Patent Publication Number: US-11660051-B2

Title: Esophageal monitoring

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/625,929, filed Jun. 16, 2017, titled ESOPHAGEAL MONITORING (“the &#39;929 Application”), issued as U.S. Pat. No. 11,033,232 on Jun. 15, 2021, which claims the benefit of priority to the Jun. 16, 2016 filing date of U.S. Provisional Patent Application No. 62/350,833, titled ESOPHAGEAL MONITORING (“the &#39;833 Provisional Application”) under 35 U.S.C. § 119(e). The entire disclosures of the &#39;833 Provisional Application and the &#39;929 Application are hereby incorporated herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to esophageal monitoring, as may be conducted while conducting an ablation procedure on the left atrium of a subject&#39;s heart. More specifically, this disclosure relates to esophageal monitoring methods that occur in conjunction with visualization of the esophagus. Even more specifically, a subject&#39;s esophagus may be visualized before and after an ablation procedure has been conducted on the left atrium of the subject&#39;s heart. In addition, this disclosure relates to esophageal monitoring systems and to esophageal monitoring devices. 
     RELATED ART 
     A variety of techniques have been developed in which tissues or organs in a patient&#39;s body are heated or cooled. Tissues may be heated by a variety of techniques, including high frequency ultrasound, radiofrequency (RF) treatments, laser treatments, use of infrared radiation, and by direct application of thermal energy. Cooling is often effected cryogenically. Techniques that heat and cool tissues may be collectively referred to as “thermal techniques.” 
     Thermal techniques are useful for treating a variety of disease states. The degree of heating or cooling that is required to optimize the efficiency of some thermal techniques may adversely affect tissues or organs that are adjacent to a treated tissue or organ. For example, a great deal of heat is generated by radiofrequency (RF) waves when electrophysiological ablation techniques are used to remove faulty electrical pathways from the hearts H of human subjects who are prone to developing cardiac arrhythmias, such as fibrillation in the left atria LA of their hearts H. In addition to heating and treating the diseased tissue in the heart H, the esophagus E, which is located close to the left atrium LA of the heart H, as shown in  FIG.  1   , may also be heated. 
     As  FIG.  1    illustrates, a typical human esophagus E typically has a narrow, or flat, oval cross-sectional shape, taken along a length of the esophagus E, that resembles a pancake, with a large portion of the outer surface of the esophagus E located between the posterior wall of the left atrium LA (i.e., the location where ablation procedures are typically conducted in the left atrium LA) and the vertebral column VC, although the size, shape, and/or position of the esophagus E may vary. In an average human adult, about 70 mm of the length and the majority of the front side of a 18 mm width of esophagus E is located in proximity to or contacts the posterior wall of the left atrium LA. As a consequence of the intimate arrangement between the esophagus E and the left atrium LA, the heat generated during ablation of the left atrium LA may damage the esophagus E and may, in some cases, create an esophageal fistula. Unfortunately, the complications that arise from esophageal fistula may not present themselves until weeks after the left atrial ablation procedure and, in many cases, at too late a time to treat and/or cure the sometimes fatal damage that has been done. 
     In recognition of the potentially dire consequences of overheating the esophagus E during ablation of the left atrium LA, physicians have started using devices that monitor temperature within a subject&#39;s esophagus E during left atrial ablation procedures. If the sensed temperature reaches a predetermined level, the physician may momentarily discontinue the left atrial ablation procedure to allow the esophagus E to cool and, hopefully, to prevent any damage to the esophagus E. 
     The use of temperature probes has been shown to reduce or eliminate the damage, including the formation of one or more fistulas, that could otherwise be incurred by the esophagus E as ablation procedures are being performed on the posterior wall of the left atrium LA of the heart H. Nevertheless, healthcare providers typically do not receive any feedback regarding the usefulness of temperature probes unless complications arise from damage caused to the esophagus E by the left atrial ablation procedure. Again, that damage may not present itself for days or weeks and, by the time it does present itself, it may not be correctable. 
     SUMMARY 
     A method for monitoring an esophagus of a subject, or “esophageal monitoring,” during ablation of the left atrium of the subject&#39;s heart includes visualizing the esophagus after the left atrial ablation procedure, while removing an esophageal monitoring device from the subject&#39;s esophagus. In some embodiments, the esophagus may also be visualized while inserting the esophageal monitoring device into the esophagus. 
     A method for esophageal monitoring according to this disclosure may be performed as part of a procedure for ablating faulty electrical pathways in the posterior wall of the left atrium; i.e., left atrial ablation. In such a method, an esophageal monitoring device may be introduced into a subject&#39;s esophagus prior to ablation of the posterior wall of the left atrium. In some embodiments, the esophagus and its condition prior to the left atrial ablation procedure may be visualized and optionally recorded as the esophageal monitoring device is introduced into the esophagus. With the esophageal monitoring device in place against an inner surface of a portion of the esophagus that is located in proximity to the posterior wall of the left atrium, the posterior wall of the left atrium may be ablated. During left atrial ablation procedure, the esophageal monitoring device is used to monitor the inner surface of the portion of the esophagus against which the esophageal monitoring device has been placed. Once the left atrial ablation procedure is complete, the esophageal monitoring device may be removed from the esophagus. As the esophageal monitoring device is removed from the esophagus, the esophagus and its condition following the left atrial ablation procedure may be visualized and optionally recorded. As used herein, the term “visualize” includes obtaining images (e.g., still images, video images, etc.) of the inner surface of the esophagus and making the images available to a healthcare provider for viewing. Viewing of the images may occur contemporaneously with introduction of the esophageal monitoring device into the esophagus and/or with removal of the esophageal monitoring device from the esophagus. Alternatively, the images may be viewed at a later time (e.g., after completion of the left atrial ablation procedure, etc.). 
