Magnetic Catheters Research Articles

A Human-Scale Clinically Ready Electromagnetic Navigation System for Magnetically Responsive Biomaterials and Medical Devices.

Magnetic navigation systems are used to precisely manipulate magnetically responsive materials enabling the realization of new minimally invasive procedures using magnetic medical devices. Their widespread applicability has been constrained by high infrastructure demands and costs. The study reports on a portable electromagnetic navigation system, the Navion, which is capable of generating a large magnetic field over a large workspace. The system is easy to install in hospital operating rooms and transportable through health care facilities, aiding in the widespread adoption of magnetically responsive medical devices. First, the design and implementation approach for the system are introduced and its performance is characterized. Next, in vitro navigation of different microrobot structures is demonstrated using magnetic field gradients and rotating magnetic fields. Spherical permanent magnets, electroplated cylindrical microrobots, microparticle swarms, and magnetic composite bacteria-inspired helical structures are investigated. The navigation of magnetic catheters is also demonstrated in two challenging endovascular tasks: 1) an angiography procedure and 2) deep navigation within the circle of Willis. Catheter navigation is demonstrated in a porcine model in vivo to perform an angiography under magnetic guidance.

Fast-Response Variable-Stiffness Magnetic Catheters for Minimally Invasive Surgery.

In minimally invasive surgery, such as cardiac ablation, magnetically steered catheters made of variable-stiffness materials can enable higher dexterity and higher force application to human tissue. However, the long transition time between soft and rigid states leads to a significant increase in procedure duration. Here, a fast-response, multisegmented catheter is described for minimally invasive surgery made of variable-stiffness thread (FRVST) that encapsulates a helical cooling channel. The rapid stiffness change in the FRVST, composed of a nontoxic shape memory polymer, is achieved by an active cooling system that pumps water through the helical channel. The FRVST displays a 66 times stiffness change and a 26 times transition enhancement compare with the noncooled version. The catheter allows for selective bending of each segment up to 127° in air and up to 76° in water under an 80 mT external magnetic field. The inner working channel can be used for cooling an ablation tip during a procedure and for information exchange via the deployment of wires or surgical tools.

Gradiometer-Based Magnetic Localization for Medical Tools

Remote magnetic navigation (RMN) offers various possibilities for medical interventions. Magnetic catheters can be wirelessly steered with high precision and accuracy through complex structures, as they are generally more dexterous and flexible than their manually steered counterparts. Position feedback is essential for many tasks. However, most of the commercially available systems do not integrate well with the magnetic navigation systems (MNSs). As a result, fluoroscopy is still widely used in many interventions despite the known associated health risks. In this study, we propose a localization method that uses multiple Hall sensors to measure the magnetic fields produced by the MNS and estimate the full sensor pose without the need for a separate dedicated mapping system. This makes the MNS a two-in-one system that can be used for simultaneous navigation and localization of a medical tool. We perform an optimization of the sensors’ array design in simulation and investigate the influence of the magnetic fields and gradients on the localization accuracy to provide information on the minimal requirements for an MNS for this task.

Magnetic Soft Continuum Robots With Braided Reinforcement

Flexible catheters are used in a wide variety of surgical interventions including neurological, pancreatic and cardiovascular. In many cases a lack of dexterity and miniaturization along with excessive stiffness results in large regions of the anatomy being deemed inaccessible. Soft continuum robots have the potential to mitigate these issues. Due to its enormous potential for miniaturization, magnetic actuation is of particular interest in this field. Currently, flexible magnetic catheters often rely on interactive forces to generate large deformations during navigation and for soft anatomical structures this could be considered potentially damaging. In this study we demonstrate the insertion of a high aspect ratio, 50 mm long by 2 mm diameter, soft magnetic catheter capable of navigating up to a 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> bend without the aid of forces of anatomical interaction. This magnetic catheter is reinforced with a lengthwise braided structure and its magnetization allows it to shape form along tortuous paths. We demonstrate our innovation in a planar silicone pancreas phantom. We also compare our approach with a mechanically equivalent tip driven magnetic catheter and with an identically magnetized, unreinforced catheter.

A Simulation Framework for Magnetic Continuum Robots

Remote magnetic navigation is a technology used to robotically steer magnetic medical instruments, such as magnetic catheters and guidewires, for minimally invasive surgery. The ability to model and simulate the behavior of these magnetic instruments in complex anatomies is important for their clinical use in many ways. Simulation frameworks can improve their design, characterization, and automatic control capabilities, as well as provide training simulators for physicians. In this work we introduce a new simulation framework that accounts for both magnetic actuation and interactions forces with meshed collision models. The simulations are validated experimentally in planar rigid models using a pre-clinical electromagnetic navigation system. We also demonstrate the use of our framework to build training simulators for two endovascular navigation tasks including the exploration of the aortic arch and the internal carotid artery.

