Abstract:
An esophageal mapping catheter enables a physician to map the location of the esophagus so as to avoid damaging the esophagus during radio frequency (RF) ablation procedures. Information from the esophageal mapping catheter is communicated to a patient information unit, communications unit and/or electroanatomic mapping system. The electroanatomic mapping system uses the information from the esophageal mapping catheter to develop a three-dimensional map of the esophagus and to monitor the temperature within the esophagus in order to prevent the creation of esophageal fistula.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/828,885, filed Oct. 10, 2006, which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device for catheter-based anatomic mapping of the esophagus for use during an electrophysiology ablation procedure. More particularly, the device is placed in the esophagus via the transpharyngeal or transnasal approach to provide esophagus reference location and orientation data during an ablation procedure. 
     BACKGROUND OF THE INVENTION 
     Electrophysiology ablation procedures use energy sources, such as radio frequency (RF) energy, to ablate tissue in order to correct or prevent arrhythmias such as super ventricular tachycardia, paroxysmal atrial tachycardia or atrial fibrillation. Some procedures require the use of the catheter-delivered energy sources near the esophagus resulting in the risk of damage to the esophagus including the creation of esophageal fistula. Due to the proximity of the esophagus to the cardiac atria, it is critical for physicians to know the location of the esophagus during cardiac ablation procedures in the atria in order to minimize the risk of esophageal fistula. 
     Esophageal fistula associated with ablation used to treat atrial fibrillation have resulted in a high incidence of mortality. The need exists for a device or method to reduce or eliminate the risk of esophageal fistula formation by enabling the electrophysiologist to avoid damaging the esophagus with the energy source used for ablation. 
     Electroanatomic mapping systems enable a user to develop detailed electroanatomic maps of the heart providing three-dimensional images of the heart to users. Such systems are used to precisely guide ablation catheters to different areas of interest within a heart and can be used to decrease procedure time and reduce exposure to fluoroscopy. One such electroanatomic mapping system is the Carto system produced by Biosense Webster. Such systems that use a catheter to provide three-dimensional location information are described in U.S. Pat. No. 5,546,951 entitled “Method and Apparatus for Studying Cardiac Arrhythmias”, U.S. Pat. No. 6,368,285 entitled “Method and Apparatus for Mapping a Chamber of A Heart” and U.S. Pat. No. 6,650,927 entitled “Rendering of Diagnostic Imaging Data on a Three-Dimensional Map” which are hereby incorporated by reference. 
     Additionally, U.S. Pat. No. 5,738,096, which disclosure is incorporated herein by reference, describes methods for geometrical mapping of the endocardium based on bringing a probe into contact with multiple locations on a wall of the heart, and determining position coordinates of the probe at each of the locations. The position coordinates are combined to form a map of at least a portion of the heart. Once the position of the catheter is known, external sensors can be used to provide local physiological values of heart tissue adjacent to the tip of the catheter. 
     Further methods for creating a three-dimensional map of the heart based on these data are disclosed, for example, in U.S. Pat. No. 6,226,542, which is assigned to the assignee of the present patent application, and whose disclosure is incorporated herein by reference. Position coordinates (and optionally electrical activity, as well) are initially measured at about 10 to 20 points on the interior surface of the heart. These data points are generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is preferably combined with data taken at additional points in order to generate a more comprehensive map. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to a catheter-based solution to the above-described problem that provides the user the ability to record and display the location of the esophagus on an electroanatomic mapping system such as the Biosense Webster CARTO™ System. Esophagus location information will enable the user to perform RF ablations in the left atrium such that the esophagus is not in close proximity to the ablation sites, reducing the risk of energy delivery close to the esophagus, thus reducing the risk of esophageal fistula formation. 
     The esophageal mapping catheter of the current invention includes a flexible, tubular device with a location sensor and thermocouples located in the device tip. The device is introduced into the esophagus via the throat or nasal passage and is aligned behind the heart using fluoroscopic guidance. Prior to performing left atrial (LA) ablations, the physician records location data points within the esophagus by advancing and withdrawing the device within the esophagus while recording catheter location information from the location sensor, tagging location points. The points serve to record device tip position within the esophagus, in turn recording the relative position of the esophagus with respect to the left atrium on the electroanatomic map. Esophagus points displayed on the electroanatomic map enable the physician to direct RF energy delivery away from the esophagus reducing the risk of esophageal fistula formation. 
     In addition, the device can be placed within the esophagus, behind the left atrium, during RF energy delivery to measure esophagus temperatures. Esophagus temperature changes during ablation may provide the user feedback during the ablation to prevent thermal damage to the esophagus. 
     The catheter placement in the esophagus can be guided using x-ray to insure that the radiopaque catheter aligns along the posterior wall of the left atrium. The device may be coated with a lubricious material to facilitate easy introduction into and manipulation within the esophagus. 
