POSITION INDICATOR

FIELD OF THE INVENTION

[0001] This invention relates to deflectable medical catheters, namely steerable sheaths used in interventional vascular procedures to deliver tools (e.g. electrophysiology catheters, guidewires, balloons catheters, stents, instruments, etc.) into the human body and handles for operating the steerable sheath. More particularly, the present invention is related to a family of sheaths that is safe for use in the magnetic resonance environment and handles for operating the sheaths, as the materials used in the invention are compatible with strong electromagnetic fields.

BACKGROUND OF THE INVENTION

[0002] MRI has achieved prominence as a diagnostic imaging modality, and increasingly as an interventional imaging modality. The primary benefits of MRI over other imaging modalities, such as X-ray, include superior soft tissue imaging and avoiding patient exposure to ionizing radiation prorduced by X-rays. MRI's superior soft tissue imaging capabilities have offered great clinical benefit with respect to diagnostic imaging. Similarly, interventional procedures, which have traditionally used X-ray imaging for guidance, stand to benefit greatly from MRI's soft tissue imaging capabilities. In addition, the significant patient exposure to ionizing radiation associated with traditional X-ray guided interventional procedures is eliminated with MRI guidance.

[0003] A variety of MRI techniques are being developed as alternatives to X-ray imaging for guiding interventional procedures. For example, as a medical device is advanced through the patient's body during an interventional procedure, its progress may be tracked so that the device can be delivered properly to a target site. Once delivered to the target site, the device and patient tissue may be monitored to improve therapy delivery. Thus, tracking the position of medical devices is useful in interventional procedures. Exemplary interventional procedures include, for example, cardiac electrophysiology procedures including diagnostic procedures for diagnosing arrhythmias and ablation procedures such as atrial fibrillation ablation, ventricular tachycardia ablation, atrial flutter ablation, Wolfe Parkinson White Syndrome ablation, AV node ablation, SVT ablations and the like. Tracking the position of medical devices using MRI is also useful in oncological procedures such as breast, liver and prostate tumor ablations; and urological procedures such as uterine fibroid and enlarged prostate ablations.

[0004] MRI uses three fields to image patient anatomy: a large static magnetic field, a time- varying magnetic gradient field, and a radiofrequency (RF) electromagnetic field. The static magnetic field and time-varying magnetic gradient field work in concert to establish both proton alignment with the static magnetic field and also spatially dependent proton spin frequencies (resonant frequencies) within the patient. The RF field, applied at the resonance frequencies, disturbs the initial alignment, such that when the protons relax back to their initial alignment, the RF emitted from the relaxation event may be detected and processed to create an image.

[0005] Each of the three fields associated with MRI presents safety risks to patients when a medical device is in close proximity to or in contact either externally or internally with patient tissue. One important safety risk is the heating that may result from an interaction between the RF field of the MRI scanner and the medical device (RF-induced heating), especially medical devices that have elongated conductive structures, such as braiding and pull-wires in catheters and sheaths.

[0006] The RF-induced heating safety risk associated with elongated metallic structures in the MRI environment results from a coupling between the RF field and the metallic structure. In this case several heating related conditions exist. One condition exists because the metallic structure electrically contacts tissue. RF currents induced in the metallic structure may be

[0007] delivered into the tissue, resulting in a high current density in the tissue and associated Joule or Ohmic tissue heating. Also, RF induced currents in the metallic structure may result in increased local specific absorption of RF energy in nearby tissue, thus increasing the tissue's temperature. The foregoing phenomenon is referred to as dielectric heating. Dielectric heating may occur even if the metallic structure does not electrically contact tissue, such metallic braiding used in a deflectable sheath. In addition, RF induced currents in the metallic structure may cause Ohmic heating in the structure, itself, and the resultant heat may transfer to the patient. In such cases, it is important to attempt to both reduce the RF induced current present in the metallic structure and/or eliminate it all together by eliminating the use of metal braid and long metallic pull-wires. [0008] The static field of the MRI will cause magnetically induced displacement torque on any device containing ferromagnetic materials and has the potential to cause unwanted device movement. It is important to construct the sheath and control handle from non-magnetic materials, to eliminate the risk of unwanted device movement.

[0009] When performing interventional procedures under MRI guidance, clinical grade image quality must be maintained. Conventional steerable sheaths are not designed for the MRI and may cause image artifacts and/or distortion that significantly reduce image quality. Constructing the sheath from non-magnetic materials and eliminating all potentially resonant conductive structures allows the sheath to be used during active MR imaging without impacting image quality. Similarly, it is as important to ensure that the control handle is also constructed from non-magnetic materials thereby eliminating potentially resonant conductive structures that may prevent the control handle being used during active MR imaging.

