Review Article

J. Med. Devices. 2016;10(4):040801-040801-11. doi:10.1115/1.4033876.

Understanding basic science and technical aspects is essential for scientists and engineers to develop and enhance ablative modalities, and for clinicians to effectively apply therapeutic ablative techniques. An overview of ablative modalities, anatomical locations, and indications for which ablations are performed is presented. Specifically, basic concepts, parameter selection, and underlying biophysics of tissue injury of five currently used therapeutic ablative modalities are reviewed: radiofrequency ablation (RFA), cryoablation (CRA), microwave ablation (MWA), high-intensity focused ultrasound (HIFU), and chemical ablation (CHA) (ablative agents: acetic acid, ethanol, hypertonic sodium chloride, and urea). Each ablative modality could be refined for expanding applications, either independently or in combination, for future therapeutic use.

Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2016;10(4):041001-041001-11. doi:10.1115/1.4033325.

Designing optimal pneumatic muscles for a particular application requires an accurate model of the hyperelastic bladder and how it influences contraction force. Previous work does not fully explain the influence of bladder prestrain on actuator characteristics. We present here modeling and experimental data on the actuation properties of artificial muscles constructed with varying bladder prestrain and wall thickness. The tests determine quasi-static force–length relationships during extension and contraction, for muscles constructed with unstretched bladder lengths equal to 55%, 66%, and 97% of the stretched muscle length and two different wall thicknesses. Actuator force and maximum contraction length are found to depend strongly on both the prestrain and the thickness of the rubber, making existing models inadequate for choosing bladder geometry. A model is presented to better predict force–length characteristics from geometric parameters, using a novel thick-walled tube calculation to account for the nonlinear elastic properties of the bladder. It includes axial force generated by stretching the bladder lengthwise, and it also describes the hoop stress created by radial expansion of the muscle that partially counteracts the internal fluid pressure exerted outward on the mesh. This effective reduction in pressure affects both axial muscle force and mesh-on-bladder friction. The rubber bladder is modeled as a Mooney–Rivlin incompressible solid. The axial force generated by the mesh is found directly from contact forces rather than from potential energy. Modeling the bladder as a thin-walled tube gives a close match to experimental data on wall thickness, but a thick-walled bladder model is found to be necessary for explaining the effects of prestrain.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041002-041002-9. doi:10.1115/1.4033327.

Ankle foot orthoses (AFOs) are used to correct motor impairments of the ankle. While current AFOs are passive, advances in technology and wearable robotics have opened the opportunity for a powered AFO. The hydraulic ankle foot orthosis (HAFO) is a device that takes advantage of the exceptional power-to-weight and force-to-weight of hydraulic fluid power. The device is untethered, and the power transmission chain is battery–electric motor–hydraulic pump–hose–cylinder, with the power supply worn at the waist and the cylinder actuators at the ankle. The fluid power circuit is configured as an electrohydraulic actuator (EHA) that is controlled by controlling the electric motor. The first prototype weighs 3.3 kg of which 0.97 kg is worn at the ankle. Steady-state torque–velocity performance showed that the prototype can provide 65 N·m of assistance torque and a no-load velocity of 105 deg/s. Closed-loop position control showed low steady-state error but a slow response. The current prototype demonstrates the potential of hydraulics for providing large torques in a compact, lightweight device. The speed performance of the prototype is inadequate for normal walking but can be improved by switching to servo valve control or by developing a custom hydraulic pump.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041003-041003-7. doi:10.1115/1.4033332.

