Abstract:
Cardiac catheterization is carried out by constructing a left atrial model of a heart of a living subject, selecting a global catheter that is dimensioned to conform to the left atrial model, representing the catheter in the left atrial model; extending the length axis of the catheter in the left atrial model to form an intersection with the foramen ovale, and reporting the intersection as a recommended site of transseptal puncture for insertion of the catheter therethrough.

Description:
COPYRIGHT NOTICE 
       [0001]    A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to cardiac physiology. More particularly, this invention relates to the evaluation of electrical propagation in the heart. 
         [0004]    2. Description of the Related Art 
         [0005]    Cardiac arrhythmias such as atrial fibrillation are an important cause of morbidity and death. Commonly assigned U.S. Pat. No. 5,546,951, and U.S. Pat. No. 6,690,963, both issued to Ben Haim and PCT application WO 96/05768, all of which are incorporated herein by reference, disclose methods for sensing an electrical property of heart tissue, for example, local activation time, as a function of the precise location within the heart. Data are acquired with one or more catheters having electrical and location sensors in their distal tips, which are advanced into the heart. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. Pat. No. 6,226,542, and U.S. Pat. No. 6,301,496, both issued to Reisfeld, which are incorporated herein by reference. As indicated in these patents, location and electrical activity is typically initially measured on about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface. The preliminary map is often combined with data taken at additional points in order to generate a more comprehensive map of the heart&#39;s electrical activity. Indeed, in clinical settings, it is not uncommon to accumulate data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity. The generated detailed map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart&#39;s electrical activity and to restore normal heart rhythm. 
         [0006]    Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096, issued to Ben Haim, which is incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart. 
         [0007]    Electrical activity at a point in the heart is typically measured by advancing a multiple-electrode catheter to measure electrical activity at multiple points in the heart chamber simultaneously. A record derived from time varying electrical potentials as measured by one or more electrodes is known as an electrogram. Electrograms may be measured by unipolar or bipolar leads, and are used, e.g., to determine onset of electrical propagation at a point, known as local activation time. 
         [0008]    When evaluating the left atrium, catheters, such as basket catheters may be introduced percutaneously via transseptal puncture. The document  Consideration Regarding the Technique for Transseptal Left Heart Catheterization , J. Ross. Circulation 10/1966; 34(3):391-9 points out a number of difficulties with this procedure, caused, for example, by lack of tactile appreciation of the movement of the catheter tip. As a result, the structures engaged by the catheter tip are not recognized, and the degree of pressure exerted against them is uncontrolled. For example, undesired contact of the needle with the posterior wall of the left atrium could occur. Moreover, the optimum site for puncture of the septum is influenced by such considerations as right or left atrial enlargement. 
       SUMMARY OF THE INVENTION 
       [0009]    One method of mapping the left atrium is based on a global mapping catheter, typically in the form of a multi-electrode basket catheter, which is introduced into the left atrium by puncture of the interatrial septum, usually through the fossa ovalis. Basket catheters are relatively large in comparison to the left atrium and do not fit the human left atrium well. Consequently, mapping quality is impaired. These catheters have little to no deflection capabilities. The location of the puncture constitutes an anchoring point, which is a constraint, making it difficult or even impossible to manipulate a basket catheter into good contact with target regions of the atrium, particularly if the location of transseptal puncture is suboptimal. 
         [0010]    Disclosed embodiments of the invention optimize the transeptal location of a global catheter in order to maximize the reach of a mapping catheter within the left atrium and the contact of the catheter with the left atrial wall. 
         [0011]    There is provided according to embodiments of the invention a method, which is carried out by constructing a left atrial model of a heart of a living subject, selecting a global catheter that is dimensioned to conform to the left atrial model, representing the catheter in the left atrial model; extending the length axis of the catheter in the left atrial model to form an intersection with the foramen ovale, and reporting the intersection as a recommended site of transseptal puncture for insertion of the catheter therethrough. 
