JP2004511271A - MRI ablation catheter - Google Patents

Abstract

At least one electrode made of an MRI compatible material is supported on the distal end assembly, a shaft and the distal end assembly each made of an MRI compatible material and connected to the electrode. An ablation catheter compatible with the MRI system, comprising: at least one MRI compatible wire made of an MRI compatible material extending from the electrode to a proximal end of the shaft.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
This application is based on 35 USC 119, from US Provisional Patent Application No. 60 / 204,419, filed May 12, 2000, which is hereby incorporated by reference in its entirety. Claim priority.
The present invention relates to ablation catheters that can be guided by magnetic resonance imaging.
[0002]
[Prior art]
Since first described in 1982, catheter ablation has been used for the majority of supraventricular arrhythmias, including atrioventricular nodal recurrent tachycardia, Wolf Parkinson-White syndrome and localized atrial tachycardia from advanced experimental techniques. It has evolved to gain its current role as first-line therapy. More recently, clinical indications for radiofrequency catheter ablation have been extended to include more complex arrhythmias that require accurate positioning of multiple, linearly aligned lesions, rather than single lesion ablation . For example, atrial flutter and atrial fibrillation, as opposed to catheter ablation of accessory conduction pathways and atrioventricular node recurrent tachycardia, for which detailed mapping is required to identify sites suitable for energy delivery The site for catheter ablation is identified almost completely based on anatomy. Thus, the development of alternative approaches to guide the positioning of catheter ablation lesions based on strictly anatomical considerations and further confirm the location and presence of continuous linear lesions is warranted.
[0003]
Magnetic resonance imaging (MRI) offers an alternative to X-ray fluoroscopy because it offers several special practical advantages over other imaging modalities for inducing and monitoring therapeutic intervention, including: 1) real-time catheter positioning using detailed intracardiac anatomical information, 2) fast high-resolution 3D visualization of the atrial chamber, 3) atrial function and blood during treatment High-resolution functional atrial imaging to assess flow dynamics, 4) real-time spatial and temporal lesion monitoring capability during treatment, and 5) elimination of radiation exposure of patients and physicians. However, to date, no studies have evaluated the feasibility of using MRI to induce intracardiac ablation therapy.
[0004]
[Problems to be solved by the invention]
It is an object of the present invention to provide an improved method and apparatus for guiding an ablation and / or mapping catheter in conjunction with treatment of supraventricular tachycardia, ventricular tachycardia, atrial flutter, atrial fibrillation and other arrhythmias. It is to provide.
It is also an object of the present invention to provide an ablation catheter that can be used with an MRI tracking and guiding system.
[0005]
[Means for Solving the Problems]
In one embodiment of the present invention, ablation for use with MRI, comprising non-ferrous or non-magnetic materials for components of catheters that contact the MRI tracking and guiding system on components within the body of the patient A catheter is provided. Note that in (b) there is no evidence of artifacts and the catheter tip is clearly visible in the right ventricle. Starting from the first frame (a), the catheter is advanced through the jugular vein sheath into the superior vena cava. The catheter is then advanced into the right atrium (bc), rotated 180 ° (d), and advanced down into the inferior vena cava (IVC). In the final frame (f), the catheter was retracted to the side wall of the RA, the target site for catheter positioning. Note that the electrode-tissue interface is clearly visible (frame f). The catheter may otherwise be of a conventional design, either fixed curve or steerable. The catheter can be used with computed tomography (CT), which also requires the use of a non-magnetic structure. Preferred materials are shown below, but other non-magnetic materials can be used.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
For overview and introduction, FIG. 10 illustrates a steerable ablation catheter 20 equipped with a snap-on distal end assembly 34. Catheter 20 includes a control handle 24 having wires 26 extending from control handle 24 to proximal connector 28. The catheter comprises a flexible elongate shaft 30 having a relatively flexible distal segment or tip stock 32 connected to its distal end in a conventional manner. The shaft 30 and tip stock 32 are intended to be advanced through the patient's vasculature to the site to be treated in a conventional manner. The catheter preferably has a total length of approximately 115 cm for use in cardiac ablation with a tip stock 32 that extends about 4.5-7 cm so that the catheter can be advanced through the femoral vein into a chamber in the heart. have. On the other hand, the control handle 24 is operated by the operator 35 shown in FIG. 11 while being left outside the patient. Select different shaft 30 and tip stock 32 lengths based on the procedure to be performed, where the catheter will be introduced percutaneously, and the predicted path along which the shaft 30 must be steered along the predicted path. be able to. Preferably, the shaft 30 and tip stock 32 are made from polyurethane tubing, and the shaft 30 includes Uvundacron blades in the tubing to increase stiffness and impart greater column and rotational strength to the shaft. I have. Uvundaklon products have been available since the 1960's. For example, one type of Uvundacron product is commercially available from CR Bird Inc., Glens Falls Division, under catalog model number 200150-4F.
[0007]
The electrical wires 26 include a plurality of electrodes, temperature sensors, other electrical devices that can be included in the catheter 20, or conductive leads of copper or copper alloy from any combination of the above. The electrical wires 26 may be connected to electronic components such as an electrocardiogram (ECG) monitoring device and a radio frequency (RF) energy source either directly through a connector 28 or through an intervening patient cable 29 (not shown). I will provide a.
[0008]
Knob 36 on control handle 24 can be rotated by operator 35 relative to the handle to move a slide block (not shown) in control handle 24 away from proximal end 22 of shaft 30 (see FIG. 1). (FIG. 11). A steering wire 38 (see 15A) slidably received within the tip stock 32 and shaft 30 is secured to the slide block at the proximal end of the steering wire 38. The steering wire 38 is pulled proximally, for example, by turning the knob 36 in the direction of arrow A (FIG. 11). Conversely, as the slide block moves toward the proximal end 22 of the shaft 30 as a result of turning the knob 36 in the opposite direction, the steering wire 38 advances distally. The control handle 24 is disclosed in U.S. patent application Ser. No. 08/518, filed Aug. 23, 1995 to Bowden et al., Incorporated herein by reference in its entirety as if fully set forth herein. , 521, may be used.
[0009]
As described more fully below, steering wire 38 extends distally from the slide block through shaft 30 to distal end assembly 34 to which steering wire 38 is secured. As the steering wire 38 is secured to the distal end assembly 34, the proximal pull on the steering wire 38 will cause the tip stock 32 to move in a single plane, as shown in FIG. It causes deflection at a radius of curvature determined by the length of 32 and the compressive strength. The radius of curvature may be in the range of about 2 to 4.5 cm. The steering wire 38 must have sufficient tensile strength to overcome the compressive strength of the tip stock 32 that causes the tip stock 32 to deflect. Rotating knob 36 in the opposite direction to arrow A releases the compressive force on the tip stock and causes the catheter tip to return to its undeflected state. In a preferred embodiment, the steering wire 38 is a stainless steel wire having a tensile strength of about 15.5 pounds.