This paper presents a new method for estimating the tilt angles of endoscopic images. Disorientation is one of the major challenges during natural orifice translumenal endoscopic surgery (NOTES). Reorientation allows surgeons or gastroenterologists to work in off-axis conditions and provides an important reference for coupling a secondary image. Some published studies of angle estimation for NOTES still have the limitation under the influence of movement or vibration. This study proposes a new sensor-fusion method for reducing the shock-based error. A triaxial accelerometer measures the gravitational vector (g-components) in all static states. When motion appears, the angular velocity from a triaxial gyroscope is used to calculate the elemental changes in g-components. A so-called predict-and-choose process relies on this data to predict the future state by giving many prediction values. The relationship between these values, the newest accelerometer readings, and their variation determine the final choice. Hence, under all conditions, the gravitational components are iteratively estimated to calculate the tilt angles. The result is evaluated by being applied in a well-known application, endoscopic horizon stabilization. Compared with the reference method, the proposed method has notable advantages. The simulation and experimental results show small errors, smooth angle change, and a small delay time. The tilt angles are reliable without any cumulative error under the prolonged motion. Therefore, this study gives surgeons or gastroenterologists an improved rectified image for reorienting under off-axis conditions. Further research will identify more applications for the development of surgical instruments for NOTES.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041004-041004-6. doi:10.1115/1.4033602.

This paper describes an improved design of an external fixator. The new fixator comprises 13 parts which are assembled together. The proposed device materials consist of polyether ether-ketone (PEEK) and stainless steel 316L. The design was subjected to finite-element analysis, and a working model was manufactured and subjected to cyclic mechanical testing. The finite-element analysis showed that the maximum stress was 242.9 MPa and this was less than the yield strength and the fatigue endurance limits for the selected materials. Mechanical testing showed that testing reached run-out of 170,000 cycles with no cracks or damage visible in the device parts.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041005-041005-9. doi:10.1115/1.4033014.

Biomechanical energy harvesters (BMEHs) have shown that useable amounts of electricity can be generated from daily movement. Where access to an electrical power grid is limited, BMEHs are a viable alternative to accommodate energy requirements for portable electronics. In this paper, we present the detailed design and dynamic model of a lower limb-driven energy harvester that predicts the device output and the load on the user. Comparing with existing harvester models, the novelty of the proposed model is that it incorporates the energy required for useful electricity generation, stored inertial energy, and both mechanical and electrical losses within the device. The model is validated with the lower limb-driven energy harvester in 12 unique configurations with a combination of four different motor and three different electrical resistance combinations (3.5 Ω, 7 Ω, and 12 Ω). A case study shows that the device can generate between 3.6 and 15.5 W with an efficiency between 39.8% and 72.5%. The model was able to predict the harvester output peak voltage within 5.6 ± 3.2% error and the peak force it exerts on the user within 9.9 ± 3.4% error over a range of parameter values. The model will help to identify configurations to achieve a high harvester efficiency and provide a better understanding of how parameters affect both the timing and magnitude of the load felt by the user.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041006-041006-8. doi:10.1115/1.4033668.

Robot-assisted minimally invasive surgery (MIS) has shown tremendous advances over the traditional techniques. To improve dexterity and back-drivability of the existing planar remote center-of-motion (RCM) mechanism, on which an active prismatic joint is required to drive the surgical tool move in–out of the patient's body, a two degrees-of-freedom (DOFs) planar RCM mechanism is proposed by constructing virtual parallelograms in this paper. The mechanism can be considered as a generalized double parallelogram; both of the actuated joints are revolute joints. This feature enhances the intrinsic back-drivability of the mechanism. The mathematical framework is introduced first to prove that the mechanism could execute RCM. Then, the inverse kinematics of the planar mechanism is solved, and the Jacobian matrix is derived in this paper. Further, the singularity and the kinematic performance based on the kinematic equations are investigated, and the workspace of the mechanism is verified. Finally, a prototype was built to test the function of the proposed RCM mechanism. The results show that the mechanism can fulfill the constraint of MIS, and it can be used as the basic element of the active manipulator in an MIS robot.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041007-041007-10. doi:10.1115/1.4033600.

