Multi-purpose sensing and radiofrequency (RF) ablation spiral electrode for catheter

An electrical apparatus includes a spiral electrode and an interface circuit. The spiral electrode is disposed on a distal end of a probe for insertion into a body of a patient. The interface circuit is configured to (a) transfer a radiofrequency (RF) ablation signal to the electrode for ablating tissue in the body, (b) output a voltage that develops across the electrode in response to an external magnetic field, for measuring a position of the distal end in the body, and (c) transfer electrical current through the electrode for measuring a resistivity that is indicative of tissue temperature in a vicinity of the electrode.

FIELD OF THE INVENTION

The present invention relates generally to medical probes, and particularly to cardiac sensing and ablation catheters.

BACKGROUND OF THE INVENTION

Cardiac catheters for tissue ablation may include multiple sensors and ablation electrodes at their distal end with the different devices typically electrically isolated one of the other. For example, temperature sensors may be embedded in an area covered by an ablation electrode to measure an ablation temperature of that electrode, but have separate electrical conductors.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides an electrical apparatus including a spiral electrode and an interface circuit. The spiral electrode is disposed on a distal end of a probe for insertion into a body of a patient. The interface circuit is configured to (a) transfer a radiofrequency (RF) ablation signal to the electrode for ablating tissue in the body, (b) output a voltage that develops across the electrode in response to an external magnetic field, for measuring a position of the distal end in the body, and (c) transfer electrical current through the electrode for measuring a resistivity that is indicative of tissue temperature in a vicinity of the electrode.

In some embodiments, the spiral electrode is configured as a single axis coil position sensor.

In some embodiments, the spiral electrode is disposed on a first facet of a Printed Circuit Board (PCB), wherein a first end of the spiral electrode is disposed on the first facet and a second end of the spiral electrode is connected to a second facet of the PCB through a via hole.

In an embodiment, the interface circuit includes high-pass filters on the conductors between a source of the RF ablation signal and the electrode.

In another embodiment, the electrical apparatus further includes a surface electrode configured to close an electrical circuit for the RF ablation signal applied by the spiral electrode.

In some embodiments, the interface circuit includes isolation capacitors on electrical conductors between the spiral electrode and a source of the RF ablation signal.

There is additionally provided, in accordance with another embodiment of the present invention, a method including inserting a spiral electrode disposed on a distal end of a probe into a body of a patient. A radiofrequency (RF) ablation signal is transferred to the electrode for ablating tissue in the body. A voltage that develops across the electrode in response to an external magnetic field is outputted for measuring a position of the distal end in the body. Electrical current is transferred through the electrode for measuring a resistivity that is indicative of tissue temperature in a vicinity of the electrode.

There is further provided, in accordance with another embodiment of the present invention, a manufacturing method including disposing a spiral electrode on a distal end of a probe for insertion into a body of a patient. An interface circuit is connected to the spiral electrode, with the interface circuit configured to (a) transfer a radiofrequency (RF) ablation signal to the electrode for ablating tissue in the body, (b) output a voltage that develops across the electrode in response to an external magnetic field, for measuring a position of the distal end in the body, and (c) transfer electrical current through the electrode for measuring a resistivity that is indicative of tissue temperature in a vicinity of the electrode.

In some embodiments, disposing the spiral electrode includes disposing the spiral electrode, including a first end of the electrode, on a first facet of a Printed Circuit Board (PCB), and connecting a second end of the spiral electrode to a second facet of the PCB through a via hole.

DETAILED DESCRIPTION OF EMBODIMENTS

Overview

A catheter used for radiofrequency (RF) ablation requires an electrode capable of delivering the ablation power. In addition, the catheter position may be tracked, and electrode temperature measured during ablation. These three conditions may be served by three separate systems: an electrode, a tracking device such as a single- or triple-axis magnetic sensor, and a temperature sensor such as a thermocouple. The three separate systems require three separate sets of connections, some of which may themselves be problematic. (For example, the constantan in copper-constantan thermocouples is brittle and easily broken.) Notwithstanding the existence of problems, integration of three separate systems on a tip of a catheter tip is inherently complicated.

