Steerable introducer torque loss in the vascular path: a comparative assessment

Ideally, introducers would have a lossless rotational translation from handle to tip enabling physicians to make predictable device adjustments and reducing risks. In the real world there is torque loss incurred along the vascular path. Minimizing rotational loss requires maximizing torsional strength from the handle to distal end of the shaft.

The study demonstrates the clockwise (CW) and counterclockwise (CCW) rotation and torque transmission differences between two 13F deflectable introducers.

Two FDA approved 13F Introducers, Agilis NxT Steerable Introducer (N=3) & the steerable introducer for a pentaspline PFA catheter (N=3), were used to assess the rotation angle & torsional strength using bench test methods, 3 trials with each device.

Simulating a clinical application, each introducer was positioned through a water filled soft 3D silicone model (human femoral vein tract to heart) targeting the LA with the distal end deflected to 90° and positioned for 180° of free rotation. A flexible 6F magnetic sensor enabled catheter was passed through the introducer until the catheter tip was aligned with the introducer tip. A controlled rotational velocity profile with steady angular velocity of 10°/s covering a sweep angle range of CW (0°-180°) and CCW (180°-0°) was applied at the handle while tracking the tip location using a magnetic sensing system. Time-varying tip position data was projected on the sweep plane and converted into angular velocity. The tip angular velocity profile was compared with the input and loss of rotation was calculated and reported.

A second assessment compared the torsional strength between the 2 introducers over a CCW (0°-90°) and CW (90°-0°) rotation with a straight shaft in free space.

With handle rotated to 180°, the tip rotation angles in the heart model resulted in 145.7°±15.6° CW & 147.7°±14.9° CCW for the Agilis and 89.1°±7.5° CW & 90.46°±8.6° CCW for the pentaspline catheter introducer. In the torsional strength assessment, dividing the resultant introducer torques over the 0°-90°-0° rotation showed an Agilis/pentaspline introducer torque ratio of 1.99 (StDev=0.86) CW and 2.03 (StDev=0.258) CCW in 45 paired measurements. Due to its lower torsional strength, the pentaspline catheter introducer loses 50% tip rotation angle compared to Agilis’ 18.5%.

This assessment shows that higher torsional strength in an introducer shaft significantly improves the tip rotational performance.