Flexible polymer electrode for MRI-guided positioning and radio frequency ablation

An electrode for use on a medical device is disclosed. The electrode may have a main body of electrically conductive material extending along an axis and may have a proximal end and a distal end. The electrode may also include a magnetic resonance imaging (MRI) tracking coil disposed in the body. The MRI tracking coil may comprise electrically insulated wire. A catheter including an electrode, as well as a method for determining the location of an electrode, are also disclosed.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention is directed toward a flexible polymer electrode, including a flexible polymer electrode for MRI-guided positioning and RF ablation.

b. Background Art

Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within a body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is commonly inserted into a vessel near the surface of the body and is guided to a specific location within the body for examination, diagnosis, and/or treatment. For example, one procedure often referred to as “catheter ablation” utilizes a catheter to convey an electrical stimulus to a selected location within the human body to create tissue necrosis. Another procedure often referred to as “mapping” utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body.

Catheters are also used for medical procedures involving the human heart. Typically, the catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and directed, sometimes with the aid of a guide wire or introducer, through the vessels until a distal tip of the catheter reaches the desired location for the medical procedure in the heart.

Conventional ablation procedures utilize a single distal electrode secured to the tip of an ablation catheter. Increasingly, however, cardiac ablation procedures utilize multiple electrodes affixed to the catheter body. These ablation catheters often contain a distal tip electrode and a plurality of ring electrodes. Mapping catheters also often contain a plurality of sensing electrodes to monitor various forms of electrical activity in the human body.

An application may be utilized to create images of the catheter's surroundings. Images may be acquired through visible light, ultrasound, or magnetic resonance (MR). The application may be used to acquire high resolution radiographic images of tissue surrounding the catheter, for example, the acquisition of high resolution magnetic resonance images of blood vessel walls for the visualization and differentiation of various types of tissues and plaques.

Magnetic resonance imaging (MRI) may also be employed during a medical procedure to assist a physician in guiding a catheter and/or a portion of a catheter, such as an electrode. For example, tracking devices may be attached to a catheter (or other medical device) to be tracked. The tracking device may comprise a coil (e.g., induction coil). An MR pulse sequence may be performed using the coil to acquire a signal which indicates the location of the tracked device (e.g., catheter). The location of the coil may be determined and superimposed at the corresponding location in a medical image acquired with an MR imaging system.

Conventional designs for catheters for MRI-guided electrode positioning may rely on a plurality of tracking devices placed at discrete locations along the longitudinal axis of the catheter shaft. The tracking devices may be located on the shaft proximal to an electrode. The tracking devices may be utilized to sense and indicate the location and orientation of the catheter within a body through a control system. The control system may also be used to control a set of imaging coils to image selective areas of the body cavity and/or to control the amount of energy applied to electrodes (e.g., ablation elements) on the catheter to treat target tissue. The energy may cause heating, and at certain temperatures, tissue cells may be destroyed. The tracking devices may be used to compute the curve of the shaft as an interpolated polynomial, such as a cubic spline. The computed curve may then be extrapolated to estimate the projected location of the electrode at the distal end of the catheter shaft. The location of the electrode at the distal end of the catheter shaft may thus be an indirectly computed estimate, not a directly measured value. Further, it may be desirable for an electrode to conform to the tissue surface that has been targeted for treatment. For example, the electrode may undergo deflection or deformation when the electrode comes into physical contact with the tissue. Any deflection or deformation of the electrode may not be estimated by extrapolating from the shape of the catheter shaft. Accordingly, an electrode that conforms to the tissue surface as desired may complicate and/or render useless the extrapolation method.

Thus, there remains a need for a system and method for directly measuring the location of an electrode disposed on a catheter (e.g., the electrode disposed at the distal tip of a catheter) without having to resort to extrapolation or estimation.

BRIEF SUMMARY OF THE INVENTION

It is desirable to provide an electrode that may be configured for compatibility with MR imaging applications, while retaining the electrical, thermal, and mechanical properties of conventional electrodes.

