Abstract:
A cardiac ablation catheter has an energy emitting surface for thermally destroying tissue. The surface normally presents a compact, low profile for introduction into the heart. Once introduced, the energy emitting surface can be significantly enlarged. The enlarged surface emits ablation energy sufficient to create a lesion that is significantly larger in terms of volume and geometry than the surface&#39;s initial low profile would provide.

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 08/099,994, filed on Jul. 30, 1993, now U.S. Pat. No. 6,086,581, which is a continuation-in-part of U.S. application Ser. No. 07/951,728, filed Sep. 25, 1992, now U.S. Pat. No. 5,471,982, and entitled “Cardiac Mapping and Ablation Systems.” 
    
    
     FIELD OF THE INVENTION 
     The invention relates to systems and methods for ablating the interior regions of the heart for treating cardiac conditions. 
     BACKGROUND OF THE INVENTION 
     It is believed that lesions larger than those created by current electrophysiological therapy are needed to more consistently cure myocardial ventricular tachycardia (MVT) of ischemic origins. 
     Conventional cardiac ablation systems designed to cure re-entrant supra ventricular tachycardia (SVT), often create lesions in myocardial tissue with a penetration depth of about 3 to 5 mm and a lesion volume of less than 0.2 cm 3 , depending upon the size of the electrode and the amount of power that is applied. 
     However, to consistently cure MVT by ablation, a penetration depth greater than 3 to 5 mm and a lesion volume of at least 1 cm 3  is estimated to be required. 
     The solution lies in larger electrodes. Yet, larger electrodes themselves pose problems of size and maneuverability that weigh against safe and easy introduction through a vein or artery into the heart. 
     A need exists for cardiac ablation catheters having that flexibility and maneuverability that permits safe and easy introduction into the heart and, once deployed inside the heart, emit energy sufficient to cause permanent, irreversible thermal damage to large regions of myocardial tissue. 
     SUMMARY OF THE INVENTION 
     The invention provides a cardiac ablation catheter having an energy emitting surface for thermally destroying tissue. The surface normally presents a compact, low profile for introduction into the heart. 
     Once introduced, the energy emitting surface can be significantly enlarged. The enlarged surface emits ablation energy sufficient to create a lesion that is significantly larger in terms of volume and geometry than the surface&#39;s initial low profile would provide. 
     The catheter of this invention is configured to produce lesions with a greater surface area, compared to standard cardiac ablation catheters, while maintaining a standard (6, 7, or 8 French) introducer size (a “French” equals 0.013 inches). 
     The enlarged surface area creates larger lesions, since the lesion volume and geometry are factors which are controlled according to the shape and size of the energy emitting surface. 
     In accordance with a further aspect of the invention, an inflatable surface is produced using a thermoplastic polymeric material such as polyethylene. The inflatable surface is coated, all or partially, with an energy emitting material. When deflated, such a surface presents a compact profile. When inflated, the same surface has an significantly enlarged dimension of, for example, approximately 7 to 12 mm. 
     Another aspect of the invention is an expandable energy emitting surface with an associated temperature sensor. 
     In an alternative arrangement, the expandable surface can also be used for obtaining electrogram recordings or for similar mapping procedures. 
     The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view with parts broken away showing an ablation catheter system of the present invention; 
     FIG. 2 is a greatly magnified broken-away plan view of a tip portion of an electrode in accordance with the invention; 
     FIG. 3 is a view of the enlarged fragmentary tip portion, shown in FIG. 2, with an electrode shown in the expanded condition; 
     FIG. 4 is a yet, more greatly enlarged fragmentary view of the tip portion of an electrode of the present invention with parts shown in cross-section for clarity. 
     FIG. 5 shows a diagrammatic view of the cardiac ablation system shown in FIG. 3 coupled to a source of radio frequency electromagnetic energy and an indifferent electrode for electrically heating and ablating myocardial tissue; and 
     FIG. 6 is a view of the enlarged fragmentary tip portion, as shown in FIG. 3, with the conductive coating applied in a pattern. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a system  10  for performing ablation on cardiac tissue that embodies the features of the invention. 
