Patent Publication Number: US-2017354338-A1

Title: Dual-function sensors for a basket catheter

Description:
FIELD OF THE INVENTION 
     Embodiments of the present invention relate generally to the field of medical devices, and particularly to catheters for recording intracardiac electrocardiogram (ECG) signals. 
     BACKGROUND 
     In some applications, a basket catheter, comprising a large number of electrodes disposed on a plurality of splines, is used to acquire intracardiac electrocardiogram (ECG) signals. Such signals may be used, for example, to construct an electroanatomical map of the heart. 
     US Patent Application Publication 2011/0118590, whose disclosure is incorporated herein by reference, describes an interventional system for internal anatomical examination that includes a catheterization device for internal anatomical insertion. The catheterization device includes at least one magnetic field sensor for generating an electrical signal in response to rotational movement of the at least one sensor about an axis through the catheterization device within a magnetic field applied externally to patient anatomy, and a signal interface for buffering the electrical signal for further processing. A signal processor processes the buffered electrical signal to derive a signal indicative of angle of rotation of the catheterization device relative to a reference. The angle of rotation is about an axis through the catheterization device. A reproduction device presents a user with data indicating the angle of rotation of the catheterization device. 
     US Patent Application Publication 2003/0093067, whose disclosure is incorporated herein by reference, describes systems and methods for imaging a body cavity and for guiding a treatment element within a body cavity. A system may include an imaging subsystem having an imaging device and an image processor that gather image data for the body cavity. A mapping subsystem may be provided, including a mapping device and a map processor, to identify target sites within the body cavity, and provide location data for the sites. The system may also include a location processor coupled to a location element on a treatment device to track the location of the location element. The location of a treatment element is determined by reference to the location element. A treatment subsystem including a treatment device having a treatment element and a treatment delivery source may also be provided. A registration subsystem receives and registers data from the other subsystems, and displays the data. 
     U.S. Pat. No. 6,272,371, whose disclosure is incorporated herein by reference, describes an invasive probe apparatus including a flexible elongate probe having a distal portion adjacent to a distal end thereof for insertion into the body of a subject, which portion assumes a predetermined curve form when a force is applied thereto. First and second sensors are fixed to the distal portion of the probe in known positions relative to the distal end, which sensors generate signals responsive to bending of the probe. Signal processing circuitry receives the bend responsive signals and processes them to find position and orientation coordinates of at least the first sensor, and to determine the locations of a plurality of points along the length of the distal portion of the probe. 
     US Patent Application Publication 2006/0025677, whose disclosure is incorporated herein by reference, describes a surgical navigation system for navigating a region of a patient that may include a non-invasive dynamic reference frame and/or fiducial marker, sensor tipped instruments, and isolator circuits. The dynamic reference frame may be placed on the patient in a precise location for guiding the instruments. The dynamic reference frames may be fixedly placed on the patient. Also the dynamic reference frames may be placed to allow generally natural movements of soft tissue relative to the dynamic reference frames. Also methods are provided to determine positions of the dynamic reference frames. Anatomical landmarks may be determined intra-operatively and without access to the anatomical structure. 
     U.S. Pat. No. 6,892,091, whose disclosure is incorporated herein by reference, describes an apparatus and method for rapidly generating an electrical map of a chamber of a heart that utilizes a catheter including a body having a proximal end and a distal end. The distal end has a distal tip and an array of non-contact electrodes having a proximal end and a distal end and at least one location sensor. Preferably, two location sensors are utilized. The first location sensor is preferably proximate to the catheter distal tip and the second location sensor is preferably proximate to the proximal end of the non-contact electrode array. The catheter distal end further preferably includes a contact electrode at its distal tip. Preferably, at least one and preferably both of the location sensors provide six degrees of location information. The location sensor is preferably an electromagnetic location sensor. The catheter is used for rapidly generating an electrical map of the heart within at least one cardiac cycle and preferably includes cardiac ablation and post-ablation validation. 