     Visualization of the esophagus during insertion of the esophageal monitoring device or during removal of the esophageal monitoring device may be accompanied by position reference monitoring, in which the position of the esophageal monitoring device relative to the esophagus (e.g., a depth the esophageal monitoring device has been inserted into the esophagus, etc.) is periodically determined. Position reference monitoring may include sensing position reference features on an insertion component (e.g., a catheter, another tube, etc.) for the esophageal monitoring device or on the esophageal monitoring device as the position reference features pass one or more fixed locations. More specifically, position reference monitoring may occur as position reference features move past one or more position sensors, which may be located at substantially fixed locations relative to the subject&#39;s esophagus (e.g., at a location outside the subject&#39;s body in embodiments where the position reference features are carried by the insertion component or the esophageal monitoring device, along a length of an insertion component in embodiments where the position reference features are carried by the esophageal monitoring device, etc.). The position reference features may be spaced at various intervals (e.g., 5 mm, 1 cm, etc.) along a length of the insertion component or the esophageal monitoring device (e.g., a proximal element of the esophageal monitoring device, etc.). In embodiments where visualization of the inner surface of the esophagus includes capturing still images of the esophagus, as each position reference feature passes the position sensor, the position sensor or the position reference feature may cause a camera carried by the esophageal monitoring device to capture a still image, synchronizing each image with the depth, or location, of the esophageal monitoring device in the esophagus. In embodiments where visualization of the inner surface of the esophagus comprises capturing video images, the position sensor or the position reference feature may cause a mark (e.g., a depth interval mark, a depth mark, etc.) to be placed on the video image to synchronize the depth, or location, of the esophageal monitoring device in the esophagus with the images shown in the video. In any event, position reference monitoring may enable correlation of the images of the inner surface of the esophagus to their relative positions along the length of the esophagus. 
     In embodiments where visualization of the esophagus occurs while introducing the esophageal monitoring device into the esophagus, the images obtained by such visualization may provide a baseline, or reference, for subsequent comparison. Thus, by comparing the images obtained after the ablation procedure, which may be referred to as “after images,” to the images obtained before the ablation procedure, which may be referred to as “before images,” a healthcare provider (e.g., a physician, a physician&#39;s assistant, etc.) can identify any new trauma to the inner surface of the esophagus during the left atrial ablation procedure, while introducing the esophageal monitoring device into the esophagus, or while removing the esophageal monitoring device from the esophagus. In some embodiments, light may be used to facilitate visualization of the inner surface of the esophagus. So-called “white light” (i.e., a combination of various colors of visible light) may be used to illuminate the dark spaces and surfaces within the esophagus. Various wavelengths of electromagnetic radiation (e.g., ultraviolet radiation, infrared radiation, etc.) may be used to reveal trauma or evidence of trauma (e.g., increased blood flow to a particular location, etc.) before it would otherwise be visible when illuminated with white light. 
     The monitoring that occurs during the left atrial ablation procedure may provide some indication of the danger of the ablation procedure to the esophagus. In some embodiments, temperature may be monitored across the inner surface of the portion of the esophagus located adjacent to the posterior wall of the left atrium. Temperature monitoring may occur at a plurality of locations (e.g., arranged in an area array, etc.) across the area of the inner surface of the portion of the esophagus located adjacent to the posterior wall of the left atrium. Such temperature monitoring may occur in real-time throughout the left atrial ablation procedure (e.g., frequently, continuously, etc.). By monitoring the temperature of the esophagus, a healthcare provider may be able to readily determine whether or not the left atrial ablation procedure is heating the esophagus to a potentially damaging temperature and, thus, inform the healthcare provider when one or more affirmative actions (e.g., temporary termination of ablation, reducing the force of the ablation catheter against the interior surface of the left atrium, movement of the esophagus away from the left atrium, etc.) should be taken to prevent damage to the esophagus. 
     In the event that visualization of the inner surface of the esophagus after a left atrial ablation procedure has been performed on the posterior wall of the left atrium of a subject&#39;s heart reveals that the esophagus has been traumatized or damaged, a healthcare professional may diagnose and treat the damage. Such treatment may be provided immediately following the left atrial ablation procedure or shortly after the left atrial ablation procedure (e.g., within one day of the left atrial ablation procedure, within two days of the left atrial ablation procedure, etc.). In some cases, visualization of the interior surfaces of the esophagus in connection with a left atrial ablation procedure may enable healthcare professionals to treat damage to the esophagus before the subject experiences any adverse symptoms from the left atrial ablation procedure. 
     Another embodiment of monitoring may include monitoring pressure or force across the inner surface of the portion of the esophagus located adjacent to the posterior wall of the left atrium. More specifically, the force of the esophageal monitoring device against the wall of the esophagus may be monitored and/or the force of the esophagus against the esophageal monitoring device may be monitored. Even more specifically, the amount of pressure applied against the esophageal monitoring device by the inner surface of the relevant portion of the esophagus (i.e., the portion of the esophagus in proximity to the left atrium of the heart) may be monitored. Pressure monitoring may occur at a plurality of locations (e.g., arranged in an area array, etc.) across the area of the inner surface of the portion of the esophagus located adjacent to the posterior wall of the left atrium. Such pressure monitoring may occur in real-time, frequently throughout the ablation procedure or continuously throughout the left atrial ablation procedure. Pressure monitoring may also occur before and/or after the ablation procedure). Monitoring the pressure or the force applied by the esophageal wall to the esophageal monitoring device may be used to provide an indication of the potential or actual effects that the application of force by the ablation catheter to the interior surface of the left atrium and/or of the application of force by the esophageal monitoring device against the esophageal wall on the proximity of the esophagus to the left atrium, on the pressure or force between the left atrium and the esophagus (although such pressure or force is indirect as it is applied directly against the pericardium) and, thus, on the potential for damage to the esophagus during the left atrial ablation procedure. As a specific, but non-limiting example, monitoring the pressure or force applied to the esophageal monitoring device by the inner surface of the portion of the esophagus located adjacent to the posterior wall of the left atrium may indicate whether or not the individual performing the left atrial ablation procedure is forcing the posterior wall of the left atrium toward the outer surface of the esophagus and, thus, increasing the likelihood that potentially damaging temperatures (e.g., heat or cold) would be transmitted from the left atrium to the esophagus. 