Patient-Specific Magnetic Catheters for Atraumatic Autonomous Endoscopy.

Despite increasing interest in minimally invasive surgical techniques and related developments in flexible endoscopes and catheters, follow-the-leader motion remains elusive. Following the path of least resistance through a tortuous and potentially delicate environment without relying on interaction with the surrounding anatomy requires the control of many degrees of freedom. This typically results in large-diameter instruments. One viable solution to obtain dexterity without increasing size is via multiple-point magnetic actuation over the length of the catheter. The main challenge of this approach is planning magnetic interaction to allow the catheter to adapt to the surrounding anatomy during navigation. We design and manufacture a fully shape-forming, soft magnetic catheter of 80 mm length and 2 mm diameter, capable of navigating a human anatomy in a follow-the-leader fashion. Although this system could be exploited for a range of endoscopic or intravascular applications, here we demonstrate its efficacy for navigational bronchoscopy. From a patient-specific preoperative scan, we optimize the catheters' magnetization profiles and the shape-forming actuating field. To generate the required transient magnetic fields, a dual-robot arm system is employed. We fabricate three separate prototypes to demonstrate minimal contact navigation through a three-dimensional bronchial tree phantom under precomputed robotic control. We also compare a further four separate optimally designed catheters against mechanically equivalent designs with axial magnetization profiles along their length and only at the tip. Using our follow-the-leader approach, we demonstrate up to 50% more accurate tracking, 50% reduction in obstacle contact time during navigation over the state of the art, and an improvement in targeting error of 90%.

A Variable Stiffness Magnetic Catheter Made of a Conductive Phase‐Change Polymer for Minimally Invasive Surgery

AbstractVariable stiffness (VS) is an important feature that significantly enhances the dexterity of magnetic catheters used in minimally invasive surgeries. Existing magnetic catheters with VS consist of sensors, heaters, and tubular structures filled with low melting point alloys, which have a large stiffness change ratio but are toxic to humans. In this paper, a VS magnetic catheter is described for minimally invasive surgery; the catheter is based on a novel variable stiffness thread (VST), which is made of a conductive shape memory polymer (CSMP). The CSMP is nontoxic and simultaneously serves as a heater, a temperature sensor, and a VS substrate. The VST is made through a new scalable fabrication process, which consists of a dipping technique that enables the fabrication of threads with the desired electrical resistance and thickness (with a step size of 70 µm). Selective bending of a multisegmented VST catheter with a diameter of 2.0 mm under an external magnetic field of 20 mT is demonstrated. Compared to existing proof‐of‐concept VS catheters for cardiac ablation, each integrated VST segment has the lowest wall thickness of 0.75 mm and an outer diameter of 2.0 mm. The segment bends up to 51° and exhibits a stiffness change factor of 21.

Design and Evaluation of a Steerable Magnetic Sheath for Cardiac Ablations

Precise catheter control is crucial to the success of radiofrequency cardiac arrhythmia ablations. Remote control using external magnetic fields to directly steer the catheter tip is a promising strategy to accurately and easily perform cardiac catheter steering. Magnetic catheters must be flexible enough to be deflected by a magnetic field but rigid enough to provide sufficient force and stability during ablation. These conflicting requirements have limited the design options and effectiveness of magnetic catheters. Furthermore, the ablation force achievable by magnetic catheters depends strongly on the catheter's bending angle; at angles greater than 90°, it can be very difficult to achieve any significant force during ablation. To overcome these shortcomings, we propose to magnetically control a flexible segment at the distal tip of the introducer sheath, rather than the catheter. Control of the tip orientation is thus decoupled from catheter insertion, enabling more robust and intuitive manipulability of the catheter. Usability testing with the Aeon Phocus, a magnetic navigation system, has shown that the control of this magnetic sheath is indeed more intuitive than the control of a standard magnetic catheter.

