Correspondence *Thoraxcenter, Building Ba583a, Dr Molerwaterplein 40, 3015–GD Rotterdam, The Netherlands

Email p.w.j.c.serruys@erasmusmc.nl

Introduction

The growth of interventional cardiology has led to numerous technological developments:¹ the development of metallic and biodegradable stents that elute novel bioactive molecules;² specialized guidewires with subtle differences for accessing different types of lesion;³ and various new pharmacological agents.⁴ One area that has not seen substantial progress thus far is the technology used to precisely guide a wire across a lesion. In most instances, crossing a lesion still relies heavily on both the skills of the interventional cardiologist performing the procedure and the mechanical properties of the guidewire. The Niobe^® Magnetic Navigation System (MNS; Stereotaxis Inc., St Louis, MO) is a novel technology that can precisely control the tip of a magnetically enabled wire or device in vivo.⁵ Preliminary data suggest that the MNS could be useful in tortuous vessels or in complex lesions such as bifurcations, in which the initial bend placed on the wire might not be ideal for crossing tandem lesions.⁶ Magnetic navigation also means the wire is less likely to deviate into side branches, therefore, reducing radiation exposure and the amount of contrast required.⁷ The combination of dedicated magnetically enabled devices with three-dimensional (3D) imaging methodologies such as multislice CT (MSCT) and the NOGA^® mapping system (Cordis Corporation, Miami Lakes, FL), can increase the accuracy in targeting chronic total occlusions (CTOs) and stem-cell implantation.

To date, the transition of this technology into interventional cardiology has been slow. In many centers the MNS was first used in cardiac electrophysiological procedures, for which the benefits are well established; only now are centers extending the use of this technology to the interventional setting, despite the obvious advantages that the MNS offers. This somewhat cautionary approach stems from the fact that no randomized clinical trials have currently compared the MNS with older, more-established techniques. This issue clearly needs addressing, with future developments in both the software and hardware designs being investigated in timely clinical trials. At present, the expenses incurred in setting up an MNS will also influence its popularity. This Review discusses some of the major technological developments in the context of interventional cardiology and provides an insight into what is currently possible and what might be possible with this novel technology in the future.

Early developments

Vascular studies using magnetic navigation first began over 50 years ago when Llander,⁸ and later Tillander,⁹ used magnetic fields to guide an articulated steel-tip catheter in rabbit aorta. After these initial investigations, small external permanent magnets were used to stereotactically direct iron particles for thrombosis of intracranial aneurysms,^{10, 11, 12} later, rotating electromagnets were used, enabling better control.¹³ In 1991, Ram and Meyer performed the first magnetically guided angiography in a human. They successfully used a magnetized catheter controlled with external permanent magnets in a neonate with anatomically complex congenital heart disease.¹⁴ Despite initial success, further development was hampered by low field strengths, the need for large magnets and the lack of precise 3D control.^{15, 16} In order for stereotactic localization and computer-controlled vector guidance to be possible, considerable advances in both medical physics and magnet design were required.¹⁷ Further advancements in these areas and the use of MRI coregistered with real-time fluoroscopy enabled the navigation of both a small object in a canine brain¹⁸ and magnetically enabled catheters in pig brains.¹⁹ These experiments led to the MNS first being used in interventional radiology and cardiac electrophysiology, and now in interventional cardiology.^{20, 21, 22} Across these disciplines there are now more than 100 systems installed worldwide. It should be noted, however, that applying this technology in interventional cardiology presents a greater challenge than in more established indications such as neurosurgery. Unlike the brain, the heart is a dynamic structure, and the patient's chest moves with respiration.

