Abstract:
A medical device includes an insertion tube, having a distal end for insertion into a body of a subject. A distal tip is fixed to the distal end of the insertion tube and is coupled to apply energy to tissue inside the body. The distal tip has an outer surface with a plurality of perforations through the outer surface, which are distributed circumferentially and longitudinally over the distal tip. A lumen passes through the insertion tube and is coupled to deliver a fluid to the tissue via the perforations.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 12/173,150, filed Jul. 15, 2008, now U.S. Patent Publication No. 2010/0030209, published Feb. 4, 2010, the entire content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to medical devices, and specifically to cooling of tissue contacted by an invasive probe within the body. 
       BACKGROUND OF THE INVENTION 
       [0003]    In some medical procedures, energy is imparted to body tissue locally, in a concentrated dose, and it is desirable to cool the treatment area in order to reduce collateral tissue damage. 
         [0004]    For example, cardiac ablation therapy is used to treat arrhythmias by heating tissue with radio-frequency (RF) electrical energy to create non-conducting lesions in the myocardium. It has been found that cooling the area of the ablation site reduces tissue charring and thrombus formation. For this purpose, Biosense Webster Inc. (Diamond Bar, Calif.) offers the ThermoCool® irrigated-tip catheter as part of its integrated ablation system. The metal catheter tip, which is energized with RF current to ablate the tissue, has a number of peripheral holes, distributed circumferentially around the tip, for irrigation of the treatment site. A pump coupled to the catheter delivers saline solution to the catheter tip, and the solution flows out through the holes during the procedure in order to cool the catheter tip and the tissue. 
       SUMMARY OF THE INVENTION 
       [0005]    Despite the general usefulness of irrigation in reducing collateral tissue damage, the inventors have found that in some cases, the tissue and treatment device in the vicinity of the treatment area are not adequately or uniformly cooled. Problems may arise, for example, due to blockage of the irrigation holes in the treatment catheter. 
         [0006]    Embodiments of the present invention that are described hereinbelow provide multiple perforations in the distal tip of a treatment device, such as a catheter or other probe. The perforations are distributed both circumferentially and longitudinally over the distal tip. The large number of perforations and their longitudinal distribution help to ensure adequate irrigation of the entire distal tip and treatment area and thus reduce collateral tissue damage, as well as preventing adhesion of the distal tip to the tissue. 
         [0007]    There is therefore provided, in accordance with an embodiment of the present invention a medical device, comprising an insertion tube, having a distal end for insertion into a body of a subject at a treatment area. A conductive hollow distal tip having a length and a thickness between an inner surface and an outer surface is fixed to the distal end of the insertion tube and coupled to a generator. The conductive hollow distal tip and the generator are configured to directly apply energy to tissue at the treatment area inside the body. The conductive hollow distal tip further includes a distribution of perforations that extend from the inner surface to the outer surface, wherein at least a portion of the perforations are circumferentially and longitudinally arranged over the outer surface of the hollow distal tip and sized and configured to ensure equal flow of a cooling fluid over the entire length of the conductive hollow distal tip while not overloading the treatment area with the cooling fluid. The medical device further comprises a lumen passing through the insertion tube and coupled to deliver the cooling fluid to the tissue at the treatment area via the perforations. 
         [0008]    There is additionally provided a medical apparatus, comprising an elongate probe for insertion into a body of a subject. The elongate probe includes an insertion tub, having a distal end for insertion into the body. A conductive hollow distal tip having a length is fixed to the distal end of the insertion tube and is coupled to an energy generator to directly apply energy to tissue inside the body at a treatment area. A distribution of a plurality of perforations are distributed through the conductive hollow distal tip, wherein at least a portion of perforations are circumferentially and longitudinally arranged over the outer surface of the conductive hollow distal tip and sized and configured to ensure equal flow of a cooling fluid over the entire length. The medical apparatus further includes a lumen passing through the insertion tube and in fluid communication with the distribution of the perforations, and an irrigation pump, for coupling to the lumen so as to supply the cooling fluid via the lumen and the distribution of the perforations to the tissue. 
         [0009]    The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic, pictorial illustration of a system for cardiac ablation therapy, in accordance with an embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic sectional view of the distal end of a catheter in engagement with heart tissue, in accordance with an embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic side view of the distal tip of a catheter, in accordance with an embodiment of the present invention; and 
           [0013]      FIG. 4  is a schematic side view of apparatus used in producing a perforated catheter tip, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0014]      FIG. 1  is a schematic, pictorial illustration of a system  20  for cardiac ablation therapy, in accordance with an embodiment of the present invention. An operator  26  inserts a catheter  28  through a blood vessel into a chamber of a heart  24  of a subject  22 , and manipulates the catheter so that a distal end  32  of the catheter contacts the endocardium in an area that is to be treated. The distal tip of the catheter is perforated to enable optimal irrigation of the treatment area, as shown and described hereinbelow. In other respects, however, system  20  resembles systems for cardiac ablation treatment that are known in the art, such as the above-mentioned Biosense Webster system, and the components of such systems may be adapted for use in system  20 . 
