WO2001087173A2 - Catheter d'ablation pour irm - Google Patents

Catheter d'ablation pour irm Download PDF

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Publication number
WO2001087173A2
WO2001087173A2 PCT/US2001/015475 US0115475W WO0187173A2 WO 2001087173 A2 WO2001087173 A2 WO 2001087173A2 US 0115475 W US0115475 W US 0115475W WO 0187173 A2 WO0187173 A2 WO 0187173A2
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WO
WIPO (PCT)
Prior art keywords
ablation catheter
shaft
catheter according
electrode
wire
Prior art date
Application number
PCT/US2001/015475
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English (en)
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WO2001087173A3 (fr
Inventor
Gary S. O'boyle
Charles A. Gibson, Iii
Original Assignee
C.R. Bard, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by C.R. Bard, Inc. filed Critical C.R. Bard, Inc.
Priority to EP01935451A priority Critical patent/EP1280468A2/fr
Priority to US10/275,727 priority patent/US20030208252A1/en
Priority to JP2001583644A priority patent/JP2004511271A/ja
Publication of WO2001087173A2 publication Critical patent/WO2001087173A2/fr
Publication of WO2001087173A3 publication Critical patent/WO2001087173A3/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M25/00—Catheters; Hollow probes
    • A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
    • A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
    • A61M25/0133—Tip steering devices
    • A61M25/0147—Tip steering devices with movable mechanical means, e.g. pull wires
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
    • A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
    • A61B18/14—Probes or electrodes therefor
    • A61B18/1492—Probes or electrodes therefor having a flexible, catheter-like structure, e.g. for heart ablation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
    • A61B17/00234—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery
    • A61B2017/00238—Type of minimally invasive operation
    • A61B2017/00243—Type of minimally invasive operation cardiac
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B17/00—Surgical instruments, devices or methods, e.g. tourniquets
    • A61B17/00234—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery
    • A61B2017/00292—Surgical instruments, devices or methods, e.g. tourniquets for minimally invasive surgery mounted on or guided by flexible, e.g. catheter-like, means
    • A61B2017/003—Steerable
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
    • A61B2018/0091—Handpieces of the surgical instrument or device
    • A61B2018/00916—Handpieces of the surgical instrument or device with means for switching or controlling the main function of the instrument or device
    • A61B2018/0094—Types of switches or controllers
    • A61B2018/00952—Types of switches or controllers rotatable
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
    • A61B90/36—Image-producing devices or illumination devices not otherwise provided for
    • A61B90/37—Surgical systems with images on a monitor during operation
    • A61B2090/374—NMR or MRI
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M25/00—Catheters; Hollow probes
    • A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
    • A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
    • A61M25/0133—Tip steering devices
    • A61M2025/0161—Tip steering devices wherein the distal tips have two or more deflection regions

Definitions

  • This invention relates to ablation catheters which can be guided by magnetic resonance imaging.
  • catheter ablation Since its initial description in 1982, catheter ablation has evolved from a highly experimental technique to its present role as first-line therapy for most supraventricular arrhythmias including atrioventricular nodal reentrant tachycardia, the Wolff-Parkinson- White syndrome, and focal atrial tachycardia. More recently, the clinical indications for radio-frequency catheter ablation have expanded to include more complex arrhythmias that require accurate placement of multiple linearly-arranged lesions rather than ablation of a single focus.
  • Magnetic resonance imaging may be an alternative to x-ray fluoroscopic techniques, as it offers several specific practical advantages over other imaging modalities for guiding and monitoring therapeutic interventions including; 1) real time catheter placement with detailed endocardial anatomic information, 2) rapid high- resolution three-dimensional visualization of cardiac chambers, 3) high resolution functional atrial imaging to evaluate atrial function and flow dynamics during therapy, 4) the potential for real-time spatial and temporal lesion monitoring during therapy, and 5) elimination of patient and physician radiation exposure. No studies to date, however, have evaluated the potential use of MRI to guide ablation therapy in the heart.
  • an ablation catheter for use with MRI which consists of nonferrous or nonmagnetic materials for the components of the catheter which came in contact with the MRI tracking and guiding system, on the components which are internal to the, patient. Note in b) there is no evidence of artifact and the catheter tip is clearly visualized in the right ventricle.
  • the catheter is advanced through a jugular sheath into the superior vena cava.
  • the catheter is then advanced into the right atrium (b-c), rotated 180 degrees (d) and advanced inferiorly into the Inferior Vena Cava ( VC) (e).