Embodiments of the present invention that are described hereinafter use one electrode which is able to provide the three functions. In some embodiments, a spiral electrode is disposed on a distal end of a probe for insertion into a body of a patient. An interface circuit of an electrical apparatus is configured to (a) transfer a radiofrequency (RF) ablation signal to the electrode for ablating tissue in the body, (b) output a voltage that develops across the electrode in response to an external magnetic field, for measuring a position of the distal end in the body, (c) and transfer electrical current through the electrode for measuring a resistivity that is indicative of tissue temperature in a vicinity of the electrode.

In some embodiments, the electrode is formed as a planar high-density spiral on one side of a flexible printed circuit board (PCB), with one end of the spiral being connected on one facet of the PCB. The other facet of the PCB is used to connect to the other end of the spiral through a plated hold (“via”) in the PCB. The spiral is typically formed from metal, such as gold. In one embodiment, the spiral is in the form of an approximately 4 mm×4 mm square, the lines of the spiral being approximately 25 μm wide separated by approximately 25 μm. Any general spiral shape in rectilinear, curves or curvilinear spiral is possible, and in particular elliptical or circular shapes may be utilized.

As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the component or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±20% of the recited value, e.g. “about 90%” may refer to the range of values from 71% to 99%.

The spiral has a large area, and thus is able to transfer RF ablation power and act as an ablation electrode. Furthermore, since the ablation RF power is connected to both ends of the spiral, as shown below, no RF power is transferred along the lines of the spiral. Instead, all the power transfers out from the spiral surface, through the patient, and to a return electrode attached to the patient's skin. The ablation RF power typically has a frequency range of 350-500 kHz, which, in an embodiment, is provided to the spiral electrode through isolating capacitors (or other suitable high-pass filters), as shown below.

Since the electrode is in the form of a spiral, it can act as a single axis magnetic sensor that is responsive to alternating magnetic fields traversing the spiral electrode, the fields generating potentials Vfacross the two ends of the spiral. (The alternating magnetic fields have frequencies typically equal to approximately 20 kHz, so they can be easily isolated from the ablation power, using, for example, isolating capacitors). The potentials Vfcan be used to find the position and orientation of the sensor, so that the electrode acts as a location sensor.

The specific resistance of the metal (e.g., gold) spiral changes with its with temperature, in a very well-known relation (the temperature coefficient of gold is 0.003715° C.−1). Measuring the resistance R of the spiral thus provides a measure of the temperature. For example, a gold spiral having a resistance of 30Ω (the approximate resistance of the 4 mm×4 mm spiral described above) at 20° C. has a resistance of 30.1Ω at 21° C. The resistance R of the spiral may be measured using an impedance reading circuitry, for example, by connecting the spiral as one arm of a Wheatstone bridge. The electrode can thus act as a resistance thermometer. In an embodiment, the aforementioned electrically isolating capacitors ensure that the resistance measured is that of the spiral.

There is no restriction as to the type of catheter for which a spiral of the invention may be used, i.e., the spiral may be incorporated into a focal, basket, balloon, lasso, or other type of catheter.

There is also no requirement for implementation of all three functions of a spiral. Thus, in some embodiments only one function is used, in other embodiments only two of the three functions are used, and in other embodiments all three functions are used.

By providing a multipurpose electrode of a catheter as described above, the complexity and price of a catheter may be lowered and thereby increase availability of catheter-based RF ablation treatments.

System Description

FIG.1is a schematic, pictorial illustration of a catheter-based position-tracking and radiofrequency (RF) ablation system20, in accordance with an embodiment of the present invention. System20comprises a catheter tip40(seen in inset25) that is fitted at a distal end22aof a shaft22of a catheter21. RF ablation tip40comprises a spiral electrode50(detailed inFIG.2A) that further acts as a magnetic sensor and as a temperature sensor. In the embodiment described herein, spiral electrode50is used to ablate tissue of an ostium51of a PV in a heart26.

The proximal end of catheter21is connected to a control console24comprising an RF ablative power source45. An ablation protocol comprising ablation parameters is stored in a memory48of console24.