Remote magnetic versus manual catheters: evaluation of ablation effect in atrial fibrillation by myocardial marker levels

BackgroundA remote magnetic navigation (MN) system is available for radiofrequency ablation of atrial fibrillation (AF), challenging the conventional manual ablation technique. The myocardial markers were measured to compare the effects of the two types of MN catheters with those of a manual-irrigated catheter in AF ablation.MethodsAF patients underwent an ablation procedure using either a conventional manual-irrigated catheter (CIR, n = 65) or an MN system utilizing either an irrigated (RMI, n = 23) or non-irrigated catheter (RMN, n = 26). Levels of troponin T (TnT) and the cardiac isoform of creatin kinase (CKMB) were measured before and after ablation.ResultsMean procedure times and total ablation times were longer employing the remote magnetic system. In all groups, there were pronounced increases in markers of myocardial injury after ablation, demonstrating a significant correlation between total ablation time and post-ablation levels of TnT and CKMB (CIR r = 0.61 and 0.53, p < 0.001; RMI r = 0.74 and 0.73, p < 0.001; and RMN r = 0.51 and 0.59, p < 0.01). Time-corrected release of TnT was significantly higher in the CIR group than in the other groups. Of the patients, 59.6% were free from AF at follow-up (12.2 ± 5.4 months) and there were no differences in success rate between the three groups.ConclusionsRemote magnetic catheters may create more discrete and predictable ablation lesions measured by myocardial enzymes and may require longer total ablation time to reach the procedural endpoints. Remote magnetic non-irrigated catheters do not appear to be inferior to magnetic irrigated catheters in terms of myocardial enzyme release and clinical outcome.

Irrigated-tip magnetic catheter ablation of AF: A long-term prospective study in 130 patients

Nonirrigated magnetic ablation may result in potential char, ineffective lesions, and longer procedure times. This study sought to report the safety and long-term efficacy of irrigated-tip magnetic ablation of atrial fibrillation (AF). Catheter ablation was remotely performed using a new irrigated-tip magnetic catheter (ThermoCool NaviStar-RMT, Biosense Webster, Diamond Bar, CA) in 130 consecutive patients (mean age 59.7 ± 10.5 years) with symptomatic paroxysmal (81 patients) or persistent (49 patients) AF. The radiofrequency (RF) generator was set to fixed power of 30 W. The primary end point of the study was freedom from atrial tachycardia (AT)/AF off antiarrhythmic drugs. The procedure was safely performed in all conventional ablation targets, but crossover to manual catheters was required in 12 patients to complete the mitral isthmus line. The total procedure time was 94.6 ± 15.3 minutes. Impedance values significantly decreased during RF applications (P < .001) and the maximum temperature on the catheter tip was 36.4°C ± 0.8°C. The follow-up duration was 15.3 ± 4.9 months. The primary end point was achieved in 66 of 81(81.4%) patients with paroxysmal AF and in 33 of 49 (67.3%) with persistent AF (P = .035, by log-rank test). Patients with paroxysmal AF had higher late AF recurrence (P =.044). Overall, postablation incessant left AT developed in 7 of 130 (5.4%) patients. Major complications were not observed. Left atrial diameter (P < .001) and heart failure (P = .032) predicted arrhythmia recurrence after remote irrigated-tip ablation. Remote ablation with irrigated-tip magnetic catheters can be safely and effectively performed in patients with AF, but longer follow-up periods are required to evaluate late AF recurrences.

Mapping and ablation of ventricular arrhythmias with magnetic navigation: comparison between 4- and 8-mm catheter tips

Remote magnetic navigation (RMN) has been reported as an effective and safe tool to overcome the need for advanced operator skill in the treatment of complex arrhythmias. We report a series of patients undergoing radiofrequency catheter ablation of ventricular arrhythmias (VAs) using RMN with either a 4-mm catheter tip or an 8-mm catheter tip at four different centers. Sixty-five patients with clinical and symptomatic history of Vas were included. Two different magnetic catheters were used to deliver radiofrequency applications remotely. When ablation with the RMN catheters failed, a manual irrigated catheter was used to eliminate the VAs. Post-ablation pacing maneuvers were utilized to verify the inducibility of Vas. Twenty-eight patients (43%) had ischemic cardiomyopathy [coronary artery disease (CAD)], 16 patients (25%) had non-ischemic cardiomyopathy [idiopathic dilated cardiomyopathy (IDC)], and 21 patients (32%) had structurally normal hearts (SNH) or right ventricle outflow tract tachycardia (RVOT). In patients with structural heart disease (CAD, IDC), success was achieved in 22% with the 4-mm catheter tip and in 59% with the 8-mm catheter tip (p = 0.014). In patients with SNH/RVOT, success was achieved in 85% with the 4-mm catheter tip and in 87% with the 8-mm catheter tip (p = 1.00). Our findings showed that, with RMN, there is an increased success related to the catheter tip utilized. However, in patients with right ventricular outflow origin, the standard 4-mm tip provided adequate lesions for successful ablation in most patients.