Due to the need of high-speed and efficient biodosimetric assays for triage and therapy in the event of radiological or nuclear attack, a robotically based automated biodosimetry tool (RABiT) has been developed over the past few years. Adapting the micronucleus assay from filter plates to V-shaped plates presented challenges in the liquid handling, namely, cell splashing out of the V-shaped well plate during the cell harvesting, poor cell distribution on the bottom of the image plate during the dispensing, and cell loss from the image plate during the aspiration in the liquid handling process. Experimental and numerical investigations were carried out to better understand the phenomena and mitigate the problems. Surface tension and contact angle among the fluids and the plate wall were accounted for in the discrete and multiphase numerical models. Experimental conditions were optimized based on the numerical results showing the relationship between nozzle speed and amount of splashed liquid, and the relationship between aspiration speed and number of escaped cells. Using these optimized parameters, numbers of micronuclei in binucleated cells showed the same dose dependence in the RABiT-prepared samples as those in the manually prepared ones. Micronucleus assay protocol was fully realized on RABiT.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041008-041008-7. doi:10.1115/1.4034465.

The management of health through daily monitoring of respiration is of major importance for early diagnosis to prevent respiratory and circulatory diseases. Such daily health monitoring is possible only if the monitoring system is physically and psychologically noninvasive. However, current unconstrained measurement methods cannot distinguish chest and abdominal movements in diagnosing sleep apnea. In this study, a flexible and stretchable tactile sensor sheet was developed to measure the static body pressure of a subject who lies on it and measure the pressure fluctuations induced by respiration or respiratory efforts. The results were compared with the measurements by band sensors that are widely used for measuring chest and abdominal movements in clinic. It was demonstrated that the sensor sheet can distinguish chest and abdominal movements in a supine position. The reasons why the pressure fluctuations measured by the sensor sheet are antiphase with the outputs of band sensors are discussed using a simple dynamic model.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041009-041009-6. doi:10.1115/1.4034576.

Point-of-care diagnostic devices, micrototal analysis (μTAS) systems, lab-on-a-chip development, and biomedical research rely heavily upon microfluidic management and innovative micropump design. Here, we describe the design and prototype deployment of a magnetic shape memory (MSM) micropump capable of submicroliter per minute flow rates. The pump contains no valves or moving parts in the fluid channel and is capable of bidirectional fluid transport. This pump was employed as the mechanism to deliver small intracranial dosages of ketamine and tetrodotoxin (TTX) at 0.33 μl/min during in vivo electrophysiological recordings in anesthetized rats, performing to required specifications.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):041010-041010-8. doi:10.1115/1.4033301.

This paper presents a robust algorithm for automatic tracking of feature points on the human heart. The emphases and key contributions of the proposed algorithm are uniform distribution of the feature points and sustained tolerable tracking error. While in many methods in the literature, detection takes place independently from the tracking procedure, adopting a different approach, we selected a data-driven detection stage, which works based on the feedback from tracking results from the Lucas–Kanade (LK) tracking algorithm to avoid unacceptable tracking errors. To ensure a uniform spatial distribution of the total detected feature points for tracking, a cost function is employed using the simulated annealing optimizer, which prevents the newly detected points from accumulating near the previously located points or stagnant regions. Implementing the proposed algorithm on a real human heart dataset showed that the presented algorithm yields more robust tracking and improved motion reconstruction, compared with the other available methods. Furthermore, to predict the motion of feature points for handling short-term occlusions, a state space model is utilized, and thin-plate spline (TPS) interpolation was also employed to estimate motion of any arbitrary point on the heart surface.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2016;10(4):044501-044501-6. doi:10.1115/1.4033329.

This paper presents a linkage system designed to guide a natural ankle trajectory with the corresponding foot orientation. A six-bar linkage was designed to coordinate the joint angles of an RR chain (R denotes a revolute or hinged joint) that models the leg to achieve the desired ankle trajectory. The design is shown to be adjustable to meet a range of trajectories obtained in an individual's normal gait. Control of the foot position is obtained using a cam-driven parallel chain that has the same input as the six-bar linkage. The design of the linkage was carried out using linkage synthesis theory and optimization methods. The result is a one degree-of-freedom system that guides a natural walking movement of the leg and foot. A solid model of the complete device is presented. The results of this research provide a procedure that focuses on the kinematics and mechanical design of a device named the UCI gait mechanism.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044502-044502-5. doi:10.1115/1.4033601.