THE Niobe^® magnetic navigation system

Navigation hardware

The Niobe^® MNS (Figure 1a) has four key components: two permanent adjustable magnets mounted on mechanical frames situated at either side of the fluoroscopy table; navigation software (Navigant^®, Stereotaxis, St Louis, MO) to control the magnets by creating a virtual roadmap and magnetic vectors after imaging data are gathered; a real-time fluoroscopy system to display a virtual map of the live image; and finally, a sterile touch-screen monitor for controlling the system, ideally placed at the operating table. In the second-generation system, Niobe^® II, the mechanical frames enabling the magnets to be positioned were adapted to allow the magnets to translate or tilt about their axes. This tilting action enabled more angiographic projections—the previous version of Niobe^® had limited right anterior oblique and left anterior oblique views because of the bulkiness of the magnets. The majority of systems are integrated with a modified C-arm flat-panel detector fluoroscopic imaging suite (AXIOM Artis dFC; Siemens AG, Malvern, PA), but there are systems that can also incorporate biplane fluoroscopic imaging and rotational angiography. Biplane fluoroscopy has the advantage of reducing the amount of contrast used during image acquisition, but once the images are transferred into the Navigant^® software the lateral C-arm must be stored in order for the magnets to be positioned. Rotational angiography, on the other hand, enables a 3D image to be generated directly from a single acquisition.

Figure 1 The Niobe^® Magnetic Navigation System.

(A) A typical magnetic navigation system set-up showing the magnets, C-arm and the control room. (B) The Titan^® magnetic navigation wire showing the 2 or 3 mm magnet located at its tip.

Full figure and legend (37K)Figures & Tables indexDownload Power Point slide (242K)

When the patient is correctly positioned and isocentered, the magnets interact to produce a spherical magnetic field 15 cm in diameter and uniformly of 0.08 Tesla—the 'magnetic volume'. Within this volume any applied magnetic vector can precisely direct a 2–3 mm magnet mounted on the tip of a wire (Figure 1b) or steerable device so that a full 360° rotation can be achieved. Clinically approved devices include guidewire and electrophysiological ablation catheters; other devices currently in development include coronary and peripheral ablative radiofrequency wires, multidirectional probing catheters, and catheters fitted with needles that are designed for cell implantation.

Navigation software

Free-mode navigation

Magnetic navigation is performed by presetting a magnetic vector using the touch-screen monitor. Following programming, the vector is displayed as a dotted line on the live fluoroscopy image, and the permanent magnets—illustrated by a solid vector line—move to align a magnetic field to this vector. Wire advancement is controlled manually to follow a desired incremental distance and is guided by either two-dimensional (2D) or 3D software features in Navigant^®. The 2D navigational modes include the use of preset navigational vectors that are adapted to a particular coronary anatomy. This software also allows the user to create new presets if necessary, for example in patients who have vascular anomalies or to target coronary artery bypass grafts. Other approaches include the 'bulls eye view', which allows navigation around a central axis, and is, hence, a particularly useful technique for CTOs. The 3D Navisphere^® program (Stereotaxis, Inc., St Louis, MO) is a spherical navigation object that contains regularly spaced polar lines (e.g. latitude and longitude lines). The aim of this program is to improve recognition of the 3D structure of the coronary artery tree. Navigation is also feasible through the 'clock face' mode, which mimics the dial of a clock (Figure 2). This technique permits fast navigation relative to other techniques, but does require some understanding of the spatial coronary anatomy. Direct anatomical navigation is possible by directly introducing a fluoroscopic image in Navigant^®; however, 2D image representation of a 3D structure has obvious limitations.

Figure 2 The clockface navigational mode.

By touching the perimeter the vector moves in that direction; controls for anterior and posterior movements are at the edges.

Full figure and legend (12K)Figures & Tables indexDownload Power Point slide (218K)

True-vessel navigation

True-vessel navigation uses an accurate 3D representation of the coronary artery. Navigant^® software can create such a virtual map from two X-ray images provided that they are 30° apart. This program uses a feature called constellations to map identical points on both images, thus, generating a 3D navigational path or 'centerline' through the vessel lumen (Figure 3a). Alignment of the centerline with the live fluoroscopy image is required for navigation. A 3D representation of the coronary anatomy and centerline can also be created from two fluoroscopic images using the CardiOp^®-B software (Paieon Inc., New York, NY; Figures 3 and 4). The advantage of using this program is that it can limit vascular foreshortening²³ and improve the accuracy of quantitative coronary angiography measurements.^{24, 25} Using this software, navigational vectors can be directed through a virtual representation of the vessel lumen, so subtle changes in the vessel morphology can be accentuated (Figure 3c).²⁶

Figure 3 True-vessel navigation using an accurate three-dimensional representation of the coronary artery.

(A) A constellation road map created from two-dimensional X-ray images; chosen points are depicted by squares along the navigational path. (B) Navigation using a three-dimensional reconstruction created with the CardiOp^®-B software. (C) Navigation by means of the endoluminal view. Abbreviation: OM, obtuse marginal branch.