[0010]
The steering wire 38 is preferably guided eccentrically with respect to the longitudinal axis of the catheter 20, and even more preferably is guided eccentrically within the tip stock 32 (see FIGS. 15A and 17). Thus, the tip stock 32 supports deflection in a known plane due to the thickness difference on either side of the steering wire 38 in the tip stock 32. The entire control handle 24 can be torqued by an operator 35 to operate the shaft 30 through the patient's vasculature. Additional steering wires can be provided and radius of curvature adjustment means can be provided in the manner described in the above-referenced U.S. patent application Ser. No. 08 / 518,521. The steering wire is preferably a nylon (Spectra) cable.
[0011]
FIG. 14 is an embodiment of a steering catheter. Alternative configurations of catheters having maneuverability features are within the scope of the invention. For example, as shown and described in U.S. Patent No. 5,383,852 to Debbie Stevens-Wright et al., Issued January 24, 1995, which is hereby incorporated by reference in its entirety. Some steerable catheters can be implemented using MRI compatible materials.
[0012]
In FIG. 14, the shaft 30 includes a non-ferrous or non-magnetic hypotube 37 at the distal end of the shaft 30 that serves as a stiffening element, for example, immediately proximal to the distal end assembly 34 (FIG. 17a). has been edited. Thus, rotation of the knob 36 causes deflection of the tip stock 32 while keeping the distal most portion 32b (FIG. 13) of the tip stock 32 generally straight. The proximal portion 32a (FIG. 13) of the tip stock 32 that does not include the hypotube 37 assumes a predetermined radius of curvature based on its length and compressive strength. The tube or stiffening member 37 preferably extends about 1-3 cm along the catheter 20 and secures to the steering wire 38, distal end assembly 34, or the most distally used portion 32b of the tip stock. be able to. Instead of the hypotube 37, a reinforcing wire or similar stiffening element can be used.
[0013]
Knob 36 preferably includes an indicator 39 (FIG. 11) to indicate that the knob has been rotated from its neutral position (where no force is applied to steering wire 38). This means that the pulling force is applied to the steering wire 38 and the tip stock 32 is deflected. Indicator 39 may be, for example, a tab affixed to the upper edge of knob 36 that is visible through an opening in control handle 24 only when the slide block is proximate to proximal end 22 of shaft 30. In this state, the tab is visible, indicating that no pulling force has been applied to the steering wire 38. Turning the knob 36 from the neutral position moves the indicator 39 out of the aperture registry, indicating to the operator that a pulling force is being applied to the steering wire 38. Indicator 39 and knob 36 are preferably molded from a plastic material having a color different from the color of the rest of control handle 24.
[0014]
Turning now to FIG. 14, an exploded perspective view of the distal end assembly 34 is shown. Distal end assembly 34 includes a core 40 having a proximal portion 41 adapted to be received in distal end 34 of tip stock 32 and a compressible head 42 at the distal end of core 40. . The compressible head 42 includes anchor tabs 47a, 47b. The core 40 allows the anchor tabs 47a, 47b to flex resiliently toward each other such that the core 40 is received within the opening 45 of the hollow non-magnetic (eg, gold) ablation electrode 46 (FIG. 15a). A longitudinal slot 44 extending proximally from the distal surface of the core 40. The continuous insertion of the core 40 into the ablation electrode 46 causes the anchor tabs 47a, 47b to snap into grooves 48 (FIG. 15a) in the ablation electrode 46 so that both the core 40 and the ablation electrode 46 are together. Locked. Due to tolerance control or other design considerations, the head 42 remains partially compressed even after the core and ablation electrodes snap together, as long as the two components are intermeshed. Can stay. The compressible head 42 has a beveled leading edge camming the anchor tabs 47a, 47b together, thereby facilitating insertion of the core 40 into the opening of the ablation electrode 46 by compressing the head 42 to a reduced profile. 50. Groove 48 has a shoulder 51 (FIG. 15a) that prevents core 40 from slipping out of ablation electrode 46 once anchor tabs 47a, 47b snap into groove 48 (FIG. 15A) and the proximal edge of groove 48. Have.
[0015]
Alternatively, the core 40 and the ablation electrode 46 may be molded to mate with a groove 48 in the ablation electrode 46 made of a ratchet and pawl or an essentially compressible plastic such as polycarbonate or ULTEM®. May also include a generally annular protrusion. For example, the annular protrusion may project about 1-3 mils (0.0254-0.0762 mm) on either side of the core 40, and the groove 48 in the ablation electrode 46 can receive the annular protrusion in an uncompressed state. It may be of such a size. In one embodiment, what is important in these alternative configurations is that the core 40 and the ablation electrode 46 mesh with each other via snap action.
[0016]
The core 40 is preferably manufactured from a non-magnetic material having a low temperature coefficient, such as ULTEM® polyetherimide® 1000 resin manufactured by the General Electric Company Pittsfield, Mass., GE Plastics Division. Have been. The low temperature coefficient material provides thermal insulation between the ablation electrode 46 and the tip stock 32, and preferably, the core 40 has a lower thermal mass than the ablation electrode. The provision of the core 40 between the tip stock 32 and the ablation electrode 46 makes it better that a single catheter can be used for a given procedure, or perhaps (after sterilization once) for reuse in a subsequent procedure. Ensures a low risk of catheter breakage during the ablation procedure. The cap electrode 46 and the distal end 34 of the tip stock 32 may be remoted by thin epoxy beads once the core 40 is positioned between its proximal end 41 and the compressible head 42, or by an annular ring on the core 40. When attached to the distal end 34, they can be spaced from one another. In addition, a wide range of materials can be selected for chip stock 32, including materials having a melting temperature significantly lower than the expected ablation temperature, such as polyurethane.
[0017]
Still referring to FIGS. 14 and 15A, the distal end assembly preferably functions as an anchor for the steering wire, and more preferably houses a temperature sensor. The core 40 includes a central lumen 94 and several off-axis lumens 98 for passing non-magnetic wires 52, 56 from each of the ablation electrode 46 and the temperature sensor 54 to the connector 28 (FIG. 10). Temperature sensor 54 is preferably a thermistor and may be located within cavity 96 in ablation electrode 46 about 4-7 mils (0.1016-0.1778 mm) from the ablation electrode distal end. For example, a potting compound 102 such as TRA-BOND @ FDA-2 epoxy manufactured by Tra-Con, Inc. of Medford, Mass. Stiffness can be added.