     The system  10  also includes a steerable catheter  14  carrying an expandable energy emitting body  16 . 
     In FIG. 1, the catheter  14  includes a handle  20 , a guide tube  22 , and a distal tip  24 . In this embodiment, the tip  24  carries the energy emitting body  16  (see FIG.  2 ). 
     As FIG. 2 shows, a series of ring electrodes  25  encircle the guide tube  22  close to the energy emitting body  16 . These ring electrodes  25  can be used for sensing electrograms to locate the region that is to be ablated. 
     The handle  20  encloses a steering mechanism  26  for the catheter tip  24 . A cable  28  extending from the rear of the handle  20  has plugs  29  which connect the catheter  14  to a source of ablation energy. The ablation energy is conveyed through the wires  12  to the body  16  for creating lesions in tissue within the heart. 
     While the type of ablation energy used can vary, in the illustrated embodiment (see FIG.  5 ), radio frequency (RF) electromagnetic energy is used. The energy source therefore comprises a radio frequency  50 . While the RF  50  can be constructed in various ways, the RF generator preferably delivers up to about 150 watts of power at a frequency of about 350 to 700 kHz, and most preferably, about 500 kHz. 
     Left and right steering wires (not shown) extend through the guide tube  22  to interconnect the steering mechanism  26  with the distal tip  24 . The steering mechanism  26  includes a steering lever  15 . 
     Various steering mechanisms can be used, for example, the type shown in U.S. Pat. No. 5,195,968. 
     As FIG. 1 shows, rotation of the steering lever  15  to the left pulls on the left steering wire, causing the tip  24  to bend to the left. Rotation of the steering lever  15  to the right pulls on the right steering wire, causing the tip  24  to bend to the right. 
     As FIG. 1 also shows, the energy emitting body  16  moves along with the tip  24  from left and right as the steering lever  15  is manipulated. 
     In use, a physician holds the catheter handle  20  and introduces the catheter  14  through a main vein or artery (typically the femoral) into the interior region of the heart that is to be treated. The physician then further steers the distal tip of the catheter  14  by means of the steering lever  15 , to place the body  16  into contact with the tissue within the heart that is targeted for ablation. 
     The body  16  has a hollow interior. The guide tube  22  includes an interior lumen  27  (see FIG. 2) that communicates with the hollow interior of the body  16 . 
     The catheter assembly  10  includes an injection port  18  for injection of a fluid medium into the lumen  27 . The fluid caused the body  16  to expand or inflate from its normal, low profile condition (as FIG. 2 shows) to an enlarged operating condition (as FIG. 3 shows). 
     The inflating fluid medium can vary. Preferably, it comprises a liquid like as water, saline solution, or other biocompatible fluid. 
     Alternately the inflating fluid medium can comprise a gaseous medium such as carbon dioxide or air. 
     Regardless of the type of fluid medium, the inflation preferably occurs under relatively low pressures of up to 30 psi. The pressure used depends upon the desired rate of inflation, the strength and material used for the body  16 , and the degree of flexibility required (i.e., high pressure leads to a harder, less flexible body  16 . 
     After reaching its desired inflated condition, the physician directs ablation energy through wires  12  into the body  16 . The body emits the ablation energy to heats the tissue. The tissue is thermally destroyed, forming a lesion. 
     The body  16  can be variously constructed. In the illustrated and preferred embodiment, the body  16  is made of a thermoplastic polymeric material of a pliant nature, like polyethylene. The body  16  is formed by either a free-blown process or a mold process. 
     The body  16  includes an energy emitting coating applied upon its exterior surface. In the illustrated embodiment, where the body  16  emits RF ablation energy, the coating comprises an electrically conducting material, like platinum or gold. 
     Coating of the body  16  may be accomplished by conventional painting or sputter coating techniques. For example, gold can be sputtered onto the exterior surface of the body  16 . Alternatively, a two phase sputter coating process may be employed in which an initial layer of titanium is applied followed by an outer coating of gold. 