  • the catheter was retracted to the lateral wall of the RA, which was the target site for catheter placement. Note the electrode-tissue interface is clearly visualized (frame f).
  • the catheter may otherwise be of conventional design and either fixed curve or steerable.
  • the catheter can be used with computer tomography (CT) which also requires the use of a nonmagnetic construction. Although preferred materials are indicated below, other nonmagnetic materials can be used.
  • Figures la and lb are photographs acquired during RF delivery without (la) and with (lb) radio frequency filters;
  • Figures 2a to 2f are photographs of catheter placement on the inferior- lateral wall of the right atrium
  • Figure 3 a is a photograph of a Pre-ablation fast spin echo image including the electrode-tissue interface in the Right Ventricular Apex (RVA);
  • Figure 3b shows the corresponding high amplitude intracardiac electrogram acquired during imaging
  • Figures 4a and 4b are photographs of Pre and post-ablation FSE images following right ventricular apex Radio Frequency Ablation (RFA);
  • RFA Radio Frequency Ablation
  • Figure 4c is the corresponding mean intensity versus time data for a right ventricular apex lesion with a temporal resolution of approximately 2.0 minutes;
  • Figures 5a and 5b are photographs of pre and post lesion created images a) tip n position, and b) ablated tissue, including T I -weighted gradient echo images before
  • Figure 5 c is the corresponding lesion intensity data with the temporal response for a fight ventricular lesion and adjacent segment of normal myocardium with the temporal resolution was approximately 30 seconds;
  • Figures 6a and 6b are photographs of fast spin echo images of the right ventricular free wall pre and 10 minutes post-ablation (6b);
  • Figures 6c and 6d are the corresponding intracardiac electrode tracings for Figures 6a and 6b respectively;
  • Figure 7a is a right ventricular apex lesion with the spatial location of the intensity profile line
  • Figure 7b is the resulting intensity versus location data for a single point in time during the temporal assessment of the lesion
  • Figure 7c is a three-dimensional surface plot with the temporal and spatial development of right ventricular lesions, created by plotting several intensity profiles in time;
  • Figures 8a and 8b are photographs of direct visual comparisons of a right ventricular apex lesion appearance at gross examination (8a) and b) by MRI 8b;
  • Figure 9 is a graphical comparison of a MR and a post-mortem lesion area
  • Figure 10 is a plan view of a steerable ablation catheter fitted with a distal assembly according to the invention.
  • Figure 11 is a detailed perspective view of a control handle that may be used to steer the catheter of Figure 10;
  • Figure 12 is a plan view of the distal end of the catheter of Figure 10 having a predetermined radius of curvature;
  • Figure 13 is a plan view of the distal end of the catheter of Figure 10, as modified to have a generally linear configuration distal to a predetermined radius of curvature;
  • Figure 14 is an exploded perspective view of the distal tip assembly of
  • Figure 15 A is an elevational view, partially in section, of the catheter of Figure 10;
  • Figure 15B is an elevational view, partially in section, of a more proximal portion of the catheter of Figure 15 A, and connects thereto along match line A- A;
  • Figure 16 is a cross sectional view substantially taken along line 16-16 of Figure 15 A;
  • Figure 17 is a cross sectional view substantially taken along line 17-17 of Figure 15 A;
  • Figure 17A is a cross sectional view substantially taken along line 17A-17A of Figure 15A illustrating the catheter of Figure 10 as modified to have a generally straight segment distal of a predetermined radius of curvature when steered; and
  • Figure 18 is a cross sectional view substantially taken along line 18-18 of Figure 15B.
  • Figure 10 illustrates a steerable ablation catheter 20 fitted with a snap-fit distal assembly 34.
  • the catheter 20 includes a control handle 24 from which electrical wires 26 extend to a proximal connector 28.
  • the catheter comprises a flexible, elongate shaft 30 which has a comparatively flexible distal segment or tipstock 32 connected to its distal end in conventional fashion.
  • the shaft 30 and tipstock 32 are intended to be advanced through a patient's vasculature in conventional manner to the site to be treated.
  • the catheter preferably has an overall length of approximately 115 cm for use in cardiac ablation procedures with the tipstock 32 extending from about four and a half to seven centimeters so that the catheter may be advanced through the femoral vein to a chamber within the heart, while the control handle 24 remains outside the patient to be manipulated by an operator 35 shown in Figure 11.
  • the shaft 30 and tipstock 32 lengths can be chosen based on the procedure to be performed, the location at which the catheter is to be percutaneously introduced, and the anticipated path along which the shaft 30 must be steered.