Physician30inserts distal end22aof shaft22through a sheath23into heart26of a patient28lying on a table29. Physician30advances the distal end of shaft22to a target location in heart26by manipulating shaft22using a manipulator32near the proximal end of the catheter and/or deflection from the sheath23. During the insertion of distal end22a, catheter tip40is maintained inside sheath23to minimize vascular trauma along the way to target location.

In an embodiment, physician30navigates the distal end of shaft22to the target location by tracking a direction of catheter tip40. During navigation of distal end22ain heart26, console24receives signals from spiral electrode50at catheter tip40, which acts as a magnetic sensor in response to magnetic fields from external field generators36. Magnetic field generators36are placed at known positions external to patient28, e.g., below patient table29. Console24also comprises a driver circuit34, configured to drive magnetic field generators36.

For example, using the signal, a processor41of the system estimates a direction of catheter tip40in the heart and, optionally, presents the tracked direction on a display27, e.g., relative to an orientation of an axis of approximate symmetry of ostium51. In an embodiment, console24drives a display27, which shows the tracked position of catheter tip40inside heart26.

The method of direction sensing using external magnetic fields is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense-Webster and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, which prior applications are hereby incorporated by reference in their entirety herein into this application as if set forth in full with a copy attached in the Appendix. In an embodiment, signals from spiral electrode50are further used for position sensing using the aforementioned CARTO™ system.

Once distal end22aof shaft22has reached heart26, physician30retracts sheath23and further manipulates shaft22to navigate catheter tip40to an ostium51the pulmonary vein. Next, while catheter tip40contacts the tissue, the physician causes RF electric currents to be passed between spiral electrode50on tip40and an indifferent (i.e., neutral) electrode patch that is coupled externally to the subject, e.g., to the subject's back. The patch can be a single electrode or made of several electrodes, such as electrodes38, which are shown connected by wires running in a cable37. Processor41adjusts the parameters of the ablating currents by outputting appropriate instructions to RF generator45that generates the currents.

To further perform its functions, processor41includes a temperature sensing module47. In the exemplified system, temperature sensing module47receives electrical impedance signals, measured between the two ends of spiral electrodes50and conducted by wires running through shaft22to processor41.

Processor41is typically a general-purpose computer, with suitable front end and (a) ECG interface circuits44for receiving ECG signals from electrodes38, and (b) an electrical interface circuit55for receiving signals from catheter21, as well as for applying RF energy treatment via catheter21in a left atrium of heart26and for controlling the other components of system20. Processor41typically comprises a software in a memory48of system20that is programmed to carry out the functions described herein. The software may be downloaded to the computer in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. In particular, processor41runs a dedicated algorithm as disclosed herein, included inFIG.3, that enables processor41to perform the disclosed steps, as further described below.

WhileFIG.1describes a tip catheter, the principles of the present technique apply to any catheter having a distal end fitted with multiple electrodes, such as Pentaray and Octaray catheters (made by Biosense-Webster).

Multi-Purpose Sensing and RF Abaltion Spiral Electrode for Catheter

FIG.2Ais a schematic, pictorial illustration of catheter tip40of the catheter ofFIG.1comprising a spiral multi-purpose electrode50and its electrical interface circuit55, in accordance with an embodiment of the invention. Electrical interface circuit55comprises conductors (52,54,46,49) and capacitors (57,59) or other suitable high-pass filters, and is used for (a) transferring a radiofrequency (RF) ablation signal to electrode50for ablating tissue in the body, (b) outputting a voltage that develops across electrode50in response to an external magnetic field, for measuring a position of the distal end in the body, and (c) transferring electrical current through electrode50for measuring a resistivity that is indicative of tissue temperature in a vicinity of electrode50.

As seen, electrode50is formed as a 2D planar high-density metal spiral. While the shown outline of the spiral electrode is of a square, any general rectilinear, curve or curvilinear spiral shape is possible, and in particular elliptical or circular shapes. In an embodiment, the metal spiral is disposed on a flexible PCB60, seen in cross-section. However, other types of substrates that can be manufactured to conform to the shape of the tip may be used. As further seen, the center of the spiral is electrically connected to a conductor52on the backside of the PCB, using a via62in PCB60. The perimeter of the spiral is connected to a conductor54.