     SUMMARY OF THE INVENTION 
     There is provided, in accordance with some embodiments of the present invention, a catheter, which includes a plurality of splines at a distal end of the catheter, and a plurality of helical conducting elements disposed on the splines. 
     In some embodiments, the plurality of splines are arranged to define a basket. 
     In some embodiments, the helical conducting elements are printed onto the splines. 
     In some embodiments, each of the helical conducting elements includes electrically-conductive paint that is helically painted onto the splines. 
     In some embodiments, the catheter further includes an electrically-insulative layer covering at least a majority of each of the helical conducting elements. 
     In some embodiments, the electrically-insulative layer does not cover a portion of exactly one respective turn of each of the helical conducting elements. 
     There is further provided, in accordance with some embodiments of the present invention, apparatus that includes circuitry and a processor. The circuitry is configured to generate a first output, based on an intracardiac electrocardiogram (ECG) voltage received from a helical conducting element, and to generate a second output, based on a voltage difference that was induced across the conducting element by a magnetic field. The processor is configured to build an electroanatomical map, based on the first output and the second output. 
     In some embodiments, 
     the circuitry is further configured:
         to cause a proximity-indicating voltage to be received from the conducting element, by passing a current between the conducting element and a reference electrode, and   to generate a third output, based on the proximity-indicating voltage, and       

     the processor is configured to build the electroanatomical map based on the third output. 
     In some embodiments, the processor is configured to derive, from the third output, a proximity of the conducting element to tissue. 
     In some embodiments, the circuitry includes: 
     a first differential amplifier, configured:
         to generate the first output by amplifying a difference between the ECG voltage and a reference voltage, and   to generate the third output by amplifying a difference between the proximity-indicating voltage and the reference voltage; and       

     a second differential amplifier, configured to generate the second output by amplifying the induced voltage difference. 
     In some embodiments, the circuitry includes exactly two connections to the conducting element. 
     In some embodiments, the processor is configured: 
     to derive electrical-activity information from the first output, 
     to derive anatomical information from the second output, and 
     to build the electroanatomical map by combining the electrical-activity information with the anatomical information. 
     There is further provided, in accordance with some embodiments of the present invention, a method that includes receiving an intracardiac electrocardiogram (ECG) voltage from a conducting element, receiving a voltage difference induced across the conducting element by a magnetic field, and building an electroanatomical map, using the ECG voltage and the voltage difference. 
     In some embodiments, receiving the voltage difference includes receiving the voltage difference while receiving the ECG voltage. 
     In some embodiments, the conducting elements are disposed on a plurality of splines at a distal end of a catheter. 
     The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a basket catheter, in accordance with some embodiments of the present invention; and 
         FIGS. 2-3  are schematic illustrations of circuitry for processing signals received from conducting elements, in accordance with some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Embodiments described herein include a basket catheter that may be used, for example, to build an electroanatomical map. The basket catheter comprises a plurality of splines at its distal end, and further comprises a plurality of helical conducting elements, which are disposed on the splines. During the electroanatomical mapping procedure, the helical conducting elements function as inductors, in that a generated magnetic field induces respective voltage differences across the conducting elements. Based on the induced voltage differences, the respective locations and orientations of the conducting elements—and hence, the location and orientation of the basket catheter—may be precisely determined. 
     Typically, embodiments described herein are rendered even more advantageous, in that the helical conducting elements may additionally function as electrodes for acquiring ECG signals, such that it may not be necessary to equip the basket catheter with separate ECG-acquiring electrodes. For example, an electrically-insulative layer may cover the majority of each of the helical conducting elements, but leave a small portion of each of the helical conducting elements exposed. This exposed portion, when brought into contact with the intracardiac tissue, acquires ECG signals from the tissue. 
