Helical guide channel with variable pitch

A system comprising:

• an elongated primary electrode defining a lumen therein;
• an elongated secondary electrode slidably receivable within the lumen;
• a sheath configured to slidably receive the primary electrode therein, the sheath being further configured to convey the primary electrode and the secondary electrode toward a target region;
• a housing operably coupled with the sheath and movably mounted to slidably motivate the sheath relative to the target region;
• a primary actuator operably coupled with the primary electrode and slidably coupled with the housing to motivate the primary electrode to slide relative to the sheath along an axis and including a guide defining a generally helical channel;
• a secondary actuator operably coupled with the secondary electrode and rotatably received within the guide of the primary actuator, wherein the secondary actuator supports a guide member that is configured to engage the helical channel, and wherein the secondary actuator is rotatable relative to the primary actuator to motivate the secondary electrode to move relative to the primary electrode, wherein a pitch of the helical channel is varied along a length of the guide to reduce axial movement of a guide member relative to the axis per unit of rotation of the secondary actuator around the helical channel as the secondary actuator travels distally relative to the primary actuator,
• wherein the pitch is varied to reduce a distance traveled by the secondary actuator along the axis per unit of rotation of the secondary actuator at a position at which the secondary electrode is anticipated to exert an increased resistance on the secondary actuator to movement along the axis, and
• wherein the position at which the secondary electrode is anticipated to exert the increased resistance corresponds to a location at which movement of a distal end of the distal end is expected to be impeded by an obstruction.

A method comprising:

• coupling an elongated implement at a proximal end thereof to an actuator that is movable along an axis;
• and
• motivating the implement by rotatably moving the actuator in reference to a guide through a generally helical path around the axiscreated by the guide, the helical path having a pitch that is varied along a length of the guide to change a distance traveled by the actuator along the axis per unit of rotation of the actuator as the actuator travels distally relative to the guide,
• wherein the pitch is varied to reduce a distance traveled by the actuator along the axis per unit of rotation of the actuator at a position at which the implement is anticipated to exert an increased resistance on the actuator to movement along the axis, and
• wherein the position at which the elongated implement is anticipated to exert the increased resistance corresponds to a location at which a configuration of a distal portion of the implement resists movement of the implement.