  • the shaft 30 and tipstock 32 are made of a polyurethane tubing, the shaft 30 including a woven Dacron braid within the tubing to enhance stiffness and impart greater column and torsional strength to the shaft.
  • the woven Dacron product has been available since the 1960s.
  • one type of woven Dacron is commercially available as catalog model number 200150 4F from C.R. Bard Inc., Glens Falls Operations.
  • the electrical wires 26 include conductive leads of copper or a copper alloy from a plurality of electrodes, temperature sensors, other electronic devices which may be included in catheter 20, or any combination of the above.
  • the electrical wires 26 provide electrical signals to electronic components such as electrocardiogram (ECG) monitoring equipment and radio frequency (RF) RF energy sources directly through the connector 28, or through an intervening patient cable 29 (shown broken away).
  • ECG electrocardiogram
  • RF radio frequency
  • a knob 36 on the control handle 24 is rotatable relative to the handle
  • FIG. 11 by the operator 35 to cause a slideblock (not shown) within the control handle 24 to move away from a proximal end 22 of the shaft 30.
  • a steering wire 38 which is slidably housed within the tipstock 32 and the shaft 30 (see Figure 15 A), is secured at its proximal end to the slideblock.
  • the steering wire 38 is pulled proximally due to rotation of the knob 36, for example, in the direction of arrow A ( Figure 11).
  • the steering wire 38 advances distally when the slideblock moves toward the proximal end 22 of the shaft 30 as a result of rotation of the knob 36 in the opposite direction.
  • the control handle 24 may be as described in U.S. Patent Application Serial No. 08/518,521, filed August 23, 1995 for Steerable Electrode Catheter to Bowden et al., the disclosure of which is hereby incorporated by reference as if set forth fully herein.
  • the steering wire 38 extends distally from the slideblock, through the shaft 30, to the distal tip assembly 34 where it is anchored, as described more fully below. Because the steering wire 38 is anchored to the distal tip assembly 34, a proximal pulling force on the steering wire 38 causes the tipstock 32 to deflect in a single plane and with a radius of curvature which is determined by the length and compressive strength of the tipstock 32, as shown in Figure 13. The radius of curvature may be in the range of about two to four and a half centimeters.
  • the steering wire 38 must have a tensile strength sufficient to overcome the compressive strength of the tipstock 32 to cause the tipstock 32 to deflect.
  • the steering wire 38 is a stainless steel wire having a pull strength of about 15.5 pounds .
  • the steering wire 38 is preferably guided eccentrically with respect to the longitudinal axis of the catheter 20, and more preferably guided eccentrically within the tipstock 32, so that the tipstock 32 will favor deflection in a known plane due to a wall thickness differential on either side of the steering wire 38 in the tipstock 32 (see Figures. 15A and 17).
  • the entire control handle 24 can be torqued by the operator 35 to steer the shaft 30 through the patient's vasculature. Additional steering wires can be provided, and a radius of curvature adjusting means can be provided in the manner described in the aforementioned U.S. Patent Application Serial No. 08/518,521.
  • the steering wires preferably are nylon (Spectra) cables.
  • Figure 14 is an embodiment of a steering catheter.
  • the steerable catheter shown and described in U.S. Patent No. 5,383,852 to Debbie Stevens- right et al., issued on January 24, 1995, the entirety of which is hereby incorporated by reference can be implemented using the MRI compatible materials herein.
  • the shaft 30 has been modified to include a non-ferrous or magnetic hypotube 37 at its distal end which serves as a rigidifying element, for example, just proximal to the distal tip assembly 34 ( Figure 17a), so that rotation of the knob 36 causes deflection of the tipstock 32 with the distalmost portion 32b ( Figure 13) of the tipstock 32 remaining generally straight.
  • a proximal portion 32a ( Figure 13) of the tipstock 32 which is clear of the hypotube 37 assumes a curve of a predetermined radius based on its length and its compressive strength.
  • the tube or stiffening member 37 preferably extends about one to three centimeters along the catheter 20 and may be anchored to the steering wire 38, the distal assembly 34, or the distalmost used portion 32b of the tipstock.
  • a stiffening wire or similar rigidifying element can be used in lieu of the hypotube 37.
  • the knob 36 preferably includes an indicator 39 ( Figure 11) which indicates that the knob has been rotated from its neutral position (where no force is applied to the steering wire 38). This means that a pulling force is being applied to the steering wire 38 and that the tipstock 32 is being deflected.
