Constant Force Application on a Beating Swine Heart: Robotic Assistance for Mapping and Ablation Procedures

Robot assisted surgery has been widely accepted by the medical community. Surgeons utilize robots in many different procedures worldwide. However, cardiothoracic surgeons do not regularly use robotic tools to aid them in performing even simple, catheter based procedures such as cardiac ablation or mapping. Some cardiac Monophasic Action Potentials (MAPs) and ablation catheters require a specific window of force to either effectively characterize or scar cardiac tissue. This is challenging to maintain through the cardiac cycle, so the application of a constant force is not a trivial task for surgeons. Robotic assistance to control the force applied to a catheter through ablation and mapping procedures is needed to improve the outcome for patients. The purpose of this work is to develop a single degree of freedom robot that controls the force applied to a beating swine heart. Rather than trying to predict the motion and timing of the heartbeat, or tracking its movement this robot senses and reacts to the force produced by the myocardium. Through the cardiac cycle, the robot applies a constant force to the surface of a beating heart. The kinematics of the cardiac tissue were characterized by utilizing piezoelectric transducers. Hardware to control the catheter motion was designed to fit most commercially available devices. The controller was designed by first building a mathematical model using measured data, and then a control law was implemented considering the heartbeat as disturbances to the system. Finally, testing was completed with dry runs, and in situ and ex-vivo testing in the Visible Heart® Laboratory.

Problem of Pin Breakage in Equine Transfixation Pin Casting: Biomechanical Ex Vivo Testing of Four Different Pins

Objective The aim of this study was to evaluate cyclic fatigue behaviour of a new pin with a thread run-out design in comparison with three other types of pins commonly used for equine transfixation pin casting. Materials and Methods Twenty-four pairs of equine cadaveric third metacarpal bones (MC3) equipped with one transfixation pin placed horizontally in the distal metaphysis were tested using a simplified model, mimicking the biomechanical situation of equine transfixation pin casting. A 6.3/8.0-mm Imex Duraface pin with thread run-out design (ITROP) was compared with a 6.1-mm smooth Steinmann pin (SSP), a Securos 6.2-mm, positive-profile pin (SPPP) and an Imex 6.3-mm, positive-profile pin (IPPP) under cyclic loading until failure in axial compression of MC3. Results All pins broke at clinically relevant load levels and cycle numbers. The SSP endured significantly (p = 0.0025) more cycles before failure (mean: 48685) than the ITROP (mean 25889). No significant differences in cycles to failure were observed comparing the SPPP versus ITROP, and the IPPP versus ITROP, respectively. Clinical Significance A thread run-out design does not necessarily lead to higher resistance against pin breakage under cyclic loading conditions. The SSP was most resistant against cyclic failure in these testing conditions, even though it was associated with more lateromedial displacement and cortical wear-out. This could outweigh reported disadvantages of the SSP such as reduced resistance to axial extraction and pin loosening.

Development of an adjustable suture for trabeculectomy

This study reports a new suture design that enables simple, controlled intraocular pressure (IOP) adjustments in the postoperative period after trabeculectomy surgery, a common operation used in the treatment of glaucoma. Detailed configuration of this novel suture design and the process of fabricating the new sutures are demonstrated. Ex-vivo testing with prototyped sutures has demonstrated IOP drops of over 50% following suture adjustment. The concept of using adjustable suture to realize controllable IOP drop in the post trabeculectomy treatment is proved to be feasible.