     The coating process may also use an ion beam assisted deposition (IBAD) process. This process implants the conductive material into the polymer of the body  16 . 
     The wires  12  conduct ablating energy to the coating on the body  16 . 
     The body  16  shown in FIGS. 2,  3  and  5  is operated in a unipolar ablation mode. The energy transmitted by the body  16  flows through myocardial tissue to an external indifferent electrode  52  on the patient (see FIG.  5 ), which is typically an epidermal patch. 
     In the illustrated and preferred embodiment, the conductive coating covers the entire exposed area of the body  16 . In this case, the body  16 , when inflated, functions as a single ablation electrode. 
     Alternatively, the conductive coating can be applied in a defined portion  54  (such as one third or one half) of the circumference of the body  16  (as shown in FIG.  6 ), or any variety of patterns that may enhance the ablation performance and/or optimize the ablation procedure. 
     Additionally, the coated, inflatable body  16  can serve to carry electrical signals from the heart tissue along wires  12  through cable  28  and plugs  29  for recording of electrogram potentials by recording equipment. 
     The inflatable body  16  can be attached to the distal tip  24  of guide tube  22  in various ways. 
     In the illustrated embodiment, as best seen in FIG. 4, the distal end of guide tube  22  is adhered over a high resistivity layer  30  of a polymer, such as an epoxy resin. The layer  30 , in turn, overlies a conductive ring  32 . 
     The distal end of the signal wire  12  is attached to conductive ring  32 , which is conductively connected to the outer electrically conductive coating  34  on the outer surface of tip  16 , preferably using a highly conductive material, like epoxy resin. 
     In this arrangement, the inflation lumen  27  forms a fluid pressure transmitting conduit which communicates with the interior of body  16 . The lumen  27  extends from the injection port  18  through the bore  25  of the guide tube  22  to the distal tip  24 . 
     The physician has the option to maneuver the distal catheter tip  24  toward the desired endocardial location. The physician may inflate the body  16  whenever the physiology and safety of the patient allows, either within the heart or while in transit toward the heart, by conducting positive fluid pressure through the lumen  27  to the inflatable body  16 . 
     The positive fluid pressure causes the body  16  to expand or inflate. The inflating body  16  deploys outward, assuming a prescribed three dimension shape. The shape can vary, depending upon the premolded configuration of the body  16 . In the illustrated embodiment, the body  16  assumes a somewhat spherical shape when inflated. 
     The inflation is conducted to the extent that the body  16  is filled and expanded, but not stretched. The electrical conductivity of the coating on the body  16  is thus not disturbed or impaired. 
     Due to its pliant nature, the body  16 , when inflated, naturally conforms to the topography of the endocardial surface next to it. 
     Release of the positive fluid pressure and the application of negative pressure through the supply conduit will drain fluid from the body  16 . The body  16  collapses back into a deflated condition and, depending on the specific catheter design, may be retracted back into the catheter. 
     Alternatively, a movable sheath controlled by a retraction mechanism can be used to selectively enclose the body  16  before and after use, during insertion into and retraction from the body. The retraction mechanism is retracted to free the body  16  for inflation and use. 
     The body  16  can be carried on existing catheter assemblies. When in its normal, low profile condition, shown in FIG. 1, the body  16  maintains a standard 6, 7, or 8 French size. When in its inflated condition, shown in FIG. 2, the same body  16  has an significantly enlarged dimension ranging from approximately 7 mm to 12 mm. 
     In the illustrated and preferred embodiment (see FIG.  4 ), the system  10  includes monitoring means  42  for sensing the temperature. 
     While the monitoring means  42  may be variously constructed, in the illustrated embodiment, it temperature sensing means  44  associated with the body  16 . The means  44  includes a small bead thermistor with associated lead wires  46  that pass through the interior of the body  16 . A sheath  48  provides a protective conduit for the lead wires  46 . The wires  46  extend back to the handle  20  for electrical connection to cable  28 . 
     Preferably, the system  10  also includes control means (not shown) for the energy power supply that is responsive to the sensed temperature for performing generator control functions.