         [0015]    After positioning distal end  32  at an ablation site, and ensuring that the tip is in contact with the endocardium at the site, operator  26  actuates a radio frequency (RF) energy generator  44  in a control console  42  to supply RF energy via a cable  38  to distal end  32 . Meanwhile, an irrigation pump  48  supplies a cooling fluid, such as saline solution, via a tube  40  and a lumen in catheter  28  to the distal end. Operation of the RF energy generator and the irrigation pump may be coordinated in order to give the appropriate volume of irrigation during ablation, so as to cool the tip of the catheter and the tissue without overloading the heart with irrigation fluid. A temperature sensor (not shown in the figures) in distal end  32  may provide feedback to console  42  for use in controlling the RF energy dosage and/or irrigation volume. 
         [0016]      FIG. 2  is a schematic sectional view of distal end  32  of catheter  28  in engagement with endocardial tissue in heart  24 , in accordance with an embodiment of the present invention. The catheter terminates in a distal tip  50 , which is fixed to the distal end of an insertion tube  60  of the catheter. The distal tip typically comprises a conductive material, such as platinum, while the insertion tube has an insulating flexible outer sheath. The outer surface of the distal tip is penetrated by multiple perforations  52 , which are distributed over the surface of the distal tip both longitudinally (i.e., along the direction parallel to the longitudinal axis of catheter  28 ) and circumferentially (along circumferences around the axis). 
         [0017]      FIG. 3  is a schematic side view of distal tip  50 , showing details of perforations  52 , in accordance with an embodiment of the present invention. The distal tip is hollow, with an outer surface  66  that encloses an interior space  64 . Perforations  52  extend from the outer surface into the interior space. For cardiac ablation applications, the distal tip shown in  FIG. 3  is typically about 2.5 mm in diameter and 6 mm long, with a wall thickness in the distal part of the tip of about 0.25 mm. These dimensions, however, are given solely by way of illustration, and larger or smaller dimensions may be used depending on application requirements. The edges of the distal tip, at both the distal and proximal extremities of the tip, are typically rounded in order to avoid possible concentration of the RF electric field around the edges. 
         [0018]    Typically, distal tip  50  has at least eight perforations, which are less than 0.5 mm in diameter, in order to distribute the irrigation over the tip both longitudinally and circumferentially without overloading the heart with the cooling fluid. The inventors have found it advantageous, however, to have at least fifty perforations in the distal tip, with diameters no greater that 0.2 mm. In the actual embodiment that is shown in  FIG. 3 , tip  50  has ninety-six perforations, with diameters of approximately 0.1 mm. The sizes of the perforations may optionally be varied over the length of the distal tip to compensate for pressure variation and ensure equal flow over the entire length. For this purpose, the perforations at and near the most distal part of the tip may be made larger than the more proximal perforations, which are nearer to the fluid inlet. 
         [0019]    Returning now to  FIG. 2 , the proximal end of distal tip  50  is closed off by a plug  54 , which has a fluid inlet  56  feeding interior space  64 . A lumen  58  passing through insertion tube  60  of catheter  28  conveys fluid from irrigation pump  48  ( FIG. 1 ) to inlet  56 , filling interior space  64 . The fluid exits tip  50  through perforations  52  to the surrounding tissue. A conductor conveys RF energy from RF generator  44  to the conductive tip, which thus serves as an electrode for delivering the energy in order to ablate the tissue. 
         [0020]      FIG. 4  is a schematic side view of apparatus used in creating perforations  52  in distal tip  50 , in accordance with an embodiment of the present invention. In this embodiment, the perforations in the tip are produced by electrical spark discharge. Tip  50  is mounted in a suitable rotating jig  70  (such as a lathe chuck). A needle electrode  72 , such as a carbon needle, is held at a potential of several thousand volts by a high-voltage power supply  76 . A motion assembly  74  gradually brings the needle electrode into proximity with the point on the catheter tip at which a perforation is to be made. The procedure is typically carried out in a controlled gas environment (such as an argon atmosphere). At a distance of about 1 mm, a spark jumps from the electrode to the catheter tip. The discharge creates a small perforation, typically about 100 μm in diameter, in the tip. The size of the hole may be controlled by varying the discharge voltage. 
         [0021]    Jig then rotates tip  50  so that the location of the next perforation is positioned opposite needle electrode  72 , and the next perforation is created in similar fashion. The electrode is shifted longitudinally along the catheter tip to make multiple sets of holes, which are distributed longitudinally and circumferentially over the catheter tip as described above. 
         [0022]    This method of creating holes in distal tip  50  permits a large number of holes to be made precisely and inexpensively, without structurally weakening the catheter tip. It allows the sizes of the irrigation holes to be controlled in production to give precisely the desired volume of irrigation, without clogging of the holes on the one hand or overloading of the heart with irrigation fluid on the other. 
         [0023]    Although the embodiments described above relate specifically to catheters used in RF ablation treatment within the heart, the principles of the present invention may similarly be applied to other organs and in other types of therapy that involve application of energy to body tissues. For example, a device with a similar sort of irrigated tip may be used in therapies that involve microwave-based or ultrasonic tissue heating. 
         [0024]    It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.