Abstract:
The present invention includes a device and a method for preventing injury of the esophagus during thermal ablation of the left atrium. The device has an esophageal probe with a balloon tip for insertion into the esophagus of a patient. During usage, coolant passes into the esophageal probe and then fills its balloon. The coolant, when circulating through the balloon and an external cooling machine, protects the esophageal tissue in contact with the esophageal probe from thermal damage during ablation of the posterior wall of the left atrium of the heart, or other procedure.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This non-provisional application claims priority to the provisional application for patent Ser. No. 60/713,301 which was filed on Sep. 2, 2005 which is incorporated by reference and the aforesaid application is commonly owned by the same inventors. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention generally relates to medical devices utilized in protecting the digestive tract of a person. More specifically, the present invention relates to an esophageal probe with a cooled tip that protects the esophagus when the adjacent left atrium of the heart is ablated.  
         [0003]     Cardiac arrhythmias generally require a critical anatomic region of abnormal impulse formation, or propagation, to initiate or sustain themselves. If the ablation can alter, or destroy, this critical region, the arrhythmia ceases. Potential energy sources for ablation include radiofrequency, ultrasound, microwave, laser, cryothermy, and other electromagnetic radiation. These modalities may be applied endocardially or epicardially by either a percutaneous or surgical approach.  
         [0004]     One risk of thermal injury to the myocardium by any ablation is collateral damage to nearby structures in the body of a patient. Potential complications associated with thermal ablation of heart tissue include injury to the coronary arteries, phrenic nerve, lung, aorta, esophagus, or other thoracic structures.  
         [0005]     Radiofrequency is currently the most common source of energy for catheter ablation of cardiac arrhythmias. The flow of radiofrequency current through myocardial tissue causes resistive heating at the electrode-tissue interface. Direct resistive heating depends on the power density within the tissue, which decreases in proportion to the distance from the ablation electrode. Thus the depth of tissue which is heated resistively is generally less than 2 mm. Thermal injury to deeper myocardium, as well as any contiguous noncardiac structure, occurs by heat conduction.  
         [0006]     Atrial fibrillation is the most common sustained arrhythmia present in humans, occurring in 0.4-0.9% of the general population and 3-4% of those over the age of 60. Atrial fibrillation has significant patient morbidity and mortality, as well as economic cost. In recent years, radiofrequency ablation has become an important alternative to anti-arrhythmic therapy for atrial fibrillation. The pulmonary veins and the posterior left atrium are critical areas in the initiation and maintenance of atrial fibrillation in many patients. Radiofrequency ablation around the pulmonary veins and in the posterior atrium has effectively treated atrial fibrillation (Oral H., et al.  Circulation  2003).  
         [0007]     A potential complication of performing ablation in this region of the left atrium, however, is causing damage to the esophagus which is in close proximity to the posterior wall. Conduction of heat to the esophagus from a nearby endocardial lesion site has caused several fatal atrio-esophageal fistulas following atrial fibrillation ablation (Pappone C., et al.  Circulation  2004).  
         [0008]     Several strategies have been employed to avoid this potentially catastrophic complication. Some physicians have reduced the amount of power delivered to this area, or tried to avoid ablation in the posterior atrium altogether. However, the posterior left atrium appears to be a critical region in the initiation and maintenance of atrial fibrillation in many patients, and thus is likely a necessary target of any efficacious ablation approach. Other physicians have begun using esophageal temperature monitoring during ablation. If a rise in temperature is detected in the esophagus, the ablation lesion is terminated. However, simply monitoring temperature at some position within the lumen of the esophagus may not reliably prevent injury. If the endocardial ablation site and contiguous esophageal tissue are at some distance from the temperature sensor, the extent of thermal injury may not be appreciated.  
         [0009]     The present invention seeks to prevent thermal injury to the esophagus during ablation by cooling the esophageal tissue just prior to and during ablation  
       SUMMARY OF THE INVENTION  
       [0010]     The cooling device of the present invention is an esophageal probe with a balloon tip for insertion into the esophagus of a patient. Coolant enters the esophageal probe and fills the balloon tip of the esophageal probe. During ablation, any heat conducted from the heart into the contiguous structure, particularly esophageal tissue, would rapidly dissipate by the coolant in the balloon. Thus, the coolant protects the esophageal tissue in contact with the probe from thermal damage during ablation of the posterior wall of the left atrium of the heart.  