Full figure and legend (15K)Figures & Tables indexDownload Power Point slide (220K)

Figure 4 Three-dimensional representation of the coronary artery.

(A) A three-dimensional reconstruction of the artery using the CardiOp^®-B software. (B) The same arteries extracted from a multislice CT data set (C and D), displayed as navigational centerlines with a directional vector on the live fluoroscopic images.

Full figure and legend (37K)Figures & Tables indexDownload Power Point slide (242K)

A 3D road map can also be created from an MSCT dataset. The importance of MSCT in interventional cardiology stems from its ability to detect early-stage coronary artery disease,^{27, 28} identify vascular anomalies and provide information on coronary plaques composition.²⁹ Using Navigant^®, the vessels can be isolated from the dataset and a 3D volume-rendered reconstructed MSCT image can be incorporated into the virtual roadmap for magnetic navigation (Figure 4b). The mapping of points along the vessel is used to create a virtual lumen and a centerline (Figure 4d), which is coregistered and aligned to the fluoroscopic image for navigation. The ability of MSCT to 'fill in' the occluded vessel segments that are not seen angiographically means that it is a useful tool for navigating through CTOs (Figure 5a), with newer versions of Navigant^® able to show both the endoluminal view and the multiplaner reconstructed cross-sections (Figure 5b).

Figure 5 Using the Navigant^® system the multislice CT data set can be used to create: (A) a road map of a chronic total occlusion not seen angiographically and (B) cross-sections along the map.

 

Full figure and legend (19K)Figures & Tables indexDownload Power Point slide (226K)

The MNS and intervention: what is currently possible?

Occluded coronary arteries

CTOs have been described as one of the last frontiers in interventional cardiology.⁴⁰ Despite advances in technology and the development of specialized devices and dedicated wires, the rate of successful crossings is still unsatisfactory.⁴¹ An attractive strategy for treatment of CTOs was postulated by Serruys in 2006.¹ The first stage of this strategy involves magnetic navigation to steer a guidewire through the occlusion. Second, optical coherence tomography, intravascular ultrasonography or MSCT cross sections are employed to 'look forward' within the vessel to ensure that the wire is ideally positioned in the true lumen. Finally, ablative power at the tip of the wire is used to recanalize the CTO.⁴² The first successful study to demonstrate the feasibility of MSCT angiography and magnetic-enabled PCI used a system that 'looked forward' at the occlusion—the bull's eye view—making the search pattern for microchannels through the occlusion more uniform by avoiding repetitions.⁴³ Although mapping the occluded segments was easily accomplished, the bulky 2–3 mm magnetic tips used were a notable limitation. Furthermore, the fact that navigation was performed using a fixed roadmap (centerline) rather than a dynamic one gated to the electrocardiogram meant that there was discordance between the live fluoroscopy image and the centerline—another limitation. Ordinarily, when navigating through a patent vessel this discordance is not a problem as the wire is contained within the vessel's lumen, so that when the heart moves with each beat the wire can still follow the trajectory of the predetermined vectors. In CTOs, however, the lack of a patent lumen means that as the heart moves, the tip of the wire can be perpendicular to the vascular wall and when pushed can protrude. Hence, it is of paramount importance to develop technologies that allow dynamic road mapping (centerline) to be superimposed on the live fluoroscopy image, especially when considering magnetic-enabled radiofrequency ablation. Paieon Inc. is developing a dynamic road-mapping system based on their software that can recognize systolic and diastolic phases on fluoroscopic images. This system might have a role in patent vessels or those with subtotal occlusion, but not necessarily in CTOs because contrast media is needed to demarcate the vessel contours.

Much more appealing are methods aimed at electrocardiographic phase gating of the MSCT-derived centerline to the live fluoroscopic image following alignment to recognizable landmarks such as spinous processes and the catheter tip. This technique ensures that at a designated point in the cardiac cycle both the centerline and the live fluoroscopic image of the vessel are superimposed, enabling safe advancement of the ablating wire. Development of the magnetic-enabled wire with radiofrequency ablation functionality is nearing completion (Figure 6). This device is composed of a 0.014 inch wire with a small radiofrequency electrode at its tip and three small magnets embedded proximally. An external generator supplies the radiofrequency energy needed for ablation. A safety and feasibility pilot study of this wire in 'within-stent' CTOs is planned for early 2008 at the Thoraxcenter, Rotterdam, The Netherlands.