[0018]
In FIG. 15A, a central lumen 62 is visible at the distal end 34 of the tip stock 32. The central lumen 62 is sized to fit the proximal end of the core 40. Tip stock 32 includes a steering wire 38 and a surrounding Teflon sheath 104 (FIGS. 15A-18), a temperature sensor lead 56 (eg, made of copper / Constantin), and a distal end assembly. It defines a lumen 70 for receiving the beryllium copper conductor 52 from. Mounted in spaced relation along tip stock 32 are ring electrodes 72a, 72b, and 72c that may be sized for intracardiac ECG recording, mapping, stimulation or ablation. Each ring electrode 72 may extend approximately 0.5-4 mm longitudinally along tip stock 32 from the proximal edge to the distal edge of the ring electrode. Ring electrode 72 is electrically connected to the appropriate components via beryllium copper conductors 74a, 74b and 74c extending through respective openings 76a-c into lumen 70 on the side of tip stock 32.
[0019]
The ring electrodes 72 may be made of gold and may be spaced within a range of about 1-5 mm, and more than 60 mm proximally along the tip stock 32 from the distal end of the distal end assembly 34. Can stretch. For example, ring electrode 74a may be 2 mm from distal end 64 of shaft 30, ring electrode 74b may be spaced 5 mm from the proximal edge of ring electrode 74a, and ring electrode 74c may be near ring electrode 74b. It may be spaced apart from the margin by 2 mm.
[0020]
The tipstock 32 is conventionally tapered along the region of complementary taper and overlap at the distal end of the shaft 30 and the proximal end of the tipstock 32, preferably by ultrasonic welding (FIG. 15B). It is connected to the distal end of the shaft 30.
[0021]
The lumen 70 of the tip stock 32 and the through lumen 78 of the shaft 30 are in communication with each other. Lumen 70 is preferably eccentrically disposed with respect to the longitudinal axis of tip stock 32. Accordingly, the proximally-directed force applied to the steering wire 38 causes the tip stock 32 to tend to deflect in a predictable single plane. Similarly, the eccentric lumen 70 creates an interface 80 (FIG. 15b) near the junction of the tip stock 32 and the shaft 30. In a preferred embodiment, a non-magnetic reinforced spring 84 (eg, made of brass) extends from the proximal end 22 of the shaft 30 to the mating surface 80. In yet another embodiment, as shown in FIG. 15 b, a non-magnetic stiffening tube 86 can be interposed between the distal end 88 of the stiffening spring 84 and the mating surface 80.
[0022]
Referring now to FIGS. 14 and 16, the core 40 is attached to the ablation electrode 46 by snapping the anchor tabs 47a, 47b of the compressible head 42 into the groove 48, just distal to the shoulder 51. It is engaged (FIG. 15a). The anchor tabs 47a, 47b cannot be pulled out beyond the shoulder 51. Further, the steering cable 38 is shown looping through two of the off-axis lumens 98 in the core 40 and passing through the coil spring 100. This acts as a pressure reduction mechanism in the preferred embodiment, a so-called "cheese knife" action that causes the steering wire to cut into the distal surface of the core 40 when a pulling force is applied to the steering wire 38. Alleviate or remove. The coil spring 100 prevents the steering wire 39 from slicing the core by distributing the tensile force that would be applied to the steering wire 38 across the coil of the spring. Comparing FIGS. 15A and 16, the steering wire 38 is seen extending distally through one of the lumens 98 at the core 40. To function, 38 passes through one of the lumens 98 and provides steering, i.e., through the spring 100 at the loop junction and through the other of the lumens 98, preferably for steering wires. Have to pass through to the point at the proximal end of the core 40 where the core 40 winds itself to form the anchor. Preferably, the steering wire 38 winds itself at least twice. A favorable result is that the steering wire 38 is arranged to pass partially back through one of the lumens 98, the spring 100 and also the other of the lumen 98, and the steering wire is soldered to the spring 100. Has also been observed.
[0023]
FIG. 18 shows an eccentric lumen 70 in the tipstock 32 that causes a pulling force, which can be applied to the steering wire 38 via the control handle 24, to be eccentrically directed in the tipstock 32. The eccentric lumen 70 provides a low wall thickness lumen wall on one side of the steering wire 38. In addition, the off-axis lumen 98 to which the steering wire 38 is secured better assures that the tip stock 32 repeatedly deflects in a predictable plane to reliably steer the distal end of the shaft 30.
[0024]
In FIG. 17A, shaft 30 includes a hypotube 37 within tip stock distal portion 32b. The hypotube 37 causes the distal end of the catheter to maintain a generally straight shape, even when tension is applied (see FIG. 4).
[0025]
FIG. 17 is a cross-sectional view taken through the shaft 30 and extending proximally from the steering wire 38, the plurality of leads 56, the leads 52, and the ring electrode 72 through the reinforcing spring 84 toward the control handle 24. A plurality of conducting wires 74 are shown.
[0026]
The assembly of the distal end assembly 24 is as follows. The plastic core 40 is preferably injection molded. The ablation electrode 46 is machined to have the desired overall volume for the size of the catheter used therewith. The machining preferably defines a first drill bit, generally for cutting out the ablation electrode 46, followed by a cavity 96, and finally a key cutter by, for example, circular interpolation as understood by those skilled in the machining arts. Implemented under computer control using a machine that can be used to select a second small bit to form groove 48.
[0027]
The conductor 52 is preferably wound like a lasso and resistance welded to the ablation electrode 46. Next, STYCAST (registered), preferably mixed with catalyst 24LV, for example, both manufactured by Emerson & Cumming Composite Materials, Inc., located in Canton, Mass. (Emerson & Cumming Composite Materials, Inc.) A thermally conductive but not conductive epoxy, such as TM2850FT epoxy encapsulant, is inserted into the central lumen 96 and the temperature sensor 54 is adhered therein. Leads 52 and 56 from ablation electrode 46 and temperature sensor 54 are passed through lumens 98 and 94, respectively, either before or after being attached to ablation electrode 46.
[0028]
The steering wire 38 is attached to the core by passing the lumen in the core in a U-shape. In particular, the steering wire 38 is passed through one of the off-axis lumens 98, the coil spring 100, and then another off-axis lumen 98. The steering wire may extend to a point proximal to the core 40 where it can be wound by itself to complete its fixation, or may be bent into a U-shape in one of the lumens 98 After, or alternatively, it may end after being soldered or brazed to coil spring 100. Preferably, a Teflon-coated steering wire 38 is selected, and the portion of the steering wire 38 secured to the core 40 and control handle 24 is preferably stripped of Teflon. Teflon is difficult to bond and is removed to secure exposed steering cables. Alternatively, a lubricating sleeve, such as Teflon, may be used to reduce the frictional force exerted by the walls of the lumens 70, 78 when moving the steering wire and to electrically insulate the steering wire. Can be adhered to the steering wire 38. The second steering wire 38A can also be passed through a lumen 98 located on the opposite side of the central lumen 94.
