Embolization coils and microcoils are permanent proximal embolization devices used in interventional procedures to block blood flow in medium to large-sized target vessels and pathological pathways.
They consist of stainless steel, platinum, or Inconel (nickel-based superalloy) coils that can be bare or fibered with materials such as nylon fiber, dacron, polyester, silk, PVA, or wool to increase thrombogenicity.
They come in different shapes, sizes, and configurations and are often used in combination with other embolic materials, such as liquid embolic agents (e.g. cyanoacrylate glue, onyx) depending on the specific needs of the patient and the characteristics of the blood vessel being treated.
On this page:
Terminology
The term "microcoil" is used for 0.018" sized coils. The term "coil" is used for devices that have a size of 0.035"- 0.038" ref.
Mechanism of action
Similar to a surgical ligature, coils make a focal occlusion, leaving the vessel distal to the coil patent,
The combination of slow blood flow and endothelial vessel damage due to the presence of coils stimulates thrombogenesis mechanisms and the release of local thrombogenic factors that contribute to the formation of a clot.
Advantages
good radiopacity
easy control and deployment
Disadvantages
occlusion of non-target vessels
coil migration
vessel dissection, perforation or rupture
infection
allergic reaction
Indications
They can be used in every indication where a precise vessel occlusion is needed, but no tissue devascularization is necessary.
-
intracranial aneurysm embolization
to prevent rupture
to prevent rebleeding in ruptured aneurysms
preoperative graft occlusion
Types
Pushable coils
These coils are deployed by pushing them out of the catheter using a straight soft guidewire.
Advantages
readily available
relative cost and ease of use
Disadvantages
reposition is not possible
can be trapped at sharp curves of vessels
can become jammed in the catheter if incompatible with the catheter
Injectable coils or liquid coils
These coils are delivered in target destination by forceful contrast or saline flush.
Advantages
fast deployment
tight coil compaction
accommodate to tortuous vessels
Disadvantages
risk of non-target embolization
the injection can result in pushing the catheter back
Detachable coils
These coils are delivered by mechanical detachment, electrolysis or via hydrostatic means.
Advantages
fully retrievable, and can be repositioned even after full deployment
Disadvantage
expensive
long setup time
friction between microcoil and microcatheter
Preprocedure planning
To prevent distal embolization or migration, the first selected coil should be at least 2 mm oversized or 20-30% larger than target vessel on pre-deployment angiogram.
Coil delivery technique
after securing access, and reaching target destination
perform an angiogram to determine the best catheter position
flush the catheter with saline
fully insert the loading cartridge into the catheter
move the Luer lock connector towards the catheter hub and lock it by turning the Luer lock adapter
-
for 0.018 microcoils
load the coil into the microcatheter using the pusher stylet and push it as far as possible into the loading cartridge
Remove the pusher stylet and loading cartridge
use the pusher stylet to further advance the microcoil into the microcatheter
-
for 0.035"- 0.038" coils
push the coil into the first 30 cm of the catheter using the stiff portion of the guidewire
remove the guidewire and loading cartridge
push the coil to the tip of the catheter using the floppy tip of the guidewire
confirm the good position of the catheter tip in target vessel
-
deliver the coil into the target vessel either by flushing with saline/contrast or by using the push technique with an appropriately sized guidewire; several techniques are described:
perform an angiogram to verify the precise position of the coil within the target vessel
Precautions
To reduce the risk non-target embolization due to a dislodged, loose coils
ensure that coils are not delivered too close to the artery ostia
should be intermeshed with previously placed coils
a minimal arterial blood flow should persist to hold the coils against the previously placed ones until a permanent clot ensures solid fixation
should not be used with catheters that have sideholes (sideports)
History and etymology
The first embolization coils were described by S. Mullan in 19744.
Unable to process the form. Check for errors and try again.