     The present invention is a flexible device, suitable for introduction into the esophagus that is instrumented to allow for recording of esophagus position with respect to the ablation site during an electrophysiology ablation procedure. Esophagus position information enables user to direct ablation away from the esophagus reducing risk of esophageal fistula formation. Temperature information may allow the user to control power delivery during ablation to prevent thermal damage to the esophagus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram depicting the placement of an esophageal mapping catheter in accordance with the present invention in connection with an electroanatomic mapping system. 
         FIG. 2  is an elevational view of an embodiment of an esophageal mapping catheter in accordance with the present invention. 
         FIG. 3  is an elevational view of the distal portion of the esophageal mapping catheter of  FIG. 2  in accordance with the present invention. 
         FIG. 4  is a longitudinal sectional view of the esophageal mapping catheter of  FIG. 2  in accordance with the present invention. 
         FIG. 5  is a longitudinal sectional view of the transition between the catheter shaft and the handle of the esophageal mapping catheter of  FIG. 2  in accordance with the present invention. 
         FIG. 6  is a longitudinal sectional view of the distal end of the esophageal mapping catheter of  FIG. 2  in accordance with the present invention. 
         FIG. 7  is a cross-sectional view of the esophageal mapping catheter of  FIG. 2  through line B-B. 
         FIG. 8  is a cross-sectional view of the esophageal mapping catheter of  FIG. 2  through line C-C. 
         FIG. 9  is a cross-sectional view of the esophageal mapping catheter of  FIG. 2  through line D-D. 
         FIG. 10  is a diagram depicting the elements of the location sensor used in an esophageal mapping catheter in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a diagram depicting the placement of an esophageal mapping catheter  100  in the esophagus near the left atrium of the heart of a patient. Esophageal mapping catheter  100  is electrically connected to the patient interface unit (PIU)  200  in communication with the communications (COM) unit  210  which is further in communication with the electroanatomic mapping system  220 . Electrical signals from the esophageal mapping catheter  100  are thereby received and operated upon by the electroanatomic mapping system  220  as described below. 
     The close anatomical relationship of the posterior wall of the left atrium of the heart and the thermosensitive esophagus, creates a potential hazard in catheter ablation procedures. Esophageal mapping catheter  100  is introduced through the patient&#39;s nose or throat into the esophagus. Once in the desired position, the device&#39;s location sensor is used to “tag” the 3-D position of the esophagus lumen, using the location software executed in the hardware system that is part of the electroanatomic mapping system  220 , as the device is slowly pulled towards the initial entry port. 
     Referring to  FIGS. 2-3 , the esophageal mapping catheter  100  comprises a shaft  105  which is preferably a radiopaque Pellethane tube having a usable length  106  of approximately 125 centimeters sealed by an atraumatic tip made of a polyurethane (PU) dome  124  protecting the location sensor  120  at the distal end and closed by a handle  110  at the proximal end. The catheter materials are of sufficient stiffness to enable placement but are not so stiff as to cause mechanical damage to the tissues contacted during introduction and use. Although Pellethane is the preferable material for shaft  105  other materials may be used such as Silicone or other Polyurethane compounds compatible with the esophagus environment. The catheter  100  is sufficiently radiopaque to be uniquely identifiably under fluoroscopic visualization. Numerical distance markers  130  on the shaft  105  mark the distance in centimeters from the distal end of the catheter starting at 5 centimeters and increasing by 5 centimeters until approximately 120 centimeters at the proximal end. These markers assist the physician in determining if the esophageal mapping catheter  100  is in the desired position inside the esophagus of the patient. The catheter  100  is manufactured from materials compatible with the environment of the esophagus. The shaft  105  of the catheter is generally non-deflectable. The shaft  105  should be of sufficient reach length to achieve catheter tip positioning in the esophagus below the level of the heart. 
     Located at the proximal end of the catheter is a handle  110  with electrical connector  115  that connects to the PIU  200  via an interface cable (not shown). The hollow handle or handle housing  110  houses the printed circuit board (PCB) and associated microprocessor for storing and pre-processing the data collected from the location sensor  120 . The interface cable is a standard cable terminated on both ends with multi-pin connectors such as that used with the Biosense Navistar® catheter. The interface cable connects to the PIU  200  of the electroanatomic mapping system enabling the user to record catheter tip location/orientation within the esophagus. 