[0029]
After the wires 52, temperature sensor 54, and steering wires 38 are properly attached, the ablation electrodes 46 are filled with a potting compound 102, such as FDA-2 epoxy, and the core and ablation electrodes are assembled in the manner described above. Both can be snapped together. The snap action of core 40 and ablation electrode 46 are both audible and tactile. In addition, steering wires, thermistor wires, and ablation electrodes are accepted without any torsional action, unlike other known methods of making ablation catheters. Further, potting compound 102 electrically and thermally insulates steering wire 38 from ablation electrode 46.
[0030]
The steering wire 38, the plurality of leads 56 and the leads 52 can then be threaded through the lumen 70 and the through lumen 78 to the control handle 24 to assemble the distal end assembly 34 on the catheter 20. The proximal end of core 40 can be coated with epoxy prior to insertion into central lumen 62 at the distal end of tip stock 32. Thin epoxy beads (not shown) can space the cap electrode 46 and the distal end 64 of the tip stock 32 when the distal end assembly 34 is attached to the catheter 20, or The core 40 can include an annular ring that spaces the ablation electrode 46 and the distal end 64 when the core is inserted into the distal end. Assembly is completed by attaching the steering wire 38 to the slide block and the conductors 52, 56 and 74 to each of the wires 26.
[0031]
Using a catheter of the type described above, 1) to develop and characterize a novel MR ablation system capable of conducting, delivering, and monitoring cardiac RF therapy, 2) in cardiac tissue following RF induced thermal injury A series of experiments were performed to quantify temporal and spatial MR signal changes and 3) to correlate MR lesion size with postmortem lesion size and quantitative histological markers of cell death.
[0032]
Method
Magnetic resonance imaging system
The experiments were performed on a short 1.5T closed bore real-time interactive cardiac MRI system (Signa @ LX, General Electric Medical Systems, Milwaukee, Wyoming) using a standard cardiac phased array coil for a short time. ). The new system provides rapid data acquisition, data transfer, image reconstruction and real-time interactive control and display of slice images, while allowing direct access to the groin or neck for catheter insertion and manipulation. Thereby overcome the limitations of conventional MR systems based on static scanning protocols. The real-time hardware platform consists of a workstation and a bus adapter that can be added to a conventional scanning device. Details of this system are described elsewhere (Yang PC, @Kerr AB, Liu AC, Liang DH, Hardy C, Meyer CH, Macovski A, Pauly JM, Hu BS, New Real-time mechanical actor). resonance imaging system components echocardiography (a real-time interactive cardiac magnetic resonance imaging system complements echocardiography) ", {J Am Coll CARDOL 1998; 32 (7): 2049-56; and Kerr AB JM, AB, MJ, Paul "Real-time @ i teractive MRI on a conventional scanner (real-time interactive MRI on conventional scanning devices) ", Magn Reson Med 1997; 38: 355-67).
[0033]
High frequency catheter ablation system
Radiofrequency catheter ablation was performed using a standard clinical RF generator with an open loop controller (Atakr®, Medtronic, Minneapolis, Minn.). This generator was located outside the operating room and was electrically connected to the experimental animals via the ablation catheter described above.
[0034]
A technical limitation of high frequency energy delivery and electrophysiological signal acquisition in scanning devices is electromagnetic interference. The frequency of the high frequency generator (-500 kHz) is much lower than the proton precession frequency of 64 MHZ at 1.5 T, but harmonics of higher frequency high frequency signals can cause significant image degradation. To overcome this problem, special RF filters and shielding were designed and constructed to suppress these harmonic signals to allow simultaneous RF ablation and electrophysiological monitoring during imaging. These multi-stage low-pass filters consist of devices of non-magnetic electrical components that achieve a cut-off frequency of about 10 MHz. The output from the RF generator is directed to the ablation catheter through these completely shielded filter assemblies that pass through electrical patch panels between the operating room and console room. The dispersive ground electrode consists of a large conductive adhesive pad that is applied to the animal's skin to complete the circuit. Electrocardiograms were acquired using the same catheter via a similar 12-channel occluded filter box and recorded using automated data acquisition software. The effect of the RF ablation signal on image quality is shown in FIG. The left panel shows images acquired during RF delivery without filtering, and the right image shows the same slice during RF delivery with filtering. Note that there is no evidence of noise or artifacts, and that the catheter tip is clearly visible at the right ventricular apex (arrow).
[0035]
Animal preparation and experimental protocols
The whole animal protocol has been reviewed and approved by the Animal Care and Use Committee of the University of John Hopkins School of Medicine, and is a "Position of the American American Heart Association" on "Research Animal" Use (American Heart Association's position on research animal use). In accordance with published guidelines. Six mongrel dogs weighing 28-36 kg were premedicated with an intramuscular injection of ketamine 10 mg and used with Narcomed anesthesia ventilator (North American Dräger, Telford, PA) throughout the experiment. Anesthesia was maintained with 80% oxygen and 1% isofluorane gas. Surface electrocardiogram (ECG) leads 1, 2 and 3 were continuously monitored throughout the experiment. Using standard methods, an 8F introducer guide sheath was placed in the right jugular vein for catheter access and in the right femoral vein for fluid and drug administration.
[0036]
Under MR guidance, a 3F non-magnetic single electrode ablation catheter was placed on the lower wall of the right atrium of three animals (no ablation) to determine the accuracy of catheter positioning under MR guidance. In the same animal, two ablation sites in the right ventricle (apical and free wall) were subjected to a fast gradient entry call echo (FGRE) sequence (TF = 5 ms, TE = 1.2 ms, field of view = 22 cm, slice thickness = 7 mm, Ablation from right jugular vein access using a 256 × 128 matrix, tip angle = 13 °, read band = 31.0 kHz). Once the electrode-wall contact was visualized and confirmed by electrocardiography, the catheter was imaged to isolate the optimal tomographic slice containing the catheter electrode. After obtaining the baseline image to define this slice, RF ablation was performed between the distal electrode and the large surface area skin patch in the right ventricle at 20 W power for 60 seconds. To avoid electrode agglomeration, the impedance was monitored by an automatic open loop feedback system that terminated RF delivery when the impedance exceeded 220 ohms. Subsequently, a T2-weighted fast spin echo (FSE) sequence (TR = 2XRR, TE = 68 ms, ETL = 16) every 2 minutes for 20 minutes to monitor temporal signal changes and lesion growth over time (Field = 22 cm, slice thickness = 7 mm, 256 x 192 matrix, reading width = 62.5 kHz) using a single slice and two adjacent slices. Following this imaging series (30 minutes after ablation), an intravenous line was administered as a bolus injection of 0.3 mL / kg gadolinium-DTPA, using the same T1-weighted gradient echo sequence described above at a tip angle of 40 degrees. The same slice was imaged every 30 seconds for 12 minutes.
