Abstract:
The invention relates to an ablation catheter which controls the temperature and reduces the coagulation of biological fluids on an electrode of a catheter, prevents the impedance rise of tissue in contact with the electrode, and maximizes the potential energy transfer to the tissue, thereby allowing an increase in the lesion size produced by the ablation. The electrode includes passages positioned to allow saline flow out of an inner cavity of the electrode. This fluid flow produces the desired cooling effect and is accomplished, for example, by saline irrigation flow with a valve element to block flow of blood into the inner cavity of the electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. applications (serial numbers not yet available) entitled Irrigated Ablation Catheter System With Pulsatile Flow To Prevent Thrombus (Docket No. 0B-051300US); Irrigated Ablation Catheter Having A Pressure Sensor to Detect Tissue Contact (Docket No. 0B-051900US); and Cooled Ablation Catheter With Reciprocating Flow (Docket No. 0B-052500US), all filed 28 Dec. 2006 and now pending. These applications are all hereby incorporated by reference as though fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    a. Field of the Invention 
         [0003]    The instant invention relates to catheters. In particular, the instant invention relates to an irrigated ablative catheter tip with an irrigated catheter tip having a valve to prevent backflow. 
         [0004]    b. Background Art 
         [0005]    Electrical stimulation of myocardial tissue controls the pumping action of the heart. Stimulation of this tissue in various regions of the heart is controlled by a series of conduction pathways contained within the myocardial tissue. In a healthy heart, contraction and relaxation of the heart muscle (myocardium) occur in an organized fashion as electro-chemical signals pass sequentially through the myocardium from the sinoatrial (SA) node, which consists of a bundle of unique cells disposed in the wall of the right atrium, to the atrioventricular (AV) node, and then into the left and right ventricles via a route that includes the His-Purkinje system. The AV node is located near the ostium of the coronary sinus in the interatrial septum in the right atrium. Each cell membrane of the SA node has a characteristic tendency of a gradual leak of sodium ions over time leading to a periodic break down of the cell membrane periodically, thus allowing an inflow of sodium ions, and thereby causing the SA node cells to depolarize. The SA node cells are in communication with the surrounding atrial muscle cells such that the depolarization of the SA node cells causes the adjacent atrial muscle cells to also depolarize. This depolarization results in atrial systole, during which the atria contract to empty and fill blood into the ventricles. The AV node detects the atrial depolarization from the SA node and, in turn, relays the depolarization impulse into the ventricles via the bundle of His and Purkinje fibers following a brief conduction delay. The His-Purkinje system begins at the AV node and follows along the membranous interatrial septum toward the tricuspid valve through the AV septum and into the membranous interventricular septum. At about the middle of the interventricular septum, the His-Purkinje system splits into right and left branches, which straddle the summit of the muscular part of the interventricular septum. 
         [0006]    Abnormal rhythms generally referred to as arrhythmia can occur in the heart. Cardiac arrhythmias arise when the pattern of the heartbeat is changed by abnormal impulse initiation or conduction in the myocardial tissue. The term tachycardia is used to describe an excessively rapid heartbeat resulting from repetitive stimulation of the heart muscle. Such disturbances often arise from additional conduction pathways that are present within the heart either from a congenital developmental abnormality or an acquired abnormality, which changes the structure of the cardiac tissue, such as a myocardial infarction. 
         [0007]    A common arrhythmia is Wolff-Parkinson-White syndrome (W-P-W). The cause of W-P-W is generally believed to be the existence of an anomalous conduction pathway or pathways that connect the atrial muscle tissue directly to the ventricular muscle tissue, thus bypassing the normal His-Purkinje system. These pathways are usually located in the fibrous tissue that connects the atrium and the ventricle. 
         [0008]    Atrial arrhythmia may also occur. Three of the most common atrial arrhythmia are ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Atrial fibrillation can cause significant patient discomfort and even death because of a number of associated problems, including e.g., an irregular heart rate (which causes patient discomfort and anxiety), loss of synchronous atrioventricular contractions (which compromises cardiac hemodynamics, resulting in varying levels of congestive heart failure) and stasis of blood flow (which increases the likelihood of thromboembolism). 
         [0009]    In the past, problems associated with arrhythmia have been treated with pharmacological treatment. Such treatment may not be effective in all patients and is frequently plagued with side effects, including, e.g., dizziness, nausea, vision problems, and other difficulties. 