An electrode for use on a medical device is disclosed. The electrode may have a main body of electrically conductive material extending along an axis and may have a proximal end and a distal end. The electrode may also include a magnetic resonance imaging (MRI) tracking coil disposed in the body. The MRI tracking coil may comprise electrically insulated wire, for example. In a preferred embodiment, at least a portion of the body may comprise a flexible, polymer material.

A catheter including the electrode is also disclosed. The catheter may include a shaft and an electrode disposed on the shaft. The electrode may have a main body of electrically conductive material extending along an axis and may have a proximal end and a distal end. The electrode may also include a magnetic resonance imaging (MRI) tracking coil disposed in the body. The MRI tracking coil may comprise electrically insulated wire, for example.

A method for determining the location of an electrode is also disclosed. The method may include the step of providing an electrode having a main body extending along an axis and having a proximal end and a distal end. The method may further include the step of disposing a magnetic resonance imaging (MRI) tracking coil in the body. The MRI tracking coil may comprise electrically insulated wire. The method may further include the steps of transmitting a signal from the MRI tracking coil to a magnetic resonance imaging (MRI) system and depicting the location of the electrode.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a longitudinal, cross-sectional view of a catheter shaft10including an electrode12in accordance with an embodiment of the invention. Shaft10may be designed for insertion into a main lumen of a sheath for eventual insertion into the body of a patient. Shaft10may comprise one or a plurality of layers. For example and without limitation, shaft10may comprise a braided layer of metal fibers for additional stability and one or more layers of polymeric materials to create the desired stiffness and/or flexibility for the catheter. Shaft10may define one or more lumens for electrical leads, steering wires, or various other items that may be utilized within shaft10. Shaft10may include a proximal section and a distal section. As used herein, “proximal” generally refers to a direction away from the body of a patient and toward a clinician. In contrast, “distal” generally refers to a direction toward the body of the patient and away from the clinician. While electrode12may be disclosed and described in connection with a catheter, the use of a catheter is for illustration purposes only, and electrode12may also be utilized in connection with other medical devices.

Electrode12may be mechanically connected (e.g., attached) to the distal section of shaft10. Although electrode12is described as connected to the distal section of shaft10, an electrode12may be connected to one or more other locations along shaft10in other embodiments. Electrode12may be utilized for radio frequency (RF) ablation and may have the electrical, thermal, and mechanical properties required of an electrode used for RF ablation. For example, at least a portion of electrode12may comprise an electrically conductive material. In an embodiment, electrode12may comprise a main body14extending along an axis16. Body14of electrode12may have a distal end18and a proximal end20. Body14of electrode12may be generally cylindrical in shape. Although a cylindrical shape is described and illustrated, electrode12may be formed in other shapes. Distal end18may include a rounded tip. Distal end18may be rounded so as to minimize irritation to the body cavity into which a medical device including the electrode12may be inserted. Body14of electrode12may include a lumen in an embodiment. The lumen may be porous or non-porous. The lumen may extend along axis16of body14and may be open at both ends. In another embodiment, the lumen may be a blind bore22with a closed end and an open end. Blind bore22may have a circular sidewall extending from a floor thereof (e.g., the closed end) and may open toward the proximal end20of body14.

At least a portion of electrode12may be generally flexible in an embodiment. For example, at least a portion of electrode12may be configured to conform to the tissue surface targeted for treatment, and may therefore, deflect and/or undergo deformation when electrode12comes into physical contact with tissue. Body14of electrode12may comprise a polymer material in an embodiment. In particular, body14may comprise an electrically conductive polymer. The polymer may comprise a silicone material, for example. Body14may have electrically conductive particles dispersed therein at a predefined density. The density of the electrically conductive particles may be defined to achieve a desired electrical conductivity. The electrically conductive particles may comprise metal particles in an embodiment. For example and without limitation, the electrically conductive particles may comprise a metal such as gold, silver, platinum, iridium, titanium, tungsten, or a combination thereof. The electrically conductive particles may be non-magnetically responsive. In an embodiment, the electrically conductive particles may have magnetic susceptibility less than 1×10−4. Magnetic susceptibility may refer to the degree of magnetization of a material (e.g., the extent that the material is affected by a magnetic field) in response to a magnetic field.