[0037]
autopsy
Following the experiment, animals were sacrificed by anesthesia overdose, the heart was excised, and sliced into slices corresponding to tomographic MR imaging slices through the right ventricular lesion. The location, morphology, width, length and transmural extent of the lesions were measured and recorded by gross examination, and right ventricular lesions were photographed and matched with corresponding T2 and contrast-enhanced T1-weighted lesion images. Sections from heat-injured tissue were longitudinally bisected and submitted for histological staining (Masson's trichrome and hematoxylin-eosin). Specimens then characterize global morphological changes (9) (eg, well-depicted cell junctions and nuclei, and interstitial edema) to measure the extent of heat-induced cell injury and necrosis For analysis under a microscope at 40X.
[0038]
Data analysis
To measure the temporal response of heart tissue following RF delivery, lesion signal intensity, using an off-line quantitative analysis package (Image @ Tool, Scion @ Image, Bethesda, Md.) Length, width and area were measured directly from the MR images. Each parameter was measured 10 times for each time frame from the baseline to 20 minutes after ablation. The average signal strength measurements from the region of interest (ROI) were then normalized (average ROI signal strength at time t divided by baseline signal strength) and plotted as a function of time. A similar method was used after gadolinium injection on T1-weighted imaging. In addition, IEGMs were analyzed for changes in single amplitude and waveform before and after ablation. For accurate and consistent measurement of MR lesion size by freehand area measurement, it was necessary to establish quantitative exclusion criteria for the spatial distribution of signal intensity through the lesion. This was achieved by rejecting pixel values around the lesion that were lower than normal myocardial signal intensity plus one standard deviation of the background noise measured from the ROI intensity measurement. Lesions parameters at gross examination were measured independently of the lesion parameters by MR manual area measurement and compared.
[0039]
Statistical analysis
Changes in average signal intensity, intracardiac electrogram amplitude and tissue birefringence intensity before and after ablation were considered significant at the level of p <0.05 using a paired t-test. Comparison of lesion area measurements between MR and gross examinations was analyzed by linear regression using a paired t-test at the level of p <0.05.
[0040]
result
Catheter positioning
A non-steerable catheter was successfully positioned at the atrial and ventricular target sites in all animals using the MR fluoroscopy sequence. In three animals, placement of the MR catheter was attempted targeting the lower wall of the right atrium from the jugular vein access (FIG. 2). Images were acquired without breath holding every heartbeat updated in one second. Several key intracardiac anatomical goals including superior and inferior vena cava, atrial septum, right atrial appendage, coronary sinus, inferior vena cava ridge, fossa ovalis and tricuspid valve successfully completed Identified the details of the right atrial anatomy in all animals. The catheter remains in the imaging plane during the entire navigation sequence in two out of three animals. Electrode-tissue contact was visible without significant electrode artifacts (FIG. 2f), and positioning of the lower wall catheter was successful and reproducible in each animal. The right ventricular ablation site could be successfully targeted in all animals, and the electrode-tissue interface was confirmed by high performance IEGMs (amplitude = 10.7 mV) as shown in FIG. 3b. It was clearly visible during FGRE imaging with visual catheter stability (FIG. 3a).
[0041]
MRI lesion visualization and spatial signal response
Lesions were successfully created and visualized at the right ventricular target site in all animals. The ventricular lesion appeared as a clearly outlined high intensity area immediately adjacent to the ablation catheter tip and was detectable 2 minutes after RF delivery (FIG. 4). The lesion signal intensity response is shown in FIG. 4c with a temporal resolution of about 2 minutes, with the first three time points representing the baseline myocardial signal intensity before ablation. The average intensity increased linearly over the first 10 minutes, followed by a plateau. The average FSE signal intensity 15 minutes after ablation was 1.9 ± 0.4 times higher than baseline myocardial intensity (p <0.05), and the average time to signal plateau was 12.2 ± 2.1 minutes. Met. The FSE imaging time averaged 1.7 ± 0.3 minutes per slice. Approximately 30 minutes after this image sequence, T1-FGRE images of the same tomographic slice were acquired before and after 7 mL peripheral gadolinium injection (FIGS. 5a, b). Lesion boundaries were clearly defined 60 seconds after contrast injection. Intensity versus time data for contrast-enhanced lesions (time resolution = 30 seconds) showed a rapid initial absorption of gadolinium and a gradual washout over the next few minutes (FIG. 5c). Data for adjacent regions of undamaged myocardium showed a statistically significantly lower level of enhancement, following a similar time course over the imaging interval (L 13 ± 0.12 vs 1.55 ± 0). .16, p <0.05). Under MR fluoroscopy, the catheter was moved from the apex of the right ventricle and repositioned on the free wall of the right ventricle. FSE images before and after RF delivery are shown in FIG. 6, along with their respective IEGM recordings. Large lesions were visible immediately adjacent to the ablation catheter tip and showed a temporal response similar to that measured in right ventricular apical lesions, with the peak intensity occurring 11.2 minutes after ablation. Considering data from all animals, IEGM amplitude was reduced from a mean of 10.3 ± 3.1 mV before ablation to 2.2 ± 3.3 mV after RF delivery (p <0.05). FIG. 7 is a plot of a series of lesion profiles characterizing the spatial and temporal formation of ventricular lesions. The lesion profile is a simple signal strength plot across a fixed spatial domain passing through the lesion, as shown in FIG. 7a for a single time frame. The three-dimensional surface plot represents a series of these profiles over time, with the z-axis representing color-coded signal strength and the x-axis and y-axis representing position and time after RF delivery, respectively. Lesions increase dramatically in signal strength and size from baseline levels indicated by arrows. Maximum signal intensity and lesion area were achieved after 12.2 ± 2.1 minutes and 5.3 ± 1.4 minutes, respectively, after RF delivery.
[0042]
Correlation between macroscopic examination and histopathological examination
Direct visual comparison of right ventricular apical lesions at gross examination with images extracted by MR 10 minutes after ablation showed similar lesion shapes (FIG. 8). Lesions width and length measured by gross examination correlated well with MR-derived measurements (width: 6.7 ± 0.5 vs 7.1 ± 0.9 nim, p <0.05, length (9.4 ± 1.5 vs. 9.9 ± 0.9, p <0.05). MR lesion depth could be assessed quantitatively in three animals, which was also in good agreement with macroscopic measurements (depth: 3.4 ± 2.1 vs 3.1 ± 1.2 mm, p < 0.05). All lesions consisted of a series of three afferent elliptical zones. The dark inner part representing the area of coagulation necrosis (first zone), the pale peripheral circular zone around the bleeding and inflammatory cells extending about 4 mm from the center of the lesion (second zone), and a thin extending another 2-3 mm The outermost area (third zone) composed of purple edges. Low power trichrome stained histology specimens clearly defined the boundaries of pathological lesions from natural undamaged tissue in all animals. A convincing agreement and correlation was observed between the spatial extent of right ventricular MR-derived lesions measured by gross and histopathological examination and the actual extent of the injury (55.4 ± 7.2 vs. 49). 0.7 ± 5.9 mm, r = 0.958, p <0.05).