         [0010]    Alternatively, such disturbances are treated by identifying the conductive pathways and then severing part of this pathway by destroying these cells, which make up a portion of the pathway. Traditionally, this has been done by either cutting the pathway surgically; freezing the tissue, thus destroying the cellular membranes; or by heating the cells, thus denaturing the cellular proteins. The resulting destruction of the cells eliminates their electrical conductivity, thus destroying, or ablating, a certain portion of the pathway. By eliminating a portion of the pathway, the pathway may no longer maintain the ability to conduct, and the tachycardia ceases. 
         [0011]    Catheters are a common medical tool that has been used for many years. They are employed, e.g., for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. In such procedures, a catheter is first inserted into a vessel near the surface of the body and the guided to a specific location within the body. For example, a catheter may be used to convey an electrical stimulus to a selected location within the human body or a catheter with sensing electrodes may be used to monitor various forms of electrical activity in the human body. 
         [0012]    Catheters have increasingly become a common medical procedure for the treatment of certain types of cardiac arrhythmia. Catheter ablation is based on the idea that by ablation (i.e., destroying) abnormal tissue areas in the heart, its electrical system can be repaired and the heart will return to a normal rhythm. During catheter ablation, the catheter is typically inserted in an artery or vein in the leg, neck, or arm of the patient and then threaded, sometimes with the aid of a guide wire or introducer, through the vessels until a distal tip of the catheter reaches the desired location for the medical procedure in the heart. 
         [0013]    Most often, cardiac ablation is used to treat supraventricular tachycardias, or SVTs. Types of SVTs are atrial fibrillation, atrial flutter, AV nodal reentrant tachycardia, AV reentrant tachycardia, and atrial tachycardia. Less frequently, ablation can treat heart rhythm disorders that begin in the heart&#39;s lower chambers, known as the ventricles. The most common, ventricular tachycardia may also be the most dangerous type of arrhythmia because it can cause sudden cardiac death. For patients at risk for sudden cardiac death, ablation often is used along with an implantable cardioverter device (ICD). The ablation decreases the frequency of abnormal heart rhythms in the ventricles and therefore reduces the number of ICD shocks a patient may experience. For many types of arrhythmias, catheter ablation is successful in 90-98 percent of cases, thus eliminating the need for open-heart surgeries or long-term drug therapies. 
         [0014]    During conventional catheter ablation procedures, an energy source is in contact with cardiac tissue to heat the tissue and create a permanent scar or lesion that is electrically inactive or non-contractile. These lesions are designed to interrupt existing conduction pathways commonly associated with arrhythmias within the heart. The particular area for ablation depends on the type of underlying arrhythmia. One common ablation procedure treats atrioventricular nodal reentrant tachycardia (AVNRT). The use of electrode catheters for ablating specific locations within the heart has also been disclosed in, e.g., U.S. Pat. Nos. 4,641,649, 5,228,442, 5,231,995, 5,263,493, and 5,281,217. 
         [0015]    Many variations of ablations procedures are known. For example, ablation of fast or slow AV nodal pathways is disclosed in Singer et al., Catheter Ablation for Arrhythmias, Clinical Manual of Electrophysiology, 421-431 (1993). 
         [0016]    Another medical procedure using ablation catheters with sheaths to ablate accessory pathways associated with W-P-W using both a transseptal and retrograde approach is discussed in Saul et al., Catheter Ablation of Accessory Atrioventricular Pathways in Young Patients: Use of long vascular sheaths, the transseptal approach and a retrograde left posterior parallel approach,  Journal of the American College of Cardiology,  21(3), 571-583 (1993). Additional catheter ablation procedures are disclosed in Swartz, Radiofrequency Endocardial Catheter Ablation of Accessory Atrioventricular Pathway Atrial Insertion Sites,  Circulation,  87 (2), 487-499 (1993). 
         [0017]    Ablation of a specific target requires precise placement of the ablation catheter within the heart. Precise positioning of the ablation catheter is especially difficult due the physiology of the heart, particularly since the heart continues to beat throughout the ablation procedures. Typically, the choice of placement of the catheter is determined by a combination of electrophysiological guidance and fluoroscopy. Fluoroscopy is placement of the catheter in relation to known features of the heart, which are marked by radiopaque diagnostic catheters that are placed in or at known anatomical structures, such as the coronary sinus, high right atrium, and the right ventricle. 
         [0018]    Ablation procedures using guiding introducers to direct an ablation catheter to a particular location in the heart for treatment of atrial arrhythmia have been disclosed in, e.g., U.S. Pat. Nos. 5,427,119, 5,497,774, 5,564,440, 5,575,766, 5,628,316, and 5,640,955. During these procedures, ablation lesions are produced in the heart. 