       FIG. 3  depicts the distal portion  109  of catheter  100  which shows the numerical markers  130  and line makers  132  of shaft  105  in more detail. Line markers begin approximately 10 millimeters from the polyurethane dome  124  and are spaced at approximately every 10 millimeters (distance X) proximally from the distal end. Near the proximal end of the catheter  100  adjacent the distal end of handle  110  shaft  105  is covered by sleeves  107  and  108  which are heat shrink materials used to provide a transition between shaft  105  and intended to keep fluids from the interior of handle  110 . Sleeves  107  and  108  are preferably made from Polyolefin, but may also be any flexible plastic that serves as a strain relief. 
       FIGS. 4-6  are longitudinal sectional view of the catheter  100  with the PCB subassembly  150  substantially surrounded by MU shield assembly  155 . Electrical conductors  142  are connected (using solder, brazing or other electrical connection  151 ) to the circuitry on PCB subassembly  150 . PCB subassembly  150  comprises the circuitry necessary to convert the electrical signals to from location sensor  120  from the analog format to a digital format and to generate a data format compatible with the format expected by the COM unit  210  as the data is sent to the anatomical mapping system  220 . Electrical conductors  142  run through the central lumen  135  of shaft  105  and are connected at their distal end to location sensor  120 . 
     As can bee seen in  FIG. 5  which is a close-up of transition region  140 , at the transition between shaft  105  and handle housing  110  transition sleeves  107  and  108  are sealed at the interface to the handle housing with a layer of polyurethane glue  114  which may be similar to the polyurethane used at distal tip  124 . Sleeve  107  is approximately 2.0 inches in length and sleeve  108  is approximately 2.5 inches in length. Other sleeve arrangements may be used or alternatively shaft  105  could terminate within handle housing  110  and could be affixed within the handle housing with a polyurethane or other type of glue without using intermediary sleeves  107  and  108 . 
       FIG. 6  is a close-up of the distal tip portion  109   b  of the catheter  100  of  FIG. 4 . Shaft  105  has a central lumen  135  in which electrical conductors  142  reside. Electrical conductors  142  are connected at their distal end to location sensor  120 . Location sensor  120  is housed within a nylon zytel tube  122  which is held in place within shaft  105  by a layer of polyurethane glue  126  or other type of glue or cement. Location sensor  120  is held in place within tube  122  by a circumferential layer of polyurethane  123  which is capped by PU dome  124 . PU dome  124  is approximately 0.10 to 0.12 inch in diameter at its widest portion (W) and is approximately 0.05 to 0.07 inches in length (L). 
       FIG. 7  depicts the cross-sectional view of the esophageal mapping catheter in accordance with the present invention through line B-B of  FIG. 2 . Layers of polyurethane  114  can be used between sleeves  107  and  108  and shaft  105  in addition to the layer at the interface between the housing  110  and sleeve  107 . 
       FIG. 8  depicts the cross-sectional view of the esophageal mapping catheter of  FIG. 2  through line C-C in the shaft region and shows the continuation of electrical conductors  142  through central lumen  135  of shaft  105 . 
       FIG. 9  cross-sectional view of the esophageal mapping catheter of  FIG. 2  through line D-D in the distal tip of the device. Position tracking is provided by a location sensor  120  that is located at the distal tip of the esophageal mapping catheter  100  and an external magnetic field (not shown). The location sensor  120  provides catheter tip location (x, y, z co-ordinates) as well as orientation (pitch, roll and yaw) information that is processed and displayed by the electroanatomic mapping system  220 . 
     One embodiment of the esophageal mapping catheter  100  is 8 F in diameter with a usable length  106  of 125 cm although other diameters and lengths could be made. The catheter has a flexible polyurethane shaft  106  with an atraumatic tip section  124 . Esophageal mapping catheter  100  has a magnetic location sensor  120  embedded in the distal tip that provides information to an electroanatomic mapping system such as the C ARTO ™ EP Navigation System and a R EF S TAR ™ with Q WIK P ATCH ™ External Reference Patch, which provides location information to construct a 3D electroanatomical map of the esophagus in real-time. The location sensor  120  provides catheter tip location (x, y, z co-ordinates) as well as orientation (pitch, roll and yaw) information that is processed and displayed by the electroanamtomic mapping system. 
     The esophageal mapping catheter  100  is used in conjunction with a navigational catheter, such as the N AVI S TAR ® Mapping and Ablation Catheter, to provide supplemental information for maps created with the navigational catheter and the electroanatomical mapping system. The esophageal mapping catheter  100  is intended to create esophageal reference points on the electroanatomical map in addition to the cardiac reference points created by the navigation catheter. 
