Patent Publication Number: US-2023157616-A1

Title: Transient Event Identification

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical systems, and in particular, but not exclusively, to catheter devices. 
     BACKGROUND 
     A wide range of medical procedures involve placing probes, such as catheters, within a patient&#39;s body. Location sensing systems have been developed for tracking such probes. Magnetic location sensing is one of the methods known in the art. In magnetic location sensing, magnetic field generators are typically placed at known locations external to the patient. A magnetic field sensor within the distal end of the probe generates electrical signals in response to these magnetic fields, which are processed to determine the coordinate locations of the distal end of the probe. These methods and systems are described 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 International Publication No. WO 1996/005768, and in U.S. Patent Application Publications Nos. 2002/0065455 and 2003/0120150 and 2004/0068178. Locations may also be tracked using impedance or current based systems. 
     One medical procedure in which these types of probes or catheters have proved extremely useful is in the treatment of cardiac arrhythmias. Cardiac arrhythmias and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. 
     Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Such ablation can cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Various energy delivery modalities have been disclosed for forming lesions, and include use of microwave, laser, pulsed field, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall. In a two-step procedure, mapping followed by ablation, electrical activity at points within the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the endocardial target areas at which the ablation is to be performed. 
     Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral vein, and then guided into the chamber of the heart of concern. A typical ablation procedure involves the insertion of a catheter having a one or more electrodes at its distal end into a heart chamber. A reference electrode may be provided, generally taped to the skin of the patient or by means of a second catheter that is positioned in or near the heart. RF (radio frequency) current is applied between the tip electrode(s) of the ablating catheter, and the reference electrode, flowing through the media between the electrodes it, i.e., blood and tissue. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. 
     SUMMARY 
     There is provided in accordance with an embodiment of the present disclosure, a medical system, including a catheter configured to be inserted into a chamber of a heart of a living subject, and including catheter electrodes configured to contact tissue at respective locations within the chamber of the heart, a display, and a processing circuitry configured to receive respective signals from the catheter captured by respective ones of the electrodes, assess conformity of each of the respective signals to at least one signal characteristic, find a given one of the signals of a given one of the electrodes not conforming to the at least one signal characteristic for a given time period, and render to the display an indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display a representation of the catheter with the indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period, wherein the indication is linked to the given electrode on the representation of the catheter. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display a representation of the catheter with the indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period, wherein the indication is disposed on the given electrode on the representation of the catheter. 
     Additionally in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the indication disposed on the given electrode on the representation of the catheter for a given time interval, remove the indication from the given electrode on the representation of the catheter, and repeat rendering to the display of the indication disposed on the given electrode on the representation of the catheter responsively to finding that the given signal of the given electrode does not conform to the at least one signal characteristic for a subsequent time period. 
     Moreover, in accordance with an embodiment of the present disclosure the processing circuitry is configured to render to the display the indication disposed on the given electrode on the representation of the catheter so that the indication repeatedly flashes on and off responsively to multiple detections of the given signal of the given electrode not conforming to the at least one signal characteristic for respective subsequent time periods. 
     Further in accordance with an embodiment of the present disclosure the respective subsequent time periods correspond to respective windows of interest of respective cardiac cycles. 
     Still further in accordance with an embodiment of the present disclosure the processing circuitry is configured to receive a user input requesting display of an electrogram captured by the given electrode, and render to the display the electrogram captured by the given electrode. 
     Additionally in accordance with an embodiment of the present disclosure the given time period is equal to a window of interest in one cardiac cycle. 
     Moreover, in accordance with an embodiment of the present disclosure the given time period is equal to multiple windows of interest of respective cardiac cycles. 
     Further in accordance with an embodiment of the present disclosure the processing circuitry is configured to save the given signal to a memory for future rendering to the display. 
     There is also provided in accordance with another embodiment of the present disclosure a medical method, including receiving respective signals from a catheter inserted into a chamber of a heart of a living subject captured by respective electrodes of the catheter contacting tissue at respective locations within the chamber of the heart, assessing conformity of each of the respective signals to at least one signal characteristic, finding a given one of the signals of a given one of the electrodes not conforming to the at least one signal characteristic for a given time period, and rendering to the display an indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period. 