         [0019]    A variety of energy sources can be used to supply the energy necessary to ablate cardiac tissue and create a permanent lesion. Such energy sources include direct current, laser, microwave, and ultrasound. Because of problems associated with the use of DC current, radiofrequency (RF) has become the preferred source of energy for ablation procedures. The use of RF energy for ablation has been disclosed, e.g., in U.S. Pat. Nos. 4,945,912, 5,242,441, 5,246,438, 5,281,213, 5,281,218, and 5,293,868. The use of RF energy with an ablation catheter contained within a transseptal sheath for the treatment of W-P-W in the left atrium is disclosed in Swartz et al., Radiofrequency Endocardial Catheter Ablation of Accessory Atrioventricular Pathway Atrial Insertion Sites,  Circulation,  87: 487-499 (1993). See also Tracey, Radio Frequency Catheter Ablation of Ectopic Atrial Tachycardia Using Paced Activation Sequence Mapping,  J. Am. Coll. Cardiol.  21: 910-917 (1993). 
         [0020]    Conventional ablation procedures use a single electrode secured to the tip of an ablation catheter. It has become increasingly more common to use multiple electrodes affixed to the catheter body. Such ablation catheters often contain a distal tip electrode and a plurality of ring electrodes as disclosed in, e.g., U.S. Pat. Nos. 4,892,102, 5,228,442, 5,327,905, 5,354,297, 5,487,385, and 5,582,609. 
         [0021]    During conventional ablation procedures, the ablating energy is delivered directly to the cardiac tissue by an electrode on the catheter placed against the surface of the tissue to raise the temperature of the tissue to be ablated. The increase in tissue temperature also results in a rise in the temperature of blood surrounding the electrode. This rise in temperature often results in the formation of coagulum on the electrode, which in turn reduces the efficiency of the ablation electrode. Thus, to achieve efficient and effective ablation, coagulation of blood should be avoided. This coagulation problem can be especially significant when linear ablation lesions or tracks are produced because such linear ablation procedures take more time than ablation at only a single location. 
         [0022]    The formation of linear lesions within a heart via conventional ablation tip electrode requires use of procedures such as e.g., a “drag burn.” A “linear lesion” means an elongate, continuous lesion, which may be straight or curved, that blocks electrical conduction. During a “drag burn” procedure, while energy is supplied to the electrode, the electrode is drawn across the tissue to be ablated, producing a line of ablation. Alternatively, a series of points of ablation are formed in a line created by moving the tip electrode incremental distances across the cardiac tissue. The effectiveness of these procedures depends on a number of variables such as e.g., (i) the position and contact pressure of the tip electrode of the ablation catheter against the cardiac tissue, (ii) the time that the tip electrode of the ablation catheter is placed against the tissue, (iii) the amount of coagulum formed as a result of heat generated during the ablation procedure, and (iv) other variables associated with a beating heart, especially an erratically beating heart. An uninterrupted track of cardiac tissue needs to be ablated as unablated tissue or incompletely ablated tissue may remain electrically active, thereby permitting the continuation of stray circuits that cause arrhythmia. 
         [0023]    More efficient ablation can be achieved if a linear lesion of cardiac tissue is formed during a single ablation procedure. The production of linear lesions in the heart by use of an ablation catheter is disclosed in, e.g., U.S. Pat. Nos. 5,487,385, 5,582,609, and 5,676,662. A specific series of linear lesions formed in the atria for the treatment of atrial arrhythmia are disclosed in U.S. Pat. No. 5,575,766. 
         [0024]    Physical contact of the cardiac tissue with an electrode of the ablation catheter is typically used to perform these procedures on electrically inactive or non-contractile tissue. Conventional tip electrodes with adjacent ring electrodes cannot perform this type of procedure, however, due to the high amount of energy necessary to ablate sufficient tissue to produce a complete linear lesion. In addition, conventional ring electrode ablation may leave holes or gaps in a lesion, which can provide a doorway for the creation of unwanted circuits. 
         [0025]    U.S. Pat. No. 5,334,193 discloses an ablation catheter for use in the heart that contains a pair of intertwined helical electrodes. The helically wound electrode is affixed to the surface of the catheter body over a distance of about eight centimeters from the distal tip of the catheter body. Other helical electrodes are disclosed in WO 95/10319 as well as U.S. Pat. Nos. 4,161,952, 4,776,334, 4,860,769, 4,934,049, 5,047,026, and 5,542,928. 