  • the indicator 39 may be a tab affixed to the upper margin of the knob 36 which is visible through an aperture in the control handle 24 only when, for example, the slideblock is in a position proximate the proximal end 22 of the shaft 30. In this state, the tab is visible and indicates that no pulling force is being applied to the steering wire 38. Rotation of the knob 36 from the neutral position moves the indicator 39 out of registry with the aperture which indicates to the operator that a pulling force is being applied to the steering wire 38.
  • the indicator 39 and knob 36 are preferably molded from a plastic material having a color which differs from that of the remainder of the control handle 24.
  • the distal assembly 34 comprises a core 40 which has a proximal portion 41 adapted to be received in the distal tip 34 of the tipstock 32, and a compressible head 42 at its distal end.
  • the compressible head 42 includes anchor tabs 47a, 47b.
  • the core 40 has a longitudinal slot 44 extending proximally from its distal face which permits the anchor tabs 47a, 47b to resiliently flex toward each other as the core 40 is received within an aperture 45 in a hollow non-magnetic (e.g. gold) ablation electrode 46 ( Figure 15a).
  • the compressible head 42 includes a chamfered leading edge 50 which facilitates insertion of the core 40 into the aperture 45 of the ablation electrode 46 by camming the anchor tabs 47a, 47b together and thereby compressing the head 42 to a reduced profile.
  • the groove 48 has a shoulder 51 ( Figure 15a) at its proximal edge which prevents the core 40 from being withdrawn from the ablation electrode 46 once the anchor tabs 47a, 47b have snapped into the groove 48 ( Figure 15 A).
  • the core 40 and ablation electrode 46 may include a ratchet and pawl arrangement, or a generally annular projection made of an intrinsically compressible plastic such as polycarbonate or ULTEM ® , shaped to mate with the groove 48 in the ablation electrode 46.
  • the annular projection may project about one to three mils on either side of the core 40, and the groove 48 in the ablation electrode 46 may be sized to receive the annular projection in an uncompressed state.
  • all that is important in these alternative configurations is that the core 40 and ablation electrode 46 interlock via a snap action.
  • the core 40 is preferably made of a nonmagnetic material having a low temperature coefficient, such as the ULTEM ® polyetheraide 1000 resin produced by the GE Plastics division of the General Electric Company, Pittsfield, MA.
  • the low temperature coefficient material provides thermal insulation between the ablation electrode 46 and the tipstock 32, and, preferably, the core 40 has a lower thermal mass than the ablation electrode.
  • the provision of the core 40 between the tipstock 32 and the ablation electrode 46 reduces the likelihood of catheter damage during an ablation procedure which better ensures that a single catheter can be used for a given procedure, or perhaps reused (once sterilized) in subsequent procedures.
  • the cap electrode 46 and the distal tip 34 of the tipstock 32 may be spaced from each other once the core 40 has been mounted in the distal tip 34 by a thin bead of epoxy, or by an annular ring on the core 40, disposed between its proximal end 41 and the compressible head 42. Further, a wider range of materials can be selected for the tipstock 32, including materials with melt-temperatures that are significantly less than the expected ablation temperature, such as polyurethane. With further reference to Figures 14 and 15 A, the distal assembly 34 preferably serves as an anchor for the steering wire 38 and also preferably houses a temperature sensor 54.
  • the core 40 includes a central lumen 94 and several off-axis lumens 98 for conveying non-magnetic wires 52, 56 from the ablation electrode 46 and temperature sensor 54, respectively, to the connector 28 ( Figure 10).
  • the temperature sensor 54 is preferably a thermistor and may be positioned within a cavity 96 in the ablation electrode 46 about four to seven mils from the ablation electrode distal tip.
  • a potting compound 102 for example, TRA-BOND FDA-2 epoxy made by Tra-Con, Inc. of Medford, Massachusetts may add rigidity to the entire distal assembly 34, as described below.
  • FIG 15 A there is seen a central bore 62 at the distal tip 34 of the tipstock 32.
  • the central bore 62 is sized to fit the proximal end of the core 40.
  • the tipstock 32 defines a lumen 70 for receiving the steering wire 38 and a surrounding teflon sheath 104 ( Figures 15A-18), the temperature sensor conductive wires 56 (for example, made of copper/constantine), and the copper beryllium conductive wire 52 from the distal assembly 34.
  • Mounted in spaced relation along the tipstock 32 are ring electrodes 72a, 72b, and 72c which may be sized for intracardiac ECG recording, mapping, stimulation, or ablation.
  • Each ring electrode 72 may extend longitudinally about one half to four millimeters along the tipstock 32 from the ring electrode's proximal edge to its distal edge.