         [0011]     It is, therefore, the principal object of this invention to provide thermal protection to tissues in the proximity of an ablation.  
         [0012]     Another object of this invention is to provide a stable temperature environment while an ablation is performed.  
         [0013]     A further object of this invention is to provide a complete connection around the perimeter of the invention to the surrounding tissue resulting in even distribution of temperature protection.  
         [0014]     A further object of this invention is to provide a pressurized coolant within safe limits for the tissue proximate to an ablation.  
         [0015]     These and other objects may become more apparent to those skilled in the art upon review of the summary of the invention as provided herein. In addition, the invention will be better understood upon undertaking a study of the description of its preferred embodiment, in view of the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     In referring to the drawings,  
         [0017]      FIG. 1A  is a partial front sectional view of the human body illustrating the position of the heart;  
         [0018]      FIG. 1B  is a cross sectional view of the human body, at the seventh thoracic vertebra illustrating the relative position of the left atrium of the heart and the esophagus;  
         [0019]      FIG. 2  is a partial sectional view of the human body taken along the mid-sagittal plane;  
         [0020]      FIG. 3A  is a longitudinal side view of the esophageal probe of the present invention;  
         [0021]      FIG. 3B  is a cross sectional view of the esophageal probe of the present invention;  
         [0022]      FIG. 3C  is a cross sectional view of the esophageal probe of the present invention;  
         [0023]      FIG. 3D  is a partial longitudinal sectional view of the esophageal probe taken through the balloon and the distal portions of the coolant in-flow and out-flow lines; and,  
         [0024]      FIG. 4  is a partial sectional view of the human body taken along the mid-sagittal plane showing the relative position of the left atrium of the heart and esophagus with the esophageal probe in place and the balloon inflated and in contact with the esophagus near the left atrium of the heart. 
     
    
       [0025]     The same reference numerals refer to the same parts throughout the various figures.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     In reference to the drawings,  FIG. 1A  is a partial front sectional view of the human body illustrating the position of the heart  10  within the chest.  FIG. 1B  is a cross sectional view of the human body, at the level of the seventh thoracic vertebra  21  illustrating the relative position of the left atrium  11  of the heart  10  and the esophagus  13 . It should be noted from  FIGS. 1A and 1B , that the esophagus  13  is essentially in direct contact with the left atrium  11  for a portion of its course through the chest. The esophagus  13  is also flanked by the left lung  17  and right lung  18 . The aorta  15  is positioned between the esophagus  13  and the left lung  17  and is in close proximity to the thoracic vertebra  21 . It is well demonstrated in  FIG. 1B  that application of thermal energy to the posterior wall of the left atrium  11  of the heart  10  can potentially injure the anterior wall of the adjacent esophagus  13 .  
         [0027]      FIG. 2  is a partial longitudinal sectional view of the human body taken along the mid-sagittal plane and again demonstrates the relative position of the left atrium  11  of the heart  10  and esophagus  13 , the nasal passage  23  and the pharynx  25 . An ablation catheter  31  is shown passing through the left ventricle  12  and into the left atrium  11  of the heart  10 . The tip  33  of the ablation catheter  31  is shown in contact with the posterior wall of the left atrium  11  of the heart  13 .  
         [0028]     During a prior art therapy session utilizing thermal ablation to treat atrial fibrillation, a therapist would direct the ablation catheter  31  such that thermal energy would pass from the catheter tip  33  and into the tissues of the posterior wall of the left atrium  11 . Heating of the posterior wall of the left atrium  11  would then occur, ideally leading to localized injury of the left atrium  11  and resolution of atrial fibrillation. Depending upon the type of ablation catheter used, the length of the therapy session, and the amount of energy supplied to catheter tip  33 , tissue heating could extend beyond the posterior wall of the left atrium  11  and encompass the anterior wall of the esophagus  13 . As is well known, due to the close proximity of the esophagus  13  to the left atrium  11 , the esophagus  13  can be injured during thermal ablation of the posterior wall of the left atrium  11 . Should this occur, it is possible for a fistula tract to form between the left atrium  11  and the esophagus  13 , and death can ensue from massive bleeding. This possible complication has led to many therapists avoiding the posterior wall of the left atrium  11  during therapy to minimize the risk of injury to the esophagus  13 . This prior art approach also tends to decrease the effectiveness of ablation in the treatment of atrial fibrillation. The present invention is a balloon tipped esophageal probe that provides a means to cool the esophagus  13  during thermal ablation of the left atrium  11  and thus minimize the possibility of developing a fistula tract between the left atrium  11  and the esophagus  13 .  