Figure 6 A diagrammatic representation of the magnetically enabled radiofrequency ablating wire for chronic total occlusions.

 

Full figure and legend (10K)Figures & Tables indexDownload Power Point slide (216K)

Stem-cell injection

Intramyocardial injection of bone-marrow-derived stem cells is a novel technology that has the potential to induce myocardial regeneration and improvement in left ventricular function.⁴⁴ Currently, electromechanically guided injection is the preferred mode of delivery in patients with chronic myocardial ischemia.⁴⁵ Indeed, clinical studies have shown that transendocardial injections of stem cells using the NOGA^® mapping system are feasible and safe⁴⁶ In this system, once the mapping electrode makes a good contact with the myocardium and the operator recognizes the appropriate electrical signal strengths, stem cells are injected through a needle linked to the device. One major drawback with this system is the difficulty of reaching remote areas of the left ventricle with manual manipulation of the catheter. This drawback can be addressed by using the magnetically enabled MNS-guided NOGA^® electromechanical mapping catheter (Stereotaxis Inc.; Figure 7). The guiding can be performed remotely to reduce operator radiation exposure. Moreover, the magnetic momentum at the catheter tip precludes the need for shaft support, allowing the use of a softer catheter that is less likely to penetrate the myocardium and cause a perforation. By using MSCT or MRI to identify the infarcted area, relevant data can be integrated into Navigant^® to further augment the accuracy of target localization.

Figure 7 A diagrammatic representation of magnetically enabled cell injection catheter following an automatic map in the myocardium.

 

Full figure and legend (12K)Figures & Tables indexDownload Power Point slide (218K)

A recent animal study showed the preclinical feasibility of Stereotaxis-compatible NOGASTAR mapping and MYOSTAR^® injection catheters (Cordis Corporation, Miami Lakes, FL) both equipped with a small permanent magnet at the tip.⁴⁷ Remote NOGA^® mapping was possible with a computer-controlled catheter advancement system (Cardiodrive unit; Stereotaxis Inc., St Louis, MO). The introduction of the NOGA^® map into Navigant^® provided 3D vectors for the navigation of a magnetically enabled MYOSTAR^® catheter. The combination of these technologies resulted in a 95.8% success rate of magnetic-guided injection of mesenchymal precursor cells into the myocardium. When labeled, cells were detected in all but one segment on histology.

What does the future hold?

Magnetic navigation is still in the developmental phase and as such will not revolutionize the way we currently perform PCI. By considering magnetic navigation as an adjunct technique to current practices, however, this technique could be used to beneficial effect in clinical situations that are technically difficult or associated with low procedural success. The development of both software and hardware is, therefore, in the context of adjunct therapy. More powerful magnetic fields (i.e. 0.1–0.12 Tesla, increased from the current 0.08) and software upgrades to further improve the precision of wire control are in development. In terms of CTOs, future developments include dynamic road mapping and appropriate gating of the MSCT images with real-time fluoroscopic images. In addition, alignment between angiographically determined 3D reconstructed nonoccluded segments and the occluded sections obtained through MSCT will be more accurate. Moreover, as MSCT cross-section analysis provides important information on plaque composition and can accurately identify the vessel's border—a 'true' centerline can be reconstructed by 'stacking' the gated cross sections if the center of each cross section (Figure 5b) is determined precisely. Incorporation of this idea in future versions of the Navigant^® software is being contemplated, so that a gated wire can be advanced in a frame-like fashion to ensure central wire transit. The unwarranted complexity of several MNS workstations, which can slow processing speed, will be reduced in the future by a new single-screen user interface (Odyssey^™ Network Solutions, Stereotaxis, St Louis, MO) that links diagnostic information from several sources. To further improve the speed of navigation without compromising safety there will, however, need to be improvements in alignment of the centerline to the real-time fluoroscopy image, possibly through dynamic electrocardiographic gating. This improvement would allow the operator to drag the vector with confidence, instead of using 1–5 mm jumps along the centerline. With this development, the MNS could then compete with conventional wires in all lesions, not just complex cases.