     A system for monitoring a condition of a subject&#39;s esophagus while an ablation procedure is being performed on the posterior wall of the left atrium of the subject&#39;s heart includes an esophageal monitoring device capable of providing images of an inner surface of the esophagus. More specifically, the esophageal monitoring device may include a proximal element, a monitoring element at a distal end of the proximal element, and a camera (e.g., a CMOS (complementary metal-oxide semiconductor) imager, a CCD (charge-coupled device camera), etc.). Optionally, the esophageal monitoring device may include an insertion component that facilitates insertion of the monitoring element into the esophagus, and that may facilitate withdrawal of the monitoring element from the esophagus. 
     The proximal element of the esophageal monitoring device may comprise an elongated element. The proximal element may carry various features (e.g., proximally located electrical connectors, wires, electrical traces, etc.) that enable the communication of signals between corresponding features at or near a distal end of the esophageal monitoring device (e.g., temperature sensors and/or pressure sensors or force sensors of the monitoring element, the camera, one or more lights (LEDs (light-emitting diodes), etc.), etc., within the subject&#39;s esophagus) and equipment connected to a proximal end of the proximal element (e.g., monitors and other devices outside of the subject&#39;s body). These features may be carried by (e.g., laminated onto, integrally formed with, etc.) a substrate of the proximal element. 
     The monitoring element of the esophageal monitoring device may be located at a distal end of the proximal element. In various embodiments, the monitoring element may have a width or may be capable of assuming an expanded width; i.e., a width that exceeds a width of the proximal element. In some embodiments, the expanded width of the monitoring element may effectively impart the monitoring element with an area that is about the same as or larger than the area of a portion of the esophagus located adjacent to the posterior wall of the left atrium of the heart (e.g., at least about 58 mm by at least about 14 mm, or at least about 812 mm 2 ; about 60 mm by about 15 mm, or about 900 mm 2 ; about 70 mm by about 18 mm, or about 1,260 mm 2 ; about 100 mm by about 20 mm, or about 2,000 mm 2 ; etc.). Sensors may be positioned across an area occupied by the monitoring element. The sensors may include temperature sensors, pressure sensors and/or force sensors, or a combination thereof. In some embodiments, positional markers of the type used in anatomic mapping (e.g., impedance electrodes used in impedance-based anatomical mapping, etc.) may also be positioned across an area occupied by the monitoring element. 
     In a specific embodiment, the monitoring element may include a plurality of branches that may be oriented somewhat parallel to one another, substantially parallel to one another, or parallel to each other. Even more specifically, the monitoring element may include three branches, with a center branch being collinear with, or even an extension of, the proximal element of the esophageal monitoring device. The branches diverge from the proximal element of the esophageal monitoring device at a proximal end of the monitoring element; the separate free ends of the branches are located at a distal end of the monitoring element. 
     The branches of the monitoring element may be capable of being folded, one atop another. For example, the branches may be folded upon one another into a retracted arrangement while the monitoring element resides within the lumen of the insertion component, but unfold as the monitoring element is deployed, or extends, distally beyond the distal end of the insertion component. Conversely, the distal end of the insertion component and a proximal end of the monitoring element may be mutually configured to enable the branches of the monitoring element to fold upon one another as the esophageal monitoring device is pulled proximally and the monitoring element is pulled proximally back into the insertion component. 
     When the monitoring element is in an expanded (e.g., deployed, unfolded, etc.) configuration, it may occupy an area that is about the same as or larger than the area of a portion of the esophagus located adjacent to the posterior wall of the left atrium of the heart (e.g., at least about 58 mm by at least about 14 mm, or at least about 812 mm 2 ; at least about 70 mm by at least about 18 mm, or at least about 1,260 mm 2 ; etc.). In a specific embodiment, the area occupied by the expanded monitoring element may be about 60 mm by about 15 mm, or about 900 mm 2 . In another specific embodiment, the area occupied by the expanded monitoring element may be about 70 mm by about 18 mm, or about 1,260 mm 2 . In yet another specific embodiment, the area occupied by the expanded monitoring element may be about 100 mm by about 20 mm, or about 2,000 mm 2 . 
     The area occupied by the branches of the monitoring element may be substantially two-dimensional. Alternatively, the branches of the monitoring element may be arranged to occupy a three-dimensional space. For example, the branches of the monitoring element may be bent or curved and arranged in a manner that enables them to be placed against an interior surface of a subject&#39;s esophagus without requiring that a remainder of the esophageal monitoring device or the insertion component be forced against an internal surface of the esophagus. As another example, the branches of the monitoring element may be arranged in a manner that approximates a shape or curvature of the interior surface of the esophagus against which they are to be placed. 