     Still further in accordance with an embodiment of the present disclosure the rendering includes rendering to the display a representation of the catheter with the indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period, wherein the indication is linked to the given electrode on the representation of the catheter. 
     Additionally in accordance with an embodiment of the present disclosure the rendering includes rendering to the display a representation of the catheter with the indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period, wherein the indication is disposed on the given electrode on the representation of the catheter. 
     Moreover in accordance with an embodiment of the present disclosure the rendering includes rendering to the display the indication disposed on the given electrode on the representation of the catheter for a given time interval, the method further including removing the indication from the given electrode on the representation of the catheter, and repeating rendering to the display of the indication disposed on the given electrode on the representation of the catheter responsively to finding that the given signal of the given electrode does not conform to the at least one signal characteristic for a subsequent time period. 
     Further in accordance with an embodiment of the present disclosure the rendering includes rendering to the display the indication disposed on the given electrode on the representation of the catheter so that the indication repeatedly flashes on and off responsively to multiple detections of the given signal of the given electrode not conforming to the at least one signal characteristic for respective subsequent time periods. 
     Still further in accordance with an embodiment of the present disclosure the respective subsequent time periods correspond to respective windows of interest of respective cardiac cycles. 
     Additionally in accordance with an embodiment of the present disclosure, the method includes receiving a user input requesting display of an electrogram captured by the given electrode, and wherein the rendering includes rendering to the display the electrogram captured by the given electrode. 
     Moreover, in accordance with an embodiment of the present disclosure the given time period is equal to a window of interest in one cardiac cycle. 
     Further in accordance with an embodiment of the present disclosure the given time period is equal to multiple windows of interest of respective cardiac cycles. 
     Still further in accordance with an embodiment of the present disclosure, the method includes saving the given signal to a memory for future rendering to the display. 
     There is also provided in accordance with still another embodiment of the present disclosure a software product, including a non-transient computer-readable medium in which program instructions are stored, which instructions, when read by a central processing unit (CPU), cause the CPU to receive respective signals from a catheter inserted into a chamber of a heart of a living subject captured by respective electrodes of the catheter contacting tissue at respective locations within the chamber of the heart, assess conformity of each of the respective signals to at least one signal characteristic, find a given one of the signals of a given one of the electrodes not conforming to the at least one signal characteristic for a given time period, and render to the display an indication that the given signal of the given electrode does not conform to the at least one signal characteristic for the given time period. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood from the following detailed description, taken in conjunction with the drawings in which: 
         FIG.  1    is a schematic, pictorial illustration of a catheter tracking system constructed and operative in accordance with an embodiment of the present invention; 
         FIG.  2    is a flowchart including steps in a method of operation of the system of  FIG.  1   ; 
         FIG.  3    is a schematic view of a representation of a catheter in an anatomical map with an indication of an electrode capturing a non-standard signal rendered in the system of  FIG.  1   ; and 
         FIG.  4    is a schematic view of the representation of the catheter of  FIG.  3    with an electrogram. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     During the mapping process, unexpected signals that do not fit into the category of expected mapping signals may be captured by catheter electrodes. These unexpected signals may be due to noise and/or physiological factors leading to complex signals including late activations, or double/multiple activations per cardiac cycle. Although these unexpected signals may be interesting for the physician, these unexpected signals are difficult to treat algorithmically (and may cause errors in the mapping process) and are generally filtered out as non-mapping signals and ignored by the mapping algorithm. Nevertheless, complex signals may be the most interesting signals for the physician and may indicate a heart defect which should be treated. However, as mentioned above these complex signals are generally excluded from the mapping process. 
     Embodiments of the invention use the signals filtered out as non-mapping signals and provide respective indications to the physician that such non-mapping signals exist. The physician may then select the non-mapping signals for viewing to determine if the signals are physiologically relevant. 
