Torqueable Steerable Sheath Helical Pull Wire Design
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Solution Overview
Problem
Steerable introducers experience sudden, unpredictable movements and pull wire breakage due to stored energy when torque is applied, leading to whipping of the distal end during deflection.
Innovation Solution
The steerable sheath incorporates pull wires configured in a non-overlapping helical pattern along the non-deflectable portion and straight paths through the deflectable portion, reducing stored energy and allowing smooth torque application without breaking or whipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pull wires extend in a straight line from proximal end to distal end of the sheath, then the sheath can be deflected by shortening the pull wires, but sudden unpredictable movements and whipping occur when torque is applied
Solution Approach 1:
The pull wires are configured to extend along a helical path around the circumference of the inner liner in the non-deflectable portion of the sheath, rather than in a straight line. This helical curvature allows the pull wires to gradually accommodate torque application, distributing the mechanical stress and preventing sudden whipping movements while maintaining deflection control capability.
2Ease of operation
If torque is applied to the steerable introducer, then the distal end can be rotated and positioned, but stored energy causes sudden whipping movements
Solution Approach 1:
The helical configuration of pull wires in the non-deflectable portion creates a gradual transition zone that dissipates stored energy during rotation. As torque is applied, the helical path allows progressive unwinding rather than sudden release, eliminating whipping movements while preserving rotational control.
Solution Approach 2:
The pull wire system transitions from a static straight-line configuration to a dynamic helical configuration that can adapt to applied torque. The helical path allows the pull wires to dynamically adjust their length and tension distribution as the sheath rotates, smoothly managing energy storage and release.
3Ease of operation
If pull wires are fixedly coupled to the sheath at the distal end, then deflection can be achieved by shortening the wires, but the wires may break under torque stress
Solution Approach 1:
The helical path of the pull wires in the non-deflectable portion distributes mechanical stress along a longer, curved path rather than concentrating it in a straight line. This reduces peak stresses on the pull wires and their fixed couplings at the distal end, preventing breakage while maintaining the deflection mechanism.
Solution Approach 2:
The helical configuration allows the pull wires to dynamically accommodate stress during torque application, gradually transitioning from a taut straight-line state to a relaxed helical state. This dynamic behavior prevents sudden stress spikes that would cause wire breakage.
Data Source
AI summary
A steerable sheath includes an inner liner extending from a proximal end to a distal end of the steerable sheath. The inner liner includes a non-deflectable portion and a deflectable portion. The steerable sheath includes a first pull wire positioned along a first helical path around the circumference of the inner liner from a proximal end to a distal end of the non-deflectable portion of the inner liner and along a first straight path from a proximal end of the deflectable portion to a distal end of the deflectable portion. The steerable sheath includes a second pull wire positioned along a second helical path around the circumference of the inner liner from the proximal end to the distal end of the non-deflectable portion and along a second straight path from the proximal end of the deflectable portion to the distal end of the deflectable portion.