[0043]
Key observations
This study relates to a novel MRI compatible interventional electrophysiology hardware system with a newly developed real-time interactive cardiac MRI system to characterize the temporal and spatial development of cardiac lesions after radiofrequency ablation. The observations are: 1) MR images and IEGMs can be acquired during radiofrequency ablation therapy using special radiofrequency filters. 2) Non-magnetic MR compatible interactive scanning catheters can be used for fast MR imaging sequences with interactive scan plane modification. 3) Local changes in ablated heart tissue can be detected and visualized using FSE and FGRE images. 4) Spatially induced heat-induced necrosis. The range indicates that MRI can be accurately quantified immediately after thermal injury and 5) lesion transmurality can be assessed. These results will have important implications for the induction, delivery and monitoring of cardiac ablation therapy by interventional MRI.
[0044]
Positioning of MR guiding catheter
The right atrial and right ventricular sites were successfully targeted in all animals using a non-steerable catheter using a real-time MR fluoroscopy pulse sequence. High-resolution images of intracardiac anatomy, with the ability to interactively modify the scan plane, allow for the definition of standard fluoroscopic images in real-time using a graphical interface, greatly simplifying targeting and accurate lesion location Improved. Accurate atrial catheter positioning is of clinical importance for the study of various supraventricular arrhythmias as the relationship between the intracardiac anatomy and the arrhythmic substrate becomes increasingly understood. Current techniques for mapping and identifying arrhythmogenic lesions are based on low resolution voltage maps generated by catheter movement under fluoroscopy. In addition to the limited anatomical information, catheter manipulation under fluoroscopy is laborious and poorly reproducible. Anatomical MRI-guided electrophysiological mapping will significantly improve the positioning accuracy of critical arrhythmogenic substrates.
[0045]
Another very important feature of the positioning of MR guiding catheters is the ability to view the electrode-intracardiac tissue interface, indicating that it increases lesion size by improving the efficiency of RF tissue delivery. I have. While traditional indicators of electrode contact such as fluoroscopy catheter stability and electrocardiogram are useful, these parameters are relatively insensitive indicators of electrode-tissue contact. However, an important limitation of passive MR catheter tracking is that it requires manipulating the catheter within an imaging slice (typically 5-10 mm wide), which may cause the curvature or loop of the catheter to be of a general geometry. It will be especially difficult during catheter positioning in chemically complex vessels and the atrioventricular chamber of the heart. This requires the MRI system to be able to quickly sweep through the location of the slice. Active tracking techniques are currently under development to provide x, y, z spatial coordinates of a superimposed ablation catheter tip on an interactive 3D image of the atrioventricular chamber to improve the positioning accuracy of the MRI catheter.
[0046]
In vivo lesion visualization
Perhaps one of the greatest strengths of MRI-guided therapy is the ability to view and monitor lesion formation with a high degree of temporal and spatial resolution. In this study, right ventricular lesions were created and viewed using both a T2-weighted fast spin echo sequence and a gadolinium-enhanced T1-weighted fast gradient entry echo sequence. The lesions imaged using FSE were sharply visible in the elliptical high intensity area immediately adjacent to the catheter tip, but no reversible and irreversible damage zones were visible. FGRE contrast-enhanced lesions 30 minutes after ablation showed rapid gadolinium absorption after injection and showed affected areas similar to FSE images. The mechanisms of lesion enhancement for these two sequences are quite different and will provide biophysical insights into tissue injury and lesion formation in vivo.
[0047]
Fast spin echo imaging. MRI detects one or more specific changes in T1 and T2 relaxation parameters resulting from heat-induced biophysical changes in heart tissue, such as interstitial edema, hyperemia, structural changes, cell contraction and tissue coagulation can do. Considering a general series of effects in the context of parameters detectable by MRI, acute interstitial edema may be responsible for the high intensity area representing the area of damage observed by T2-weighted FSE imaging Is considered the highest. The edema response is a matter of seconds from the local inflammatory cells within seconds of the injury that causes water and proteins to leak through interstitial spaces in the endothelial cells lining the blood vessels and enter the interstitial space. It is mediated by the release of vasoactive polypeptides. This near-immediate local increase in the number of unbound protons increases the T2 relaxation constant of the tissue, producing a high intensity region that is likely to represent the spatial extent of the anatomical lesion. Furthermore, lesion detection 1-2 minutes after ablation with subsequent lesion formation for 10-15 minutes is consistent with the temporal physiologic response of local acute interstitial edema.
[0048]
Contrast-enhanced high-speed gradient entry echo imaging. Ablation lesions were not visible with T1-FGRE imaging alone, but the spatial extent of the lesions was very clearly demarcated using this sequence following peripheral administration of gadolinium-DTPA. This enhancement is distinctly different from the dynamic lesion detection described for T2-FSE images and is explained by considering the physical and physiological mechanisms by which gadolinium achieves enhanced signal strength in damaged myocardium. it can. Gadolinium-DTPA exerts a signal enhancing effect by interacting with water protons and inducing a shorter T1 relaxation time. In intact myocardium, this large molecule is unable to penetrate cell membranes and is thus limited to the extracellular space. However, after intracardiac ablation, the damaged / ruptured cell membrane allows the contrast agent to penetrate into the intracellular space, significantly increasing the distribution of the contrast agent and consequently the tissue on the T1-weighted image. Produces "brighter" voxels (three-dimensional pixels).
[0049]
FGRE imaging is preferred over FSE for cardiac ablation therapy because, in practice, imaging time is significantly reduced and high quality images can be acquired without cardiac gating and breath hold. An important parameter for contrast-enhanced lesion imaging is the time required after ablation for optimal gadolinium absorption. In this study, a contrast agent was injected 30 minutes after ablation, and rapid absorption of gadolinium in the affected area of the myocardium was observed. However, it is not known how quickly the lesion can absorb the contrast agent. The answer to this question has direct clinical implications and will also provide additional insight into the biophysical mechanisms of in vivo pathogenesis.
[0050]
Comparison with other imaging modalities
Several studies have shown the benefits of intracardiac ultrasound to induce cardiac ablation therapy in vitro to visualize thermal lesions. A recent study by Epstein et al. Compared intracardiac ultrasound and fluoroscopic guidance for creating a linear right atrial lesion in a dog model. Ultrasound significantly improved targeting, energy delivery and lesion formation. Although these reports are promising, the limitations of this approach include the relatively poor spatial resolution, limited visibility of the left and right atrium, and the inability to distinguish between multiple intracardiac catheters , The need for supplemental X-ray fluoroscopy, and the inability to accurately quantify the spatial extent of thermal injury in vivo. Direct in vivo visualization of right atrial anatomy and high frequency lesions using fiber optic probes has also been successfully performed where thermal injury is monitored based on heat-induced myocardial color changes. In addition to the relatively small field of view created by the probe, this method is subjective and cannot accurately represent irreversibly damaged tissue.