         [0029]      FIG. 3A  demonstrates a longitudinal side view of the esophageal probe  40  of the present invention.  FIG. 3B  demonstrates a cross sectional view of the esophageal probe  40  of the present invention. This view shows the balloon  44  with the coolant contained therein and the inflow line  51  admitting additional coolant through its lumen  52 . Then,  FIG. 3C  demonstrates a cross sectional view of the esophageal probe  40  of the present invention. This view shows the in-flow line  51  as contiguous with the out flow line  61  from the junction, as at  46 , to the interior of the balloon  44 . And,  FIG. 3D  demonstrates a partial longitudinal sectional view of the esophageal probe  40  taken through the balloon  44  with lines of flow  105  demonstrating the movement of coolant through the coolant volume  102  within the expanded balloon  44 .  
         [0030]     The principal components of the esophageal probe  40  include a distensible, thermally conductive balloon  44 , a coolant in-flow line  51 , and a coolant out-flow line  61 . The proximal end of the coolant in-flow line  51  has an inline in-flow valve  57  and pressure relief valve  55 . The proximal end of the coolant out-flow line  61  also has an out-flow valve  67 . During use, the coolant in-flow line  51  can be connected to a coolant source by means of the connector  58 . The lumen  52  of the coolant in-flow line  51  and the lumen  62  of the coolant out-flow line  61  provide a path for coolant to be transmitted from the coolant supply to coolant space  102  of the balloon  44  and then out through another connector  68  for additional cooling by the coolant supply.  
         [0031]     The balloon  44  may be composed of any distensible, chemically inert, non-toxic and thermally conductive material. The coolant in-flow line  51  and the coolant out-flow line  61  may be composed of any suitable flexible, chemically inert, non-toxic material for withstanding operating pressures without significant expansion. The coolant in-flow line  51  and the coolant out-flow line  61  have suitable length for placement in the esophagus  13  near the left atrium  11  of the heart  10 , approximately 80 cm. The coolant in-flow line  51  and the coolant out-flow line  61  may desirably have markings or other indicator (not shown) along their length to indicate distance there-along so that the balloon  44  may be initially positioned approximately adjacent the left atrium  11 .  
         [0032]     Though inflow line  51  and outflow line  61  are contiguous,  FIG. 3D  shows the measures taken to prevent cross connection, siphoning, or back flow between the two lines within the balloon  44 . The inflow line  51  enters one end of the balloon  44  and extends through the length of the balloon. The inflow line  51  reaches the opposite end of the balloon and connects to the balloon. Opposite the ending of the inflow line, the balloon has the tip  45 . With the tip opposite the inflow line, the tip transmits maximum cooling by conduction when the tip is placed upon a point within the body. Near the tip  45 , the inflow line  51  has an aperture  53  that releases coolant into the balloon  44 . The coolant flows within the balloon and then is collected into the outflow line  61  at its opening  63 . The opening  63  is generally at the end of the outflow line  61  and collects coolant from any direction.  
         [0033]      FIG. 4  is a partial sectional view of the human body taken along the mid-sagittal plane showing the relative position of the left atrium  11  of the heart  10  and esophagus  13  with the esophageal probe  40  in place and the balloon  44  inflated and in contact with the esophagus  13  near the left atrium  11  of the heart  10 .  
         [0034]     Referring to  FIG. 4 , an esophageal probe  40  with the balloon  44  fits within the esophagus  13  of a human body for the purpose of protecting the anterior wall of the esophagus  13  from thermal injury that may occur during thermal ablation of the left atrium  11  of the heart  10 . The esophageal probe  40  is inserted tip  45  first through the nasal passage  23 , through the pharynx  25 , and then into the esophagus  13 . Alternatively, the esophageal probe  40  may be inserted through the mouth of the patient.  