     In some embodiments, a mapping system assesses conformity of each signal to one or more signal characteristics for a given time period (e.g., for a window of interest of each signal in one or more cardiac cycles). The signals for a given time period may also be referred to as signal segments for the given time period. The signal characteristics for classifying a signal segment (for a given time period) as a valid mapping signal may include a signal having a single activation early enough in the cardiac cycle. Signal segments with late, double, multiple, or unclear activations may be excluded as not conforming with the signal characteristics. In some embodiments, peaks above a given threshold are considered as possible activations, whereas peaks below the given threshold are not considered as possible activations for determining how many activations a signal segment has in the window of interest and how late the activations are in the window of interest. The activation time may be defined by the steepest negative slope of a candidate peak or any other suitable criteria. The definition of “early enough” in the cardiac cycle, the window of interest, and the given threshold for identifying peaks may be implementation specific and/or physician defined. In some embodiments, the physician defines the “window of interest”. For example, in atrial procedures, the “window of interest” may be defined by setting limits around the P wave, which may be identified based on the R peak of the QRS complex. The definition of late activation may be dependent on the region on the map. In some embodiments, “late” may be considered to be about 10 milliseconds later than all the points surrounding the specific map region under consideration. With regards to the given threshold for identifying peaks, the threshold may be set to any suitable level, for example, 10 micro-Volts. 
     The mapping system then finds the signal segments not conforming to the signal characteristic(s) for the given time period and saves non-conforming signal segments to a memory for future retrieval and inspection by the physician. The non-conforming signal segments may be saved with metadata such as the electrode which captured the signal segment, the time of capture, and optionally the nature of the non-conformity (e.g., late activation, double activation etc.). The mapping system may then render an indication to a display indicating that an electrode captured the non-conforming signal segment optionally with an identification of the capturing electrode. 
     In some embodiments, the indication may be implemented by highlighting or otherwise coloring or shading the relevant electrode on a representation of the catheter. In some embodiments, the indication remains visible until removed by the physician. 
     In other embodiments, the indication may be removed automatically after a time-out (e.g., within a cardiac cycle). If the same electrode is still capturing a non-conforming signal segment for the next time period, the indication is rendered again. In this manner if the non-conforming signal segment is a one-off occurrence (or repeating a few times for example) e.g., due to noise, the indication will disappear, whereas if the non-conforming signal segment is repetitive (e.g., due to a physiological effect) then the indication will flash on and off repetitively thereby alerting the physician that a non-conforming signal segment has been captured. The physician may then request rendering of the non-conforming signal segment on the display for inspection. 
     System Description 
     Reference is now made to  FIG.  1   , which is a schematic, pictorial illustration of a catheter tracking system  20 , in accordance with an embodiment of the present invention. The system  20  includes a catheter  40  configured to be inserted into a body part (e.g., a chamber of a heart  26 ) of a living subject (e.g., a patient  28 ). A physician  30  navigates the catheter  40  (for example, a basket catheter produced by Biosense Webster, Inc. of Irvine, Calif., USA), seen in detail in inset  45 , to a target location in the heart  26  of the patient  28 , by manipulating a deflectable segment of an insertion tube  22  of the catheter  40 , using a manipulator  32  near a proximal end  29  of the insertion tube  22 , and/or deflection from a sheath  23 . In the pictured embodiment, physician  30  uses catheter  40  to perform electro-anatomical mapping of a cardiac chamber. 
     The catheter  40  includes a distal end  33 . The distal end  33  of the catheter  40  includes an assembly  35  (e.g., a basket assembly as shown in  FIG.  1    or a balloon assembly or any suitable distal end assembly, e.g., grid, flexible splines or a focal catheter) on which at least one (e.g., multiple) catheter electrode(s)  48  (only some labeled for the sake of simplicity) are disposed. The electrodes  48  are configured to contact tissue at respective locations with the chamber of the heart. The assembly  35  is disposed distally to the insertion tube  22  and may be connected to the insertion tube  22  via a coupling member of the insertion tube  22  at the distal end  33 . The coupling member of the insertion tube  22  may be formed as an integral part of the rest of the insertion tube  22  or as a separate element which connects with the rest of the insertion tube  22 . 
     The assembly  35  further comprises multiple flexible strips  55  (only two labeled for the sake of simplicity), to each of which are coupled the electrodes  48 . The assembly  35  may include any suitable number of electrodes  48 . In some embodiments, the assembly  35  may include ten flexible strips  55  and  120  electrodes, with twelve electrodes disposed on each flexible strip  55 . 