         [0012]    According to an aspect of the method, constructing a left atrial model includes forming a 3-dimensional bounding box centered on a point of the left atrial model that corresponds to a center of mass of the left atrium, and selecting a global catheter includes referencing a database of global catheters to identify a selected catheter that conforms to the bounding box according to predefined box-conforming criteria. 
         [0013]    According to another aspect of the method, representing the catheter in the left atrial model includes transforming the catheter into an ellipsoid and selecting a global catheter also includes determining that the ellipsoid approximates the bounding box according to the predefined box-conforming criteria. 
         [0014]    According to still another aspect of the method, the predefined box-conforming criteria comprise a deviation of the major semi axis of the ellipsoid from the length dimension of the bounding box that is within a first range. 
         [0015]    According to an additional aspect of the method, the predefined box-conforming criteria comp rise a deviation of a sum of the two minor semi-axes of the ellipsoid from a sum of the height dimension and the width dimension of the bounding box that is within a second range. 
         [0016]    According to yet another aspect of the method extending the length axis of the catheter is performed by extending the major semi axis of the ellipsoid, and prior to extending the major semi axis of the ellipsoid performing a surface registration of the ellipsoid and the bounding box by adjusting the semi axes of the ellipsoid relative to the length dimension, the width dimension and the height dimension of the bounding box. 
         [0017]    According to another aspect of the method, adjusting the semi axes of the ellipsoid includes minimizing a root-mean-square deviation between the surface of the ellipsoid and the borders of the bounding box. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0018]    For a better understanding of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 
           [0019]      FIG. 1  is a pictorial illustration of a system for performing catheterization of a heart of a living subject in accordance with an embodiment of the invention; 
           [0020]      FIG. 2  is a flow chart of a method of optimizing contact between a cardiac probe or catheter with the interatrial septum, in accordance with an embodiment of the invention; 
           [0021]      FIG. 3  is a reconstructed image of a left atrium in accordance with an embodiment of the invention; 
           [0022]      FIG. 4  is a diagram illustrating an ellipsoid as a transformation of a global catheter; 
           [0023]      FIG. 5  is a composite diagram including a cut-away view of the heart and an atrial reconstruction in accordance with an embodiment of the invention; and 
           [0024]      FIG. 6  is a flow chart of a method for identifying a catheter that best matches the left atrial anatomy of a subject in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily needed for practicing the present invention. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily. 
         [0026]    Documents incorporated by reference herein are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
         [0027]    Turning now to the drawings, reference is initially made to  FIG. 1 , which is a pictorial illustration of a system  10  for performing medical procedures on a heart  12  of a living subject, which is constructed and operative in accordance with a disclosed embodiment of the invention. The system comprises a catheter  14 , which is percutaneously inserted by an operator  16  through the patient&#39;s vascular system into a chamber or vascular structure of the heart  12 . The operator  16 , who is typically a physician, brings the catheter&#39;s distal tip  18  into contact with the heart wall, for example, at a selected region of atrial septum  13  in preparation for septal puncture. When the catheter is in an operative position, electrical activation maps may be prepared, according to the methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Pat. No. 6,892,091, whose disclosures are herein incorporated by reference One commercial product embodying elements of the system  10  is available as the CARTO® 3 System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif. 91765. This system may be modified by those skilled in the art to embody the principles of the invention described herein. 
         [0028]    The catheter  14  typically comprises a handle  20 , having suitable controls on the handle to enable the operator  16  to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator  16 , the distal portion of the catheter  14  contains position sensors (not shown) that provide signals to a processor  22 , which can be located in a console  24 . The processor  22  may fulfill several processing functions as described below. Alternatively, the catheter  14  may be provided with collectors of electrical information, and circuitry in the console  24  may be accept and process the information. The EnSite™ system used with NavX surface electrode patches is an example. Indeed, the principles of the invention apply to many systems and methods that support navigation of a catheter into the left atrium via the interatrial septum. 