Major studies have shown that discogenic pain is the most common cause of chronic lower back pain, accounting for 40% of all the causes. Provocation discography—inducing pains by pressing nerve structures around the annular fissures—is recognized as the only method for diagnosing discogenic pain. However, the method is not available to the patient with full-thickness fissures because of a contrast media leakage through the fissure. In this paper, intradiscal microprobes (IDMPs) affecting direct mechanical stimulus on the nerve fiber are presented for diagnosis of the fissure. The plastic optical fiber (POF), located in the flexible polymer tube, can be navigated to fissure vicinities. Then, a linear or rotational motor placed inside the probe grip generates a minute axial or radial vibration of the fiber tip, which irritates the tiny pain nerve fiber around the fissure. The intensity of the pain can serve as a guideline to determine the level of discogenic disease. The frequency and amplitude of the axial (radial) vibration discography were 2.9–5.7 (4.0–7.0) Hz and 1.5–3.4 (0.06–3.25) mm, respectively. Furthermore, the optical experiments for evaluation of thermal therapy application were successfully confirmed.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044503-044503-4. doi:10.1115/1.4033451.

This paper explores the design of a dynamically weighted therapy bar, which can provide real-time quantitative performance information and adjustments during rehabilitation exercise. In contrast, typical therapy equipment is passive, offering no feedback to the patient or clinician. The dynamic weighted bar (DWB) was designed and fabricated containing an inertial sensor which tracks the orientation of the bar and adjusts the position of an internal weight accordingly, in turn providing a targeted force imbalance between the patient's two arms. Step input experiments were performed on the device while it was held in various stationary positions. The DWB was able to successfully function and transmit motion information. It was able to produce a center of mass shift of 101.6 mm, and a complete travel time between 0.96 s and 1.41 s over the entire length. The use of the DWB device can offer many benefits during rehabilitation including access to more quantitative information for clinicians as well as the potential for more personalized therapy programs.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044504-044504-6. doi:10.1115/1.4033035.

In this paper, we present a soft robotic glove designed to augment hand rehabilitation for stroke patients with clenched fist deformity. The robotic glove provides active finger extension for hand rehabilitative training, through its embedded inflatable actuators that are fabricated by heat bonding of flexible plastic sheets. Upon pressurization, the actuators inflate, stiffen, and extend the fingers. The actuators were embedded in the finger pockets of a glove. In this work, the device was evaluated in terms of its extension torque generated on the metacarpophalangeal (MCP) joint of a dummy finger model and a healthy subject. A stroke patient with finger spasticity was recruited to demonstrate the feasibility of the device to assist in finger extension. Preliminary results showed that the device was able to generate significant extension torques to provide assistance in finger extension for both healthy and stroke participants.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044505-044505-4. doi:10.1115/1.4034297.

Mandibular sagittal split osteotomy (SSO) is an operation performed for the correction of mandibular deformities. In this operation, sharp rotary tools are used during osteotomies and this can induce some complications. For example, if the inferior alveolar nerve is damaged, paralysis of the teeth, the lateral side of the tongue, and the corner of the lip can occur. To decrease the occurrence of such possible complications, we designed and manufactured a novel computer-assisted, patient-specific SSO guide and soft tissue retractor in our previous study. And, we first tested this apparatus on a cadaveric bone in vitro. Now, in this study, a surgical application of the instrument, which was designed and manufactured according to the requirements of the mandibular sagittal split osteotomies, was performed. This paper gives and discusses the results obtained from in vivo application of the apparatus.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044506-044506-7. doi:10.1115/1.4033015.