     The catheter  40  includes a pusher  37 . The pusher  37  is typically a tube that is disposed in a lumen of the insertion tube  22  and spans from the proximal end  29  to the distal end  33  of the insertion tube  22 . A distal end of the pusher  37  is connected to distal ends of the flexible strips  55 , typically via a coupling member of the pusher  37 . The coupling member of the pusher  37  may be formed as an integral part of the rest of the pusher  37  or as a separate element which connects with the rest of the pusher  37 . The distal end of the insertion tube  22  is connected to proximal ends of the flexible strips  55 , typically via the coupling member of the distal end  33 . The pusher  37  is generally controlled via the manipulator  32  to deploy the assembly  35  and change an ellipticity of the assembly  35  according to the longitudinal displacement of the pusher  37  with respect to the insertion tube  22 . The actual basket assembly  35  structure may vary. For example, flexible strips  55  may be made of a printed circuit board (PCB), or of a shape-memory alloy, or any suitable material. 
     Embodiments described herein refer mainly to a basket distal-end assembly  35 , purely by way of example. In alternative embodiments, the disclosed techniques can be used with a catheter having a balloon-based distal-end assembly or of any other suitable type of distal-end assembly. 
     Catheter  40  is inserted in a folded configuration, through sheath  23 , and only after the catheter  40  exits sheath  23  is catheter  40  able to change shape by retracting pusher  37 . By containing catheter  40  in a folded configuration, sheath  23  also serves to minimize vascular trauma on its way to the target location. 
     The distal end  33  of the catheter  40  comprises magnetic coil sensors  50 A and  50 B. The magnetic coil sensor  50 A is shown in inset  45  at the distal edge of insertion tube  22  (i.e., at the proximal edge of basket assembly  35 ). The sensor  50 A may be a Single-Axis Sensor (SAS), or a Double-Axis Sensor (DAS) or a Triple-Axis Sensor (TAS). Similarly, the sensor  50 B may be a SAS, DAS, or TAS. Magnetic coil sensors  50 A and  50 B and electrodes  48  are connected by wires running through insertion tube  22  to various driver circuitries in a console  24 . 
     In some embodiments, system  20  comprises a magnetic-sensing sub-system to estimate an ellipticity of the basket assembly  35  of catheter  40 , as well as its elongation/retraction state, inside a cardiac chamber of heart  26  by estimating the elongation of the basket assembly  35  from the distance between sensors  50 A and  50 B. Patient  28  is placed in a magnetic field generated by a pad containing multiple magnetic field generator coils  42 , which are driven by a unit  43 . The magnetic field generator coils  42  are configured to generate respective alternating magnetic fields, having respective different frequencies, into a region where a body-part (e.g., the heart  26 ) of a living subject (e.g., the patient  28 ) is located. The magnetic coil sensors  50 A and  50 B are configured to output electrical signals responsively to detecting the respective magnetic fields. For example, if there are nine magnetic field generator coils  42  generating nine respective different alternating magnetic fields with nine respective different frequencies, the electrical signals output by the magnetic coil sensors  50  will include components of the nine different frequency alternating magnetic fields. The magnitude of each of the magnetic fields varies with distance from the respective magnetic field generator coils  42  such that the location of the magnetic coil sensors  50  may be determined from the magnetic fields sensed by the magnetic coil sensors  50 . Therefore, the transmitted alternating magnetic fields generate the electrical signals in sensors  50 A and  50 B, so that the electrical signals are indicative of position and orientation of the magnetic coil sensors  50 . 
     The generated signals are transmitted to console  24  and become corresponding electrical inputs to processing circuitry  41 . The processing circuitry  41  may use the signals to compute: the elongation of the basket assembly  35 , in order to estimate basket ellipticity and elongation/retraction state from the calculated distance between sensors  50 A and  50 B; and compute a relative orientation between the axes of the sensors  50 A and  50 B to estimate a shape of the expandable distal end assembly  35  (e.g., a basket shape) responsively to the relative orientation, as described in more detail below. 
     The bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) may be measured for various distances between the magnetic sensors  50 A,  50 B and for various relative orientation angles between the magnetic sensors  50 A,  50 B. For example, the positions of the electrodes  48  with respect to the fixed point on the catheter  40  may be measured for every 0.2 mm movement of the pusher  37  with respect to the insertion tube  22  and for every 1 degree of relative orientation between the magnetic sensors  50 A,  50 B (up to a maximum sideways movement of the assembly  35 ). At each different distance/relative-orientation combination, the computed distance and computed relative orientation angle between the magnetic sensors  50 A,  50 B is recorded along with the position data of the electrodes  48 . This data may then be used to estimate the bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) responsively to the computed distance and relative orientation angle between the magnetic sensors  50 A,  50 B. 