  • the ring electrodes 72 are electrically connected to suitable components via copper/beryllium conductive wires 74a, 74b, and 74c which extend through respective apertures 76a-c in the side of the tipstock 32 into the lumen 70.
  • the ring electrodes 72 may be made of gold and spaced apart in the range of about one to five millimeters and may extend proximally sixty millimeters or more from the tip of the distal assembly 34 along the tipstock 32.
  • the ring electrode 74a may be two millimeters from distal tip 64 of the shaft 30, the ring electrode 74b may be spaced five millimeters from the proximal edge of the ring electrode 74a, and the ring electrode 74c may be spaced two millimeters from the proximal edge of the ring electrode 74b.
  • the tipstock 32 is connected to the distal end of the shaft 30 in conventional manner, preferably along complementary tapered and overlapping regions at their distal and proximal ends, respectively, by ultrasonic welding (Figure 15B).
  • the lumen 70 of the tipstock 32 and the throughlumen 78 of the shaft 30 are in communication with each other.
  • the lumen 70 is preferably disposed eccentrically relative to the longitudinal axis of the tipstock 32, so that proximally directed forces applied to the steering wire 38 cause the tipstock 32 to favor deflection in a predictable, single plane.
  • the eccentric lumen 70 creates an abutment 80 ( Figure 15b) in the vicinity of the union of the tipstock 32 and the shaft 30.
  • a non-magnetic stiffening spring 84 e.g. made of brass
  • a nonmagnetic stiffening tube 86 may be interposed between the distal end 88 of the stiffening spring 84 and the abutment 80.
  • the core 40 is interlocked to the ablation electrode 46, with the anchor tabs 47a, 47b of compressible head 42 snapped into the groove 48, just distal to the shoulder 51 ( Figure 15a).
  • the anchor tabs 47a, 47b cannot be withdrawn beyond shoulder 51.
  • the steering cable 38 is shown looped through two of the off-axis lumens 98 in the core 40 and passing through a coil spring 100, which serves as a pressure reducing mechanism in the preferred embodiment to mitigate or eliminate a so called "cheese knife” effect in which the tensile force applied to the steering wire 38 causes the steering wire to cut into the distal face of the core 40.
  • the coil spring 100 prevents the steering wire 38 from slicing the core by distributing a pulling force which may be applied to the steering wire 38 across the coils of the spring.
  • the steering wire 38 is seen to extend distally through one of the lumens 98 in the core 40.
  • the steering wire 38 should pass through one of the 98 lumens to provide steering, i.e., in a loop joint, through the spring 100, and back through another of the lumens 98, preferably, to a point proximal of the core 40 where it is wrapped around itself to form an anchor for the steering wire 38.
  • the steering wire 38 is wrapped at least two times about itself.
  • the steering wire 38 is arranged to pass through one of the lumens 98, through the spring 100, and then partially back through another of the lumens 98, with the steering wire soldered to the spring 100.
  • Figure 18 illustrates the eccentric lumen 70 in the tipstock 32 which causes a pulling force, which may be applied to the steering wire 38 via the control handle 24, to be directed eccentrically within the tipstock 32.
  • the eccentric lumen 70 provides a reduced thickness lumen wall on one side of the steering wire 38.
  • the off-axis lumens 98 about which the steering wire 38 is anchored better ensures that the tipstock 32 repeatedly deflects in a predictable plane for reliable steering of the distal end of the shaft 30.
  • the shaft 30 includes the hypotube 37 within the tipstock distal portion 32b.
  • the hypotube 37 causes the distal end of the catheter to retain a generally straight configuration even when a pulling force is applied (see Figure 4).
  • Figure 17 is a cross section taken through the shaft 30 and illustrates the steering wire 38, conductive wires 56, conductive wire 52, and conductive wires 74 from the ring electrodes 72 extending proximally within the stiffening spring 84 toward the control handle 24.
  • the assembly of the distal tip assembly 24 is as follows.
  • the plastic core 40 is preferably injection molded.
  • the ablation electrode 46 is machined to have the desired overall dimension for the size of catheter with which it is to be used.
  • the machining is preferably performed under computer control using a machine that can select a first drill bit to generally hollow out the ablation electrode 46, then a second, smaller bit to define the cavity 96, and finally to form the groove 48 using a key cutter, for example, by circular interpolation as understood by those of ordinary skill in the art of machining.
  • Conductive wire 52 is preferably wrapped like a lasso and resistance welded to the ablation electrode 46.