         [0026]    As discussed a variety of energy such as radiofrequency (RF), microwave, ultrasound, and laser energy have been used for ablation. With RF energy, a catheter with a conductive inner core and a metallic tip are placed in contact with the myocardium and a circuit is completed with a patch placed on the patient&#39;s body behind the heart. The catheter is coupled to a RF generator such that application of electrical energy creates localized heating in the tissue adjacent to the distal (emitting) electrode. The peak tissue temperatures during catheter delivered application of RF energy to the myocardium occur close to the endocardial surface, such that the lesion size produced is limited by the thermodynamics of radiant heat spread from the tip. The amount of heating which occurs is dependent on the area of contact between the electrode, and the tissue and the impedance between the electrode and the tissue. The higher the impedance, the lower the amount of energy transferred into the tissue. 
         [0027]    During RF catheter ablation, local temperature elevation can result in coagulum formation on the ablation electrode, resulting in impedance rise. As the impedance increases, more energy is passed through the portion of the tip without coagulation, creating even higher local temperatures and further increasing coagulum formation and the impedance. Finally, enough blood coagulates onto the tip that no energy passes into the tissue. The catheter must now be removed from the vascular system, the tip area cleaned and the catheter repositioned within the heart at the desired location. Not only can this process be time consuming, but also it may be difficult to return to the previous location because of the reduced electrical activity in the regions, which have previously been ablated. A recent study has also demonstrated the formation of a so-called soft thrombus during experimental ablations (Demonlin et al., Soft thrombus formation in radiofrequency catheter ablation,  Pacing clin. electrophysiol.  25(8): 1219-1222 (2002)). The formation of the so-called soft thrombus results from heat induced protein denaturation and aggregation and occurs independent of heparin concentration in serum. 
         [0028]    In order to effectively cool the electrode at any possible catheter electrode orientation, it is important to maintain a saline flow rate of, for example, 20-30 ml/minute. The high saline volume can result in a deterioration of the patient&#39;s condition. In part, this occurs due to hemodilution affecting the volume, placing additional stresses on the heart/circulatory system. This can lead to edema and swelling. Thus, there is a need for a method of cooling the electrode during ablation without using an excess of saline in irrigation. 
         [0029]    Another possible problem with open irrigated ablation catheters is that there are no physical blocks to prevent the backflow of blood when saline irrigation flow stops. There is a potential problem of blood&#39;s flowing back into the catheter through the irrigation orifices due to blood pressure inside the heart—especially inside the ventricle. This blood backflow could cause blood clotting inside the catheter, potentially resulting in catheter malfunction. 
         [0030]    The current method of preventing backflow of blood into the catheter is maintaining a low irrigation flow rate at all times during a procedure. However, this method can result in delivery of an excess of saline to the patient&#39;s bloodstream over a long procedure. Fluid overload or hemodilution can cause many complications in heart patients. Thus, it is desirable to have a catheter which can prevent blood backflow into the catheter. 
       BRIEF SUMMARY OF THE INVENTION 
       [0031]    It is desirable to have a catheter that will prevent backflow of blood into a catheter when irrigation flow is stopped. 
         [0032]    A first embodiment of the invention is an irrigated ablation catheter comprising: a distal member which includes an electrode, the distal member having an inner cavity with an open proximal end and one or more through holes from the inner cavity to an outer surface of the distal member; a self-actuated valve element disposed in the inner cavity of the distal member for preventing backflow of fluids into the inner cavity of the distal member, the self-actuated valve element having a proximal end and a distal end; and a fluid tube having a distal end and a proximal end, the fluid tube distal end being connected to the open proximal end of the distal member. 
         [0033]    In one variation of the first embodiment of the invention, the valve element is umbrella-shaped, and collapsible and expandable inside the inner cavity of the distal member, the valve member expanding to cover the one or more through holes of the distal member, and the valve element collapsing to uncover the one or more through holes of said distal member. The valve element may be collapsible and expandable in response to a variable pressure generated in the inner cavity of the distal member. 
         [0034]    The first embodiment of the invention may further comprise a support core that supports the valve element inside the inner cavity of the distal member. The support core may be attached to the distal member. In another variation of the first embodiment of the invention, the valve element comprises an elastic material. The elastic material may be a synthetic rubber. 
         [0035]    The first embodiment of the invention may also further comprise a spring attached to the distal end of the valve element; wherein the valve element is movable between a closed position preventing fluid flow into the inner cavity of the distal member through the one or more through holes, and an open position allowing fluid flow from the inner cavity of the distal member through the one or more through holes; wherein the valve element is resiliently biased by the spring toward the closed position, and wherein the valve element is moved to the open position if a fluid pressure within the inner cavity of the distal member exceeds a set pressure. 
