Abstract:
A catheter system having a tip with fixation means for use in treatment of tissues, such as ablating tumors in a natural body conduit or cavity by applying RF energy through the tip, wherein the catheter system passes through a natural body opening to reach the target tissue, wherein the catheter system stays at a desired position via its fixation means, and delivers therapeutic RF energy to the target tissue for improved tissue treatment.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to novel constructions for a catheter system. More particularly, this invention relates to a mapping and/or ablation catheter system with fixation means for use in mapping and/or treatment of cardiac tissues and in other medical applications, such as ablating tumors in a natural body conduit or cavity by applying RF energy. The catheter system passes through a natural body opening to reach the target tissue, where the catheter stays in a desired position via its fixation means and maps the cardiac electrical potential as well as delivers therapeutic energy to the target tissue for improved treatment. 
     BACKGROUND OF THE INVENTION 
     Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an &#34;arrhythmogenic site&#34; or &#34;accessory atrioventricular pathway&#34; close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways which are responsible for the propagation of electrical signals from upper to lower chamber necessary for performing normal systole and diastole function. The presence of arrhythmogenic site or accessory pathway can bypass or short circuit the normal pathway, potentially resulting in very rapid heart contractions, referred to here as tachycardias. 
     Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to the exact site for ablation. Once at the site, it is important for a physician to control the emission of energy to ablate the tissue within the heart. 
     Of particular interest to the present invention are radiofrequency (RF) ablation protocols which have proven to be highly effective in tachycardia treatment while exposing a patient to minimal side effects and risks. Radiofrequency catheter ablation is generally performed after conducting an initial mapping study where the locations of the arrhythmogenic site and/or accessory pathway are determined. After a mapping study, an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the ablation tip electrode lies exactly at the target tissue site. Radiofrequency energy or other suitable energy is then applied through the tip electrode to the cardiac tissue in order to ablate the tissue of arrhythmogenic site or the accessory pathway. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated. 
     Typically a conventional electrophysiology catheter has had a tip which is very smooth and generally are hemispherically shaped and thus have a tendency to slip around in the chamber of the heart during the pumping of the heart. This is particularly true in certain areas of heart where it is difficult to apply positive pressure to the tip of the catheter. Because of the difficulty of retaining the tip of the catheter in certain position, the effectiveness of mapping and ablation is significantly compromised. 
     The tip section of a catheter is referred to here as the portion of that catheter containing at least one electrode. For illustration purpose, a catheter utilized in the endocardial radiofrequency ablation is inserted into a major vein or artery, usually in the neck or groin area. The catheter is then guided into an appropriate chamber of the heart by appropriate manipulation through the vein or artery. The tip of a catheter must be manipulatable by a physician from the proximal end of the catheter, so that the electrodes at the tip section can be positioned against the tissue site to be ablated. The catheter must have a great deal of flexibility in order to follow the pathway of major blood vessels into the heart. It must permit user manipulation of the tip even when the catheter body is in a curved and/or twisted configuration. The tip section of a conventional electrophysiology catheter that is deflectable usually contains one large electrode about 4 mm in length for ablation purpose. 
     After the exact location of a target tissue is identified, the ablation catheter may still not easily approach the target site. An external ultrasonic imaging capability therefore becomes in need so that ablation is not taking place in an inappropriate location. The fluoroscope time can be substantially cut short when an external ultrasonic imaging is used instead. In the U.S. Pat. No. 4,794,931, there has been disclosed a catheter and system which can be utilized for ultrasonic imaging. However, there is no disclosure to how such a catheter and system can be utilized in conjunction with an endocardial ablation catheter having a tip section with fixation means to achieve the desired ultrasonic imaging and ultimately the desired ablation. 
     While a radiofrequency electrophysiology ablation procedure using an existing catheter has had promising results, the tip of a known catheter may not continuously contact the cardiac tissue intimately during the mapping and/or ablation period. Therefore there is a need for an improved catheter which can be utilized for mapping and ablation and in which is possible to temporarily affix the tip section of the catheter so that it will remain in a desired position on the wall of the heart during beating of the heart. 
     SUMMARY OF THE INVENTION 
     In general, it is an object of the present invention to provide an improved catheter which can be used in mapping and/or ablating cardiac tissue in the wall of a heart and which is provided with fixation means for retaining the tip section in a desired position on the wall of the heart. The capability of affixing the tip section of the catheter in place may also be applicable to means of ablating the tumors in a body natural conduit or cavity. 