Fusiform and wide-neck cerebral aneurysms (CAs) can be challenging to treat with conventional endovascular or surgical approaches. Recently, flow diverters have been developed to treat these cases by diverting flow away from the aneurysm rather than occluding it. The pipeline embolization device (PED), which embodies a single-layer braided design, is best known among available flow diverters. While the device has demonstrated success in recent trials, late aneurysmal rupture after PED treatment has been a concern. More recently, a new generation of dual-layer devices has emerged that includes a novel hyperelastic thin film nitinol (HE-TFN)-covered design. In this study, we compare fluid dynamic performance between the PED and HE-TFN devices using particle image velocimetry (PIV). The PED has a pore density of 12.5–20 pores/mm2 and a porosity of 65–70%. The two HE-TFN flow diverters have pore densities of 14.75 pores/mm2 and 40 pores/mm2, and porosities of 82% and 77%, respectively. Conventional wisdom suggests that the lower porosity PED would decrease intra-aneurysmal flow to the greatest degree. However, under physiologically realistic pulsatile flow conditions, average drops in root-mean-square (RMS) velocity (VRMS) within the aneurysm of an idealized physical flow model were 42.8–73.7% for the PED and 68.9–82.7% for the HE-TFN device with the highest pore density. Interestingly, examination of collateral vessel flows in the same model also showed that the HE-TFN design allowed for greater collateral perfusion than the PED. Similar trends were observed under steady flow conditions in the idealized model. In a more clinically realistic scenario wherein an anatomical aneurysm model was investigated, the PED affected intra-aneurysmal VRMS reductions of 64.3% and 56.3% under steady and pulsatile flow conditions, respectively. In comparison, the high pore density HE-TFN device reduced intra-aneurysmal VRMS by 88% and 71.3% under steady and pulsatile flow conditions, respectively. We attribute the superior performance of the HE-TFN device to higher pore density, which may play a more important role in modifying aneurysmal fluid dynamics than the conventional flow diverter design parameter of greatest general interest, absolute porosity. Finally, the PED led to more elevated intra-aneurysmal pressures after deployment, which provides insight into a potential mechanism for late rupture following treatment with the device.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044507-044507-5. doi:10.1115/1.4034146.

Eucapnic voluntary hyperpnea (EVH) challenge is a well-established and sensitive method of determining the degree of bronchoconstriction at hospitals and clinics. This paper presents the development of a computer-controlled system for assessing exercise-induced bronchoconstriction (EIB) in humans including a computer graphic user interface (GUI) to control a low-pressure demand valve for better efficiency. GUI is designed to monitor the severity of acute lung airway narrowing using a matlab software and to present the measurement data into a simple user-friendly program consisting of patient information, EVH test analysis, and detection of exercise-induced asthma (EIA) and EIB. The proposed system is assessed using human subjects. Typical outputs from this system showed that for a female participant, a 20.25% and a 15.61% decrease from baseline in her forced expiratory volume in 1 s (FEVl) after 10 and 15 min of the challenge commencement, respectively. Her actual expiratory flow rate (45.833 L/m) and actual total volume of gas respired (275 L) were smaller than the target values. This system widens the usage of EVH challenge in medical areas, and the GUI may serve as a new clinical computer-aided diagnostic tool to help healthcare professionals noninvasively monitor the severity of asthma, EIA, and EIB.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044508-044508-7. doi:10.1115/1.4034145.

To improve arthroscopic skills, the preferred means of training is cadaveric tissue, because this gives the most realistic scenario. A drawback of cadaveric training is that objective performance tracking and accompanied feedback cannot be provided due to the absence of a suitable system. The main criteria were that the system should be compatible with any cadaveric joint, be used with any type of instrument, easy to set up, and measure two critical parameters that reflect the task efficiency (task time) and safety (forces due to instrument–tissue interaction). This resulted in the development of a force measurement system which consists of a custom-made universal vice, a custom-designed six degree-of-freedom (DOF) force measurement table (FMT) coupled to a computer equipped with customized software to record the time and forces in all directions. The FMT was calibrated and able to measure forces in the range of 0–750 N, with an accuracy of 0.1 N. During two cadaveric training courses, measurements were performed with the FMT. It was observed that the acquired force data could discriminate between novices and experts or reflect a certain phase of a navigation task performed in a cadaveric cow and human knee. A distinct phase highlighted from the force measurements is the insufficient joint stressing of novices during navigation. This results in too small a joint space for inspection and forces the novices to readjust the stressing. As forces cannot be seen, the FMT can contribute to more efficient training by providing explicit cues on the exerted loads during training. This enables a more precise supervision of the trainees.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044509-044509-4. doi:10.1115/1.4034298.