  • an epoxy which is thermally but not electrically conductive for example, STYCAST ® 2850 FT Epoxy Encapsulant, preferably mixed with Catalyst 24LV, both made by Emerson & Cuming Composite Materials, Inc. of Canton, Massachusetts, is inserted into the central cavity 96 and the temperature sensor 54 bonded therein.
  • the conductive wires 52 and 56 from the ablation electrode 46 and the temperature sensor 54 are threaded through the lumens 98, 94, respectively, either before or after their attachment to the ablation electrode 46.
  • the steering wire 38 is attached to the core by threading it in a U-shape through lumens in the core.
  • the steering, wire 38 is threaded through one of the off-axis lumens 98, through the coil spring 100, and then through another of the off- axis lumens 98.
  • the steering wire may extend to a point proximal of the core 40 at which location it may be wrapped about itself to complete its anchoring, or it may terminate after the U-shaped bend within one of the lumens 98 and instead be soldered or brazed to the coil spring 100.
  • a teflon coated steering wire 38 is selected, the portions of the steering wire 38 that are anchored to the core 40 and the control handle 24 preferably being stripped clear of the teflon. Teflon is difficult to bond and is removed to anchor the exposed steering cable.
  • a lubricous sleeve such as teflon may be bonded to the steering wire 38 to reduce the frictional forces that are imparted by the walls of lumens 70, 78 when the steering wire is moved and electrically insulate the steering wire.
  • a second steering wire 38A may be threaded through lumens 98 disposed on the opposite side of the central lumen 94.
  • the ablation electrode 46 may be filled with a potting compound 102 such as FDA-2 epoxy and the core and ablation electrode snapped together in the manner previously described.
  • a potting compound 102 such as FDA-2 epoxy and the core and ablation electrode snapped together in the manner previously described.
  • the snap action of the core 40 and ablation electrode 46 is both audible and tactile.
  • the steering wire, thermistor wires, and ablation electrode wire are received without any twisting action unlike other known methods of making an ablation catheter.
  • the potting compound 102 electrically and thermally isolates the steering wire 38 from the ablation electrode 46.
  • the steering wire 38, conductive wires 56, and conductive wire 52 may be threaded through the lumen 70 and throughlumen 78 to the control handle 24 to assemble the distal tip assembly 34 on the catheter 20.
  • the proximal end of the core 40 can be coated with an epoxy prior to insertion into the central bore 62 at the distal end of the tipstock 32.
  • a thin bead of epoxy (not shown) may space the cap electrode 46 from the distal tip 64 of the tipstock 32 when the distal assembly 34 is mounted to the catheter 20, or the core 40 may include an annular ring which spaces the ablation electrode 46 from the distal tip 64 when the core is inserted into the distal tip.
  • the assembly is completed by attaching the steering wire 38 to the slideblock and the conductive wire 52, 56, and 74 to respective ones of wires 26.
  • Radiofrequency ablation was performed using a standard clinical RF generator (Atakr®, Medtronic, Minneapolis, MN) with open loop control.
  • the generator was located outside the scan room and was electrically interfaced to the animal via the above described ablation catheters.
  • radio frequency energy delivery and electrophysiologic signal acquisition in the scanner is electromagnetic interference. While the frequency of the radio frequency generation unit (-500kHz) is well below the 64 MHZ proton precession frequency at 1.5 T, higher harmonics of the radio frequency signal can produce significant image degradation. To overcome this problem, special RF filters and shielding were designed and constructed to suppress these harmonic signals and permit simultaneous RF ablation and electrophysiological monitoring during imaging. These multi-stage, low-pass filters consist of an arrangement of non-magnetic electrical components that achieve a cut-off frequency of approximately lOMHz. The output from the RF generator is directed to the ablation catheter through these fully shielded filter assemblies that pass through an electric patch panel between the scan and console rooms.
  • the dispersive ground electrode consists of a large conductive adhesive pad that is attached to the skin of the animal to complete the circuit.
  • Intracardiac electrogram tracings were acquired using the same catheters via a similar 12-channel shielded filter box and were recorded using automated data acquisition software. The effect of the RF ablation signal on image quality is shown in Figure 1.
  • the left panel represents an image acquired during RF delivery without filtering while the image on the right shows the same slice during RF delivery with filtering. Note that there is no evidence of noise or artifact and the tip of the catheter is clearly visible in the right ventricular apex (arrow).
  • a 7F non-magnetic single electrode ablation catheter was positioned at the inferior lateral wall of the right atrium in three animals to determine the accuracy of catheter localization under MR guidance (no ablation).
