Mitral Regurgitation (MR) is a malfunction of the mitral valve where the blood flows backward because of improper closure of the valve. The blood flows back through the mitral valve to the left atrium during the contraction of the left ventricle. This condition usually causes shortness of breath, fatigue, lightheadedness, and a rapid heartbeat. It is estimated that 2% of the global population have significant mitral valve disease. In US, more than 200,000 patients are diagnosed with this condition each year [1]. Current treatments include anticoagulation medication, and surgeries to replace or repair the dysfunctional mitral valve.
Open heart surgery has been the conventional approach to repair or replace the mitral valve. However, for a large percentage of patients (almost 30%), open heart surgery carries increased risk of mortality and morbidity due to their advanced age and dysfunction of the left ventricle [2]. Recently, less invasive, transcatheter approaches to mitral valve disease have been developed to decrease the surgical risk for these patients. [3]. One of the approaches that has recently shown promising outcomes is the placement of a MitraClip system (Abbott Vascular, Inc., Santa Clara, California) to stop or decrease the undesired leakage. MitraClip is a metal clip coated with fabric that is implanted on the mitral valve leaflets to allow the valve to close more completely. After clip placement, blood flows in an assisted fashion as the mitral valve opens and closes on the either sides of the clip.
The whole procedure for placement of the MitraClip in Transcatheter Mitral Valve Repair (TMVR) takes 2 to 3 hours under general anesthesia. A transesophageal echocardiogram is used to observe the blood flow and to trace the placement of the clip. A catheter is guided inside the femoral artery after percutaneous access is established. Then a guide wire is inserted to reach the mitral valve. At this time the MitraClip is threaded into the target position between the leaflets, and then, the guide is removed. Precise placement and orientation must be achieved at this point to best secure the clip with the minimum leakage possible. Since the implantation is being done inside a beating heart, this precise placement is the most challenging part of the surgery. Currently trial and error along with precise measurements are being utilized to find the best position.
This work introduces an innovative MitraClip locator device based on the most advanced materials and actuators to assist in the positioning of the MitraClip during implantation; this would potentially facilitate the most challenging and improtant step of the procedure. Currently, doctors are spending most of their surgical time (roughly 90 min) finding the correct orientation for the clip. The proposed self-actuated MitraClip locator device uses active Shape Memory Alloys (SMAs), Nitinol wires, in order to expedite surgical procedures with a higher precision. SMA wires have been used in medical devices safely and effectively [4,5]. Fig. 1 shows the schematic picture of our novel design that includes evenly distributed SMA wires inside a shaft to enable orientations in multiple directions. This design is proposed as a scaled model for preliminary testing. After thorough testing and evaluation on this model a real size prototype will be made for the real application.
This work presents a detailed design of our innovative device. This device has been fabricated and tested to show the proof of concept. The main purpose of this work is to show the feasibility of achieving movements in multiple directions using three shape memory alloy wires. As a long term plan, the authors aim to have this mechanism (while its accuracy and safety is assured) attached behind the MitraClip to facilitate controlled, accurate positioning.
Mitral Valve Repair in Rheumatic Disease: Early Results