New advances in material science have permitted the development of several guidewires with variable degrees of support and flexibility, tailored to individual coronary lesions. The newest generation in wire design—the Pegasus^®—is made from a nitinol–stainless steel composite for improved flexibility with minimal deformity. Future wire-related developments will include magnets that can change the stiffness of the wire to improve the delivery of a device, multimagnet configurations to enable smoother transition across the tip, and wires with the ability to feedback their position in space. The ability to accurately identify a wire's position can be useful when combined with a robotic wire advancement system. To date, such systems have been successfully employed in electrophysiological procedures^{48, 49} but have not yet been extended to MNS-guided PCI. A stand-alone remote navigation system (CorPath^®, Corindus Ltd, Haifa, Israel) for wire advancement and stent deployment using a joystick to control the wire's axial (i.e. advance, retract) and rotational movements has been shown to be feasible,⁵⁰ which opens the possibility of linking such a device to the MNS to achieve full automation.

Limitations

Even though the concept of directional wire guidance has been effectively realized, the areas in which the system offers a clear advantage over current approaches still need to be identified, which explains the slow market penetration in interventional cardiology. In addition, apart from a few institutional registries, there are limited data on this new technology. The lack of randomized, controlled trials makes comparisons with existing technologies purely speculative. Furthermore, new operators experience a learning phase before achieving an adequate level of competence, irrespective of whether they are a physician or technical staff. Similarly, as the software develops, there is a need for continuing educational updates or seminars to ensure that operators are kept abreast of new developments.

At present, the main limitation with the software remains the alignment of the virtual image to the real-time image. There is also a need for dynamic road mapping of the vessel; at present operators navigate through a static image. The 3D-reconstruction packages used still have limitations with respect to accuracies in tracing the vascular contours from which the central path for navigation is ultimately derived. The physical limitations of magnets attached to the wire tip could hinder advancement in extremely tortuous vessels, highlighting the importance of the multimagnet design that offers a smoother transition. Ultimately, the success of 3D magnetic-enabled procedures still depends heavily on the time it takes to prepare the road map. The time taken can vary enormously depending on the vessel characteristics and must, therefore, be taken into account during procedural planning. The 2D navigation approach is quicker; however, the level of accuracy is compromised.

Conclusions

Magnetic navigation in coronary intervention is rapidly evolving. State-of-the-art magnetic devices are now competing with conventional nonmagnetically enabled wires and devices. These technological advances are creating new roles for stereotactic magnetic navigation, which in the future will include a wider range of invasive cardiac procedures.

Acknowledgments

Désirée Lie, University of California, Irvine, CA, is the author of and is solely responsible for the content of the learning objectives, questions and answers of the Medscape-accredited continuing medical education activity associated with this article.