         [0036]    In another variation of the first embodiment of the invention, the valve element is made of a rigid material. The valve element may have a distal stem with a diameter slightly smaller than the diameter of the distal portion of the inner cavity of the distal member such that the distal stem of the valve element is capable of sliding within the reduced distal diameter of the inner cavity of the distal member. The spring may comprise a shape memory material. The proximal end of the valve element may be cone-shaped. 
         [0037]    The first embodiment of the invention may further comprise a ring shaped seal member located on the proximal side of the valve member. 
         [0038]    In a variation of the first embodiment, the valve element comprises a balloon disposed in the inner cavity of the distal member; and the balloon is inflatable and deflatable inside the inner cavity of the distal member to block and unblock fluid flow through the one or more through holes, respectively, in response to a variable pressure generated in the inner cavity of the distal member. 
         [0039]    A second embodiment of the invention is an irrigated ablation catheter comprising: a distal member which includes an electrode, the distal member having an inner cavity with an open proximal end and one or more through holes from the inner cavity to an outer surface of the distal member; a valve element disposed in the inner cavity of the distal member, the valve element having a proximal end and a distal end, the valve element being movable between a closed position to block fluid flow through the one or more through holes and an open position to allow fluid flow through the one or more through holes, the valve member being movable to the open position to provide fluid flow from the inner cavity through the one or more through holes to a region outside the distal member; and a fluid tube having a distal end and a proximal end, the distal end of the fluid tube being connected to the open proximal end of the distal member. 
         [0040]    The second embodiment of the invention may further comprise an adjustment member connected to the valve element to move the valve element between the open position and the closed position. The adjustment member may comprise a push/pull wire or a rotation wire. 
         [0041]    The second embodiment of the invention may further comprise means for moving the valve element between the open position and the closed position if a pressure in the inner cavity exceeds a preset pressure. The valve element may be movable between the open position and the closed position in response to a variable pressure generated in the inner cavity of the distal member. The valve element may be resiliently biased toward the closed position. The proximal end of the valve element may be cone shaped. 
         [0042]    The second embodiment of the invention may further comprise a seal member disposed to contact the valve member in the closed position and form a sealed contact with the valve member to block fluid flow through the one or more through holes. 
         [0043]    In one variation of the second embodiment of the invention, the distal member includes a manifold having a distal end connected to the electrode and an open proximal end connected to the distal end of the fluid tube. The one or more through holes of the distal member may be disposed in the manifold, and the manifold may comprise a thermally insulative material. 
         [0044]    A third embodiment of the invention includes an irrigated ablation catheter comprising: a distal member which includes an electrode, the distal member having an inner cavity with an open proximal end and one or more through holes from the inner cavity to an outer surface of the distal member; a valve element disposed in the inner cavity of the distal member, the valve element having a proximal end and a distal end, the valve element being movable between a closed position to block fluid flow through the one or more through holes and an open position to allow fluid flow through the one or more through holes; means for moving the valve member to the open position to provide fluid flow from the inner cavity through the one or more through holes to a region outside the distal member. 
         [0045]    The third embodiment of the invention may further comprise a fluid tube having a distal end and a proximal end, the distal end of the fluid tube being connected to the open proximal end of the distal member. In one variation of the third embodiment, the valve element is resiliently biased toward the closed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0046]      FIG. 1(   a ) is a cross-sectional view of the distal end of an irrigated ablation catheter with a self-closing valve in the closed position. 
           [0047]      FIG. 1(   b ) is the cross-sectional view of  FIG. 1(   a ) in which the self-closing valve is in the open position. 
           [0048]      FIG. 2(   a ) is a cross-sectional view of the distal end of an insulated irrigated ablation catheter with a self-closing valve in the closed position. 
           [0049]      FIG. 2(   b ) is the cross-sectional view of  FIG. 2(   a ) in which the self-closing valve is in the open position. 
           [0050]      FIG. 3(   a ) is a cross-sectional view of the electrode at the distal end of the body of an irrigated ablation catheter with a spring-loaded self-closing valve in the closed position. 
           [0051]      FIG. 3(   b ) is the cross-sectional view of  FIG. 3(   a ) in which the self-closing valve is in the open position. 
           [0052]      FIG. 4(   a ) is a cross-sectional view of the electrode at the distal end of the body of an insulated irrigated ablation catheter with a spring-loaded self-closing valve in the closed position. 
           [0053]      FIG. 4(   b ) is the cross-sectional view of  FIG. 4(   a ) in which the self-closing valve is in the open position. 
