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REFERENCES
1. Gianturco C, Anderson JH, Wallace S. Mechanical devices for arterial
occlusion. Am J Roentgenol Radium Ther Nucl Med. 1975;124:428–435.
2. Maleux G, Deroose C, Fieuws S, et al. Prospective comparison of
hydrogel-coated microcoils versus fibered platinum microcoils in the
prophylactic embolization of the gastroduodenal artery before yttrium90 radioembolization. J Vasc Interv Radiol. 2013;24:797–803.
3. Morse SS, Clark RA, Puffenbarger A. Platinum microcoils for
therapeutic embolization: nonneuroradiologic applications. AJR Am J
Roentgenol. 1990;155:401–403.
4. Osuga K, White RI Jr. Micronester: a new pushable fibered microcoil
for embolotherapy. Cardiovasc Intervent Radiol. 2003;26:554–556.
5. Pollak JS, White RI Jr. Distal cross-sectional occlusion is the “key” to
treating pulmonary arteriovenous malformations. J Vasc Interv Radiol.
2012;23:1578–1580.
6. Funaki B, Kostelic JK, Lorenz J, et al. Superselective microcoil
embolization of colonic hemorrhage. AJR Am J Roentgenol.
2001;177:829–836.
7. White RI Jr, Pollak JS. Controlled delivery of pushable fibered coils for
large vessel embolotherapy. In: Golzarian J, Sun S, Sharafuddin MJ,
eds. Vascular Embolotherapy. A Comprehensive Approach. Vol 1. New
York, NY: Springer; 2006:35–42.
8. Trerotola SO, Pyeritz RE. PAVM embolization: an update. AJR Am J
Roentgenol. 2010;195:837–845.
G
3
Detachable Coils
Craig Greben • Eric J. Gandras • Jason J. Naidich
uido Guglielmi, the father of the detachable coil, stated that the
development of this device was the result of the merging of three
arts: electronics, neurosurgery, and interventional neuroradiology.
1
The Guglielmi detachable coil (GDC) was invented in 1990 and
revolutionized the field of neurointerventional radiology by allowing
endovascular procedures to replace neurosurgical treatment in several cases
over time. The ability to manipulate the coil and reposition it precisely into
small, delicate aneurysms via an endovascular approach before deployment
confers a significant advantage over pushable coils, which behave less
predictably. The ability to pack coils densely into an aneurysm and
successfully exclude it from the circulation represented a paradigm shift in
the field of neurosurgery that has changed the way these lesions are
managed.
2
The success of the detachable coil in the field of neurointerventions led
to the spread and cross-fertilization of this technology into the domain of
peripheral embolization. Although the GDC was invented in 1990 and was
used largely in the intracranial circulation, reports of its use for extracranial
pathologies appeared shortly thereafter.
3
GDCs detach from their delivery wire following the administration of an
electric current. As a result, they can be fully pushed out of their delivery
catheter but retracted completely if their position is unsatisfactory. In recent
years, newer coil designs with different detachment mechanisms have been
developed (Fig. 3.1). For example, the Interlock detachable coil (IDC)
(Interlock Fibered IDC Occlusion System; Boston Scientific Corporation,
Natick, Massachusetts) appeared on the market in the 1990s, and its early use
for peripheral interventions was first described by Reidy and Qureshi4 in
1996. In contradistinction to the GDC, the IDC detaches through a
mechanical release between the interlocking proximal end of the coil and the
distal end of the pusher wire. As a result, the IDC can only be retracted if this
interlocking domain remains within the delivery catheter. This can limit the
precision of deployment and lead to inadvertent embolization requiring
retrieval, as outlined by Reidy and Qureshi.
4
DEVICE DESCRIPTION
The success of the GDC drove the development of other types of detachable
coils, all of which remain attached to a wire until a release mechanism is used
to achieve deployment. Electrical, mechanical, and hydraulic detachment
mechanisms have all been used. This precise detachment allows for
manipulation until a satisfactory position is achieved and minimizes the risk
of migration or nontarget embolization. The physical properties that have
been considered important in coil design include the stiffness and
configuration of the device. Most current coil designs include a platinum
alloy because it is biologically inert and has an optimal strength and rigidity
to allow for conformational changes required for use in packing (Table 3.1
).
Because of the delicate nature of neurointerventional work, these coils have
to be relatively soft to minimize complications. The design and configuration
of the coil will determine its softness. These coils are manufactured with a
stock wire wrapped around a mandril to produce a secondary structure, which
usually has a helical configuration. A tertiary configuration can be
constructed into the coil, which can include spherical and complex threedimensional designs to optimize coil packing.
5
These three-dimensional
“framing” coils provide stability to the aneurysm wall. Softer twodimensional “finishing” or “packing” coils can be placed within the framing
coil to obliterate the space within the aneurysm with a safer margin during
packing. These coils have historically ranged in size from 0.010 to 0.018 in in
diameter and are meant to be deployed through a microcatheter, which serves
to constrain the coil before deployment.