  • FGRE fast gradient recall echo
  • the catheter was imaged to isolate the optimal tomographic slice containing the catheter electrode. After baseline images were acquired for this slice prescription, RF ablation was performed in the right ventricle between the distal electrodes and a large surface area skin patch at a power of 20 W for 60 seconds. To avoid electrode coagulum formation, impedance was monitored by an automatic open-loop feedback system that terminates RF delivery if the impedance exceeds 220 ohms.
  • FSE fast spin echo
  • the animal was sacrificed by anesthesia overdose and the heart was excised and sectioned through the right ventricular lesion into slices corresponding to the tomographic MR imaging slices. Lesion location, morphology, width, length and transmural extent were determined and recorded at gross examination and right ventricular lesions were photographed and matched with the corresponding T2 and contrast enhanced Tl -weighted lesion images. Sections from thermally damaged tissues were bisected longitudinally and submitted for histologic staining (Masson's trichrome and hematoxylin-eosin).
  • Specimens were then analyzed under light microscopy at 40X to characterize global morphologic changes (9) (e.g., delineated cellular junctions and nuclei, and interstitial edema) for determination of the degree of heat induced cellular damage and necrosis.
  • global morphologic changes 9 (e.g., delineated cellular junctions and nuclei, and interstitial edema) for determination of the degree of heat induced cellular damage and necrosis.
  • lesion signal intensity, length, width and area were measured directly from MR images using an off-line quantitative analysis package (Image Tool, Scion Image, Bethesda, MD). Each parameter was measured 10 times for each time frame from baseline to 20 minutes post-ablation. Mean signal intensity from region of interest (ROI) measurements was then normalized (mean ROI signal intensity at time t divided by the baseline signal intensity) and plotted as a function of time. A similar method was used following gadolinium injection on Tl -weighted imaging. Additionally, IEGMs were analyzed pre and post-ablation for changes in signal amplitude and waveform shape.
  • ROI region of interest
  • a MR fluoroscopy sequence was used to successfully position the non- steerable catheter at atrial and ventricular target sites in all animals.
  • MR catheter placement was attempted to target the inferior lateral wall of the right atrium from a jugular access ( Figure 2). Images were acquired without breath-hold once every heart beat with one-second updates. Details of the right atrial anatomy could be appreciated in all animals as several major endocardia! anatomic landmarks were successfully identified, including the superior and inferior vena cava, atrial septum, right atrial appendage, coronary sinus, eustachian ridge, fossa ovalis and tricuspid valve. The catheter remained in the imaging plane throughout the entire navigation sequence in 2 of 3 animals.
  • T I - FGRE images of the same tomographic slice were acquired before and following 7 ml peripheral gadolinium injection ( Figure 5a,b).
  • the lesion border was clearly demarcated 60 seconds following contrast injection.
  • FIG. 6 FSE images before and after RF delivery are shown in Figure 6 with the respective IEGM tracings.
  • a large lesion was visualized directly adjacent to the ablation catheter tip and demonstrated a temporal response similar to those measured in right ventricular apex lesions, with peak intensity occurring 11. 2 minutes post-ablation.
  • IEGM amplitude decreased from a mean pre-ablation value of 10.3 ⁇ 3. 1 mV to 2.2 ⁇ 3.3 mV following RF delivery (p ⁇ 0.05).
  • Figure 7 is a series of lesion profile plots that characterize the spatial and temporal formation of ventricular lesions.
  • a lesion profile is simply a plot of signal intensity over a fixed spatial domain passing though the lesion, as illustrated by Figure 7a for a single time frame.
  • the three- dimensional surface plot represents a series of these profiles in time, where the z-axis represents the color-coded signal intensity and the x and y-axes represent position and time following RF delivery, respectively.
  • the lesion grew dramatically in signal intensity and size from the baseline level shown by the arrow. Maximum signal intensity and lesion area were achieved 12.2 ⁇ 2.1 and 5.3 ⁇ 1.4 minutes following RF delivery, respectively.
  • This study concerns a novel MRI-compatible interventional electrophysiology hardware system in conjunction with a newly developed real-time interactive cardiac MRI system to characterize the temporal and spatial development of cardiac lesions following radiofrequency ablation.
  • This finding indicate that: 1) MR images and IEGMs can be acquired during radiofrequency ablation therapy using specialized radiofrequency filters; 2) nonmagnetic MR compatible catheters can be successfully placed at right atrial and right ventricular targets using fast MR imaging sequences with interactive scan plane modification; 3) regional changes in ablated cardiac tissue are detectable and can be visualized using FSE and FGRE images; 4) the spatial extent of heat induced necrosis can be accurately quantified by MRI immediately following thermal damage; and 5) lesion transmurality can be assessed. These results may have significant implications for the guidance, delivery, and monitoring of cardiac ablation therapy by interventional MRI.