           [0054]      FIG. 5  is a detail of a spring-loaded self-closing valve. 
           [0055]      FIG. 6(   a ) is a cross-sectional view of the electrode at the distal end of the body of an insulated irrigated ablation catheter with a seal member and a spring-loaded self-closing valve in the closed position. 
           [0056]      FIG. 6(   b ) is the cross-sectional view of  FIG. 6(   a ) in which the self-closing valve is in the open position. 
           [0057]      FIG. 7(   a ) is a cross-sectional view of the distal end of an insulated irrigated ablation catheter with an on/off valve in the closed position actuated by a push/pull wire. 
           [0058]      FIG. 7(   b ) is the cross-sectional view of  FIG. 7(   a ) in which the valve is in the open position. 
           [0059]      FIG. 8(   a ) is a cross-sectional view of the distal end of an insulated irrigated ablation catheter with a rotating valve actuated by a rotation wire. 
           [0060]      FIG. 8(   b ) is section A-A of the cross-sectional view of  FIG. 8(   a ) in both the open and closed positions. 
           [0061]      FIG. 9(   a ) is a cross-sectional view of the distal end of an irrigated ablation catheter with an on/off valve comprising a balloon in the on (deflated) position. 
           [0062]      FIG. 9(   b ) is the sectional view of  FIG. 9(   a ) with the balloon in the off (inflated) position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    Several embodiments of an irrigated ablation catheter having a valve to prevent backflow are depicted in the figures. As described further below, the irrigated ablation catheter having a valve to prevent backflow according to the present invention provides a number of advantages, including, for example, reducing delivery of saline to a patient&#39;s bloodstream and reducing blood clotting inside the catheter. 
         [0064]      FIGS. 1(   a ) and  1 ( b ) are cross-sectional views of the distal end  100  of an irrigated ablation according to one embodiment of the invention. The distal end  100  comprises an electrode  102 , a catheter body  104 , a fluid tube  106 , a valve element  108 , and a valve element support core  110 . Electrode  102  includes an inner cavity  112  which houses valve element  108  and valve element support core  110 , and a plurality of through holes  114  from the inner cavity  112  to the exterior of electrode  102 . 
         [0065]    Valve element support core  110  may be made of any stiff material and offers structural support to valve element  108 . Valve element support core  110  may be attached to electrode  102  and valve element  108  by any means well-known in the art, including, but not limited to bonding and threading. Valve element  110  is in the shape of an umbrella and made of a flexible material such as silicone rubber, polyurethane, and other synthetic rubbers. 
         [0066]    Catheter body  104  is a flexible hollow tube attached to the proximal end of electrode  102  by any means well-known in the art such as bonding and swaging. Catheter body  104  may be constructed from a number of different polymers (e.g., polypropylene, oriented polypropylene, polyethylene, crystallized polyethylene terephthalate, polyethylene terephthalate, polyester, polyvinyl chloride, etc.), in which braiding is embedded. Catheter body  104  may be guided by a user by such means well-known in the art as puller wires. 
         [0067]    Fluid tube  106  is centered within the catheter body  104 , and is attached to the proximal open end of electrode  102  by any means well-known in the art such as bonding or swaging. Fluid tube  106  allows the flow of saline through holes  114  to providing cooling for electrode  102 . 
         [0068]    The umbrella shape of valve body  110  in the absence of a set amount of pressure, prevents flow of blood into, or saline out of, through holes  114 . When the pressure of saline within electrode  102  exceeds a preset amount, valve element  108  collapses around valve element support core  110 , allowing passage of the saline through holes  114  to cool electrode  102 . 
         [0069]      FIG. 1(   a ) shows distal end  100  with valve element  108  in a position such that it blocks through holes  114 , preventing saline flow through holes  114 . This is known as the closed position.  FIG. 1(   b ) shows distal end  100  with valve element  108  in a position such that through holes  114  are uncovered, allowing flow through holes  114 . This is known as the open position. 
         [0070]    While not shown in the figures, signal wires for providing RF energy to the electrode may be routed within the wall of catheter body  104 , or in the region between the inner wall of catheter body  104  and the outer diameter of fluid tube  106 . The signal wires are preferably electrically insulated from each other to allow the wires to share a single lumen. The signal wires extend the length of catheter body  104 . The details of routing of the signal wires are not critical to any embodiment of the present invention. 