[0051]
Although MRI-guided ablation is not restricted to the above limitations, the technology and system are in the early stages of development and have a number of technical requirements including non-magnetic catheters, monitoring devices and electromagnetic filtering systems. Further, while new advances in scanner hardware have enabled real-time MR imaging (20 frames / sec), passive catheter tracking is disrupted by complex catheter movements that cause the catheter to exit the imaging plane. there is a possibility. Finally, the delayed lesion formation after the first RIF delivery confuses the immediate assessment of lesion size.
[0052]
Clinical implications
While the approach described in this report is applicable to all cardiac arrhythmias that can be cured by radiofrequency ablation, the approach is particularly useful for accurate localization of multiple linear lesions rather than single lesion ablation. It may be suitable for the required complex arrhythmias (eg, atrial flutter, ventricular tachycardia with coronary artery disease and postoperative recurrent atrial tachycardia for congenital heart disease). However, the area most likely to be affected by MR-guided interventional electrophysiology is in the management of atrial fibrillation. In addition to improved anatomical targeting of critical lesion sites, the ability to directly view the spatial extent of the atrial lesion with high spatial resolution helps to facilitate the location of linear transmural atrial lesions and provides It will allow real-time interactive detection and elimination of lesions. This potential is considered to be of special importance because ablation lines with discontinuous lesions have been shown to be not only ineffective but also arrhythmogenic. In addition, the ability to characterize the temporal evolution of a lesion can be used for titration of treatment and avoiding tissue damage outside of the ablation target volume, but the observed delayed biophysical response of the lesion can May confuse evaluation. These combined advantages can reduce the number of lesions required for conduction block, reduce procedure time, and further reduce the risk of perforation, all without the use of ionizing radiation.
[0053]
Conclusion
These studies have shown that high frequency cardiac ablation can be performed under MRI guidance in vivo. The catheter is clearly defined and easily positioned in the gradient echo image, and the spatial and temporal extent of the ventricular ablation lesion is determined by T2-weighted fast spin echo imaging and T1-weighted imaging using a standard cardiac phase array chest coil. Accurate visualization can be achieved using agent-enhanced high-speed gradient echo imaging. Furthermore, the lesion size by MRI matches well with the actual post-mortem lesion size, so that high performance intracardiac electrophysiological signals can be acquired and monitored during imaging. MRI-guided cardiac ablation is a useful technique that eliminates ionizing radiation exposure, provides accurate therapy titrations, facilitates the creation of linear, continuous and transmural lesions, and furthermore, novel ablation techniques and It will provide insight into the physiological effects of technology.
[Brief description of the drawings]
FIG.
FIG. 1 is a diagram (1a and 1b) of a photograph obtained during RF delivery, without (1a) and with (1b) a high frequency filter.
FIG. 2
FIG. 2 is a pictorial view (2a-2f) of the positioning of the catheter on the lower side wall of the right atrium.
FIG. 3
FIG. 3 is a pictorial illustration (3a) of a pre-ablation spin echo image including the electrode-tissue interface at the right ventricular apex (RVA) and the corresponding high amplitude electrocardiogram (3b) acquired during imaging.
FIG. 4
FIG. 4 shows photographs (4a, 4b) of FSE images before and after ablation of right ventricular apex radiofrequency ablation (RFA), and correspondence to right ventricular apical lesions using a time resolution of about 2.0 minutes. (4c) showing average intensity versus time data.
FIG. 5
FIG. 5 shows lesion creation of a) tip n, and b) ablated tissue, including T1-weighted gradient echo images before (5a) and after (5b) administration of peripheral 7 mL gadolinium-DTPA contrast agent. Photographs (5a and 5b) of anterior and posterior images and corresponding lesion intensity data including temporal response to adjacent segments of right ventricular lesions and normal myocardium with a temporal resolution of about 30 seconds ( 5c).
FIG. 6
FIG. 6 is a photographic view of a fast spin echo image of the right ventricular free wall before ablation and 10 minutes after ablation (6b), and electrograms corresponding to (6a) and (6b) respectively (6c, And 6d).
FIG. 7
FIG. 7 illustrates a right ventricular apex lesion using the spatial position of the intensity profile line (7a), intensity versus position data generated for a single point in time during the temporal evaluation of the lesion (7a), FIG. 7B is a three-dimensional surface plot (7b) of the temporal and spatial development of right ventricular lesions created by plotting several intensity profiles over time.
FIG. 8
FIG. 8 is a photograph of a direct visual comparison of the appearance of a right ventricular apical lesion by visual inspection (8a) and MRI (8b).
FIG. 9
FIG. 9 is a diagram showing a comparison of the MR and the post-mortem lesion area using a graph.
FIG. 10
FIG. 10 is a plan view of a steerable ablation catheter equipped with a distal assembly according to the present invention.
FIG. 11
FIG. 11 is a detailed perspective view of a control handle that can be used to steer the catheter of FIG.
FIG.
FIG. 12 is a plan view of the distal end of the catheter of FIG. 10 having a predetermined radius of curvature.
FIG. 13
FIG. 13 is a plan view of the distal end of the catheter of FIG. 10 deformed to have a generally linear shape distal to a predetermined radius of curvature.
FIG. 14
FIG. 14 is an exploded perspective view of the distal end assembly of FIG.
FIG.
FIG. 15 is a front view (15A) of the catheter of FIG. 10, partially shown in cross-section, and along the match line AA to the (15A) catheter, more proximal to the (15A) catheter. Part of the connected portion is a front view (15B) shown in a cross section.
FIG.
FIG. 16B is a cross-sectional view taken substantially along the line 16-16 of FIG. 15A.
FIG.
FIG. 15B is a cross-sectional view taken substantially along the line 17-17 of FIG. 15A and the catheter of FIG. 10 deformed to have a generally straight section distal to a predetermined radius of curvature when steered. FIG. 17B is a cross-sectional view (17A) substantially taken along line 17A-17A of FIG. 15A shown.
FIG.
FIG. 18 is a cross-sectional view taken substantially along the line 18-18 of FIG. 15B.