     Each branch of the monitoring element carries a plurality of sensors (e.g., temperature sensors, pressure sensors or force sensors, etc.). Optionally, each branch of the monitoring element may also carry one or more positional markers (e.g., impedance electrodes used in impedance-based anatomical mapping, etc., which may be used to three-dimensionally map the location of the monitoring element within the esophagus and relative to the left atrium of the subject&#39;s heart and, when used in conjunction with measurements of the pressure or force exerted on pressure sensors or force sensors of the monitoring element, may be used to map the physical relationship between the left atrium and the esophagus, as well as any changes to that physical relationship (e.g., force of the left atrium against the pericardium, which is then transmitted to the esophagus, etc.)). When the branches are positioned laterally adjacent to one another, the sensors and positional markers, if any, may be positioned across an area occupied by the branches of the monitoring element. With the monitoring element in an expanded configuration, the sensors and positional markers, if any, carried by its branches may be spread over the area occupied by the monitoring element. In some embodiments, the sensors and markers, if any, may be arranged in one or more arrays across the area occupied by the monitoring element. The monitoring element of the esophageal monitoring device may also carry a camera, one or more lights, etc., as described previously herein. 
     In embodiments of the esophageal monitoring device that include an insertion component, the insertion component may comprise a tube, a catheter, or a similar structure. At least a portion of the esophageal monitoring device may be disposed within the insertion component (e.g., a lumen thereof, a channel thereof, etc.) as that portion of the esophageal monitoring device is introduced into a subject&#39;s esophagus. In addition, the insertion component may be configured to enable the esophageal monitoring device to be pushed distally therethrough, enabling a distal portion of the esophageal monitoring device, such as the monitoring element thereof, to be deployed from the distal end of the insertion component. In embodiments where the monitoring element includes three branches, the side branches may be folded over the center branch and over each other. 
     The proximal element and the monitoring element of the esophageal monitoring device may have any suitable construction. In a specific embodiment, the proximal element and the monitoring element of the esophageal monitoring device may comprise a flexible printed circuit board, or “flex PCB” or “flex circuit” that carries conductive traces, or “wires,” contacts, sensors, and other optional components (e.g., a camera, one or more lights, positional markers, etc.). 
     A system for monitoring a condition of a subject&#39;s esophagus during a left atrial ablation procedure may also include an insertion component, such as a catheter or another tube, with a lumen within which at least a portion of the esophageal monitoring device may be disposed as that portion of the esophageal monitoring device is introduced into a subject&#39;s esophagus. The insertion component may be configured to enable a distal portion of the esophageal monitoring device, such as the camera, to protrude therefrom. In addition, the insertion component may be configured to enable the esophageal monitoring device to be pushed distally therethrough, enabling a distal portion of the esophageal monitoring device, such as the monitoring element thereof, to be deployed distally from the distal end of the insertion component. 
     In embodiments where the monitoring element includes branches, the branches may be folded upon one another while the monitoring element resides within the lumen of the insertion component, but unfold as the monitoring element is deployed, or extends, distally beyond the distal end of the insertion component. Conversely, the distal end of the insertion component and a proximal end of the monitoring element may be mutually configured to enable the branches of the monitoring element to fold upon one another as the esophageal monitoring device is pulled proximally and the monitoring element is pulled proximally back into the insertion component. 
     In some embodiments, the camera of the system may be positioned at or adjacent to a distal end of the esophageal monitoring device. More specifically, the camera of the system may be positioned at or adjacent to a distal end of the monitoring element of the esophageal monitoring system. In embodiments where the monitoring element is branched, the camera may be positioned at or adjacent to a distal end of a central branch of the monitoring element. The camera may be capable of capturing hemispherical images of the esophagus (e.g., 120° hemispherical images, 150° hemispherical images, 120° to 150° hemispherical images, up to 180° hemispherical images, 120° to 180° hemispherical images, etc.) or cylindrical images of the esophagus (e.g., a panoramic, or 360°, view, etc.). Thus, some embodiments of the camera may include a hemispherical lens (e.g. a fisheye lens, etc.) or a cylindrical lens (e.g., panoramic lens, etc.). 
     A system according to this disclosure may also include a light source. A light source may illuminate the esophagus while obtaining images of the inner surface of the esophagus with the camera. The light source may emit one or more wavelengths of visible light, including so-called “white light,” and/or one or more wavelengths of electromagnetic radiation (e.g., ultraviolet radiation, infrared radiation, etc.) may be used to reveal trauma or evidence of trauma (e.g., increased blood flow to a particular location, etc.) before it would otherwise be visible when illuminated with white light. 
     A system for monitoring a condition of a subject&#39;s esophagus according to this disclosure may include one or more position sensors. The position sensor(s) may be adapted to be placed at a fixed location relative to a path along which the esophageal monitoring device will be inserted into and removed from the subject&#39;s esophagus (e.g., along a length of an insertion component from which the esophageal monitoring device will be deployed, etc.). As a non-limiting example, a position sensor may be capable of placement adjacent to a subject&#39;s nares or mouth, past which the esophageal monitoring device will pass as the esophageal monitoring device is inserted into or removed from the subject&#39;s esophagus. As the esophageal monitoring device or features thereof (e.g., position reference features detectable by the position sensor(s), etc.) move past the position sensor(s), the position sensor(s) may determine an extent to which (e.g., a distance, etc.) the esophageal monitoring device has been inserted into the subject&#39;s esophagus. Thus, each position sensor may also be used to determine a location of a distal end of the esophageal monitoring device within the esophagus, or a distance the distal end of the esophageal monitoring device has been inserted into the esophagus. From such information, the position sensor(s) may also determine a position of the camera from a top of the esophagus. 
     In embodiments where the system includes one or more position sensors, the esophageal monitoring device may include position reference features. The position reference features may be disposed along a length of a portion of the esophageal monitoring device (e.g., along a proximal element of the esophageal monitoring device, etc.). Alternatively, position reference features may be disposed along the length of an insertion component for the esophageal monitoring device. Adjacent position reference features may be spaced apart from one another at a fixed distance, or interval. In a specific embodiment, adjacent position reference features may be spaced 5 mm apart from one another. In another specific embodiment, adjacent position reference features may be spaced 1 cm apart from each other. The position reference features may be detectable by a position sensor of a known type, which may be placed at a fixed location adjacent to the esophageal monitoring device as the esophageal monitoring device is introduced into or withdrawn from a subject&#39;s esophagus. 
