The Effect of Over-Rotating Nickel-Titanium Medical Retrieval Device Guidewires Part I: Key parameters causing kink formation resulting in premature and catastrophic failure

A variety of Nitinol-based endovascular mechanical devices have been utilized to capture and retrieve blood clots and foreign objects such as embolic coils that occasionally escape during aneurysm treatments and other interventions throughout the vascular system. Nitinol is one of a few materials possessing a novel characteristic referred to as shape memory alloy (SMA). This characteristic allows the material to be deformed, but immediately spring back to its original shape with moderate heating, hence the term ?shape memory?. Nitinol, however, also exhibits a well-documented concern when used in guidewires. i.e., a tendency to form cracks transverse to the longitudinal wire axis on the compression side of a kink that results from a loop created by over-rotating the guidewire. The cracks can then propagate through the wire causing a dramatic loss of strength accompanied by premature and catastrophic failure with only a minor applied force. It was a key objective of the research described herein to determine the critical catheter-to-attached appliance distance (CAAD) at which and below a loop would not form during a procedure. It was a further objective to determine the measured loop diameter (MLD) of a kink that results in transverse cracks on the compression side that causes premature and catastrophic guidewire failure and contributing factors for loop formation. This paper also defines design guidelines for ways to prevent the ill effects of loop formation by immediately becoming aware of their existence and then eliminating them before reaching the critical diameter.