Claims (40)

An ablation catheter compatible with an MRI system, wherein at least one electrode made of an MRI compatible material is supported on a distal end assembly, wherein each of the shafts is made of an MRI compatible material. An ablation catheter comprising a distal end assembly and at least one wire connected to the electrode and extending from the electrode to a proximal end of the shaft and made of an MRI compatible material. The ablation catheter according to claim 1, wherein the catheter includes a plurality of steering cables steerable and extending through the shaft and distal end assembly, wherein the steering cables are made from an MRI compatible material. . The ablation catheter according to claim 1, wherein the shaft is made from one of a polyurethane tube, a braided extrudate and a Uvundacron. The ablation catheter according to claim 1, wherein the shaft is made from a polyurethane tube and a blade extrusion. 2. The ablation catheter according to claim 1, wherein the shaft is made of polyurethane tubing and Uvdacron. The ablation catheter according to claim 1, wherein the shaft is made of polyurethane tubing, braided extrudate and Uvundaklon. The ablation catheter according to claim 1, wherein the wire is made of one of copper, copper alloy and beryllium copper. The ablation catheter of claim 1, further comprising a snap-on distal end assembly made of an MRI compatible material. The ablation catheter according to claim 8, wherein the snap-on distal end assembly is made from polyurethane. 9. The ablation of claim 8, wherein said snap-on distal end assembly includes a plurality of engagable components providing a snap-on structure, said engagable components being made from essentially compressible plastic. catheter. The ablation catheter according to claim 10, wherein the engagable component is made from one of polycarbonate and ULTEM®. The ablation catheter of claim 7, wherein the snap-on distal end assembly further includes a core into which the potting compound is injected. 13. The ablation catheter according to claim 12, wherein the core is contained within a distal end electrode. The ablation catheter according to claim 12, wherein the potting compound is TRA-BOND @ FDA-2 epoxy. The ablation catheter of claim 1, further comprising a temperature sensor and a temperature sensor lead made from an MRI compatible material, wherein the temperature sensor lead extends from the temperature sensor to a proximal end of the shaft. The ablation catheter according to claim 15, wherein the temperature sensor conductor is made from copper and constantin. The ablation catheter according to claim 1, wherein the shaft has a proximal end portion, and the catheter further includes a reinforcement spring at the proximal portion of the shaft, wherein the reinforcement spring is made from an MRI compatible material. 18. The ablation catheter according to claim 17, wherein the reinforcement spring is made from brass. A shaft and distal end assembly each made from an MRI compatible material, wherein the shaft has a proximal portion;
An electrode made from an MRI compatible material and supported on the distal end assembly, and made from an MRI compatible material connected to the electrode and extending from the electrode to a proximal end of the shaft. A first wire;
Said cartels being steerable and including a plurality of steering cables made of MRI compatible material extending through said shaft and said distal end assembly;
A snap-on distal end assembly made from an MRI compatible material;
A reinforcement spring in a proximal portion of the shaft made of an MRI compatible material, and a temperature sensor made of an MRI compatible material and connected to the temperature sensor and from the temperature sensor to the proximal portion of the shaft An ablation catheter compatible with an MRI system comprising a second wire made of an MRI compatible material extending up to. Said shaft is made from one of a polyurethane tube, a Woven dacron and a blade extrudate;
Said first wire is made of one of copper, copper alloy and beryllium copper;
At least one of the steering cables is made of stainless steel;
At least one component of the snap-on distal end assembly is made of polyurethane;
The reinforcing spring is made of brass,
20. The ablation catheter according to claim 19, wherein the second wire is made from copper and constantin. A shaft and the distal end assembly, each made of a non-magnetic material, having at least one electrode made of a non-magnetic material supported on the distal end assembly, and connecting to the electrode An ablation catheter compatible with an MRI system, comprising: at least one wire made of a non-magnetic material, the wire extending from the electrode to a proximal end of the shaft. 22. The ablation catheter of claim 21, wherein the catheter includes a plurality of steering cables steerable and extending through the shaft and distal end assembly, wherein the steering cables are made of a non-magnetic material. 22. The ablation catheter of claim 21, wherein said shaft is made of one of a polyurethane tube, a braided extrudate, and a Uvundacron. 22. The ablation catheter of claim 21, wherein the shaft is made from a polyurethane tube and a blade extrusion. 22. The ablation catheter of claim 21 wherein said shaft is made from polyurethane tubing and Uvundacron. 22. The ablation catheter of claim 21 wherein said shaft is made from polyurethane tubing, braided extrudate and Uvundacron. 22. The ablation catheter of claim 21, wherein the wire is made of one of copper, copper alloy, and beryllium copper. 22. The ablation catheter of claim 21, further comprising a snap-on distal end assembly made of a non-magnetic material. 29. The ablation catheter of claim 28, wherein said snap-on distal end assembly is made of polyurethane. 29. The ablation of claim 28, wherein the snap-on distal end assembly includes a plurality of engagable components providing a snap-on structure, wherein the engagable components are made from an essentially compressible plastic. catheter. 31. The ablation catheter of claim 30, wherein the engagable component is made of one of polycarbonate and ULTEM (R). 28. The ablation catheter of claim 27, wherein the snap-on distal end assembly further includes a core into which the potting compound is injected. 33. The ablation catheter of claim 32, wherein said core is contained within a distal end electrode. 33. The ablation catheter according to claim 32, wherein the potting compound is TRA-BOND @ FDA-2 epoxy. 22. The ablation catheter according to claim 21, further comprising a temperature sensor and a temperature sensor lead made from a non-magnetic material, wherein the temperature sensor lead extends from the temperature sensor to a proximal end of the shaft. 36. The ablation catheter of claim 35, wherein the temperature sensor lead is made of copper and constantin. 22. The ablation catheter of claim 21, wherein the shaft has a proximal end portion, the catheter further includes a reinforcement spring at the proximal portion of the shaft, wherein the reinforcement spring is made of a non-magnetic material. The ablation catheter according to claim 37, wherein the reinforcement spring is made of brass. A shaft and distal end assembly each made of a non-magnetic material, wherein the shaft has a proximal portion;
An electrode made of a non-magnetic material and supported on the distal end assembly, and a second made of a non-magnetic material connected to the electrode and extending from the electrode to a proximal end of the shaft. One wire,
The catheter including a plurality of steering cables made of a non-magnetic material, the catheter being steerable and extending through the shaft and the distal end assembly;
A snap-on distal end assembly made from a non-magnetic material;
A reinforcing spring in a proximal portion of the shaft, made of non-magnetic material, and a temperature sensor made of non-magnetic material and connected to the temperature sensor, and from the temperature sensor to the proximal portion of the shaft An ablation catheter compatible with an MRI system comprising a second wire made of a non-magnetic material extending up to. Said shaft is made from one of a polyurethane tube, a Woven dacron and a blade extrudate;
Said first wire is made of one of copper, copper alloy and beryllium copper;
At least one of the steering cables is made of stainless steel;
At least one component of the snap-on distal end assembly is made of polyurethane;
The reinforcing spring is made of brass,
40. The ablation catheter of claim 39, wherein the second wire is made from copper and constantin.

Images