     In another aspect, esophageal monitoring devices are disclosed. 
     Other aspects, as well as features and advantages of various aspects, of the disclosed subject matter will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG.  1    is a diagram depicting the arrangement of the left atrium of the heart and the esophagus of a subject; 
         FIGS.  2  and  3    depict an embodiment of an esophageal monitoring system according to this disclosure; 
         FIG.  4    shows a distal portion of an embodiment of an insertion component of an esophageal monitoring system according to this disclosure, with a distal feature of an embodiment of an esophageal monitoring device protruding from a distal end of the insertion component; 
         FIG.  5    shows the esophageal monitoring device within a lumen of the insertion component; 
         FIG.  6    provides a top view of the distal portion of the embodiment of insertion component shown in  FIG.  4   , with a monitoring element of the esophageal monitoring device partially deployed from the insertion component; 
         FIG.  7    is a side view illustrating the monitoring element of the esophageal monitoring device fully deployed from the insertion component and occupying a substantially two-dimensional area; 
         FIG.  8    is a top view of the arrangement illustrated by  FIG.  7   ; 
         FIG.  9    is a perspective view of the arrangement illustrated by  FIG.  7   ; 
         FIG.  10    illustrates another embodiment of an esophageal monitoring system according to this disclosure, including a proximal portion of an esophageal monitoring device and an insertion component over a remainder of the esophageal monitoring device; 
         FIG.  11    shows a monitoring element of the esophageal monitoring device within a distal portion of the insertion component; 
         FIG.  12    is a side view of the esophageal monitoring system shown in  FIG.  11   , with the insertion component pulled proximally over an elongated element of the proximal portion of the esophageal monitoring device, adjacent to or against a handle of the proximal portion, and the monitoring element of the esophageal monitoring device in a deployed orientation; 
         FIG.  13    is a top view of the arrangement shown in  FIG.  12   ; 
         FIG.  14    is an enlarged rear view of the embodiment of monitoring element shown in  FIG.  13   ; 
         FIG.  15    is a perspective view of a concave side of the embodiment of monitoring element shown in  FIG.  13   ; 
         FIG.  16    is a perspective view of a convex side of the embodiment of monitoring element shown in  FIG.  13   ; 
         FIG.  17    is a graph showing the time in which temperature sensors of the embodiment of esophageal monitoring device shown in  FIGS.  10 - 16    respond to changes in temperature, and providing a comparison of that time to the times in which temperature sensors of existing devices respond to changes in temperature; 
         FIG.  18    illustrates an embodiment of a camera of an esophageal monitoring device; and 
         FIGS.  19  and  20    illustrate embodiments of position sensors and position monitoring features of an esophageal monitoring system, which are capable of monitoring the distance the esophageal monitoring device has been inserted into the esophagus and, thus, its position along the esophagus. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  2  and  3    illustrate an embodiment of a system  10  according to this disclosure, which system  10  may also be referred to as an “esophageal monitoring system.” The system  10  is capable of monitoring a condition of a subject&#39;s esophagus while an ablation procedure is being performed on the posterior wall of the left atrium of the subject&#39;s heart (i.e., during a left atrial ablation procedure). As illustrated, the system  10  includes an insertion component  20 , an esophageal monitoring device  30 , a camera  40 , a position sensor  50 , and a monitor  60 . 
     In  FIG.  2   , the esophageal monitoring device  30  is located within a lumen  21  ( FIG.  5   ) of the insertion component  20 , but the camera  40 , which is located on a distal end  32  ( FIG.  6   ) of the esophageal monitoring device  30 , may be located at or just outside of (i.e., distal to) the distal end  22  of the insertion component  20 . 
     In  FIG.  3   , a monitoring element  34  of the esophageal monitoring device  30  has been deployed from a distal end  22  of the insertion component  20 , and branches  35   a ,  35   b ,  35   c  of the monitoring element  34  have expanded. 
     The monitor  60  of a system  10  according to this disclosure may include a display screen  62 , a processing element  64 , and one or more connectors  66  (e.g., communication ports, etc.). 
     A connector  66  of the monitor  60  may be configured to couple to, or mate with, a complementary connector of the esophageal monitoring device  30  (e.g., the connector  26 ′ shown in  FIGS.  10  and  12   , etc.). The connector  66  may comprise any suitable communication port (e.g., a USB (universal serial bus) port, a USB-C port, a proprietary communication port, etc.). 
     The processing element  64  of the monitor  60  may, under control of one or more programs or applications (or “apps”), communicate with various devices carried by the esophageal monitoring device  30 , including the camera  40 , and the position sensor  50  (e.g., receive signals and data embodied by the signals from devices carried by the esophageal monitoring device  30  and the position sensor  50 , send instructions to devices carried by the esophageal monitoring device  30 , etc.). In addition, the processing element  64  may process data conveyed as signals from devices carried by the esophageal monitoring device  30  and output such data to the display screen  62  of the monitor  60 . The processing element  34  may comprise a central processing unit (CPU), a graphics processing unit (GPU), a dedicated microcontroller, or the like. 
     The display screen  62  of the monitor  60  may function under control of the processing element  64  to provide one or more users (e.g., one or more healthcare providers, etc.) with the data in a readily comprehendible form (e.g., as numbers, graphics, etc.). As an example, the display screen  62  may display temperature data in numeric format, as well as in colors to indicate whether or not the displayed temperature values are potentially damaging to a subject&#39;s esophagus. As another example, the display screen  62  may display a position of a monitoring element  34  of the esophageal monitoring device  30  within a subject&#39;s esophagus. The display screen  62  may, in some embodiments, provide a user of the system  10  with information about the pressure, or force, between the monitoring element  34  of the esophageal monitoring device  30  and the wall of the esophagus against which the monitoring element  34  is positioned, as well as an interpretation of the potential causes, the actual causes, the potential effects, and/or the actual effects of such pressure. 