         [0071]      FIGS. 2(   a ) and  2 ( b ) show a modification of the embodiment of the invention shown in  FIGS. 1(   a ) and  1 ( b ), with similar numbers corresponding to the numbers in  FIGS. 1(   a ) and  1 ( b ). The only difference between the invention shown in  FIGS. 2(   a ) and  2 ( b ) and that described above is the presence of a thermally insulating element  220  between electrode  202  and catheter body  204 , and that the through holes  214  are in the insulating element  220  rather than in the electrode  202 . Insulating element  220  may be made from a plastic such as e.g., Acetal, polyetheretherketone (PEEK), and high-density polyethylene (HDPE). 
         [0072]      FIGS. 3(   a ) and  3 ( b ) show a cross-sectional view of another embodiment of the invention. The distal end  300  comprises an electrode  302 , a catheter body  304 , a fluid tube  306 , a valve element  308 , and a coil spring  310 . Electrode  302  includes an inner cavity  312  which houses valve element  308 , which has a slightly smaller diameter than the inner diameter of inner cavity  312 , and coil spring  310 . There is also a plurality of through holes  314  from inner cavity  312  to the outer surface of electrode  302 . The distal end of inner cavity  312  includes a reduced diameter extension  332 . Stem  330  of valve element  308  has a slightly smaller diameter than reduced diameter extension  332  of inner cavity  312  to allow stem  330  to slide back and forth, so that valve element  308  covers or uncovers through holes  314  to prevent or allow, respectively, saline flow through holes  314 . Valve element  308  may be prevented from moving too far in the proximal direction by any number of ways well-known in the art. For example, fluid tube  306  may extend far enough into inner cavity  312  to prevent valve element  308 &#39;s moving farther in the distal direction, or a reduced diameter section (not shown) of inner cavity  312  may prevent such movement. 
         [0073]    Catheter body  304  is a flexible hollow tube attached to the proximal end of electrode  302  by any means well-known in the art such as bonding and swaging. Catheter body  304  may be made of a flexible material such as thermoplastics such as nylon, in which braiding is embedded. Catheter body  304  may be guided by a user by such means well-known in the art as pull wires. 
         [0074]    Fluid tube  306  is centered within the catheter body  304 , and is attached to the proximal open end of electrode  302  by any means well-known in the art such as bonding or swaging. Fluid tube  306  allows the flow of saline through holes  314  to providing cooling for electrode  302 . 
         [0075]    Spring coil  310  may be made of any material normally used in producing springs and that is acceptable for use within the human body. Spring coil  310  biases valve element  308  toward a position in which valve element  308  covers through holes  314 , preventing flow of saline into a patient&#39;s body. If pressure of saline through fluid tube  306 , and, consequently, inner cavity  312  exceeds a set amount, valve element  308  is pushed against the biasing force of spring  310  until through holes  314  are uncovered and saline flows into the patient&#39;s body. 
         [0076]      FIG. 3(   a ) shows distal end  300  with valve element  308  in the closed position.  FIG. 3(   b ) shows distal end  300  with valve element  308  in the open position. 
         [0077]      FIGS. 4(   a ) and  4 ( b ) show a modification of the embodiment of the invention shown in  FIGS. 3(   a ) and  3 ( b ), with similar numbers corresponding to the numbers in  FIGS. 3(   a ) and  3 ( b ). The only difference between the invention shown in  FIGS. 4(   a ) and  4 ( b ) and that described above with regard to  FIGS. 3(   a ) and  3 ( b ) is the presence of an insulating element  420  between electrode  402  and catheter body  404 , and that the through holes  414  are in the insulating element  420  rather than in the electrode  402 . In addition,  FIGS. 4(   a ) and  4 ( b ) show a conical flow conditioner  440 , which reduces turbulent flow, which in turn reduces valve “hunting.”  FIG. 5  is an isometric view of valve element  408  and coil spring  410 . Note that a flow conditioner may also be used with valve element  308  shown in  FIGS. 3(   a ) and  3 ( b ). 
         [0078]      FIG. 6  is a cross-sectional view of an option available for the embodiments of the invention shown in  FIGS. 3-5 . Seal member  650  is a means of reducing saline leakage through holes  614 . Rather than relying solely on the tight clearance between the outer diameter of valve element  608  and the inner diameter of inner cavity  612 , seal member  650  provides a sealing surface for the proximal face of valve element  608 . Although seal element  650  may be constructed of a rigid material, it is preferably made of an elastomeric material to improve the seal. Seal member  650  also acts as a stop to prevent excessive travel of valve element  608  in the proximal direction. Although shown with an insulated electrode, seal member  650  may also be used in a catheter without an insulated electrode by locating seal member  650  directly inside the electrode. 