         [0035]     Once the esophageal probe  40  is properly inserted into the esophagus  13 , but prior to energizing the ablation catheter  31 , (shown earlier in  FIG. 2 ), the balloon  44  is filled with coolant from the in-flow line  51  until the balloon  44  properly occupies width of the esophagus  13 , but does not overly distend the esophagus  13  proximate the left atrium  11 . The coolant that fills and circulates through the balloon  44  maintains the temperature of the anterior wall of the esophagus  13  within physiologically normal temperature ranges and thus prevents esophageal injury. Proper inflation establishes substantially complete contact with the esophageal wall to prevent “hot spots” from occurring adjacent to the esophageal wall during thermal ablation while also ensuring that the esophagus  13  is not ruptured due to improper pressure against the esophageal wall.  
         [0036]     The balloon  44  of the esophageal probe  40  fills with coolant in a various ways. In one method, the coolant out-flow valve  67  is closed and the coolant in-flow valve  57  is opened. Coolant is able to pass through the coolant in-flow valve  57 , through the pressure relief valve  55 , down the lumen  52  of the coolant in-flow line  51  and into the balloon  44 . Coolant is prevented from leaving the balloon  44  by the closed coolant out-flow valve  67 . Coolant flow continues until the pressure within the balloon  44  equals the pressure in the coolant source or the coolant in-flow valve  57  is closed. The pressure relief valve  55  limits the maximum pressure in the coolant in-flow line  51 , by releasing coolant from the balloon  44  should the pressure in the coolant in-flow line  51  rise above a certain predetermined safe level pertinent to the surrounding tissue.  
         [0037]     With both the coolant in-flow valve  57  and the coolant out-flow valve  67  open, coolant is able to flow continuously from the coolant source through the coolant in-flow valve  57 , through the pressure relief valve  55 , down the lumen  52  of the coolant in-flow line  51 , into and through the balloon  44  and out through the lumen  62  of the coolant out-flow line  61  and the coolant out-flow line valve  67 . The flow lines  105  in  FIG. 3D  represent coolant flow through the coolant area  102  of the balloon  44 . The rate of coolant flow into the probe is controlled by adjusting the pressure within the coolant source and the positions of the coolant in-flow valve  57  and the coolant out-flow valve  67 .  
         [0038]     The esophageal probe  40  of the present invention is intended for use with any of a variety of thermal ablation catheters  31 . The esophageal probe  40  provides coolant to the balloon  44  located in the esophagus  13  near the left atrium  11 . This coolant will prevent the temperature of the anterior esophageal  13  wall from increasing above a predetermined temperature during thermal ablation of the left atrium  11 . By supplying coolant to the balloon  44 , the esophageal probe  40  also modifies the heating pattern caused by the thermal ablation catheter  31 . In particular, the heating pattern no longer encompasses the esophagus  13  and a greater portion of the tissue in the posterior wall of the left atrium  11  can be ablated while adjacent healthy esophageal  13  wall is protected.  
         [0039]     The present invention also provides a means for pre-chilling the anterior esophageal wall prior to applying energy from the catheter tip  33  to the left atrium  11 . The use of pre-chilling would permit the therapist to more quickly increase the energy to the thermal ablation catheter  31  without damaging esophageal  13  tissue.  
         [0040]     Variations or modifications of the subject matter of this invention may occur to those skilled in the art upon reviewing the disclosure provided herein. Such variations or modifications are intended to be encompassed within the scope of the invention as described herein. The description of the preferred embodiment and of the drawings showing the same are provided herein for illustrative purposes only.  
         [0041]     From the aforementioned description, a device and method for esophageal cooling has been described. The esophageal cooling device is uniquely capable of readily protecting the esophagus when the adjacent left atrium is ablated. The cooling device and its various components may be manufactured from many materials including but not limited to polymers, silicone, high density polyethylene HDPE, polypropylene PP, polyethylene terephalate ethylene PETE, polyvinyl chloride PVC, nylon, ferrous and non-ferrous metals, their alloys and composites.  
         [0042]     The phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Therefore, the claims include such equivalent constructions insofar as they do not depart from the spirit and the scope of the present invention.