         [0029]    Wire connections  35  link the console  24  with body surface electrodes  30  and other components of a positioning sub-system for measuring location and orientation coordinates of the catheter  14 . The processor  22 , or another processor (not shown) may be an element of the positioning subsystem. Electrodes  32  and the body surface electrodes  30  may be used to measure tissue impedance at the ablation site as taught in U.S. Pat. No. 7,536,218, issued to Govari et al., which is herein incorporated by reference. A temperature sensor (not shown), typically a thermocouple or thermistor, may be mounted on or near each of the electrodes  32 . 
         [0030]    The console  24  typically contains one or more ablation power generators  25 . The catheter  14  may be adapted to conduct ablative energy to the heart using any known ablation technique, e.g., radiofrequency energy, ultrasound energy, and laser-produced light energy. Such methods are disclosed in commonly assigned U.S. Pat. Nos. 6,814,733, 6,997,924, and 7,156,816, which are herein incorporated by reference. 
         [0031]    In one embodiment, the positioning subsystem comprises a magnetic position tracking arrangement that determines the position and orientation of the catheter  14  by generating magnetic fields in a predefined working volume and sensing these fields at the catheter in magnetic sensors (not shown), using field generating coils  28 . The positioning subsystem U.S. Pat. No. 7,756,576, which is hereby incorporated by reference, and in the above-noted U.S. Pat. No. 7,536,218. 
         [0032]    As noted above, the catheter  14  is coupled to the console  24 , which enables the operator  16  to observe and regulate the functions of the catheter  14 . Console  24  includes a processor, preferably a computer with appropriate signal processing circuits. The processor is coupled to drive a monitor  29 . The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter  14 , including signals generated by the above-noted sensors and a plurality of location sensing electrodes (not shown) located distally in the catheter  14 . The digitized signals are received and used by the console  24  and the positioning system to compute the position and orientation of the catheter  14  and to analyze the electrical signals from the electrodes. 
         [0033]    Typically, the system  10  includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system  10  may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, so as to provide an ECG synchronization signal to the console  24 . As mentioned above, the system  10  typically also includes a reference position sensor, either on an externally-applied reference patch attached to the exterior of the subject&#39;s body, or on an internally-placed catheter, which is inserted into the heart  12  maintained in a fixed position relative to the heart  12 . Conventional pumps and lines for circulating liquids through the catheter  14  for cooling the ablation site are provided. The system  10  may receive image data from an external imaging modality, such as an MRI unit or the like and includes image processors that can be incorporated in or invoked by the processor  22  for generating and displaying images such as electroanatomic maps. 
         [0034]    Reference is now made to  FIG. 2 , which is a flow chart of a method of optimizing contact between a cardiac probe or catheter with the interatrial septum in accordance with an embodiment of the invention. The process steps are shown in a particular linear sequence for clarity of presentation. However, some of them may be able to be performed in parallel, asynchronously, or in different orders. Those skilled in the art will also appreciate that a process could alternatively be represented as a number of interrelated states or events, e.g., in a state diagram. Moreover, not all illustrated process steps may be required to implement the method. 
         [0035]    At initial step  37  a probe is introduced transcutaneously into the right atrium of the heart. Next, at step  39  a model of the left atrium is reconstructed, i.e., geometrically defined in 3-dimensional space. This can be accomplished by analysis of images from other modalities, i.e., segmentation from pre-acquired MRI or fluoroscopy images that have been registered with the atrial model. Registration of images acquired or prepared by different modalities is known, for example from U.S. Patent Application Publication No. 2007/0049817, and commonly assigned U.S. Pat. No. 7,517,318 to Altmann et al., which are herein incorporated by reference. Yet another method of generating the reconstruction is disclosed in commonly assigned copending application Ser. No. 14/313,214, entitled  Model Based Reconstruction of the Heart from Sparse Samples , which is herein incorporated by reference. In this method, the atrium shape is represented as the isosurface of a field function, defined at all points within a bounding domain Other methods of reconstruction are known in the art and may be used, for example the methods disclosed in U.S. Pat. No. 6,226,542 to Reisfeld, and U.S. Patent Application Publication No. 2009/0177089 by Govari et al., which are commonly assigned herewith and incorporated by reference. Alternatively the CARTOMERGE™ module and other facilities of the above-noted CARTO system can accomplish this step. 