     In addition, the monitor (e.g., a touch-sensitive display screen  62 , etc.) may enable a user to provide inputs that control operation of the monitor  60  and/or the esophageal monitoring device  30 . 
     The insertion component  20  of the system  10  may be capable of facilitating introduction of the esophageal monitoring device  30  into a subject&#39;s esophagus, deploying the monitoring element  34  of the esophageal monitoring device  30 , retracting the monitoring element  34  of the esophageal monitoring device  30  (e.g., into the insertion component  20 , etc.), and/or removing the esophageal monitoring device  30  from the subject&#39;s esophagus. The insertion component  20  may comprise a flexible catheter or another flexible tubular element. That includes a distal end  22  (e.g., the end that is to be introduced into the esophagus first), a proximal end  24  configured to remain outside of the subject&#39;s body, and a lumen  21  ( FIG.  5   ) extending between the distal end  22  and the proximal end  24 . Dimensions of the lumen  21  (e.g., its inner diameter) enable it to receive the esophageal monitoring device  30 , including the monitoring element  34  of the esophageal monitoring device  30  when the monitoring element  34  is in a retracted arrangement. 
     An actuator  25  may be associated with a proximal end  24  of the insertion component  20  and/or a proximal end of the esophageal monitoring device  30  to enable a user (e.g., a healthcare provider, etc.) to control the relative positions of the insertion component  20  and the esophageal monitoring device  30 . In some embodiments, the actuator  25  may enable a user to slide the insertion component  20  along a length of the esophageal monitoring device  30 . In other embodiments the actuator may enable a user to slide the esophageal monitoring device  30  through the lumen  21  ( FIG.  5   ) of the insertion component  20 . As shown, the actuator  25  may comprise an enlarged feature, or a handle, that may be grasped and moved by the user. 
       FIGS.  4  and  5    illustrate a distal portion of the insertion component  20 , with  FIG.  4    showing an exterior of the insertion component  20  and the camera  40  protruding from the distal end  22  of the insertion component  20 , and  FIG.  5    showing features of the esophageal monitoring device  30 , including the monitoring element  34  thereof and a portion of a proximal element  33  thereof. 
     In the illustrated embodiment, position reference features  28  are positioned at fixed intervals along the length of the insertion component  20 . The position reference features  28  may be detectable by the position sensor  50  as they pass by (or through) the position sensor  50 . The position sensor  50  may send signals to the processing element  64  of the monitor  60 , which may then determine a location of the insertion component  20  and/or a distal portion of the esophageal monitoring device  30  (e.g., its distal end, the monitoring element  34 , etc.) relative to the position sensor  50  and the esophagus (e.g., a distance the insertion component and/or the esophageal monitoring device  30  has/have been inserted into the esophagus, etc.). 
       FIGS.  6 - 9    show the monitoring element  34  of the esophageal monitoring device  30  deployed from the distal end  22  of the insertion component  20 , with  FIG.  6    providing a top view prior to unfolding of branches  35   a ,  35   b ,  35   c , etc., of the monitoring element  34 ,  FIG.  7    showing a side view of a branch  35   a , and  FIGS.  8  and  9    showing the branches  35   a ,  35   b ,  35   c , etc., in a deployed, or an unfolded, arrangement. As illustrated by  FIGS.  7  and  9   , the deployed monitoring element  34  may be substantially two-dimensional. 
     The branches  35   a ,  35   b ,  35   c , etc., of the monitoring element  34  of the esophageal monitoring device  30  may be continuous with the proximal element  33  of the esophageal monitoring device  30 . In some embodiments, the proximal element  33  and the monitoring element  34  may comprise a flexible printed circuit board, or “flex PCB” or “flex circuit” that carries conductive traces, or “wires,” as well as electrical contacts. The branches  35   a ,  35   b ,  35   c , etc., of the monitoring element  34  may also include a structural support element  35   s  ( FIG.  7   ) which may enable the branches  35   a ,  35   b ,  35   c , etc., to maintain or substantially maintain their relative positions when the monitoring element  34  and its branches  35   a ,  35   b ,  35   c , etc., are in their deployed arrangement. The structural support element  35   s  may be carried by (e.g., laminated or otherwise secured to, formed within, etc.) the substrate of each branch  35   a ,  35   b ,  35   c , etc. (e.g., the flex circuit, etc.). In a specific embodiment, the structural support element  35   s  may comprise a pre-shaped elongated element formed from a shape memory alloy, such as nitinol (or NiTiNOL—nickel-titanium Naval Ordnance Laboratory), which may assume its intended shape as the structure support element  35   s  is deployed from the lumen  21  ( FIG.  5   ) of the insertion component  20  and exposed to the temperature within the esophagus (e.g., body temperature, etc.). In a more specific embodiment, the structural support element may comprise a 0.008 inch diameter nitinol wire. 
       FIGS.  8  and  9    also illustrate an arrangement of sensors  38  and  39  carried by the branches  35   a ,  35   b ,  35   c  of the monitoring element  34  and arranged across an area occupied by the monitoring element  34 . Sensors  38  may comprise temperature sensors of a known type (e.g., thermistors, etc.). Sensors  39  may comprise pressure sensors or force sensors of a known type. In some embodiments, the monitoring element  34  may carry sensors  39  that serve as positional markers (e.g., impedance electrodes, etc.), which may be used to anatomically map (e.g., three-dimensionally map, etc.) the location of the monitoring element  34  within the esophagus and relative to the left atrium of the subject&#39;s heart (e.g., by impedance-based mapping, etc.) and, when used in conjunction with measurements of the pressure or force exerted on pressure sensors or force sensors of the monitoring element  34 , may be used to map the physical relationship between the left atrium and the esophagus, as well as any changes to that physical relationship (e.g., force of the left atrium against the pericardium and the esophagus, etc.). 