As described above, electrode12may be configured for imparting energy (e.g., RF energy) to target tissue. An electrical conductor24may be configured to carry ablative energy (e.g. RF current) from an energy source in a controller (not shown) to electrode12. Electrical conductor24may have a first end coupled to body14of electrode12. Electrical conductor24may have a second end configured for connection to an energy source26. Energy source26may comprise a radio frequency ablation generator in an embodiment. Electrical conductor24may extend within shaft10along axis14. Electrical conductor24may comprise an electrically conductive wire. For example, and without limitation, electrical conductor24may comprise copper wire. Electrical conductor24may have an uninsulated portion for electrical contact with electrode12. For example, the first end (e.g., a distal end) of electrical conductor24may be uninsulated. At least a portion of the remainder of electrical conductor24may be electrically insulated. For example, the portion of electrical conductor24extending along shaft10outside of electrode12may be electrically insulated.

In an embodiment, the uninsulated portion of electrical conductor24may be electrically connected to electrode12at a point connection. For example, electrical conductor24may have a first end that is electrically coupled to proximal end20of body14at a single point. In a preferred embodiment, at least part of the uninsulated portion of electrical conductor24may be formed in a plurality of turns, as illustrated inFIGS. 1-3. Electrical conductor24may be formed (e.g., wound) into a substantially cylindrical shape and may have a longitudinal axis that is coincident with axis14of electrode12. The plurality of turns of electrical conductor24may be disposed in the lumen or blind bore22and may be configured to engage the circular sidewall of blind bore22in an embodiment. The shape of electrical conductor24in this embodiment may be formed so as to more evenly distribute the energy from RF ablation generator26throughout electrode12. In particular, the shape of electrical conductor24(e.g., wound in a plurality of turns and extending axially throughout the depth of the blind bore22) allows conduction from the coiled conductor24substantially radially through electrode12, as opposed to a more axial path of conduction along axis14of electrode12if the conductor24is connected to a point on the proximal end20of electrode12. Furthermore, the shape of electrical conductor24may provide some mechanical integrity to the electrical connection between conductor24and the electrode12

In other embodiments, the uninsulated portion of electrical conductor24(e.g., the first end of electrical conductor24nearest to the electrode12) may be electrically connected to one of a screen, a mesh, a braid, or a fabric of electrically conductive material. The screen, mesh, braid, or fabric may engage body14(e.g., the sidewall of blind bore22in an embodiment) and may also be utilized to distribute the energy from RF ablation generator26throughout electrode12in the same manner as the coiled conductor24.

Referring now toFIG. 2, which illustrates a cross-sectional view of electrode12in accordance with an embodiment of the invention, a portion28of shaft10may be disposed in body14(e.g., blind bore22in an embodiment) as well. Portion28may have a longitudinal axis that is coincident with axis16of body14. In the embodiment where electrical conductor24is coiled, conductor24may be wound in a substantially circular cross-sectional shape and may be disposed so as to encircle portion28(as illustrated). Portion28may be electrically insulative in an embodiment. Portion28may also be thermally conductive in an embodiment. A thermal sensor30may extend within at least the distal end of catheter shaft12and within electrode12along axis16. In particular, thermal sensor30may extend within thermally conductive portion28of shaft10in an embodiment. Thermal sensor30may be located along a centerline of the electrode12in an embodiment. Thermal sensor30may be located at or near the distal end18of electrode12(e.g., the tip) in an embodiment. Thermal sensor30may thus be in close proximity to the electrode/tissue interface when the electrode is oriented so that the tip of the electrode12contacts tissue during ablation, which may be advantageous in some embodiments. For example and without limitation, thermal sensor30may comprise a thermocouple. Thermal sensor30may be operatively connected to a controller and may be configured to provide temperature feedback during ablation to avoid clotting and/or blood boiling, for example, which may occur if electrode12(and hence by extension the subject tissue) reaches an excessive temperature.