Due to progressive muscle weakness, the arm function in boys with Duchenne muscular dystrophy (DMD) reduces. An arm support can compensate for this loss of function. Existing arm supports are wheelchair bound, which restricts the ability to perform trunk movements. To evaluate the function of a body-bound arm support, a prototype (based on the Wilmington robotic exoskeleton (WREX) arm support) that allows trunk movements was built. In order to examine the effect of this device and to compare it with an existing wheelchair-bound device, three healthy subjects performed single joint movements (SJMs) and activities of daily living (ADL) with and without the devices. The range of motion (RoM) of the arm and the surface electromyography (sEMG) signal of five different arm muscles were measured. The range of motion increased when compared to the wheelchair-bound device, and the trunk motion was perceived as important to make specific movements easier and more natural, especially the more extreme movements like reaching for a far object and reaching to the top of the head. The sEMG signal was comparable to that of the wheelchair-bound device. This means that an arm support with trunk motion capability can increase the range of motion of the user, while the amount of support to the arm is equal.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):044510-044510-5. doi:10.1115/1.4033877.

This paper is focused on the design of a portable and semi-automatic product that allows human blood typing in a short time interval. To solve the technical and mechanical issues, innovative technologies in the areas of industrial design, electronics, and mechanical engineering were incorporated. Thus, we have developed a mechanical system that performs a fast and secure mixing of samples based on the manual plate test. This product concept aims to determinate human blood type in less than 5 min using image-processing algorithms into the mechatronic system. It incorporates formal harmonic aspects as well as some important features, such as ergonomics, portability, safety, security, simple maintenance, and easy to use.

Topics: Blood , Design
Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2016;10(4):045001-045001-8. doi:10.1115/1.4033009.

Knee–ankle–foot orthoses (KAFOs) are prescribed to improve abnormal ambulation caused by quadriceps weakness. There are three major types of KAFOs: passive KAFOs, semidynamic KAFOs, and dynamic KAFOs. Dynamic KAFOs are the only type that enables to control knee motions throughout the entire walking gait cycle. However, those available in the market are heavy, bulky, and have limited functionality. The UT dynamic KAFO is developed to allow knee flexion and assist knee extension over the gait cycle by using a superelastic nitinol actuator, which has the potential to reduce volume and weight and reproduce normal knee behavior. In order to match the normal knee stiffness profile, the dynamic actuator consists of two actuating parts that work in the stance and swing phases, respectively. Each actuating part combines a superelastic torsional rod and a torsional spring in parallel. Geometries of the two superelastic rods were determined by matlab-based numerical simulations. The simulation response of the dynamic actuator was compared with the normal knee stiffness, verifying that the proposed design is able to mimic the normal knee performance. The surrounding parts of the dynamic knee joint have then been designed and modeled to house the two actuating parts. The dynamic knee joint was fabricated and mounted on a conventional passive KAFO, replacing its original knee joint on the lateral side. Motion analysis tests were conducted on a healthy subject to evaluate the feasibility of the UT dynamic KAFO. The results indicate that the UT dynamic KAFO allows knee flexion during the swing phase of gait and provides knee motion close to normal.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2016;10(4):045002-045002-6. doi:10.1115/1.4034574.

This paper reports recent results from an ongoing effort to develop an implantable accelerometer-based heart-monitoring device for ischemia monitoring. The latest device prototype utilizes a new and more compact accelerometer (1.2 × 1.5 × 0.8 mm3), a prototype device from Bosch SensorTec, Reutlingen, Germany. This paper presents the fabrication and testing of the device, including an explorative study of the effect of the capsule shape on the stability of the implanted device in the heart tissue. The stability study indicated sufficient stability of the device and a higher resistance to retraction for one of the capsule designs. The device was able to carry out acceleration monitoring and it meets the leakage current requirements of the IEC60601 standard.

Commentary by Dr. Valentin Fuster

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