     Turning now to  FIGS.  10 - 16   , another embodiment of a system  10 ′ for monitoring a condition of a subject&#39;s esophagus during a left atrial ablation procedure is depicted. The system  10 ′ may include all of the components of system  10  ( FIGS.  2 - 9   ) (i.e., an insertion component  20 ′, a handle  25 ′ at a proximal end  24  of the insertion component  20 ′, an esophageal monitoring device  30 ′ within a lumen (not shown) of the insertion component  20 ′, a camera  40 ′ at or near a distal end of the esophageal monitoring device  30 ′, an optional light source, a position sensor  50  ( FIGS.  2  and  3   ), and a monitor  60  ( FIGS.  2  and  3   ), with the configuration of the esophageal monitoring device  30 ′ being the primary difference between system  10 ′ and system  10  ( FIGS.  2  and  3   ). 
     In particular, as depicted by  FIGS.  12 ,  15 , and  16   , the monitoring element  34 ′ of the esophageal monitoring device  30 ′ may occupy a three-dimensional space rather than having a substantially two-dimensional arrangement. More specifically, the branches  35   a ′,  35   b ′,  35   c ′, etc., of the monitoring element  34 ′ are bent or curved. As depicted by  FIG.  15   , a structure support element  35   s  carried by the substrate (e.g., a flex circuit, etc.) of each branch  35   a ′,  35   b ′,  35   c ′, etc., (e.g., an elongated element formed from a shape memory alloy, such as nitinol, a nitinol wire (e.g., a 0.008 inch diameter nitinol wire, etc.), a thin nitinol band, etc.) may define the shape of each branch  35   a ′,  35   b ′,  35   c ′, etc., (e.g., as it is exposed to an increased temperature (e.g., body temperature, etc.) within the esophagus, etc.) and the relative positions of the branches  35   a ′,  35   b ′,  35   c ′, etc., when they are deployed from the lumen  21  of the insertion component  20 ′. The branches  35   a ′,  35   b ′,  35   c ′, etc., may be bent or curved and arranged in a manner that facilitates their placement against an interior surface of a subject&#39;s esophagus.  FIG.  16    illustrates a convex side  37 R′ of the monitoring element  34 , which is configured to be positioned against the interior surface of the esophagus, while  FIG.  15    illustrates a concave side  37 F′ of the monitoring element  34 ′, which is configured to face into a lumen of the esophagus when the monitoring element  34 ′ is positioned against the interior surface of the esophagus. In some embodiments, as the monitoring element  34 ′ is deployed in a subject&#39;s esophagus and placed against an interior surface of the esophagus, the branches  35   a ′,  35   b ′,  35   c ′, etc., may flatten out, enabling the monitoring element  34 ′ to be placed against the interior surface of the esophagus without deforming or moving the esophagus. 
     As shown in  FIGS.  14  and  16   , sensors  38 ′,  39 ′ may be carried by the concave side of each branch  35   a ′,  35   b ′,  35   c ′, etc., of the monitoring element  34 ′ (i.e., the side that will be placed against an interior surface of the subject&#39;s esophagus). 
     Due to the low thermal mass of flexible printed circuit boards, their use as the substrate for a monitoring element  34 ′, or for each branch  35   a ′,  35   b ′,  35   c ′, etc., of the monitoring element  34 ′, dramatically increases the thermal response time of each temperature sensor (e.g., each sensor  38 ′). The temperature sensors (e.g., sensors  38 ′) of the monitoring element  34 ′ of the esophageal monitoring device  30 ′ respond to temperature changes within 0.1 second (i.e., one-tenth of a second or less). By way of comparison, the temperature sensors of the CIRCA S-CATH™ esophageal temperature monitor available from CIRCA Scientific, LLC, of Englewood, Calif., respond to temperature changes in about two (2) seconds while it takes about eight (8) seconds for the temperature sensors of a general purpose esophageal probe to respond to temperature changes. These response times are illustrated by the graph of  FIG.  17   , in which twelve (12) response times were measured and averaged for temperature sensors of the monitoring element  34 ′ of the esophageal monitoring device  30 ′ (the left-most curve) and compared with average response times for temperature sensors of the CIRCA S-CATH™ esophageal temperature monitor (the center curve), and the Level 1® 9 F general purpose esophageal/rectal temperature probe available from Smiths Medical of Dublin, Ohio (the right-most curve). In those response time analyses, temperature sensors that had been heated to a temperature of 36° C. (e.g., in a warm water bath, etc.) were immersed in a warmer, 40° C. water bath, and the amount of time it took each sensor to respond to a 2° C. rise in temperature (from 36° C. to 38° C.) was measured. 
     By providing quick response times to changes in temperature, an esophageal monitoring device (e.g., esophageal monitoring device  30 ′, etc.) according to this disclosure may enable a healthcare provider to react more quickly to the exposure of the esophagus to potentially damaging temperatures. Improvement of the healthcare provider&#39;s reaction times may decrease the likelihood of damage to the esophagus during a left atrial ablation procedure. 