     In one embodiment, a catheter system comprising: a catheter sheath with a distal section, a distal end, a proximal end, and at least one lumen extending therebetween; a handle attached to the proximal end of said catheter sheath; an inner catheter, which is longer than said catheter sheath and is located inside the lumen of the catheter sheath, comprising a flexible elongate tubular member having a distal section, proximal extremity, and distal extremity, wherein said handle is attached to the proximal extremity of the inner catheter; and the distal section of said catheter sheath having a retractable fixation deployment means secured at a securing point on the flexible elongate tubular member of the inner catheter, wherein said retractable fixation deployment means including a plurality of spaced apart expandable members. The catheter system also comprises a non-deployed state for said retractable fixation deployment means when said catheter system being advanced into the body of a patient and/or being removed from the body of a patient, and further comprises a distended deployed state for said retractable fixation deployment means when said catheter system is positioned at the target location of the body. 
     Another object of the invention is to provide a catheter with retractable fixation deployment means in which the fixation means can be deployed and undeployed between the mapping and/or ablation operations. Another object of the invention is to provide a catheter with retractable fixation deployment means in which the fixation means can be readily maneuvered, applied, and controlled by a deployment mechanism at the handle. 
     The catheter system further comprises a steering mechanism at the handle for controlling the deflection of said distal section of the flexible elongate tubular member of the inner catheter. Usually a rotating ring or a push-pull plunger is employed in the steering mechanism. In another embodiment, the steerable ablation catheter comprises a bi-directional deflection or multiple curves deflection of the tip section having retractable fixation deployment means. One end of the steering wire is attached at certain point of the distal section of the flexible elongate tubular member of said inner catheter. The other end is attached to the steering mechanism at the handle. The steering mechanism on a steerable catheter or device is well-known to those who are skilled in the art. 
     At least one conducting wire which is soldered to an electrode, passes through the lumen of the inner catheter and the interior void of the handle and is thereafter soldered to a contact pin of the connector which is secured at the proximal end of the handle. Therefrom, the conducting wire is connected to an external RF generator for ablation operations and/or to an EKG monitor for recording and display of the endocardial electrical signal. 
     In an additional embodiment, the catheter system further comprises a temperature sensing and close-loop temperature control mechanism for the catheter system having at least one temperature sensor on the distal section of the inner catheter. The location of the temperature sensor is preferably in the very proximity of one of the electrodes. In a still further embodiment, a method for operating an ablation catheter system of this invention further comprises a programmed temperature control mechanism for independently controlling the delivery of RF energy of each electrode of the ablation catheter. 
     In a still further embodiment, the distal section of the flexible elongate tubular member of the inner catheter comprises at least one electrode which is formed of a conducting material, wherein the material for the electrode may consist of conductive metals such as platinum, iridium, gold, silver, stainless steel, Nitinol, or an alloy of their mixture. The conducting metal and its fabrication to form an electrode to be used in a catheter is well known to those who are skilled in the art. 
     The catheter system of this invention further comprises a plurality in excess of three spaced apart expandable members for the retractable fixation deployment means. In a preferred embodiment, the catheter system comprises a plurality in excess of five spaced apart expandable members for the retractable fixation deployment means. The construction material for the expandable members may be selected from the group of polyethylene, polyurethane, polyether block amide polymer, stainless steel, high strength Nitinol and the like. The expandable members are part of the catheter sheath which has a continuous linear smooth surface when the retractable fixation deployment means is at its undeployed state. The expandable members have a preshaped memory and extend to their preformed shape when the retractable fixation deployment means is deployed. 
     In another embodiment, the catheter system of this invention further comprises expandable members of said retractable fixation deployment means having a preshaped memory, and extending at an angle of less than 90 degrees, preferably less than 45 degrees, relative to the proximal side of the longitudinal axis of the inner catheter when the deployment means is deployed. In a further embodiment, the catheter system further comprises expandable members of said retractable fixation deployment means having a preshaped memory, and extending with a curved concave or convex fashion at an acute angle relative to the proximal side of the longitudinal axis of the inner catheter when the deployment means is deployed. 
