
Nonselective versus Selective Catheterization
As part of the angiographic assessment before embolization, a nonselective
angiogram is often performed to gain an overview of the arterial supply to the
specific part of the body being targeted for embolization. There are several
potential benefits to performing nonselective angiography before selective
catheterization and embolization. Nonselective angiography permits an
assessment regarding which vessels are actually responsible for supplying a
target organ, which can eliminate or greatly reduce the time spent
catheterizing vessels that are ultimately found to not be involved in the
pathology being treated. In addition, the variant anatomy described in the
previous section can be quickly identified so as not to allow for time being
spent on the catheterization of noncontributory vessels. Nonselective
angiography also allows for an assessment of those vessels that do require
selective catheterization and can provide information to simplify the process
of selective catheterization. Abdominal aortography, for example, can
identify the number of renal arteries before selective renal embolization and
which vessels are contributing to the abnormal target vasculature (Fig. 12.1
).
It can also identify the angle at which a renal artery originates from the
abdominal aorta and can allow for appropriate selection of a catheter
configuration that closely mimics the patient’s anatomy. This can reduce the
time needed for selective catheterization, which in turn can limit the radiation
dose and volume of contrast administered during this portion of an
embolization procedure.
Proximal versus Distal Embolization
Once a particular vessel has been embolized, the development of collateral
flow circumventing the point of vascular occlusion is a possibility that can
undermine the initial intent of embolization. Therefore, this possibility should
always be considered when determining the exact location within a target
vessel for embolization. In some cases, such as distal embolization of an end
organ such as the spleen or kidney, collateralization from one distinct
territory to another is unlikely to occur. However, when performing a
proximal embolization in the setting of trauma or aneurysmal disease, it is
entirely possible that collateral vessels will continue perfusing the target
vascular bed, effectively rendering the embolization ineffective. In these
cases, embolizing a vessel both proximal and distal to an area of focal
pathology would be appropriate to prevent this possibility from occurring.
The level of catheterization within a target vessel is also important
because it will determine how much actual end organ ischemia will occur
with embolization. As described earlier, a more proximal embolization can
potentially fail due to collateral flow development, but at other times, a more
proximal embolization with the development of collateral vessels can help
prevent unwanted end organ ischemia.
Catheter position within the target vessel is particularly important when
using a particulate or liquid embolic agent. Particulate or liquid embolic
agents often require normal antegrade flow to pass alongside the delivery
catheter within the target vessel to deliver the embolic agent into the
pathologic vascular bed. If the delivery catheter is positioned in a vessel of
similar size, minimizing flow around the catheter, then the delivery of a
particulate or liquid embolic may be hampered by spasm or true arterial
occlusion. This may lead to a less effective embolization. Therefore, an
appropriate catheter position that limits the flow of these agents into
unwanted side branches but still allows for flow-mediated delivery of the
particles or liquid into the target vascular bed is ideal in this setting. This
highlights the importance of thinking about the exact level of arterial
occlusion selected for any embolization procedure.
Risk of Reflux
The risk of refluxing an embolic agent into a side branch of the target vessels
or entirely out of the target vessel is a clearly unwanted occurrence during