[0010] Conventional steerable sheaths utilize metallic braiding for torque delivery and kink resistance; metallic pull-wires and anchor bands for distal tip deflection; metallic marker bands for fluoroscopy visualization; and ferromagnetic metals in the control handle to minimize cost. Thus because the pull-wires incorporate a conductive materials they will react with the RF field of the MRI scanner and result in RF heating and the associated danger to patients and image degradation and art facts. Additionally, the control handles incorporate ferromagnetic materials that may be attracted to the strong static magnetic field of the MRI scanner. Moreover, the fluoroscopy marker bands in conventional designs may not be compatible with the MR environment due to static field interactions and image degradation and, therefore, are not optimal for visibility in the MRI environment. Therefore, visualization within the MR environment may require the use of either passive or active MR tracking techniques. Passive tracking techniques include passive markers that may lead to image distortion due to direct currents or the use of inductively coupled coils. Active tracking is more robust than passive tracking but involve resonant RF coils that are attached to the device and directly connected to an MR receiver allowing for the determination of the three- dimensional coordinates of the resonant RF coils within the scanner.

[0011] An additional limitation of deflectable sheaths in which the deflection is accomplished via a rotation knob, is that if more than one rotation of the knob is required to fully deflect the sheath, it is difficult to correlate the amount of knob rotation with the amount of distal sheath deflection. This is especially challenging when the sheath is MR compatible, but not actively or passively tracked, and therefore not visible to the user in the MR image. This is related to another limitation in that the sheath user may not know when the sheath is in the neutral position, which is the point at which the distal portion of the sheath is straightened.

[0012] Thus, there is a need for a steerable sheath catheter and control handle that are built with MR compatible materials to eliminate the magnetic resonance environment limitations of

[0013] conventional sheaths while maintaining other characteristics of conventional sheaths. In particular, there is a need for an indicator to provide information regarding the direction and amount of distal curve deflection for steerable sheaths used in an MR environment. To the inventors' knowledge neither active nor passive tracking techniques or distal curve deflection indicators are presently utilized in conventional steerable sheaths or control handles.

BRIEF SUMMARY OF THE INVENTION

[0014] The foregoing need is addressed by the steerable sheath and control handle in accordance with the invention. In one aspect of the invention a steerable sheath is provided that may be used in an MRI environment to deliver a variety of tools (catheters, guidewires, implantable devices, etc.) into the lumens of the body. In a further aspect of the invention, the steerable sheath comprises a reinforced polymer tube in which the reinforcing material is non-metallic based (Kevlar, PEEK, Nylon, fabric, polyimide, etc.) or a hybrid of metallic and non-metallic materials and the reinforcing geometry may comprise a braid, a coil, or a slit tube that mimics a coil and combinations of the foregoing. In yet another aspect of the invention, the reinforced polymer tube may also be segmented with varying flexibility along its length to provide the user with the ability to deflect the catheter in a region in which the segment is more flexible than other segments. In yet another aspect of the invention the polymer tube may also include one or more passive visualization markers along the length of the tube and/or one or more active visualization markers along the length of the tube.

[0015] The steerable sheath in accordance with the invention also includes one or more pull- wires which are coupled with the reinforced tube and that allow the user to manipulate and deflect the polymer tube. In one aspect of the invention, the pull-wires are preferably made of a non- metallic material (Kevlar, PEEK, Nylon, fabric, etc.). One or more internal pull-wire lumens are positioned within the polymer tube construct and allow the user to manipulate the pull-wires to move smoothly during actuation. One or more anchor points connect the pull-wire in the distal portion of the polymer tube.

[0016] In another aspect of the invention a control handle on the proximal end of the reinforced tube operates longitudinal movement of the pull-wire(s). In one aspect of the invention, the handle includes paramagnetic or diamagnetic materials or combinations of paramagnetic and diamagnetic materials.

[0017] In another aspect of the invention, an MR compatible deflectable catheter is provided. The MR compatible deflectable catheter includes a steerable sheath having a tubular shaft, said tubular shaft receiving first and second longitudinal movement wires operably coupled to a distal end thereof; a control handle having a main body configured to receive first and second rack screws, said second rack screw including a threaded portion on an outer surface at a distal end thereof; said first longitudinal movement wire operably coupled to said first rack screw and said second longitudinal movement operably coupled to said second rack screw; and a rotatable adjustment knob operably engageable with said control handle, said rotatable adjustment knob having an .internal threaded portion matingly engageable with the threaded portion of said second rack screw, said rotatable adjustment knob moveable between a first position in which the internal thread is configured to engage the thread on the outer surface of said second rack screw and cause said second rack screw to move proximally to cause proximal longitudinal movement of the second longitudinal movement wire and a second position in which the internal thread is configured to move said second rack screw in a distal direction to release tension on the second longitudinal movement wire.

