Patent Application
20080147046
The present invention relates to a medical device for use in the vessel of a patient wherein a portion of the catheter is comprised of a spirally sliced tube. More particularly, the catheter uses a spirally sliced polymer or shape metal memory tube to provide a flexible yet pushable means of providing flexible support and/or enclosing one or more puller wires and/or irrigation lumens.
Many abnormal medical conditions in humans and other mammals have been associated with disease and other aberrations along the lining or walls that define several different body spaces. In order to treat such abnormal conditions of the body spaces, medical device technologies adapted for delivering various therapies to the body spaces using the least invasive means possible.
As used herein, the term “body space,” including derivatives thereof, is intended to mean any cavity within the body which is defined at least in part by a tissue wall. For example, the cardiac chambers, the uterus, the regions of the gastrointestinal tract, and the arterial or venous vessels are all considered illustrative examples of body spaces within the intended meaning.
The term “vessel,” including derivatives thereof, is herein intended to mean any body space which is circumscribed along a length by a tubular tissue wall and which terminates at each of two ends in at least one opening that communicates externally of the body space. For example, the large and small intestines, the vas deferens, the trachea, and the fallopian tubes are all illustrative examples of vessels within the intended meaning. Blood vessels are also herein considered vessels, including regions of the vascular tree between their branch points. More particularly, the pulmonary veins are vessels within the intended meaning, including the region of the pulmonary veins between the branched portions of their ostia along a left ventricle wall, although the wall tissue defining the ostia typically presents uniquely tapered lumenal shapes.
One means of treating body spaces in a minimally-invasive manner is through the use of catheters to reach internal organs and vessels within a body space. Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., the femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
Steerable catheters are generally well known. For example, U.S. Pat. No. RE 34,502 describes a catheter having a control handle comprising a housing having a piston chamber at its distal end. A piston is mounted in the piston chamber and is afforded lengthwise movement. The proximal end of the catheter body is attached to the piston. A puller wire is attached to the housing and extends through the piston and through the catheter body. The distal end of the puller wire is anchored in the tip section of the catheter to the sidewall of the catheter shaft. In this arrangement, lengthwise movement of the piston relative to the housing results in deflection of the catheter tip section.
In bidirectional steerable catheters, a pair of puller wires extends through a lumen in the main portion of the catheter shaft and then into opposing off-axis lumens in a deflectable tip section where the distal end of each puller wire is attached to the outer wall of the deflectable tip. Pulling one wire in a proximal direction causes the tip to deflect in the direction of the off axis lumen in which that wire is disposed.
In other designs, the puller wires are attached to opposite sides of a rectangular plate that is fixedly mounted at its proximal end and extends distally within a lumen in the tip section. In this arrangement, pulling one of the wires proximally causes the rectangular plate to bend in the direction of the side to which the pulled puller wire is attached, thereby causing the entire tip section to deflect. In most designs stainless steel compression coils are commonly used in conjunction with the puller wires to reduce flexure of a region of the catheter when the puller wires are tensioned.
The steerability of the catheter is directly related to the flexibility of the catheter. It would therefore be desirable to have a catheter that is sufficiently flexible to be easily steerable but that is also pushable within the body space.
In certain applications, it is desirable to have the ability to inject and/or withdraw fluid through the catheter. This is accomplished by means of an irrigated tip catheter. One such application is a cardiac ablation procedure for creating lesions that interrupt errant electrical pathways in the heart.
A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue that is electrically non-conductive.
The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue that is electrically non-conductive. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself. If the electrode temperature becomes sufficiently high, possibly above 60 degrees centigrade, a thin transparent coating of dehydrated blood protein can form on the surface of the electrode. If the temperature continues to rise, this dehydrated layer can become progressively thicker resulting in blood coagulation on the electrode surface. Because dehydrated biological material has a higher electrical resistance than endocardial tissue, impedance to the flow of electrical energy into the tissue also increases. If the impedance increases sufficiently, an impedance rise occurs and the catheter must be removed from the body and the tip electrode cleaned.
One method used to reduce the negative affects of heating is to irrigate the ablation electrode, e.g., with physiologic saline at room temperature, to actively cool the ablation electrode instead of relying on the more passive physiological cooling of the blood. Because the strength of the RF current is no longer limited by the interface temperature, current can be increased. This results in lesions which tend to be larger and more spherical, usually measuring about 10 to 12 mm. In addition to irrigation flow during ablation, a maintenance flow, typically at a lower flow rate, is required throughout the procedure to prevent backflow of blood flow into the coolant passages. Thus, it is necessary to provide for catheters that are flexible, steerable and yet contain the necessary structure to provide lumens for irrigation.