         [0079]      FIGS. 7(   a ) and  7 ( b ) are cross-sectional views of another embodiment of the invention. Rather than using a self-closing valve element as shown in  FIGS. 1-6 , the embodiment  700  shown in  FIGS. 7(   a ) and  7 ( b ) relies on a user to open and close the valve. 
         [0080]    Valve element  708  is tightly fit into the inner diameter of inner cavity  712  to provide a seal when an operator at the proximal end of catheter body  704  uses push/pull wire  770  to pull valve element  708  toward the proximal end of insulating member  720  to block saline passage through holes  714 . Using push/pull wire  770  to push valve element  708  toward the distal end of insulating member  720  to uncover through holes  714  to allow saline to flow. Push/pull wire  770  is made of a flexible material such as stainless steel, titanium, or carbon fiber. 
         [0081]    Hole  760  is provided in valve element  708  to allow fluid flow from one side of the other, facilitating movement of valve element  708 . If hole  760  is not provided, a suction pocket will form on the distal side of valve element  708  when pulling valve element  708  in the proximal direction. The tight fit between the outer diameter of valve element  708  and the inner diameter of inner cavity  712  would also make it difficult to push valve element  708  into the open position, as it would take more time for saline trapped on the distal side of valve element  708  to flow around the outer diameter of valve element  708  without hole  760 . 
         [0082]    Valve element  708  may be provided with a flow conditioner as described above. A seal element can also be provided in this embodiment. The method can also be used in an electrode without an insulating element. Rather than being manually operated by a user, push/pull wire  770  can be linked to saline flow such that starting flow will automatically open the valve and stoppage of flow will automatically close the valve. This linkage of operation may be a result of, for example, a double pole/double throw switch actuating push/pull wire  770  in coordination with starting and stopping the saline pump. Alternatively, a flow switch detecting saline flow may be used to actuate push/pull wire  770 . In both cases, a limit switch may be used to stop actuation of push/pull wire  770  when the desired valve element position is reached. 
         [0083]      FIG. 8(   a ) is a cross-sectional view of another embodiment of the invention. As with the embodiment shown in  FIGS. 7(   a ) and  7 ( b ), this embodiment relies on a user to open and close the valve rather than using a self-closing valve element. 
         [0084]      FIG. 8(   b ) is section A-A taken through insulating element  820  and valve element  808  showing both open and closed positions of valve element  808 . Valve element  808  includes scalloped portions  880 . A user&#39;s rotating rotation wire  870  places valve element  808  in the open position when scalloped portions  880  align with through holes  814  and in the closed position when scalloped portions  880  do not align with through holes  814 . Rotation wire  870  is made of a flexible material such as stainless steel, titanium, or carbon fiber. 
         [0085]    As with the embodiment shown in  FIGS. 7(   a ) and  7 ( b ), valve element  808  may be provided with a flow conditioner as described above. A seal element can also be provided in this embodiment. The method can also be used in an electrode without an insulating element. Rather than being manually operated by a user, rotation wire  870  can be linked to saline flow such that starting flow will automatically open the valve and stoppage of flow will automatically stop flow. This linkage of operation may be a result of, for example, a double pole/double throw switch actuating rotation wire  870  in coordination with starting and stopping the saline pump. Alternatively, a flow switch detecting saline flow may be used to actuate rotation wire  870 . In both cases, a limit switch may be used to stop actuation of rotation wire  870  when the desired valve element position is reached. 
         [0086]      FIGS. 9(   a ) and  9 ( b ) are cross-sectional views of yet another embodiment of the invention. In this embodiment balloon  908  inflates to fill inner cavity  912  to prevent flow through holes  914  and deflates to allow flow through holes  914 . The fluid to inflate balloon  908  is admitted and released through inflation tube  980 . A syringe pump at the distal end of catheter body  904  controls the admission and release of fluid through inflation tube  980 . As shown, inflation tube  980  passes through a bushing  990  located between the outer diameter of fluid tube  906  and the inner diameter of inner cavity  912 . However, inflation tube may also be located inside fluid tube  906 . 
         [0087]    The method can also be used in an electrode without an insulating element. Rather than being manually operated by a user, operation of the syringe pump can be linked to saline flow such that starting flow will automatically inflate the balloon and stoppage of flow will automatically deflate the balloon. This linkage of operation may be a result of, for example, a double pole/double throw switch actuating the syringe pump in coordination with starting and stopping the saline pump. Alternatively, a flow switch detecting saline flow may be used to actuate the syringe pump. In both cases, a pressure switch may be used to stop actuation of the syringe pump when the desired balloon inflation or deflation is reached. 
         [0088]    Although the embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.