References

1. Serruys PW (2006) Fourth annual American College of Cardiology international lecture: a journey in the interventional field. J Am Coll Cardiol 47: 1754–1768 | Article | PubMed |
2. Ramcharitar S et al. (2007) The next generation of drug-eluting stents: what's on the horizon? Am J Cardiovasc Drugs 7: 81–93 | Article | PubMed | ChemPort |
3. Segev A and Strauss BH (2004) Novel approaches for the treatment of chronic total coronary occlusions. J Interv Cardiol 7: 411–416 | Article |
4. Fox KA et al.; GRACE Investigators. (2007) Decline in rates of death and heart failure in acute coronary syndromes, 1999-2006. JAMA 297: 1892–1900 | Article | PubMed | ISI | ChemPort |
5. Patterson MS et al. (2006) Magnetic navigation in percutaneous coronary intervention. J Interv Cardiol 19: 558–565 | Article | PubMed |
6. Ellis SG et al. (1990) Coronary morphologic and clinical determinants of procedural outcome with angioplasty for multivessel coronary disease: implications for patient selection. Multivessel Angioplasty Prognosis Study Group. Circulation 82: 1193–1202 | PubMed | ChemPort |
7. Bernardi G et al. (2000) Clinical and technical determinants of the complexity of percutaneous transluminal coronary angioplasty procedures: analysis in relation to radiation exposure parameters. Catheter Cardiovasc Interv 51: 1–9 | Article | PubMed | ChemPort |
8. Llander H (1951) Magnetic guidance of a catheter with articulated steel tip. Acta adiol 35: 62–64 | ChemPort |
9. Tillander H (1956) Selective angiography of the abdominal aorta with a guided catheter. Acta radiol 45: 21–26 | PubMed | ChemPort |
10. Alksne JF et al. (1966) Stereotactic magnetically controlled thrombosis of intracranial aneurysms. Presented at the 34th annual meeting of the Harvey Cushing Society: 1966 April 18, St Louis, MO
11. Fingerhut AG and Alksne JF (1966) Thrombosis of intracranial aneurysms: an experimental approach utilizing magnetically controlled iron particles. Radiology 86: 342–343 | PubMed | ChemPort |
12. Meyers PM et al. (1963) Experimental approach in the use and magnetic control of metallic iron particles in the lymphatic and vascular systems of dogs as a contrast and isotopic agent. AJR Am J Roentgenol 90: 1068–1077 | ChemPort |
13. Yodh SB et al. (1968) A new magnet system for 'intravascular navigation'. Med Biol Eng 6: 143–147 | Article | PubMed | ChemPort |
14. Ram W and Meyer H (1991) Heart catheterization in a neonate by interacting magnetic fields: a new and simple method of catheter guidance. Cathet Cardiovasc Diagn 22: 317–319 | Article | PubMed | ChemPort |
15. Alksne JF (1971) Stereotactic thrombosis of intracranial aneurysms. N Engl J Med 284: 171–174 | PubMed | ChemPort |
16. Hilal SK et al. (1974) Magnetically guided devices for vascular exploration and treatment. Radiology 113: 529–540 | PubMed | ChemPort |
17. Gillies GT (1994) Magnetic manipulation instrumentation for medical physics research. Rev Sci Instrum 65: 533–562 | Article | ChemPort |
18. Grady MS et al. (1990) Nonlinear magnetic stereotaxis: three-dimensional, in vivo remote magnetic manipulation of a small object in canine brain. Med Phys 17: 405–415 | Article | PubMed | ChemPort |
19. Grady MS et al. (2000) Experimental study of the magnetic stereotaxis system for catheter manipulation within the brain. J Neurosurg 93: 282–288 | PubMed | ChemPort |
20. Chu JC et al. (2005) Performance of magnetic field-guided navigation system for interventional neurosurgical and cardiac procedures. J Appl Clin Med Phys 6: 143–149 | Article | PubMed |
21. Raizner AE (2007) Magnetic navigation: a pivotal technology. Catheter Cardiovasc Interv 69: 856 | Article | PubMed |
22. Hertting K (2005) Use of the novel magnetic navigation system Niobe^™ in percutaneous coronary interventions: the Hamburg experience. Eurointervention 1: 336–339
23. Green NE et al. (2005) Angiographic views used for percutaneous coronary interventions: a three-dimensional analysis of physician-determined vs. computer-generated views. Catheter Cardiovasc Interv 64: 451–459 | Article | PubMed |
24. Gollapudi RR et al. (2007) Utility of three-dimensional reconstruction of coronary angiography to guide percutaneous coronary intervention. Catheter Cardiovasc Interv 69: 479–482 | Article | PubMed |
25. Tsuchida K et al: In vivo validation of a novel three-dimensional quantitative coronary angiography system (CardiOp-B): comparison with a conventional two-dimensional system (CAAS II) and with special reference to optical coherence tomography. EuroIntervention, in press
26. Patterson M et al: Magnetic navigation with the endo-luminal view and the X-ray overlay—major advances in novel technology. EuroIntervention, in press