     Additionally, or alternatively, the bow of the flexible strips  55  may be estimated based on the following assumptions: (a) each of the flexible strips  55  is of a fixed and known length; (b) each of the flexible strips  55  is connected to the pusher  37  via a coupler, with the distal ends of the flexible strips  55  being substantially perpendicular (within an error of plus or minus 10 degrees) to the longitudinal axis of the insertion tube  22 ; (c) each of the flexible strips  55  is connected to the insertion tube  22  via a coupler, which couples the proximal ends of the flexible strips  55  to the insertion tube  22 , substantially parallel (within an error of plus or minus 10 degrees) to the longitudinal axis of the insertion tube  22 . Based on the above assumptions (a)-(c), and the computed positions of the couplers based on the computed positions of the magnetic sensors  50 A,  50 B, the bow of each of the flexible strips  55  may be computed using a third-degree polynomial. In some embodiments, the bow of the flexible strips  55  and/or the positions of the electrodes  48  (or other features) on the flexible strips  55  with respect to a fixed point on the catheter  40  (such as the distal tip of the insertion tube  22 ) may be computed based on the computed distance and orientation between the magnetic sensors  50 A,  50 B and a model of the catheter  40  which provides the bow of the flexible strips  55  and/or the positions of the electrodes  48  for the computed distance based on the mechanical properties and dimensions of the flexible strips  55 . 
     A method of position and/or direction sensing using external magnetic fields and magnetic coil sensors, such as sensors  50 A and  50 B, 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. 
     In some embodiments, the processing circuitry  41  uses position-signals received from the electrodes  48  or body surface electrodes  49 , and the magnetic sensor  50  to estimate a position of the assembly  35  inside a body part, such as inside a cardiac chamber. In some embodiments, the processing circuitry  41  correlates the position signals received from the electrodes  48 ,  49  with previously acquired magnetic location-calibrated position signals, to estimate the position of the assembly  35  inside the body part. The position coordinates of the electrodes  48  may be determined by the processing circuitry  41  based on, among other inputs, measured impedances, voltages or on proportions of currents distribution, between the electrodes  48  and the body surface electrodes  49 . 
     The method of position sensing using current distribution measurements and/or external magnetic fields is implemented in various medical applications, for example, in the Carto® system, produced by Biosense Webster Inc. (Irvine, Calif.), 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, 6,332,089, 7,756,576, 7,869,865, and 7,848,787, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1. 
     The Carto® 3 system applies Active Current Location (ACL) which is a hybrid current-distribution and magnetic-based position-tracking technology. In some embodiments, using ACL, the processing circuitry  41  estimates the positions of the electrodes  48 . In some embodiments, the signals received from the electrodes  48 ,  49  are correlated with a current-to-position matrix (CPM) which maps current distribution ratios (or another electrical value) with a position that was previously acquired from magnetic location-calibrated position signals. The current distribution ratios are based on measurements of the body surface electrodes  49  of current flowing from the electrodes  48  to the body surface electrodes  49 . 
     In some embodiments, to visualize catheters which do not include a magnetic sensor, the processing circuitry  41  may apply an electrical signal-based method, referred to as Independent Current Location (ICL) technology. In ICL, the processing circuitry  41  calculates a local scaling factor for each voxel of the volume in which catheters are visualized. The factor is determined using a catheter with multiple electrodes having a known spatial relationship, such as a lasso-shaped catheter. However, although yielding accurate local scaling (e.g., over several millimeters), ICL is less accurate when applied to a volume of a whole heart chamber, whose size is in the order of centimeters. The ICL method, in which positions are calculated based on current distribution proportions can have errors and may yield a distorted shape of the assembly  35 , due to the non-linear nature of the current-based ICL space. In some embodiments, the processing circuitry  41  may apply the disclosed ICL method to scale ICL space and the assembly  35  shape into a correct one, based on known smaller scale distances between electrodes of a lasso-shaped catheter, for example, as well as based on larger scale distances, themselves based on the known distance between the electrodes  48  at the ends of the assembly  35 . 
