Experimental study of coil delivery wire insertion force in intracranial aneurysm embolization: force discrepancy generated inside the microcatheter through that coil delivery wire passes

In endovascular coil embolization for intracranial aneurysms, as coils are filled in the aneurysm and the stage of procedure is advanced, the force to push forward the coil delivery wire (insertion force) increases. However, the coil insertion force that interventionist’s felt at his fingertips does not directly reflect the stress of the aneurysm and is affected by the resistance generated inside the microcatheter through that the wire passes. The authors evaluated this force discrepancy by subtracting the loading force at the tip of delivery wire from the insertion force of delivery wire and examined the relationship among them. Experiments were performed with the device that applies a constant loading force to the delivery wire tip with the coil removed. A force gauge was connected to the end-tip of the delivery wire to measure the insertion force. The force was measured by changing delivery wire in different coil brands and the conditions of microcatheter (straight or bent position). The results demonstrated that force discrepancy generated inside the microcatheter increased as the loading force increased in a linear relationship. Different coil delivery wires produced differences in the way that force discrepancy changed, thus reflecting the properties of each wire. Microcatheters with more curvature were associated with a higher force discrepancy. In conclusions, as the loading force increases, the force discrepancy increases, and it means that the coil insertion force that the interventionist feels at his fingertips also increases. This force discrepancy is impacted by the delivery wire properties and microcatheter curvature.