Ultrasonic sensor concept to fit a ventricular assist device cannula evaluated using geometrically accurate heart phantoms.

Future left ventricular assist devices (LVADs) are expected to respond to the physiologic need of patients; however, they still lack reliable pressure or volume sensors for feedback control. In the clinic, echocardiography systems are routinely used to measure left ventricular (LV) volume. Until now, echocardiography in this form was never integrated in LVADs due to its computational complexity. The aim of this study was to demonstrate the applicability of a simplified ultrasonic sensor to fit an LVAD cannula and to show the achievable accuracy in vitro. Our approach requires only two ultrasonic transducers because we estimated the LV volume with the LV end-diastolic diameter commonly used in clinical assessments. In order to optimize the accuracy, we assessed the optimal design parameters considering over 50 orientations of the two ultrasonic transducers. A test bench was equipped with five talcum-infused silicone heart phantoms, in which the intra-ventricular surface replicated papillary muscles and trabeculae carnae. The end-diastolic LV filling volumes of the five heart phantoms ranged from 180 to 480 mL. This reference volume was altered by ±40 mL with a syringe pump. Based on the calibrated measurements acquired by the two ultrasonic transducers, the LV volume was estimated well. However, the accuracies obtained are strongly dependent on the choice of the design parameters. Orientations toward the septum perform better, as they interfere less with the papillary muscles. The optimized design is valid for all hearts. Considering this, the Bland-Altman analysis reports the LV volume accuracy as a bias of ±10% and limits of agreement of 0%-40% in all but the smallest heart. The simplicity of traditional echocardiography systems was reduced by two orders of magnitude in technical complexity, while achieving a comparable accuracy to 2D echocardiography requiring a calibration of absolute volume only. Hence, our approach exploits the established benefits of echocardiography and makes them applicable as an LV volume sensor for LVADs.

Visual Behaviour Strategies of Operators during Catheter-Based Cardiovascular Interventions.

The aim was to gain insights into the visual behaviour and the perceptual skills of operators during catheter-based cardiovascular interventions (CBCVIs). A total of 33 CBCVIs were performed at the University Hospital Zurich by five operators, two experts and three novices, while wearing eye tracking glasses. The visual attention distribution on three areas of interest (AOIs) the "Echo screen", "Fluoro screen" and "Patient" was analysed for the transseptal puncture procedure. Clear visual behaviour patterns were observable in all cases. There is a significant differences in visual attention distribution of the experts compared to the novices. Experts spent 79% of dwell time on the Echo screen and 17% on the Fluoro screen, novices spent 52% on the Echo screen and 40% on the Fluoro screen. Additionally, results showed that experts focused their gaze on smaller areas than novices during critical interventional actions. Operators seem to exhibit identifiable visual behaviour patterns for CBCVIs. These identifiable patterns were significantly different between the expert and the novice operators. This indicates that the visual behaviour of operators could be employed to assist transfer of experts' perceptual skills to novices and to develop tools for objective performance assessment.

Transcatheter Mitral Valve Repair Simulator Equipped with Eye Tracking Based Performance Assessment Capabilities: A Pilot Study.

BACKGROUND: The increase in cardiovascular disease cases that require minimally invasive treatment is inducing a new need to train physicians to perform them safely and effectively. Nevertheless, adaptation to simulation-based training has been slow, especially for complex procedures. OBJECTIVES: We describe a newly developed mitral valve repair (MVR) simulator, equipped with new objective performance assessment methods, with an emphasis on its use for training the MitraClip™ procedure. METHODS: The MVR contains phantoms of all anatomical structures encountered during mitral valve repair with a transvenous, transseptal approach. In addition, several cameras, line lasers, and ultraviolet lights are used to mimic echocardiographic and fluoroscopic imaging and with a remote eye tracker the cognitive behaviour of the operator is recorded. A pilot study with a total of 9 interventional cardiologists, cardiac surgeons and technical experts was conducted. All participants performed the MitraClip procedure on the MVR simulator using standard interventional tools. Subsequently, each participant completed a structured questionnaire to assess the simulator. RESULTS: The simulator functioned well, and the implemented objective performance assessment methods worked reliably. Key performance metrics such as x-ray usage were comparable with results from studies assessing these metrics in real interventions. Fluoroscopy imaging is realistic for the transseptal puncture but reaches its limits during the final steps of the procedure. CONCLUSION: The functionality and objective performance assessment of the MVR simulator were demonstrated. Especially for complex procedures such as the MitraClip procedure, this simulator offers a suitable platform for risk-free training and education.

Quantification of Avoidable Radiation Exposure in Interventional Fluoroscopy With Eye Tracking Technology.

OBJECTIVES: Reducing avoidable radiation exposure during medical procedures is a top priority. The purpose of this study was to quantify, for the first time, the percentage of avoidable radiation during fluoroscopically guided cardiovascular interventions using eye tracking technologies. MATERIALS AND METHODS: Mobile eye tracking glasses were used to measure precisely when the operators looked at a fluoroscopy screen during the interventions. A novel machine learning algorithm and image processing techniques were used to automatically analyze the data and compute the percentage of avoidable radiation. Based on this percentage, the amount of potentially avoidable radiation dose was computed. RESULTS: This study included 30 cardiovascular interventions performed by 5 different operators. A significant percentage of the administered radiation (mean [SD], 43.5% [12.6%]) was avoidable (t29 = 18.86, P < 0.00001); that is, the operators were not looking at the fluoroscopy screen while the x-ray was on. On average, this corresponded to avoidable amounts of air kerma (mean [SD], 229 [66] mGy) and dose area product (mean [SD], 32,781 [9420] mGycm), or more than 11 minutes of avoidable x-ray usage, per procedure. CONCLUSIONS: A significant amount of the administered radiation during cardiovascular interventions is in fact avoidable.