     The helical conducting elements described herein may thus function in two capacities—e.g., simultaneously—during a single procedure. First, they may function as ECG electrodes, by sensing the intracardiac ECG signals. Second, they may function as magnetic-field sensors, by generating location signals (in the form of the above-described induced voltages) in response to the generated magnetic field. The conducting elements may thus be described as ECG electrodes that additionally function as magnetic-field sensors, or as magnetic-field sensors that additionally function as ECG electrodes. (Notwithstanding the above, in some embodiments, the conducting elements are used only as magnetic-field sensors, and separate electrodes coupled to the splines are used to acquire the ECG signals.) 
     Embodiments described herein further include circuitry for processing signals received from the helical conducting elements. In particular, the circuitry described herein generates, based on the received signals, a plurality of outputs, which are used by a processor to construct an electroanatomical map. These outputs include a plurality of first outputs, which indicate the electrical activity of the tissue, a plurality of second outputs, which indicate the respective induced voltage differences across the conducting elements, and a plurality of third outputs, which indicate the proximity to the tissue of each of the conducting elements. 
     Apparatus Description 
     Reference is initially made to  FIG. 1 , which is a schematic illustration of a basket catheter  22 , in accordance with some embodiments of the present invention.  FIG. 1  depicts a physician  34  using basket catheter  22  to perform an electroanatomical mapping of a heart  25  of a subject  26 . During the mapping procedure, the distal end of the catheter, which comprises a basket  20  of splines  28 , is inserted into heart  25 . The splines are then brought into contact with the intracardiac tissue, and conducting elements  24  on the splines acquire intracardiac ECG signals. A console  36 , which is connected to the basket catheter and comprises a computer processor  32 , receives these ECG signals. 
     While the intracardiac ECG signals are being acquired, a magnetic field is generated by a plurality of magnetic-field generators  30  located underneath subject  26  or otherwise in the vicinity of the subject. (As shown in  FIG. 1 , a signal generator (“SIG GEN”)  40  in console  36  may cause generators  30  to generate the magnetic field by supplying an alternating current to the generators.) The magnetic field induces voltage differences across conducting elements  24 . The induced voltage differences are received by the console, and, based on the induced voltages, processor  32  ascertains the position of each of the conducting elements. Processor  32  then constructs an electroanatomical map of the heart, based on the ECG signals (which indicate the electrical activity of the intracardiac tissue) and the voltages received from the helical conducting elements (which indicate the respective locations of the sources of the ECG signals). Such a map may be displayed on a monitor for viewing by physician  34 , and/or stored for later analysis. 
     Splines  28  may be arranged to define any suitably-shaped basket, such as the spheroidal basket shown in  FIG. 1 .  FIG. 1  shows an embodiment in which a plurality of helical conducting elements  24  are disposed on the surface of each of the splines. The top-left portion of the figure shows an enlarged view of a single such helical conducting element. In this enlarged view, the solid portion of the conducting element corresponds to the portion of the conducting element that is on the near side of the spline, facing the viewer. The dotted portion corresponds to the portion of the conducting element that is on the far side of the spline, facing away from the viewer. Each of the two terminals of each of the conducting elements is typically connected to the console via a wire  42  which passes through the interior of the spline. 
     In some embodiments, the conducting elements are printed onto the splines. For example, each of the conducting elements may comprise electrically-conductive paint that is helically painted onto the splines. In other embodiments, the conducting elements comprise wires that are wound (i.e., coiled) around, and glued or otherwise attached to, the splines. In any case, for embodiments in which the helical conducting elements are on the surface of the splines, an electrically-insulative layer  44  typically covers at least a majority of each of the helical conducting elements. Electrically-insulative layer  44  prevents the turns of any given conducting element from being shorted with each other. 
     Typically, the electrically-insulative layer does not cover a portion of exactly one respective turn of each of the helical conducting elements. Thus, the electrically-insulative layer prevents shorting of the turns (in that no more than one turn of each conducting element is exposed), but also allows the conducting elements to acquire ECG signals. For example, the enlarged portion of  FIG. 1  shows an embodiment in which the electrically-insulative layer exposes a portion  46  of the conducting element. Exposed portion  46  may be brought into contact with tissue, in order to acquire an ECG signal. 