     Processing circuitry  41 , typically part of a general-purpose computer, is further connected via a suitable front end and interface circuits  44 , to receive signals from body surface-electrodes  49 . Processing circuitry  41  is connected to surface-electrodes  49  by wires running through a cable  39  to the chest of patient  28 . The catheter  40  includes a connector  47  disposed at the proximal end  29  of the insertion tube  22  for coupling to the processing circuitry  41 . 
     In some embodiments, processing circuitry  41  renders to a display  27 , a representation  31  of at least a part of the catheter  40  and a body-part, (e.g., from a mapping process or from a scan (e.g., CT or MRI) of the body-part previously registered with the system  20 ), responsively to computed position coordinates of the insertion tube  22  and the flexible strips  55 . 
     Processing circuitry  41  is typically programmed in software 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. The system  20  may also include a memory  51  used by the processing circuitry  41 . 
     The example illustration shown in  FIG.  1    is chosen purely for the sake of conceptual clarity.  FIG.  1    shows only elements related to the disclosed techniques for the sake of simplicity and clarity. System  20  typically comprises additional modules and elements that are not directly related to the disclosed techniques, and thus are intentionally omitted from  FIG.  1    and from the corresponding description. The elements of system  20  and the methods described herein may be further applied, for example, to control an ablation of tissue of heart  26 . 
     Reference is now made to  FIG.  2   , which is a flowchart  100  including steps in a method of operation of the system  20  of  FIG.  1   . Reference is also made to  FIG.  1   . 
     The processing circuitry  41  is configured to receive respective signals from the catheter  40  captured by respective ones of the electrodes  48  (block  102 ). The processing circuitry  41  is configured to assess conformity of each of the respective signals to at least one signal characteristic for a given time period (block  104 ). The signal characteristic for a given time period may be a predetermined signal characteristic that is used for comparative purposes with the signals recorded by the electrodes. 
     The “given time period” may include a complete cardiac cycle, multiple cardiac cycles, a predefined time interval within a cardiac cycle, any time intervals that may include any portion of the P-wave, QRS complex or T-wave in one cardiac cycle or from one cardiac cycle to subsequent cardiac cycles. The given time period may be any suitable length. In some embodiments, the given time period is equal to a window of interest in current or most recent cardiac cycle. In other embodiments, the given time period is equal to multiple windows of interest of respective most recent cardiac cycles and therefore an indication (described in more detail below) is provided after several successive cardiac cycles of detecting non-conformity with the signal characteristics. 
     The signals (collected by the electrodes) for a given time period may also be referred to as signal segments for the given time period. The “signal characteristics” for classifying a collected or recorded signal segment (for a given time period) as a valid mapping signal may include a signal having a single activation early enough in the cardiac cycle. The term “single activation” is defined herein as a single peak below a given threshold. With regards to the given threshold for identifying peaks in the recorded signals or signal segments, the threshold may be set to any suitable level, for example, approximately 10 micro-Volts. Signal segments with late activation, double activation, multiple activation, or unclear activations may be excluded as not conforming with the signal characteristics. In some embodiments, peaks of the recorded signals or signal segments above a given threshold are considered as possible activations (i.e., signals considered to be in conformity for step  104 ), whereas peaks of the recorded signals or signal segments below the given threshold are not considered as possible activations (i.e., not conforming as in step  106 ) for determining how many activations a signal segment has in the window of interest and how late the activations are in the window of interest. The activation time of the measured or recorded signals may be defined by the steepest negative slope of a candidate peak or any other suitable criteria of the recorded signals or signal segments. The definition of “early enough” in the cardiac cycle, the window of interest, and the given threshold for identifying peaks may be implementation specific and/or physician defined. In some embodiments, the physician defines the “window of interest”. For example, in atrial procedures, the “window of interest” may be defined by setting limits around the P wave, which may be identified based on the R peak of the QRS complex. The definition of late activation may be dependent on the region on the map. In some embodiments, “late” may be considered to be about 10 milliseconds later than all the points surrounding the specific map region under consideration. With regards to the given threshold for identifying peaks in the recorded signals or signal segments, the threshold may be set to any suitable level, for example, approximately 10 micro-Volts. 