  • MR guided catheter placement Another very important feature of MR guided catheter placement is the ability to visualize the electrode-endocardial tissue interface, which has been shown to increase lesion size by improving the efficiency of RF tissue delivery. While traditional indicators of electrode contact such as fluoroscopic catheter stability and intracardiac electrogram amplitude are useful, these parameters are relatively insensitive indicators of electrode-tissue contact.
  • An important limitation of passive MR catheter tracking is the need to manipulate the catheter within the imaging slice (typically 5- 10 mm wide), which may be especially difficult during catheter placement in geometrically complex vessels and cardiac chambers where catheter curvature and loops are common.
  • MRI Fast Spin Echo Imaging.
  • MRI is able to detect one or more specific changes in Tl and T2 relaxation parameters resulting from heat-induced biophysical changes in cardiac tissue such as interstitial edema, hyperemia, confbrmational changes, cellular shrinkage and tissue coagulation.
  • acute interstitial edema is most likely responsible for the hyperintense regions representing the area of damage observed by T2- weighted FSE imaging.
  • the edema response is mediated by the release of vasoactive polypeptides from local inflammatory cells within seconds of the injury, which causes water and proteins to escape through gaps in the endothelial cells lining the vessel and enter the interstitial space.
  • FGRE imaging is preferable to FSE for cardiac ablation therapy since imaging times are decreased significantly and quality images may be acquired without cardiac gating and breath-holds.
  • An important parameter for contrast-enhanced lesion imaging is the duration post-ablation for optimal gadolinium uptake, hi this study we injected contrast 30 minutes post-ablation and observed a rapid uptake of gadolinium in the affected area of the myocardium. It is not known, however, how quickly the lesion is capable of contrast uptake. The answer to this question has direct clinical implications and may also lend additional insight into the biophysical mechanisms of in vivo lesion formation.
  • MRI guided ablation is not subject to the aforementioned limitations, the technique and system are in the early stages of development and there are number of technical requirements including non-magnetic catheters, monitoring equipment and electromagnetic filtering systems. Additionally, while new advances in scanner hardware have allowed for realtime MR imaging (20 frames/second), passive catheter tracking can be confounded by complex catheter movements that cause the catheter to leave the imaging plane. Lastly, the delayed nature of lesion formation following the initial RTF delivery confounds instantaneous assessment of lesion size.
  • the ability to directly visualize the spatial extent of atnial lesions with high spatial resolution may help facilitate the placement of linear transmural atrial lesions and allow for realtime interactive detection and elimination of skip lesions. This potential may have particular importance since it has been shown that ablation lines with skip lesions are not only ineffective but may be arrhythmogenic.
  • the ability to characterize the temporal evolution of lesions can be used for therapy titration and avoidance of damage to tissue outside the ablation target volume, although the observed delayed biophysical response of the lesion may confound an instantaneous assessment of lesion size.
  • radiofrequency cardiac ablation can be performed under MRI guidance in vivo.
  • Catheters are clearly defined and easily positioned in gradient echo images and the spatial and temporal extent of ventricular ablation lesions can be accurately visualized using T2-weighted fast spin echo imaging and Tl - weighted contrast-enhanced fast gradient echo imaging with a standard cardiac phased array thoracic coil.
  • lesion size by MRI agrees well with actual postmortem lesion size and high fidelity intracardiac electrophysiologic signals can be acquired and monitored during imaging.
  • MRI guided cardiac ablation may be a useful technique that will eliminate ionizing radiation exposure, help provide accurate therapy titration and facilitate the creation of linear, contiguous and transmural lesions, and may lend insight into the physiologic effects of novel ablation techniques and technologies.

Abstract

L'invention concerne un cathéter d'ablation compatible avec des systèmes d'IRM. Ce cathéter comprend une tige et une pointe distale constituées d'un matériau pour IRM, au moins une électrode supportée sur la pointe distale, cette électrode étant constituée d'un matériau pour IRM, et au moins un fil pour IRM relié à l'électrode et se prolongeant à partir de l'électrode vers l'extrémité proximale de la tige, ce film étant constitué d'un matériau pour IRM.
PCT/US2001/015475 2000-05-12 2001-05-14 Catheter d'ablation pour irm WO2001087173A2 (fr)

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