27. Fishman EK and Horton KM (2007) The increasing impact of multidetector row computed tomography in clinical practice. Eur J Radiol 62 (Suppl): S1–S13 | Article |
28. Hoffmann MH and Lessick J (2006) Multidetector-row computed tomography for noninvasive coronary imaging. Expert Rev Cardiovasc Ther 4: 583–594 | Article | PubMed |
29. Sanz J et al. (2006) Calcium scoring and contrast-enhanced CT angiography. Curr Mol Med 6: 525–539 | Article | PubMed | ChemPort |
30. Seshadri N et al. (2002) Emergency coronary artery bypass surgery in the contemporary percutaneous coronary intervention era. Circulation 106: 2346–2350 | Article | PubMed |
31. Schiemann M et al. (2004) Vascular guide wire navigation with a magnetic guidance system: experimental results in a phantom. Radiology 232: 475–481 | Article | PubMed |
32. Wood BJ et al. (2005) Navigation with electromagnetic tracking for interventional radiology procedures: a feasibility study. J Vasc Interv Radiol 16: 493–505 | PubMed |
33. Krings T et al. (2006) Magnetic versus manual guidewire manipulation in neuroradiology: in vitro results. Neuroradiology 48: 394–401 | Article | PubMed | ChemPort |
34. García-García HM (2005) Magnetic navigation in a coronary phantom: experimental results. EuroIntervention 1: 321–328
35. Ramcharitar S et al. (2007) A randomised controlled study comparing conventional and magnetic guidewires in a two-dimensional branching tortuous phantom simulating angulated coronary vessels. Catheter Cardiovasc Interv 70: 662–668 | Article | PubMed |
36. Atmakuri SR et al. (2006) Initial experience with a magnetic navigation system for percutaneous coronary intervention in complex coronary artery lesions. J Am Coll Cardiol 47: 515–521 | Article | PubMed | ISI |
37. Tsuchida K et al. (2006) Guidewire navigation in coronary artery stenoses using a novel magnetic navigation system: first clinical experience. Catheter Cardiovasc Interv 67: 356–363 | Article | PubMed |
38. Bach RG et al. (2006) Use of magnetic navigation to facilitate transcatheter alcohol septal ablation for hypertrophic obstructive cardiomyopathy. J Invasive Cardiol 18: E176–E178 | PubMed |
39. Ramcharitar S et al. (2007) . Magnetic navigation system used successfully to cross a crushed stent in a bifurcation that failed with conventional wires. Catheter Cardiovasc Interv 69: 852–855 | Article | PubMed |
40. Frangos C et al. (2007) Chronic total occlusion: the last frontier of the interventional cardiology? [French] Rev Med Suisse 3: 1392–1394, 1396–1398 | PubMed | ChemPort |
41. Di Mario C et al. for the EuroCTO Club JS (2007) European perspective in the recanalisation of Chronic Total Occlusions (CTO): consensus document from the EuroCTO Club. EuroIntervention 3: 30–43
42. Baim DS et al. (2004) Utility of the Safe-Cross-guided radiofrequency total occlusion crossing system in chronic coronary total occlusions (results from the Guided Radio Frequency Energy Ablation of Total Occlusions Registry Study). Am J Cardiol 94: 853–858 | Article | PubMed |
43. Garcia-Garcia HM et al.: Multi-slice computed tomography and magnetic navigation-initial experience of cutting edge new technology in the treatment of chronic total occlusions. EuroIntervention, in press
44. Mouquet F (2005) Restoration of cardiac progenitor cells after myocardial infarction by self-proliferation and selective homing of bone marrow-derived stem cells. Circ Res 97: 1090–1092 | Article | PubMed | ChemPort |
45. Perin EC et al. (2003) Transendocardial, autologous bone marrow cell transplantation for severe, chronic ischemic heart failure. Circulation 107: 2294–2302 | Article | PubMed | ISI |
46. Fuchs S et al. (2003) Catheter-based autologous bone marrow myocardial injection in no-option patients with advanced coronary artery disease: a feasibility study. J Am Coll Cardiol 41: 1721–1724 | Article | PubMed | ISI |
47. Perin E et al. (2007) First experience with remote left ventricular mapping and transendocardial cell injection with a novel integrated magnetic navigation-guided electromechanical mapping system. EuroIntervention 3: 142–148
48. Ernst S et al. (2004) Initial experience with remote catheter ablation using a novel magnetic navigation system: magnetic remote catheter ablation. Circulation 109: 1472–1475 | Article | PubMed | ISI |
49. Pappone C et al. (2006) Robotic magnetic navigation for atrial fibrillation ablation. J Am Coll Cardiol 47: 1390–1400 | Article | PubMed |
50. Beyar R et al. (2006) . Remote-control percutaneous coronary interventions: concept, validation, and first-in-humans pilot clinical trial. J Am Coll Cardiol 47: 296–300 | Article | PubMed |

Contact the journal about this article

Subject areas under which this article appears: Intervention