     In an alternate embodiment, a catheter system comprises: an inner catheter, having a flexible elongate tubular member having a distal section, and proximal and distal extremities, wherein the distal section has a thread for coupling purpose on the outside of the flexible elongate tubular member; an exchangeable handle attached to the proximal extremity of the inner catheter; at least one electrode is disposed at the distal section of the flexible elongate tubular member of said inner catheter; and a slidable catheter sheath, having a distal section, a proximal end, a distal end, and a lumen extending therebetween, wherein a matching tap hole for coupling purpose is disposed close to the distal end of the catheter sheath, and further having a retractable fixation deployment means at the distal section of the catheter sheath, wherein said retractable fixation deployment means including a plurality of spaced apart expandable members. The catheter system further comprises a non-deployed state for said retractable fixation deployment means when said catheter sheath is advanced into the body of a patient and/or being removed from the body, and further comprising a distended deployed state for said retractable fixation deployment means when said catheter system is positioned at the target location of the body. 
     A method for operating a catheter system comprises: introducing the catheter system having an inner catheter and an outer catheter sheath under a non-deployed state into the body through a small surgery hole or through the natural body openings; and once approaching the target tissue, deploying the retractable fixation deployment means at distal section of said catheter sheath by a deployment mechanism located at the handle. The method for operating a catheter system of this invention further comprises at least one electrode mounted on the distal section of the flexible elongate tubular member of the inner catheter. The method for operating a catheter system further comprises measuring the endocardial electricity from or applying RF energy to the at least one electrode on the distal section of the flexible elongate tubular member of the inner catheter. 
     Another object of the invention is to provide a catheter and methods in which it is possible to view the area to be ablated prior to ablation to ensure that ablation is being carried out in an appropriate location. The distal section of the flexible elongate member of the inner catheter having retractable fixation deployment means is encoded with plurality of markers which are visible to ultrasonic energy. The markers have been provided in the form of encapsulated air bubbles. 
     The catheter system of the present invention have several significant advantages over known catheter or ablation techniques. In particular, the catheter system having a retractable fixation deployment means may result in a firm and intimate tissue contact between the electrode and the target tissue during tissue ablation, resulting in a deep and large lesion which is highly desirable in tachycardiac treatment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and features of the present invention will become more apparent and the invention itself will be best understood from the following Detailed Description of the Preferred Embodiments, when read with reference to the accompanying drawings. 
     FIG. 1 is an overall view of the catheter system having a retractable fixation deployment means constructed in accordance with the principles of the present invention. 
     FIG. 2 is a close-up view of the distal section of the catheter system at non-deployed state. 
     FIG. 3 is a close-up view of the distal section of the catheter system at fully deployed state. 
     FIG. 4 is a cross-sectional view of the expandable members of the catheter sheath of FIG. 3. 
     FIG. 5 is a close-up view of the distal section of an alternate catheter system at non-deployed state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an overall view of the catheter system having a distal section comprising retractable fixation deployment means. A catheter system constructed in accordance with the principles of the present invention comprises: a catheter sheath 1 having a distal tip section 10, a distal end 7, a proximal end 11, and at least one lumen extending therebetween. The catheter also comprises an inner catheter 12 which is longer than the catheter sheath and is located within the lumen of the catheter sheath 1. A handle 4 is attached to the proximal end 11 of said catheter sheath 1. 
     The connector 3 secured at the proximal end of the catheter system, is part of the handle 4. The handle has one steering mechanism 5. The steering mechanism 5 is to deflect the tip section 13 of the inner catheter 12 for catheter maneuvering and positioning. By pushing the front plunger 8 of the handle 4, the tip section of the flexible elongate member of the inner catheter 12 deflects to one direction. By pulling the front plunger 8, said tip section returns to its neutral position. In another embodiment, the steering mechanism 5 at the handle 4 comprises means for providing a plurality of deflectable curves on the distal tip section 13 of the inner catheter. 
     FIG. 2 shows a close-up view of the distal section of the catheter system having retractable fixation deployment means at non-deployed state. In one embodiment, the distal section 13 of the inner catheter 12 has a tip electrode 14 and at least one band electrode 15. The electrode is constructed of a conducting material. The distal section of the catheter system having retractable fixation deployment means 16 at non-deployed state, wherein the retractable fixation deployment means 16 is secured at a securing point 7 on the flexible elongate tubular member of the inner catheter 12. 