         [0036]    Next, at step  41  a bounding box is established for the reconstructed left atrium by calculating the center of mass of the atrium, treating the atrium as an empty shell, excluding the pulmonary veins and defining three orthogonal axes that emanate from it. For example, the x-, y- and z-axes may align respectively with the length, width, and height of the bounding box, i.e., the x-axis aligns with the long axis of the bounding box. The center of the bounding box corresponds to a center of mass of the reconstructed left atrium. Reference is now made to  FIG. 3 , which is a reconstructed image of a left atrium  43 , which was prepared in step  39 , in accordance with an embodiment of the invention. A bounding box  45  has been established and encloses the left atrium  43 . A reference coordinate system  47  is shown at the left of the bounding box  45 . 
         [0037]    Next, at step  49 , A list of known global catheter models, including basket catheters is consulted. The catheter that best matches the bounding box of the left atrium that was produced in step  41  is selected from the list. Matching is done by comparing the lengths of the three axes of the catheter with those of the bounding box. Details of the matching procedure are presented below in the discussion of  FIG. 6 . 
         [0038]    Next, at decision step  51 , it is determined if a portion of the basket catheter selected in step  49 , when placed within the bounding box, would extend beyond the box by more than a predefined distance threshold. Details of this step are described in the discussion of  FIG. 6 . If the determination is affirmative, then it is concluded that a satisfactory catheter could not be obtained from the list of available catheters. The procedure ends in failure at final step  53 . 
         [0039]    If the determination at decision step  51  is negative, then control proceeds to step  55 . The basket catheter selected in step  49  is mapped to an ellipsoid. 
         [0040]    Next, at step  57 , the longest, intermediate, and shortest semi-axes are aligned with the x, y, z axis of the coordinate system  47  ( FIG. 3 ) and with the bounding box  45  produced in step  41 . 
         [0041]    Reference is now made to  FIG. 4 , which is a diagram illustrating an ellipsoid  59  produced by transformation of catheter that was selected in step  49  in accordance with an embodiment of the invention. The ellipsoid  59 , having major semi axis  61 , is in registration with the dimensions of the bounding box  45  and aligned with its length, width and height axes. 
         [0042]    Reverting to  FIG. 2 , step  57  is performed. Step  57  comprises steps  63  and step  65 . At step  63  the image of the atrium generated in step  39  is placed in registration with the ellipioid. This is done by superimposing the center of the ellipsoid with the center of mass of the left atrium and rotating the ellipsoid until the semi-axes of the ellipsoid align with the axes of the bounding box, i.e., the coordinate system  47 . 
         [0043]    In step  65  the axes of the ellipsoid are adjusted so as to minimize the root-mean-square deviation between the surface of the ellipsoid and the bounding box. The CARTOMERGE module of the above-noted CARTO 3 system can be used to perform step  65 . 
         [0044]    Next, at decision step  67 , it is determined if the root-mean-square deviation determined in step  65  exceeds a predefined threshold If the determination is affirmative, then control proceeds to final step  53 , and failure is reported. The operator is advised that a transeptal location cannot be provided. 