As with pushable coils, detachable coils work by encouraging stasis of
flow and inducing thrombosis. Bare coils can fulfill this role, but blood can
continue to flow through them, especially in high-flow regions or in the
setting of coagulopathy. This is particularly true if the coils are loosely
packed.6 Fibered coils have been developed to promote thrombosis, and the
IDC is an example of this category of device. Other materials used to coat
coils and promote thrombosis include polyglycolic acid (PGA) and nylon.
Bioactive coils containing polylactic acid (PLA) have been developed to
promote endothelialization and wound healing over the coil neck and mass.
7
A further development in coil design has been the coating of platinum coils
with a hydrogel polymer. These coils increase the density of packing by
expanding in diameter once the gel is exposed to an ionic solution such as
blood. The coils can swell between four and seven times the original diameter
and thus increase packing density for the same length of coil deployed. This,
theoretically, can lead to fewer coils required to exclude aneurysms, but this
advantage is difficult to quantify in clinical practice.
7,8
These hydrogel coils
were first employed for peripheral interventions by Greben et al.9 who used
them to exclude pulmonary arteriovenous malformations (AVMs) in 2005.
The development of a peripheral hydrogel detachable coil (AZUR Peripheral
HydroCoil Embolization System; Terumo Medical Corporation, Somerset,
New Jersey) has led to further reports of their use for extracranial
pathologies.
10–12
These hydrocoils are predominantly used as finishing coils,
as they must be detached within 3 to 5 minutes or else the expanded gel
cannot be withdrawn or retracted back into the microcatheter delivery system.
A 0.035-in hydrogel coil has been developed as well, which is considerably
stiffer than the 0.018-in coils, with a larger volume of hydrogel associated
with them. As with any detachable coil, the haptic experience of the stiffness
is appreciated greatest at the junction of the coil and the delivery wire, or
detachment zone, and this must be considered when attempting to place this
segment of the coil into a confined, delicate space to avoid complications
such as perforation.
TECHNIQUE
The ability to withdraw and reposition detachable coils before deployment
affords a level of precision that may not be reliably achieved with pushable
coils. This precision becomes more important in high-flow areas such as
renal arteriovenous fistulas or aneurysms, pulmonary AVMs, and visceral
aneurysms and pseudoaneurysms when the neck is close to the aorta or
visceral branches. Detachable coils allow these challenging lesions to be
treated safely while minimizing coil migration or inadvertent thrombosis of
the native artery. There is also a risk of reperfusion from collateral circulation
if lesions such as fistulas are closed too proximally. Occlusion at the level of
the arteriovenous communication is necessary to prevent this from occurring.
For larger high-flow fistulas, additional treatment strategies may be necessary
such as balloon occlusion or double microcatheter, single guiding catheter
technique that facilitates the building of a stable coil mass with the use of
detachable coils.13 These techniques can also be employed in the treatment of
wide-necked aneurysms, where detachable coils are safer to use than
pushable coils in these challenging lesions. The risk of coil compaction and
reperfusion or migration of the entire coil mass into the native vessel can be
minimized with the addition of a stent to cage the mass.
CLINICAL APPLICATIONS
In general, detachable coils can be used for any indication where pushable
coils are used. They are particularly useful for embolization when the
delivery catheters are in tenuous positions or when the risk of coil migration
is felt to be particularly high based on the pathology being treated (Figs. 3.2
and 3.3). However, they are significantly more expensive than pushable coils,
which means that for more routine indications, the operator must consider the
justification of the added cost. The time spent retrieving a migrated coil and
the potential morbidity of this complication are intangibles that need to be
weighed by the interventionalist. One method we employ to reduce cost is to
use a combination of pushable and detachable coils; for the initial and
completion coils, we use detachable coils with pushable coils in between.
This permits precision during the procedure when the risk of coil migration is
greatest.
POTENTIAL COMPLICATIONS
In addition to the types of complications encountered with pushable coils
such as migration, perforation, and thromboembolic events in the native
vessel, there are potential complications that are only encountered with the
use of detachable coils. Detachable coils can fail to detach or can detach
prematurely. Most manufacturers have incorporated a secondary mechanism
of detachment in the event that the primary method fails. Prematurely
detached coils may still carefully be pushed out of the catheter with the
delivery wire, but there is a risk that the wire can wedge astride the coil
within the catheter. A stretched coil can pose an extremely challenging
situation as the coil can unwind and neither be pushed into the lesion nor
withdrawn from the catheter. Snaring of the coil may be attempted, or the use
of a balloon or stent to tack the stretched coil to the vessel wall may be
considered in this situation. Knotting, interlocking, and fracture of coils can
all potentially occur because attempts at repositioning can create excessive
forces on the coil, particularly at the detachment zone.14 These complications
can lead to movement of the entire coil mass while it is being created.
Fortunately, these complications are rare and can generally be avoided with
careful attention to technique.
TIPS AND TRICKS
Peripheral Detachable Coil
Tips and Tricks
AZUR Peripheral HydroCoil
Embolization System (Terumo
Medical Corporation, Somerset,
New Jersey)
Check detachment integrity by
inserting pusher wire into handle
and noting green light before
introducing coil; detach within 3–
5 min (AZUR only), otherwise
hydrogel may swell too much to
permit retrieval; no detachment
time limit for framing coil
Interlock Fibered IDC Occlusion
System (Boston Scientific
Interlocking arm mechanism
positioned just beyond catheter