Embolization Therapy: Principles and Clinical Applications, 1 Ed.

Pushable Coils

Keigo Osuga

Pushable coils have been widely used for mechanical occlusion of peripheral and visceral vessels because they are relatively inexpensive, easily available, and simple to handle. Since the original stainless steel coils were developed in the mid-1970s,1 refinements have been made in the materials and designs used for pushable coils, including the recent addition of hydrogel coating technology.2 Similarly, detachable microcoils, although they are expensive, have been also increasingly indicated in peripheral vessels because they can be repositioned and offer more precise coil deployment. However, pushable coils still remain the standard tool for indications requiring mechanical embolic agents and can save both cost and procedure time.

DEVICE DESCRIPTION

Pushable fibered coils are composed of metallic springs with inert synthetic fibers, such as polyester or nylon, attached to the spring to induce thrombosis around the coil. Pushable coils are supplied in a straight cartridge and are typically loaded into the catheter using a guidewire or the provided mandrel. The loop sizes, lengths, thickness, and configurations vary among pushable coil designs (Fig. 2.1). Two major options are 0.035-in coils for delivery through 4-Fr to 5-Fr catheters and 0.018-in microcoils for delivery through microcatheters for more selective embolization.3 Platinum coils are softer and more radiopaque than stainless steel or Inconel alloy coils. Because stainless steel is responsible for severe local artifacts on magnetic resonance (MR) imaging, MR conditional coils made of platinum and Inconel alloy are currently preferred. Long pushable platinum coils or microcoils with an extended lengths are pliable and pack easily into a dense coil mass.4 Most recently, hydrogel-coated pushable coils (AZUR Pushable 35 and 18; Terumo Medical Corporation, Somerset, New Jersey) have become available, and they have the advantage of greater filling volume, independent of thrombus formation.2

TECHNIQUE

As a rule, the coil delivery process should be carefully monitored under fluoroscopy. The coil should be appropriately sized according to the vessel size and anatomy. The first coil should be approximately 20% larger in size than the vessel diameter to minimize the risk of coil migration. The delivery catheter should be accurately positioned within the target vessel. The coaxial technique, using a guide catheter and a coaxial delivery catheter, gives stability and control for coil deployment. A standard catheter can also serve as a guide catheter to deploy microcoils through a microcatheter. There are two methods for delivery of pushable coils. The first method is the “push” technique, in which the coil is pushed by a floppy guidewire or designated pusher wire. The other method is the “flush” technique, in which the coil is forced out of the catheter by saline flush. Although this technique can speed up the delivery process, it should be avoided when precise coil placement is critical and when coil dislodgement is a concern, especially for the first or last coil.

Clinical Application

Pushable coils are mechanical embolic agents used both in arteries and veins for various indications: to control bleeding; to occlude vascular lesions such as aneurysms, varices, and arteriovenous fistulas (AVFs); and to redistribute blood flow to protect nontarget vessels. The details for each indication will be described in later chapters. In general, to occlude a terminal artery that is unlikely to have associated collateral circulation, coils are simply pushed out at, or just before, the site to be occluded. In a larger vessel, proximal coil occlusion may allow persistent flow distal to the site of occlusion via collaterals but at a lower pressure than before embolization. For example, proximal splenic artery embolization is an accepted technique in the setting of traumatic splenic injury to control bleeding. If significant retrograde filling of an embolized vessel(s) is likely via collaterals, the sandwich technique is effective; that is, coils should be placed both proximal and distal to arterial pathology such as a wide-necked aneurysm or pseudoaneurysm (Fig. 2.2). Proximal coil embolization is not effective for arteriovenous malformations (AVMs), as it not only results in persistent flow to the nidus of the AVM via collaterals but also sacrifices the main arterial access for subsequent interventions. For pulmonary AVMs, pushable coils are often used to occlude the distal feeding artery as close to the venous sac as possible.5 Finally, for the purpose of protective embolization, the right gastric and gastroduodenal arteries are often occluded with coils before liver-directed therapy such as arterial infusion chemotherapy or radioembolization for liver tumors.2

Potential Complications

Technical failures and complications can occur during or after coil embolization, although few are specific to pushable coils. First, the coil thickness, lumen of the delivery catheter, and size of the pusher wire should be properly matched, or else the coil can become stuck inside the catheter. Catheters with a side hole should not be used for delivery because the coil can get caught in the side hole. Sizing coils is important because inappropriately sized coils may migrate distally into nontarget vessels if too small or deployed in a straight, poorly controlled manner if too large. Coils can potentially migrate upon catheter removal if the proximal end of the coil remains inside the catheter. Reversal of blood flow can also cause migration of a short straight coil placed in an arterial arcade. Retrieval devices such as a loop snare and basket should be always available to retrieve migrated coils. Rarely, coils can cause vessel wall rupture when the coil is oversized or if the vessel wall is very fragile due to severe inflammation near a pseudoaneurysm. Late recanalization can occur through the coils when the target vessel is inadequately packed or if the patient is coagulopathic. Clinically, ischemic adverse events can occur as a result of intended or nontarget embolization. When adequate perfusion distal to the site of occlusion does not remain via collaterals, organ infarction may occur in the corresponding territory, such as the kidney and lower intestinal tracts.6

TIPS AND TRICKS

• It is critical to find suitable anatomy and adequate vessel length for safe coil deployment.

• The catheter chosen for coil delivery is as important as the coils selected for embolization. A coaxial technique helps to control coil delivery and prevent coil elongation.

• Adjunctive techniques may be necessary to prevent coil migration, especially in a large high-flow vessel. If there is a side branch close to the target vessel, the initial part of the first coil can be anchored into the side branch and then deployed in the target vessel as the delivery catheter is withdrawn7 (Fig. 2.3). When there is no suitable anchor branch, oversized high-radial force coils can be initially deployed to provide a scaffold for subsequent softer platinum coils (scaffold technique).7

• Proximal balloon occlusion is useful for temporary blood flow arrest that will reduce the risk of coil migration.

• In suitable vessels, Amplatzer Vascular Plugs (St. Jude Medical, Inc., St. Paul, Minnesota) can be deployed initially with coils added proximally to the plug. In this case, the plug will help prevent coil migration.8

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 yttrium-90 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 EmbolotherapyA 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.