     The processing circuitry  41  is configured to find a given one of the signals (e.g., signal segment) of a given one of the electrodes  48  not conforming to the signal characteristic(s) for the given (current or most recent) time period (block  106 ). It may happen that more than one of the recorded signals of more than one corresponding electrode  48  may not conform to the pre-defined signal characteristic(s) for the given time period. The processing circuitry  41  is configured to save the given signal (which may be non-conforming or non-standard) to the memory  51  for future rendering to the display  27  (block  108 ). 
     Reference is now made to  FIG.  3   , which is a schematic view of a representation  53  of the catheter  40  in an anatomical map  57  with an indication  59  that least one of the electrodes  48  is capturing (or captured) a non-standard signal rendered in the system  20  of  FIG.  1   . Reference is also made to  FIG.  2   . 
     The processing circuitry  41  is configured to render to the display  27  the indication  59  that the given signal of the given electrode  48  does not conform to the signal characteristic(s) for the given time period (block  110 ). The indication  59  may include rendering the identification (e.g., electrode number(s) and/or letter(s)) of the given electrode  48  on the display  27  with an optional explanation that the given electrode  48  captured a non-conforming signal (not shown in  FIG.  3   ). 
     In some embodiments, the processing circuitry  41  is configured to render to the display  27  the representation  53  of the catheter  40  with the indication  59  that the given signal of the given electrode  48  does not conform to the signal characteristic(s) for the given time period, wherein the indication  59  is linked to the given electrode  48  on the representation  53  of the catheter  40 , for example, by pointing to the given electrode with an arrow (not shown in  FIG.  3   ). 
     In some embodiments, the processing circuitry  41  is configured to render to the display  27  the representation  53  of the catheter  40  with the indication  59  that the given signal of the given electrode  48  does not conform to the signal characteristic(s) for the given time period, wherein the indication  59  is disposed on the given electrode  48  on the representation  53  of the catheter  40  as shown in  FIG.  3   . The indication  59  may be any suitable color and/or shading and/or pattern and/or a border around the given electrode on the representation  53 . 
     In some embodiments, the indication  59  is rendered until a request is received from the physician  30  to remove the indication  59 . In other embodiments, the processing circuitry  41  is configured to render to the display  27  the indication  59  disposed on the given electrode  48  on the representation  53  of the catheter  40  for a given time interval (for example, equal to a duration about the length of the given time period). The processing circuitry  41  is configured to remove the indication  59  from the given electrode  48  on the representation  53  of the catheter  40  (after expiration of the given time interval). The steps of blocks  102 - 110  are repeated for a subsequent time period, which may lead to the processing circuitry  41  repeating rendering to the display  27  the indication  59  disposed on the given electrode  48  on the representation  53  of the catheter  40  responsively to finding that the given signal of the given electrode  48  does not conform to the signal characteristic(s) for the subsequent time period. The steps of blocks  102 - 112  are repeated for more time periods and different electrodes may be found to be capturing signal segments not conforming to the signal characteristic(s). 
     In some embodiments, the processing circuitry  41  is configured to render to the display  27  the indication  59  disposed on the given electrode  48  on the representation  53  of the catheter  40  so that the indication  59  repeatedly flashes on and off responsively to multiple detections of the given signal of the given electrode  48  not conforming to the signal characteristic(s) for respective subsequent time periods. In some embodiments, the respective subsequent time periods correspond to respective windows of interest of respective cardiac cycles (i.e., each subsequent time period corresponds to a window of interest in a cardiac cycle). In this manner, the physician  30  may observe the flashing on and off of the indication  59 , and if the flashing continues long enough (as determined by the physician  30 ), the physician  30  may realize that the signal being captured by the given electrode  48  is not just capturing an occasional noisy signal but is probably capturing a complex signal that should be displayed and examined in more detail. 
     Reference is now made to  FIG.  4   , which is a schematic view of the representation  53  of the catheter  40  of  FIG.  3    with an electrogram  61 . Reference is also made to  FIG.  2   . In response to seeing the indication  59  (e.g., the indication  59  flashing on and off), the physician  30  may request the electrogram  61  to be displayed. The processing circuitry  41  is configured to receive a user input (from the physician  30 ) requesting display of the electrogram  61  captured by the given electrode  48  (block  114 ). The processing circuitry  41  is configured to render to the display  27  the electrogram  61  captured by the given electrode (block  116 ). 
     As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part 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 72% to 108%. 
     Various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable sub-combination. 
     The embodiments described above are cited by way of example, and the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.