The tethered magnet: Force and 5-DOF pose control for cardiac ablation

Cardiac arrhythmias are commonly treated by minimally invasive catheter ablation. Because of challenges in precisely manipulating the distal end of the catheter, several magnetic manipulation systems (MMS) have been developed to aid in steering the tip inside the heart. Due to the relative stiffness of catheters, magnetic gradients that create forces acting on the catheter tip position are limited in their effectiveness and are typically ignored. This dramatically limits the tip orientations possible at any specified position in the workspace. Replacing the flexible catheter tip by a string-like tether and replacing multiple magnets by a single magnet allows the ablation tool to be positioned at any location with essentially any orientation. In addition to the five pose degrees of freedom, the tension on the tether can also be controlled. During an ablation procedure, the distal end of the tethered magnet is placed in contact with the heart wall. Extending the tether after tip contact transfers the tension on the tether to a force at the contact point. The contact force can then be precisely controlled and is no longer dependent on catheter bending radius and insertion length, as is the case with current catheter steering systems. The kinematics of a tethered magnet is modeled and tested inside a clinical MMS called the Aeon Phocus. This demonstrates the feasibility of magnetic field gradient control in a medically certified system currently in clinical use.