Spiral electrode50is able to transfer RF ablation power and act as an ablation electrode. Furthermore, since the ablation RF power is connected to both ends of the spiral, i.e., by short circuiting conductors52and54into a single conductor49(proximally to isolating capacitors57and59), no RF power is transferred along the lines of the spiral, with all the power transferred by conductor49, out from the spiral surface, through the patient, to a return electrode38attached to the patient skin, and further via cable37to close an electrical circuit at generator45output leads.

Further shown are conductors46. Spiral electrode50can act as a single axis magnetic sensor that is responsive to alternating magnetic fields traversing the spiral electrode, the fields generating potentials Vfacross the two ends of conductors46. (The alternating magnetic fields have frequencies typically equal to approximately 20 kHz, so they can be easily isolated from the ablation power using capacitors57and59.) The low frequency potentials Vfcan be used to find the position and orientation of the sensor, so that the electrode acts as a location sensor.

The metal of the spiral changes its specific resistance with temperature, in a very well-known relation, which depends on the composition of the electrode material. Measuring the resistance R of the spiral between conductors46thus provides a temperature measurement using module47. The spiral electrode can thus act as a resistance thermometer. In an embodiment, the aforementioned electrically isolating capacitors57and59ensure that the resistance measured is that of the spiral itself, and not, for example, a resistance weighted by the output resistance of generator45.

As shown inFIG.2B, the disclosed spiral electrode150can alternatively be disposed on a three-dimensional dome-shaped distal tip140of a catheter, whereby a flexible PCB with the spiral traces is conformed over the dome. As further seen, spiral electrode150is disposed in this three-dimensional shape, with the center of the spiral being electrically connected to a conductor152and the perimeter of the spiral is connected to a conductor154.

The pictorial side view shown inFIGS.2A and2Bis chosen by way of example, where other embodiments are possible. For example, in another embodiment, cooling fluid flows via irrigation holes (not shown) in electrodes50to cool ablated tissue

FIG.3is a flow chart that schematically illustrates a method for using spiral electrode50of catheter tip40ofFIG.2A or2Bfor position sensing, radiofrequency (RF) ablation, and temperature sensing, in accordance with an embodiment of the invention. The algorithm, according to the presented embodiment, carries out a process that begins when physician30navigates catheter tip40to a target tissue location within heart26of a patient, such as at ostium51, using spiral electrode50as a magnetic sensor, at a catheter tip navigation step80.

Next, physician30positions the catheter tip at ostium51, at a catheter tip positioning step82. In the process, physician30brings catheter tip40into contact with target tissue.

Next, processor41measures, using impedance sensing module47, the resistance of spiral electrode50, to determine electrode temperature, at an electrode temperature measurement step84.

Next, physician30controls interface circuits44to connect spiral electrode50to RF power supply45and to apply ablative energy via spiral electrode50, at an RF ablation step86.

During application of ablative energy, processor41measures electrode50temperature and compares the measured temperature to a preset maximal temperature, at a temperature checking step88.

If the temperature is below the preset maximal temperature, processor41controls interface circuits44to continue applying the RF power via electrode50, at a continued RF power application step90.

If, on the other hand, the temperature is above the preset maximal temperature, processor41controls interface circuits44to disconnect the RF power source from electrode50, at a switching RF power off step92.

The example flow chart shown inFIG.3is chosen purely for the sake of conceptual clarity. In alternative embodiments, additional steps may be performed, such as comparing the temperature of electrode50to a minimal preset temperature and disconnecting electrode50from the RF power source if the temperature of electrode50has not exceeded the minimal preset temperature within a given time duration after the start of application of ablative RF energy (indicative of electrode immersed in blood).

Although the embodiments described herein mainly address pulmonary vein isolation, the methods and systems described herein can also be used in other applications that require RF ablation of body tissue, such as, for example, in renal denervation, cerebrovascular applications and in otolaryngology.