Finite element modeling of the left atrium to facilitate the design of an endoscopic atrial retractor.

With the worldwide prevalence of cardiovascular diseases, much attention has been focused on simulating the characteristics of the human heart to better understand and treat cardiac disorders. The purpose of this study is to build a finite element model of the left atrium (LA) that incorporates detailed anatomical features and realistic material characteristics to investigate the interaction of heart tissue and surgical instruments. This model is used to facilitate the design of an endoscopically deployable atrial retractor for use in minimally invasive, robotically assisted mitral valve repair. Magnetic resonance imaging (MRI) scans of a pressurized explanted porcine heart were taken to provide a 3D solid model of the heart geometry, while uniaxial tensile tests of porcine left atrial tissue were conducted to obtain realistic material properties for noncontractile cardiac tissue. A finite element model of the LA was constructed using ANSYS Release 9.0 software and the MRI data. The Mooney-Rivlin hyperelastic material model was chosen to characterize the passive left atrial tissue; material constants were derived from tensile test data. Finite element analysis (FEA) models of a CardioVations Port Access retractor and a prototype endoscopic retractor were constructed to simulate interaction between each instrument and the LA. These contact simulations were used to compare the quality of retraction between the two instruments and to optimize the design of the prototype retractor. Model accuracy was verified by comparing simulated cardiac wall deflections to those measured by MRI. FEA simulations revealed that peak forces of approximately 2.85 N and 2.46 N were required to retract the LA using the Port Access and prototype retractors, respectively. These forces varied nonlinearly with retractor blade displacement. Dilation of the atrial walls and rigid body motion of the chamber were approximately the same for both retractors. Finite element analysis is shown to be an effective tool for analyzing instrument/tissue interactions and for designing surgical instruments. The benefits of this approach to medical device design are significant when compared to the alternatives: constructing prototypes and evaluating them via animal or clinical trials.

Automated knot tying for fixation in minimally invasive, robot-assisted cardiac surgery.

Cardiovascular disease (CVD) is perhaps the most significant worldwide health issue. While open-heart surgery remains the predominant treatment, significant advancements have been made in minimally invasive surgery (MIS) and minimally invasive robot-assisted (MIRA) surgery. MIRA techniques offer many advantages over open-heart procedures and have extended the capabilities of MIS. However, these benefits come at the cost of increased operating times due to time spent tying knots. The additional bypass time limits patient access and is the most significant barrier to the adoption of MIRA techniques. This research seeks to overcome this barrier by designing a device for MIRA cardiac procedures that automates the knotting of sutures. If this task can be automated while ensuring the delivery of high-quality knots, great progress can be made in transforming the field. MIRA cardiac procedures can move from novel procedures performed by a select group of surgeons on a limited pool of patients to a viable alternative available to the majority of patients with CVD. In this research we propose a design for a self-contained device that delivers a locking knot. Results suggest that consistent knots can be delivered at a time savings of 12.5% and 26.4% over manual knots for trained and untrained users of a surgical robot, respectively.