     FIG. 3 shows a close-up view of the distal section of the catheter system having retractable fixation deployment means 16 at deployed state. The distal section 10 of the catheter sheath 1 has a retractable fixation deployment means 16 secured at a securing point 7 on the flexible elongate tubular member of the inner catheter 12, wherein the securing point 7 is located proximal to the distal section 13 of the flexible elongate tubular member of the inner catheter 12. The deployment of the retractable fixation deployment means 16 is controlled by a deployment mechanism 6 at the handle 4 (FIG. 1). A controlling ring 9 is used to deploy the retractable fixation deployment means 16 at the distal section 10 of the catheter sheath 1. FIG. 4 shows a cross-sectional view of the catheter system which comprises expandable members 17 of the retractable fixation deployment means 16, having a preshaped memory. The expandable members extend with a curved concave or convex fashion at an acute angle relative to the proximal side of the longitudinal axis of the inner catheter 12 when the deployment means 16 is deployed. 
     The catheter system has at least one temperature sensor 18 and ultrasonic imaging capabilities. In order to enhance the ablation positioning of said ablation catheter, the electrode is encoded with at least one marker 19 which is visible to ultrasonic energy. Such markers 19 are provided in the form of encapsulated air bubbles. Several markers 19 are placed in the proximity of the electrodes 14 or 15 in a way so that the exact location of the distal section 13 is visible to an external ultrasonic energy. By way of example, the bubble in a marker can be formed by introducing air by a syringe (not shown) penetrating the wall of the substrate sheath of said catheter sheath and thereafter is sealed by epoxy. 
     The electrode has an insulated conducting wire 20 secured to the electrode, which passes through the lumen of the inner catheter 12 and is soldered to a contact pin of the connector 3 at the proximal end of the handle 4. The conducting wire from the connector end is externally connected to an EKG for diagnosis or to an RF generator during an electrophysiology ablation procedure. Therefrom, the RF energy is transmitted through the conducting wire to the electrode and delivered the energy to the target tissue. 
     A temperature sensor 18, either a thermocouple means or a thermister means, is constructed at the proximity of the electrode 14 or 15 to measure the tissue contact temperature when RF energy is delivered. The temperature sensing wire 21 from the thermocouple or thermister is connected to one of the contact pins (not shown) of the connector 3 and externally connected to a transducer and to a close-loop temperature controller. The temperature reading is thereafter relayed to a close-loop control mechanism to adjust the RF energy output. The RF energy delivered is thus controlled by the temperature sensor reading or by a pre-programmed control algorithm. 
     FIG. 5 shows a close-up view of the distal section of an alternate catheter system at non-deployed state. The catheter system comprises an inner catheter 22, having a flexible elongate tubular member having a distal section 23, and proximal and distal extremities, wherein the distal section has a thread 24 on the outside of the flexible elongate tubular member; an exchangeable handle attached to the proximal extremity of the inner catheter (not shown); at least one electrode 25 or 26 is disposed at the distal section 23 of the flexible elongate tubular member of said inner catheter 22; and a slidable catheter sheath 27, having a distal section 28, a proximal end, a distal end 29, and a lumen extending therebetween, wherein a matching tap hole 30 is disposed close to the distal end of the catheter sheath 27, and further having a retractable fixation deployment means 16 at the distal section of the catheter sheath 27, wherein said retractable fixation deployment means includes a plurality of spaced apart expandable members 17. During operation, the inner catheter is inserted into the body of a patient, the inner catheter alone may function as an electrophysiology catheter for the purpose of mapping and/or ablation. When the catheter fixation need arises, the exchangeble handle is removed from the inner catheter, and a catheter sheath of this invention is inserted over the inner catheter. The catheter sheath and the inner catheter is engaged by coupling the tap hole of the catheter sheath and the thread of the inner catheter. After replacing the exchangeable handle, the catheter system is ready for operation having retractable fixation deployment means. After the operation is concluded, the coupled catheter system, including the catheter sheath and the inner catheter, is deployed first and is thereafter removed from the body of a patient together as a catheter system. The cardiovascular catheter system with exchangeable handles is disclosed in a pending application Ser. No. 08/733,778, filed 1996 Oct. 18. 
     From the foregoing, it should now be appreciated that an improved ablation catheter having retractable fixation deployment means has been disclosed for mapping and/or ablation procedures, including endocardial, epicardial, or body tissue. While the invention has been described with reference to a specific embodiment, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as described by the appended claims.