Creation of Transcatheter Aortopulmonary and Cavopulmonary Shunts Using Magnetic Catheters: Feasibility Study in Swine

Surgical shunts are the basic form of palliation for many types of congenital heart disease. The Glenn shunt (superior cavopulmonary connection) and central shunt (aortopulmonary connection) represent surgical interventions that could potentially be accomplished by transcatheter techniques. We sought to investigate the efficacy of using neodymium iron boron (NdFeB) magnetic catheters to create transcatheter cavopulmonary and aortopulmonary shunts. NdFeB magnets were machined and integrated into catheters. "Target" catheters were placed in the pulmonary arteries (PAs), and radiofrequency "perforation" catheters were placed in either the descending aorta (DAo) for central shunts or the superior vena cava (SVC) for Glenn shunts. The magnet technique or "balloon target" method was used to pass wires from the DAo or the SVC into the PA. Aortopulmonary and cavopulmonary connections were then created using Atrium iCAST covered stents. Magnet catheters were used to perforate the left pulmonary artery from the DAo, thereby establishing a transcatheter central shunt. Given the orientation of the vasculature, magnetic catheters could not be used for SVC-to-PA connections; however, perforation from the SVC to the right pulmonary artery was accomplished with a trans-septal needle and balloon target. Transcatheter Glenn or central shunts were successfully created in four swine.

Abstract No. 76: Steering and Tracking of Magnetic Catheters Using MRI Systems

Abstract No. 76: Steering and Tracking of Magnetic Catheters Using MRI Systems

Remote ablation of accessory pathways

We read with interest, pleasure, and satisfaction the recent study by Chun et al. 1 which definitively confirms our previous pivotal experience on the efficacy of remote ablation in hundreds of patients with single or multiple accessory pathways.2,3 However, in our experience, soft magnetic catheters (1 M, 3 M, or 3 M quadripolar) are all able to easily record the AP potential and once …

Accurate and Reproducible Target Navigation with the Stereotaxis Niobe® Magnetic Navigation System

Introduction: The Stereotaxis Niobe® Magnetic Navigation System (MNS, Stereotaxis, Inc., St. Louis, MO, USA) allows for remote‐control navigation of magnetically enabled catheters and guidewires for clinical ablation and electrophysiology (EP) device placement using two permanent magnets located on opposite sides of the patient table. Our objective was to provide a clinical framework for expected navigational accuracy during a case by calibrating the system's reproducibility using a realistic heart phantom under various conditions. Methods and Results: We performed two sets of experiments to demonstrate the accuracy of magnetic catheters using the MNS. The first experiment calibrated deviations in the deflection of an EP catheter by the magnetic system from the expected angles using proprietary algorithms based on predicted geometry. We found that the magnetic fields produced catheter angulation movements within a mean of 4° of biophysical predictions. The second experiment used the MNS to navigate these catheters to previously labeled target positions within a phantom heart model and estimated the actual displacement from desired target positions. We found that the accuracy for reaching the desired targets was 100%. Conclusions: Remote navigation of magnetically enabled EP catheters using the MNS accurately and reproducibly navigates to target sites in a heart phantom. This may enable more complex, successful, and time‐efficient procedures in the cardiac catheterization laboratory.

Magnetic guidance system for cardiac electrophysiology: a prospective trial of safety and efficacy in humans

ObjectivesWe evaluated in humans the safety and efficacy of a novel magnetic guidance system (MGS) for electrophysiological mapping, pacing, and ablation. BackgroundCatheter ablation of atrial fibrillation and other complex arrhythmias requires precise catheter manipulation and stabilization. We have shown in animals that the MGS can precisely manipulate a mapping catheter within the heart with an external magnetic field rather than manual catheter control. MethodsThirty-one adults referred for diagnostic electrophysiology studies were enrolled in a prospective trial of the MGS. The magnetic catheter was navigated to preselected sites in the right atrium (RA) and right ventricle (RV) in the first 20 patients. Electrograms were recorded at each target site, and pacing thresholds were measured. In a subset of five patients, RA and RV electrograms and stimulation thresholds were recorded with both a standard ablation catheter and the magnetic catheter. Eleven additional patients were recruited for supraventricular tachycardia (SVT) mapping, and seven of these underwent ablation. ResultsNavigation was successful in 200 of 202 predetermined right-sided navigation targets and 13 of 13 targets in the left atria. Pacing thresholds and electrogram amplitudes in the RA and RV were not significantly different between the standard and magnetic catheters. The SVT mapping with the magnetic catheter was successful in 13 patients, including 4 with left-sided accessory pathways. The MGS was used for successful ablation of SVT in seven of seven patients. There were no procedural complications. ConclusionsThese results demonstrate that the MGS can be used for intracardiac mapping, pacing, and ablation safely and effectively.

Traumatic Posterior Urethral Injury and Early Realignment Using Magnetic Urethral Catheters

Traumatic Posterior Urethral Injury and Early Realignment Using Magnetic Urethral Catheters