[0018] In another aspect of the invention a method of using the MR compatible steerable sheath is also provided. A method of deflecting a deflectable catheter includes providing a steerable sheath having a tubular shaft, the tubular shaft receiving first and second longitudinal movement wires having first and second ends, the first end operably coupled to a distal end of the tubular shaft; providing a control handle having a main body configured to receive first and second rack screws, the first and second rack screws including an inner threaded channel and an outer surface, the outer surface of the second rack screw including a thread at a distal end thereof, wherein the second end of the first longitudinal movement wire is operably coupled to the first rack screw and wherein the second end of the second longitudinal movement is operably coupled to the second rack screw; first and second pinion gears coupled to the tubular shaft of the steerable sheath and operably engageable with the inner threaded channel of the first and second rack screws; and a rotatable adjustment knob having an internal thread engageable with the threaded outer surface of the second rack screw and moveable between a first position and second position; rotating the rotatable adjustment knob in the first position to cause engagement of the outer thread of the second rack screw such that the second rack screw moves proximally longitudinally, wherein the proximal longitudinal movement of the second rack screw causes engagement of the pinion gears on the inner threaded channel; causing the pinion gears to movably advance along the threaded internal channel in the distal direction relative to the second rack screw and in the proximal direction relative the first rack screw thereby causing the first rack screw to move distally thereby releasing tension on the first longitudinal movement wire and causing the second rack screw to move proximally thereby causing tension on the second longitudinal movement wire to moveably cause the distal end of the steerable sheath to deflect to at least 180 degrees in a first direction from a longitudinal axis of the tubular shaft; rotating the rotatable adjustment knob in the second direction; causing the pinion gears to movably advance along the threaded internal channel in the proximal direction relative to the second rack screw and in the distal direction relative to the first rack screw thereby causing the second rack screw to move distally thereby releasing tension on the second longitudinal movement wire and causing the first rack screw to move proximally thereby causing tension of the first longitudinal movement wire thereby causing the distal end of the steerable sheath to deflect to at least 180 degrees in a second direction from a longitudinal axis of the tubular shaft.

[0019] In another aspect of the invention, a design for indicating the direction and extent of distal curve deflection for a bi-directional sheath is provided. The design incorporates graphics on the top and bottom of the two rack screws described above that are visible through an opening or window in the control handle. [0020] These and other features of the invention will now be described in detail with reference to the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0022] FIG. 1 is an enlarged view of a control handle rack screw with elements indicating the direction and magnitude of the distal curve deflection.

[0023] FIG. 2 is a perspective view of a control handle rack screw with elements indicating the direction and magnitude of the distal curve deflection.

[0024] FIG. 3 is a perspective view of the control handle with the sheath deflection in the neutral position.

[0025] FIG. 4 is a cut away top view of the control handle with the sheath deflection in the neutral positon.

[0026] FIG. 5 is a perspective view of the control handle with the sheath deflected and direction and extent of the deflection indicated by markers visible on the control handle.

[0027] FIG. 6 is a cut away view of the control handle with the sheath deflected.

[0028] FIG. 7 is a perspective view of the control handle with the sheath deflected and direction and extent of the deflection indicated by markers visible on the control handle.

[0029] FIG. 8 is a cut away view of the control handle with the sheath defelcted.

[0030] FIG. 9 is a perspective view of the sheath showing the sheath fully deflected with both rack screws contained within the control handle and rotation knob.

DETAILED DESCRIPTION OF THE INVENTION [0031] Numerous structural variations of a control handle with a means for displaying information regarding the direction and extent the distal curve deflection in accordance with the invention are contemplated and within the intended scope of the invention. Those of skill in the art will appreciate that the exemplary control handle may be coupled to other types of steerable sheaths. Therefore, for purposes of discussion and not limitation, an exemplary embodiment of the MR compatible steerable sheath and control handle will be described in detail below.

[0032] Referring now to the FIGS, like elements have been numbered with like reference numerals.

[0033] Referring now to FIG. 1, the rack screw 100 in accordance with the invention. The rack screw 100 has an upper surface 101 and a lower surface 102 both containing elements for indicating the direction and extent of distal curve deflection in bi-directional sheath. The first element 103 is a symbol that indicates the extent to which the sheath is deflected. In this example, element 103 is a series of circles. The circle nearest to the center of the rack screw 106 is the smallest, and the size of the circle increases with distance from the center of the rack screw 106. The increasing size of the circle is used to indicate increased deflection angles. The second element 104 is a symbol that indicates the deflection direction. In this example, element 104 is a series of arrows pointing in the direction of deflection. The third element 105 is a symbol that indicates the neutral position. In this example, element 105 is a rectangle. It is obvious that symbols representing elements 103, 104, and 105 are not limited to those represented in FIG. 1. The symbols could consist of any visual indicator that could be interpreted by the user. Examples include not only shapes, but also numbers, colors, or other designs.

