The Mechanism of Catheter Kickback in the Final Stage of Coil Embolization for Aneurysms: The Straightening Phenomenon

Abstract

<jats:p> The catheter kickback phenomenon often occurs in the last stage of coil packing for cerebral aneurysms. This behavior is considered the result of either a lack of space in the sac or a stiff detaching zone. In order to clarify its mechanism, focused stretch-resistance (SR) coil simulation models were tested. </jats:p><jats:p> Various commercially available SR coils were inserted into a cylinder or an aneurismal sac made from a silicone tube with a smaller than prescribed diameter. A magnified SR coil model (straight type) of fishing line was created for simulation. Numerical analysis for the changes in coil behavior were verified. </jats:p><jats:p> All SR coils showed hardening and straightening at the last few millimeters, resulting in catheter kickback. In a magnified coil experiment, straightening was also realized when folding into a narrow cylinder. </jats:p><jats:p> The SR line coursed in the canal of the first loops and shifted to the outside in the middle portion. Gaps among first coil pitches were enlarged on after insertion into the narrower space. Shortage of the SR line was calculated to reach a maximum of 32%. </jats:p><jats:p> The straightening phenomenon is due to SR line shortening and subsequent condensation of pitches of the first loops at the coil end. Coil tail flexibility was lost, and the coil behaved as a stiff wire. </jats:p><jats:p> Straightening is an important factor in the kickback phenomenon. Shorter final SR coils should be selected, and coil designs should be improved. </jats:p>

Force Characterization of Intracranial Endovascular Embolization

“…However, top and middle placements were indistinguishable regarding maximum insertion force. Thus, while microcatheter placement may be dictated by aneurysm specifics and kickback prevention 11 , the findings quantitatively confirm the intuition that placing the microcatheter tip closer to the aneurysm dome results in elevated aneurysm forces. Furthermore, top placement appeared to predispose greater microcatheter “painting” motions and resulted in more drastic movement compared to middle or bottom placement.…”

“…While microcatheter perforation 2,3 and kickback 11 have been associated with complications and unsuccessful obliteration, the difference in aneurysm force by coil delivery in different positions has remained uninvestigated. Microcatheter tip placement in top-third, center, and bottom-third of the aneurysm during simulated embolization resulted in membrane and insertion force gradients with placement near the dome generating the greatest forces and placement near the neck generating the lowest forces.…”

A Novel Method for Super-selective Coil Embolization Using an Extremely Soft Bare Coil through a Liquid Embolic Delivery Microcatheter

“…First, ED extrasoft ® coil has a delivery wire with smaller diameter (0.012 inch) compared with other coils. Second, straightening phenomenon 13) has been reported in ED extrasoft ® coils due to coil folding. Therefore, ED extrasoft ® coils with small diameter and shorter length might be better to stabilize the tip of Marathon ® catheter.…”

Comparative Examination of Finishing Coils Available in Japan

“…Moreover, where the remaining space is small in the final stage of embolization, the diameter of the remaining space is often smaller than the secondary coil diameter, and the gap causes coil tail straightening, a phenomenon characteristic of the SR structure, leading to microcatheter kickback. 8,9) On the other hand, delivery wire factors are also involved in microcatheter kickback. Action-reaction law ("for every action, there is an equal and opposite reaction") the microcatheter is kicked back when the delivery wire is inserted into the microcatheter.…”