     As noted above, the exposed portion of the conducting element is confined to one turn of the conducting element. This means that the distance between the distalmost exposed portion of the conducting element and the proximalmost exposed portion of the conducting element is less than the distance D that separates between successive turns of the conducting element. 
     In some embodiments, the electrically-insulative layer is contiguous across a plurality of conducting elements. In other embodiments, as depicted in  FIG. 1 , the electrically-insulative layer is discontiguous, such that no portion of the electrically-insulative layer covers more than one of the conducting elements. Similarly, for any given conducting element, the cover provided by the electrically-insulative layer may be contiguous or discontiguous. As an example of the latter, in  FIG. 1 , the conducting element is covered by two separate, disjoint portions of the electrically-insulative layer, these portion being on respective opposite sides of exposed portion  46  of the conducting element. 
     In some embodiments, alternatively to being disposed on the splines as in  FIG. 1 , the conducting elements are contained within the splines. In such embodiments, the splines, being made of an electrically-insulative material (such as plastic), provide the “cover” that prevents the conducting elements from being shorted. For embodiments in which the conducting elements are additionally used to acquire ECG signals, the splines are shaped to define a plurality of openings that expose a portion of exactly one respective turn of each of the helical conducting elements. In other words, such embodiments are analogous to the embodiments described above, with the surface of the spline functioning analogously to electrically-insulative layer  44  in preventing shorting of the conducting elements, but also, optionally, providing for ECG-signal acquisition. 
     Reference is now made to  FIG. 2 , which is a schematic illustration of circuitry  48  for processing signals received from conducting elements  24 , in accordance with some embodiments of the present invention. Circuitry  48  is typically located within console  36 , between the catheter-console interface and the processor. As shown in  FIG. 2 , circuitry  48  is connected to each helical conducting element  24 , typically via exactly two connections (or “leads”) connected to the conducting element: a first connection  50   a  to one terminal of the conducting element, and a second connection  50   b  to the other terminal of the conducting element. As further described below, circuitry  48  generates outputs based on signals received, via connections  50   a  and  50   b , from each helical conducting element. Based on these outputs, processor  32  constructs an electroanatomical map of the subject&#39;s heart. 
     Typically, circuitry  48  comprises a first differential amplifier  52   a  and a second differential amplifier  52   b . Connections  50   a  and  50   b  are connected to second differential amplifier  52   b , while one of the connections—e.g., first connection  50   a —is also connected to first differential amplifier  52   a . Connections  50   a  and  50   b  thus carry inputs to the differential amplifiers, as further described below. 
     As described above, the exposed portion of each conducting element  24  is brought into contact with intracardiac tissue  56 , such that an ECG voltage (referred to above as an “ECG signal”) is transferred to the conducting element from the tissue. (The ECG voltage is generally constant across the conducting element, i.e., the ECG voltage at the terminal of the conducting element is not significantly different from the ECG voltage at the exposed portion of the conducting element.) First connection  50   a  carries the ECG voltage to first differential amplifier  52   a , which generates a first output  54   a  based on the ECG voltage, by amplifying a difference between the received ECG voltage and a reference voltage. The processor derives electrical-activity information from first output  54   a , and uses this information to build the electroanatomical map. Typically, the reference voltage is the voltage at a reference electrode  58  disposed on the basket catheter, e.g., on a central spline of the catheter shaft (not shown in  FIG. 1 ). (In  FIG. 2 , reference electrode  58  is connected to ground, such that the reference voltage is ground.) 
     Connection  50   a  also carries, to second differential amplifier  52   b , the voltage induced by the magnetic field at one terminal of the conducting element, while connection  50   b  carries the voltage induced at the other terminal. In other words, connections  50   a  and  50   b  collectively carry, to the second differential amplifier, the voltage difference that is induced across the conducting element. Based on this voltage difference, second differential amplifier  52   b  generates a second output  54   b , by amplifying the voltage difference. Second output  54   b  includes anatomical information, in that the second output indicates the position of the conducting element, and hence, the location of the source of the ECG signal. The processor derives this anatomical information from the second output, and then, in building the electroanatomical map, combines this anatomical information with the electrical-activity information derived from the first output. 