[0034] Referring now to FIG. 2, a perspective view of the rack screw 100 in accordance with the invention with the upper portion 101 shown. The rack screw 100, is one of two rack screws contained within in the control handle. The two rack screws, are simply mirror images of each other. The rack screw mechanism works such that when one rack screw translates backward or proximally, the other rack screw translates forward, or distaily. As a result, elements 103, 104, and 105, which respectively indicate the extent of deflection, direction of deflection, and neutral position can be identical on both rack screws. [0035] Referring now to FIG. 3, a perspective view of the control handle 300 in accordance with the invention with the sheath deflection in a neutral position. The control handle includes rotation knob 307, a first handle window 308, and a second handle window 308'. In FIG. 3, the sheath is shown in a neutral, or non-deflected, configuration and the rack screws are aligned. As such, the handle windows 308 and 308' allow neutral deflection symbols 105 and 105' to be observed by the user. The handle windows 308 and 308' are configured such that only one symbol from each of the two rack screws are visible.

[0036] Referring now to FIG. 4, a cut away view of the control handle 300 in accordance with the invention. FIG. 4 shows the sheath deflection in a neutral position. The first rack screw 100 is aligned with the second rack screw 100'. The upper surface 101 of the first rack screw and the lower surface 102 of the second rack screw are visible. In this configuration, elements 103 and 103' indicating the extent of deflection and elements 104, and 104' indicating the direction of deflection are not visible to the user. Only element 105, and 105', which indicate a neutral position are visible.

[0037] Referring now to FIG. 5, a perspective view of the control handle 300 and rotation knob 307 in accordance with the invention. The control handle 300 includes windows 308 and 308' that allow elements 104 and 103' on the first and second rack screw to be visible to the user. FIG. 5 shows the sheath deflected toward the second rack screw, as indicated by element 104 on the first rack screw, which is visible through the first control handle window 308. The extent of the deflection is indicated by element 103', which is visible through the second control handle window 308', on the second rack screw.

[0038] Referring now to FIG. 6, a cut away view of the control handle 300 in accordance with the invention. FIG. 6 shows the first rack screw 100 translated distally and the second rack screw 100' translated proximally resulting in a sheath deflected toward the second rack screw 100'. The upper surface 101 of the first rack screw 100 and the lower surface 102 of the second rack screw 100' are shown. The extent of deflection is indicated by element 103' and the direction of the deflection is indicated by element 104. In this configuration, only elements 103' and 104 are visible through the windows in the control handle. Elements 103, 104', 105, and 105' are not visible to the user. [0039] Referring now to FIG. 7, a perspective view of the control handle 300 and rotation knob 307 in accordance with the invention. In this configuration, the sheath is deflected toward the first rack screw and elements 103 and 104' on the first and second rack screws are visible to the user through windows 308 and 308' in the control handle 300.

[0040] Referring now to FIG. 8, a cut away view of the control handle 300 in accordance with the invention. FIG. 8 shows the sheath in the same configuration as FIG. 7. In this configuration, element 103 on the upper surface 101 of the first rack screw 100 indicates the extent of deflection and is visible through the first window on the control handle 300. Element 104' on the lower surface 102 of the second rack screw 100' indicates the direction of deflection and is visible through the second window on the control handle. Elements 103', 104, 105, and 105' are not visible to the user.

[0041] Referring now to FIG. 9, a perspective view of the control handle 300 and rotation knob 307 in accordance with the invention. The configuration in FIG. 9 shows the sheath fully deflected with the first rack screw 100 translated proximally and the second rack screw 100' translated distally. FIG. 9 shows that with the sheath fully deflected, the first rack screw 100 and the second rack screw 100' are contained within the control handle 300 and the rotation knob 307.

[0042] Although not explicitly shown in the figures, there are windows in both the upper and lower handle halves of the control handle and elements indicating the direction and extent of deflection on the upper and lower surfaces of the rack screws. This ensures that regardless of how the user is holding the handle, the elements indicating the direction and extent of deflection are visible. As is obvious on one skilled in the art, graphic scheme described and shown herein is for illustration purposes and other designs are contemplated and within the intended scope of the invention. This design could also be applied to a uni-directional sheath in which there would only be one rack screw and deflection direction. Moreover, this design could be employed in a sheath that had more than two deflection directions, such as in a tri- or quad-directional sheath.

[0043] Although the present invention has been described with reference to various aspects of the invention, those of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.