Electrode12may be configured for compatibility with MRI-guided applications. Accordingly, electrode12may include a magnetic resonance imaging (MRI) tracking coil32. MRI tracking coil32may be wound in a substantially cylindrical shape and may have a longitudinal axis that is coincident with axis16of body14. MRI tracking coil32may be disposed in body14of electrode12. For example, MRI tracking coil32may be embedded within body14of electrode12. In another example, MRI tracking coil32may be disposed in a lumen, for example and without limitation, blind bore22. MRI tracking coil32may be disposed so as to encircle portion28of shaft10and may or may not contact the circular sidewall of blind bore22in this example. MRI tracking coil32may comprise an electrically insulated wire capable of carrying the current required to create a coil signal. MRI tracking coil32may function as an RF antenna typically used in interventional MRI applications, and accordingly will be formed having a predetermined number of turns to ensure adequate performance, in view of the various other portions of the MRI system with which it will be required to interact. In this regard, an MR pulse sequence may be performed using MRI tracking coil32to acquire a signal that may be indicative of a position or a location of electrode12. For example, an electromagnetic force (EMF) may be induced in the MRI tracking coil32as would be understood by one of ordinary skill in the art. The signal (e.g., EMF) may be transmitted to a magnetic resonance imaging (MRI) system34. The MRI system34may be responsive to the signal from MRI tracking coil32to depict a location of electrode12in a patient. For example, MRI system34may utilize the EMF to render a graphic display of the position or location of electrode12. The MRI system34may also be configured to acquire image data from a patient (equipment for this function not shown), and to display an overall image reconstructed using the acquired image data and the acquired position-indicative data (i.e., from the induced EMF signal from the MRI tracking coil32), which may depict the location of electrode12in a patient. In an embodiment, another electrical conductor36may carry the signal (e.g., EMF) from MRI tracking coil32to MRI system34. Electrical conductor36may extend within catheter shaft12along axis14of electrode12.

As described above, in a preferred embodiment, at least a portion of body14of electrode12may be generally flexible and may be configured for deformation and/or deflection in a number of directions relative to axis16of body14. For example, a distal portion of body14may be generally flexible. Referring toFIG. 3, the body is shown in a deflected and/or deformed position, designated by reference number14deflected, and is shown deflected at an angle α relative to axis14. Although this particular deflection is illustrated, body14may be deflected and/or deformed in various other ways, including in a direction along different axes other than the axis of the shaft10. The deflection and/or deformation of electrode12may not be able to be estimated merely by extrapolating the shape of a catheter shaft that holds a rigid and/or solid electrode at its distal end. Accordingly, it may be difficult to estimate a projected location of a flexible electrode at the distal end of a catheter shaft without a direct measurement.

In an embodiment, MRI tracking coil32may be configured to move in correspondence with deflection of body14. Referring again toFIG. 3, MRI tracking coil32deflectedis shown in a new position, away from its original position, where the tip of electrode12is deflected. Accordingly, MRI tracking coil32deflectedmay be configured to track the deformation and/or deflection of electrode12through a direct measurement. MRI tracking coil32may thus be configured to provide direct localization of electrode12as electrode12conforms to the target tissue surfaces and may allow for direct measurement of the location of electrode12. In prior art embodiments, one or more MRI tracking coils38may be disposed along shaft10, as opposed to electrode12. Accordingly, the exact location of electrode12may only be extrapolated based on a curve computed using the data obtained from the prior art MRI tracking coils38on shaft10. Prior art MRI tracking coils38do not provide direct measurement of the position or location of electrode12.

A method for determining the location of an electrode12is also disclosed. The method may include the step of providing an electrode12having a main body14of electrically conductive material extending along an axis16and having a distal end18and a proximal end20. The method may also include the step of disposing an MRI tracking coil32in body14. MRI tracking coil32may comprise electrically insulated wire. The method may also include the step of transmitting a signal from MRI tracking coil32to an MRI system34(e.g., through electrical conductor36) and depicting a location of electrode12. Image data may also be obtained from a patient using MRI system34and an imaging (e.g., receive) coil disposed on shaft10, for example. MRI system34may also use this image data in displaying an image depicting the location of electrode12. In some embodiments, the method may include the steps of deflecting at least a distal portion of body14of electrode12relative to axis14. MRI tracking coil32may be configured to move in correspondence with the deflection of body14. Accordingly, MRI tracking coil32may also move to a new position, away from its original position, when the tip of electrode12is deflected.