         [0045]    If the determination at decision step  67  is negative, then the information developed in the preceding steps is used to calculate the best location for the transeptal puncture. Control proceeds to step  69 . Step  69  can be appreciated by reference to  FIG. 5 , which is a composite, partially schematic diagram including a cut-away view of right atrium  71  and right ventricle  73  and an atrial reconstruction in accordance with an embodiment of the invention. The left portion of  FIG. 5  illustrates the relevant anatomy semi-schematically. Probe  75  has been introduced through inferior vena cava  77  and its distal end approaches fossa ovalis  79 . At the upper right of  FIG. 5  is a diagram in which the ellipsoid  59  is super-imposed on the reconstructed left atrium  43  produced in step  57  ( FIG. 2 ). Major semi axis  61  is extended through fossa ovalis  81  as a broken line  83 . The line  83  also appears on the cutaway view of the right atrium  71 , where it is presented to the operator on monitor  29  ( FIG. 1 ). 
         [0046]    At final step  85 , the intersection of the line  83  with the fossa ovalis  79  is reported as to the operator as a recommended puncture site. 
         [0047]    Reference is now made to  FIG. 6 , which is a flow chart detailing step  49  ( FIG. 2 ), in which a catheter that best suits the left atrial anatomy of a particular subject is selected from a list of catheters in accordance with an embodiment of the invention. The process begins at initial step  87 . The length (L box ) of the bounding box that was generated in step  41  ( FIG. 2 ) is recorded. 
         [0048]    Next, at step  89 . A catheter is selected from a list of available catheters. The length of the selected catheter is known. 
         [0049]    Next, at step  91  the difference between the length of the catheter and the length of the bounding box (L box −L cath ) is stored. 
         [0050]    Only those catheters having lengths that fall within a predetermined range from the length of the bounding box are given further consideration. At decision step  93 , it is determined if the difference obtained in step  91  is greater than a lower limit and less than an upper limit of the range. A suitable range in mm is: 
         [0000]      −3&lt;( S   box −S cath )&lt;+6.
 
         [0051]    If the determination at decision step  93  is affirmative, then control proceeds to step  95 . The current catheter is added to a list of qualified catheters. 
         [0052]    After performing step  95  or if the determination at decision step  93  is negative, control proceeds to decision step  97 , where it is determined if more catheters are available for evaluation. If the determination at decision step  97  is affirmative, then control returns to step  89  to select another catheter. 
         [0053]    If the determination at step  95  is negative, then at decision step  99 , it is determined if the set of qualified catheters is empty, i.e., no qualified catheters were found. If the determination is affirmative, then control proceeds to final step  101  where failure is reported. No catheters matching the particular left atrium were found. However, the user may be able to manually select a suboptimum model in some cases. 
         [0054]    If the determination at decision step  99  is affirmative, then control proceeds to step  103 . The two short dimensions (width (y) and height (z)) of the bounding box are obtained (S box(y)  and S box(z) ). 
         [0055]    Next, at step  105  A catheter is selected from the list of qualified catheters that was compiled in step  95 . Then at step  109  its two minor semi-axes are obtained (S cath(y) ; S cath(z) ). Each axis of the bounding box is evaluated with respect to the corresponding axis of the catheter. 
         [0056]    Next at decision step  111  it is determined if the values S cath(y) −S box(y)  and S cath(z) −S box(z)  are both within an acceptable range in mm. The range can be from −3 mm to +3 mm. 
         [0057]    If the determination at decision step  111  is negative, then control proceeds to step  113 . The current catheter is removed from the list of qualified catheters and eliminated from further consideration. 
         [0058]    If the determination at decision step  111  is affirmative, then at step  114  a value S=(S box(y) −S cath(y) )+(S box(z) −S cath(z) )+(L box −L cath ) is computed for the current catheter. 
         [0059]    After performing step  113  or step  114 , then at decision step  115 , it is determined if more members of the list of qualified catheters remain to be evaluated. If the determination is affirmative, then control returns to step  105 . 
         [0060]    If the determination at decision step  115  is negative, then control proceeds to final step  117 . The catheter most closely approximating the left atrium, i.e., the catheter for which the value S computed in step  114  is closest to zero is reported to the operator. Several next-best matches may optionally be reported. 
         [0061]    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 the present invention includes both combinations and sub-combinations 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.