     Referring to  FIG. 10 , the location sensor  120  for the esophageal mapping catheter  100  is similar or identical to the location sensors for known navigational catheters such as the N AVI S TAR ® navigational catheter. The sensor consists of three orthogonal miniature coils  310 ,  320  and  330  made from 10 μm copper wire wound around ferrite beads. Coil  310  provides information with respect to the x axis. Coil  320  provides information with respect to the y axis and coil  330  provides information with respect to the z axis. The ferrite beads serve to increase the location signal sensitivity in the coils of the sensor before reaching the pre-amplifier located on the PCB in the catheter handle  110 . The coils  310 ,  320  and  330  are connected via electrical conductors  142  to the circuitry in handle  110 . The coils comprising the sensor are contained within an epoxy/amide housing  125 . It is embedded in the distal ends of the esophageal mapping catheter  100 . 
     To account for patient movement, the location of the mapping catheter is referenced by the electroanatomical mapping system relative to the location of an external reference patch placed on the patient&#39;s back. The external reference patch has the same location sensor technology as the mapping catheter. The location information displayed on the screen of the electroanatomical mapping system is the location of the mapping sensor in space with the control for inappropriate movement of the mapping catheter relative to the location of the reference sensor. 
     Two mapping algorithms are used in the electroanatomical mapping system to convert the data received from the esophageal mapping catheter  100  and the reference patch into a 3D map include a triangulation algorithm for location and a reconstruction algorithm to create the 3-D map. 
     The underlying principle for the location algorithm is the same as the Global Positioning Systems (GPS) developed by the U.S. military and which is now in widespread commercial use for a variety of navigation functions. For example, an airplane can deduce its position by knowing the distance to three satellites, while the electroanatomical mapping system can deduce the position of the mapping catheter by knowing the distance to the three coils in the location pad. Each coil within the location sensor detects the intensity of the magnetic fields generated by each of the three location pad coils, allowing the determination of the distance. These distances determine the radii of theoretical spheres around each location pad coil. This information is used to determine three spatial coordinates (X, Y and Z) and three orientation parameters (roll, yaw and pitch). The electroanatomic mapping system then provides a visual display of the location of the sensors in space. 
     The electroanatomical mapping system records a set of points in a random manner. The map is reconstructed using an algorithm that chooses an ellipsoid (the smallest one containing all recorded points) as the initial shape and collapsing it around the fixed recorded points, until all points touch the surface of the reconstruction. 
     The esophageal mapping catheter  100  may also be placed within the esophagus behind the left atrium during an RF ablation procedure to measure the temperature inside the esophagus thereby providing user feedback in order to prevent thermal damage to the esophagus. Thermal information is provided by a thermal sensor co-located with the magnetic location sensor in the distal end of the esophageal mapping catheter  100 . Thermal sensors of any known type may be used. Preferably the thermal sensor is Type T, made from Constantan and Copper wires. 
     A number of alternative 3D location recording technologies may be applicable to this concept e.g. impedance based location mapping. The esophageal mapping catheter  100  may be made so that it is deflectable. Esophageal mapping catheter  100  may be provided without thermocouples or lubricious coating. The esophageal mapping catheter may be provided with a balloon or cage mechanism to center the device in the esophagus. Esophageal mapping catheter  100  may be provided with electrode rings to record electrograms from within the esophagus. 
     In use by the physician or other user, the device is introduced into the esophagus via the throat or nasal passage and is aligned behind the heart using fluoroscopic guidance. Prior to performing left atrial (LA) ablations, the physician records location data points within the esophagus by advancing and withdrawing the device within the esophagus while recording catheter location information from the location sensor, tagging location points. The points serve to record device tip position within the esophagus, in turn recording the relative position of the esophagus with respect to the left atrium on the electroanatomic map. Esophagus points displayed on the electroanatomic map enable the physician to direct RF energy delivery away from the esophagus reducing the risk of esophageal fistula formation. In addition, the device can be placed within the esophagus, behind the left atrium, during RF energy delivery to measure esophagus temperatures. Esophagus temperature changes during ablation may provide the user feedback during the ablation to prevent thermal damage to the esophagus. The catheter placement in the esophagus can be guided using x-ray to insure that the radiopaque catheter aligns along the posterior wall of the left atrium. The device may be coated with a lubricious material such as PTFE or other such material to facilitate easy introduction into and manipulation within the esophagus. A hydrophilic coating may also be used to provide a device surface that eases introduction into the esophagus. Esophagus position information enables user to direct ablation away from the esophagus reducing risk of esophageal fistula formation. Temperature information may allow the user to control power delivery during ablation to prevent thermal damage to the esophagus. 
     For insertion into the esophagus, column strength is needed to avoid buckling or coiling of the device which may lead to an inability to advance the device pass the nasal passage or throat. This device stiffness can be accomplished through insertion of a stylet from an opening in the handle housing  110  through the central lumen  135  of shaft  105  up to near the distal tip. The stylet can be made of any material that is sufficiently stiff to provide pushability, such as stainless steel or other relatively low-cost but non-reactive material. Once in place in the esophagus, the stylet can be removed to return the device to a more flexible state. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. 
     Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.