     Typically, circuitry  48  further comprises a current source, or, as in  FIG. 2 , a voltage source  60  in series with a resistor  62 , which together function as a current source. The current source passes a current “I” over connection  50   a  and between the conducting element and reference electrode  58  (or a different reference electrode that is not used for the ECG reference voltage). During the passing of the current, the voltage on the conducting element indicates the impedance that is seen by the conducting element; the higher the voltage, the higher the impedance. The impedance, in turn, indicates the proximity of the conducting element to the tissue; the higher the impedance, the greater the proximity. Thus, the voltage on the conducting element indicates the proximity of the conducting element to the tissue. The first differential amplifier generates a third output  54   c  based on this proximity-indicating voltage, by amplifying the difference between the proximity-indicating voltage and the reference voltage. The processor then uses the third output to build the electroanatomical map. In particular, the processor first derives, from the third output, the proximity of the conducting element to the tissue. The processor then decides whether to accept the first (electrical-activity-related) output, based on the proximity. For example, the processor may compare the proximity to a threshold, and accept the first output only if the proximity is greater than the threshold (i.e., the distance between the conducting element and the tissue is sufficiently small). 
     It is noted that the ECG voltage, the induced voltage, and the proximity-indicating voltage are of sufficiently different frequencies, such that the three voltages may be simultaneously carried on connection  50   a  (and hence, simultaneously received by the circuitry). Thus, first output  54   a , second output  54   b , and third output  54   c  may be generated at the same time. In some embodiments, an adder  61  adds the first output, the second output, and the third output, yielding a combined output  64  having a plurality of components at various frequencies. Combined output  64  is then passed to an analog-to-digital converter (ADC)  66 , which converts the combined output to a digital signal that is passed to the processor. 
     Although, for simplicity, only a single helical conducting element  24  is shown in  FIG. 2 , basket catheter  22  typically comprises a large number of helical conducting elements. On this note, reference is now made to  FIG. 3 , which is a schematic illustration of circuitry  48 , in accordance with some embodiments of the present invention. 
       FIG. 3  shows a way in which the configuration of circuitry  48  shown in  FIG. 2  may be extended to handle a large number of inputs from a large number of helical conducting elements. In particular, in  FIG. 3 , a block  68  of circuitry that is shown in  FIG. 2  is replicated for each of the conducting elements. Thus, in  FIG. 3 , a conducting element  24   a  connects to a block  68   a  of circuitry, a conducting element  24   b  connects to a block  68   b , and a conducting element  24   c  connects to a block  68   c . Similarly, resistor  62  is replicated for each of the conducting elements, such that voltage source  60  may be connected to block  68   a  via a resistor  62   a , to block  68   b  via a resistor  62   b , or to block  68   c  via a resistor  62   c . (Typically, switches  70  ensure that the voltage source is connected to no more than one block at a time.) Thus, for example, to pass a current between conducting element  24   a  and the reference electrode, the voltage source is connected to block  68   a.    
     As indicated by the three-dot sequences in the figure, the configuration shown in  FIG. 3  may be extended to handle any number of conducting elements. 
     It is emphasized that the principles described herein may be applied in many ways. For example, the scope of the present disclosure includes using each of one or more coils, and/or other conducting elements, for both (i) magnetic tracking, and (ii) exchanging signals with tissue, in any relevant application. (Circuitry described with reference to  FIGS. 2-3  may be modified as appropriate to suit the application.) Exchanging signals with tissue includes, for example, acquiring ECG signals as described above, and/or passing ablating signals into tissue. (In the latter case, the same leads that carry the induced voltage from the conducting element may be used to deliver the ablating signal to the conducting element.) Moreover, the dual-function sensors described herein may be disposed on any suitable apparatus, including, for example, a lasso catheter, balloon catheter, or other type of catheter. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of embodiments of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.