       FIG.  18    provides a close-up view of a camera  40 , which is located at a distal end  36   b  of a branch  35   b  of the monitoring element  34  of the esophageal monitoring device  30  (or at a distal end of a branch  35   b ′ of the monitoring element  34 ′ of the esophageal monitoring device  30 ′). As illustrated, the camera  40  may include a lens  42  with a dome shape, a hemispherical shape, or any other shape that will enable the camera  40  to capture images around an entirety of the inner surface of the esophagus. A light source (e.g., a source of visible light, a source of infrared radiation, a source of ultraviolet radiation, etc.) may be associated with the camera  40  to enable or enhance visualization of the interior surface of the esophagus. 
     With reference to  FIG.  19   , an embodiment of use of the position sensor  50  and the position reference features  28  on the insertion element  20  is depicted. In particular,  FIG.  19    depicts the use of the position sensor  50  and the position reference features  28  while inserting the insertion component  20  and, thus, the esophageal monitoring device  30  ( FIGS.  2  and  5 - 8   ) into a subject&#39;s esophagus. The position sensor  50  may be placed at a fixed location, such as the nares or mouth of the subject. As the insertion component  20  is introduced into the esophagus, it passes by or passes through the position sensor  50 . The position sensor  50  may detect each position reference feature  28  on the insertion component  20  that passes thereby or therethrough. 
       FIG.  20    illustrates use of the position sensor  50  and the position reference features  28  as the insertion component  20  and, thus, the esophageal monitoring device  30  are withdrawn from a subject&#39;s esophagus. Again, as each position reference feature  28  on the insertion component  20  passes by or through the position sensor  50 , the position sensor  50  detects that position reference feature. 
     In use, the insertion component  20  may initially reside over the monitoring element  34  of the esophageal monitoring device  30 , as shown in  FIGS.  2 ,  4 , and  5   . With the insertion component  20  and the esophageal monitoring device  30  in this arrangement, they may be introduced into a subject&#39;s esophagus (e.g., through the subject&#39;s nose, through the subject&#39;s mouth, etc.). The position of the insertion component  20  and/or the esophageal monitoring device  30  may be monitored (e.g., by the position sensor  50 , etc.; see, e.g.,  FIG.  19   ) as they are introduced into the esophagus. In addition, the interior surfaces of the esophagus may be visualized (e.g., with the camera  40 , etc., with or without illumination) while the insertion component  20  and the esophageal monitoring device  30  are introduced into the esophagus. 
     Once the distal end  22  of the insertion component  20  has reached a desired location within the esophagus, the monitoring element  34  of the esophageal monitoring device  30  may be deployed from the lumen  21  of the insertion component  20 , as depicted by  FIGS.  3  and  6 - 9   . In embodiments of the system  10  where the insertion component  30  can be pulled proximally to deploy the monitoring element  34  of the esophageal monitoring device  30 , deployment of the monitoring element  34  may occur once the distal end  22  of the insertion component  20  has been advanced to a location beneath a portion of the esophagus located in proximity to the left atrium of the subject&#39;s heart. In embodiments where the esophageal monitoring device  30  can be pushed distally out of the distal end  22  of the insertion component  20 , deployment of the monitoring element  34  may occur once the distal end  22  of the insertion component  20  has been advanced to a location just above a portion of the esophagus located in proximity to the left atrium of the subject&#39;s heart. 
     Once deployed, the monitoring element  34  may be placed against an interior surface of the esophagus, at a location where the esophagus is located closest to the left atrium of the subject&#39;s heart. The monitoring element  34  or, more specifically, sensors carried by the monitoring element  34  (e.g., temperature sensors  38 , force sensors  39 , etc.) may be used to monitor the surface of the esophagus against which the monitoring element  34  has been placed. Such monitoring may occur during a left atrial ablation procedure and, optionally, before the left atrial ablation procedure (e.g., to provide baseline temperature readings, baseline pressure readings, etc.). 
     In addition, positional markers (e.g., impedance electrodes, etc.) may be used to three-dimensionally map the location of the monitoring element within the esophagus and relative to the left atrium of the subject&#39;s heart. When used in conjunction with measurements of the pressure or force exerted on pressure sensors or force sensors  39  of the monitoring element  34 , may be used to map the physical relationship between the left atrium and the esophagus, as well as any changes to that physical relationship (e.g., force of the left atrium against the pericardium and the esophagus, etc.). 
     Once the left atrial ablation procedure is complete, the monitoring element  34  may be retracted back into the lumen  21  of the insertion component  20 , and the insertion component  20  and the esophageal monitoring device  30  may be removed from the subject&#39;s esophagus. The position of the insertion component  20  and/or the esophageal monitoring device  30  may be monitored (e.g., by the position sensor  50 , etc.; see, e.g.,  FIG.  20   ) as they are removed from the esophagus. In addition, the interior surfaces of the esophagus may be visualized (e.g., with the camera  40 , etc., with or without illumination) while the insertion component  20  and the esophageal monitoring device  30  are removed from the esophagus. 
     In embodiments where the interior surfaces of the esophagus have been visualized, a healthcare provider may analyze the interior surfaces to determine whether or not the left atrial ablation procedure has damaged the esophagus. Corrective measures (e.g., surgical treatment, medical treatment, etc.) may then be initiated immediately or within a short period of time (e.g., one day, two days, etc.) of the left atrial ablation procedure. 
     While the foregoing disclosure relates to esophageal monitoring devices, systems, and methods that are useful during left atrial ablation procedures, the teachings provided herein may also be applicable to devices, systems, and methods for monitoring tissue temperatures during other procedures where adjacent tissues are heated or cooled. 
     Although the foregoing description contains many specifics, these should not be construed as limiting the scopes of the inventions recited by any of the appended claims, but merely as providing information pertinent to some specific embodiments that may fall within the scopes of the appended claims. Features from different embodiments may be employed in combination. In addition, other embodiments may also lie within the scopes of the appended claims. All additions to, deletions from, and modifications of the disclosed subject matter that fall within the scopes of the claims are to be embraced by the claims.