Another issue for catheters arises when they are used in RMT systems. In remote magnetic technology (RMT) systems, magnets external to the patient are used to product magnetic fields in the patient that can guide a catheter such as a catheter for ablation. Catheters used for this purpose must have a high degree of flexibility so that the magnetic fields can properly guide the device through the tortuous anatomy of the patient. It would, therefore be desirable to have a catheter that is highly flexible but yet has the proper magnetic characteristics for use in an RMT system.
Additionally, catheters that are used during magnetic resonance imaging (MRI) procedures need to be non-magnetic. Due to the powerful electromagnets used to align the nuclei of hydrogen atoms in the water content of the human body the use of catheters having magnetic properties is prohibited. Therefore, it would be desirable to have a flexible, steerable non-magnetic catheter for use during MRI procedures.
The present invention generally relates to a catheter having a spirally sliced tube in place of one or more solid tubular stiffening tubes or metal compression coils in a steerable catheter. More specifically, the present invention is a catheter comprising an elongate tubular member having a proximal end and a distal end and a lumen defined by the inner diameter of the tubular member and having an elongate spirally sliced tubular member disposed within the lumen of the elongated tubular member. The catheter can have the spirally sliced tubular member disposed immediately within the inner diameter of the elongate tubular member in order to provide a controllable stiffening tube. Alternatively, the catheter can use the elongate tubular member to receive one or more puller wires for steering the distal end of the catheter. Additionally, the catheter may have an irrigation lumen disposed with the lumen of the elongate tubular member wherein the irrigation lumen comprises an outer wall and an inner wall. Either the inner wall or the outer wall may be a spirally sliced catheter.
A catheter in accordance with the present invention exhibits reduced stiffness in comparison to metallic compression coils or solid tubular constructions.
Furthermore, a catheter in accordance with the present invention, particularly one using the polymeric tube, has little or no interaction with magnetic or electrical field in comparison to those having compression coils made of other metals.
Additionally, catheters in accordance with the present invention exhibit increased resilience and robustness during handling and assembly.
Still further, the stiffness of a catheter made in accordance with the present invention can have varying degrees of stiffness by varying the pitch and/or stopping the spiral slice at a specific points along the longitude of the polymer tube.
Tube 10 can be made from a variety of polymers including PEEK™ polymer from Victrex plc, polyamide, polyurethane, nylon, and PEBAX among others. VICTREX™ PEEK™ polymer, is a repeat unit that comprises of oxy-1, 4-phenyleneoxy-1, 4-phenylene-carbonyl-1, 4-phenylene. PEEK is a linear aromatic polymer that is semi-crystalline.
Tubes 10, 12 and 14 may also be made of a shape memory metal or alloy. A shape memory alloy, also known as shape memory metal, is a material that returns to an original geometry after deformation from its “original” formation. A shape memory alloy may return to its original geometry by itself during heating (one-way effect) or, at higher ambient temperatures, simply during unloading due to pseudo-elastic or superelastic properties. These properties are due to a temperature-dependent martensitic phase transformation from a low-symmetry to a highly symmetric crystallographic structure. Three types of shape memory alloys are copper-zinc-aluminum, copper-aluminum-nickel and nickel-titanium (NiTi) alloys although any type of shape-memory metal or alloy can be used. Some examples of shape-memory metals are set forth below:
The inner and outer dimensions of tubes 10, 12 and 14 can vary depending on the application within a catheter, the degree of flexure necessary and the amount of pushability desired. Preferably, the inner dimension of tubes 10, 12 and 14 are between 0.1 and 10 mm with an outer dimension of between 0.101 and 15 mm. The thickness should preferably be between 0.001 and 14.9 mm. A preferred embodiment has an inner diameter of approximately 0.45″ and an outer diameter of approximately 0.45″.
The pitch angle, θ, of the spiral slice may also be varied depending on the amount of flexure desired and the degree of pushability desired. Increasing the pitch angle, θ, will make the tube more flexible while decreasing the pitch angle will create a tube with more support and less flex. Preferably, the pitch angle is between 0 and 30 degrees. The pitch angle may be varied on the same tube.
Tubes 10, 12, and 14 can be used in any combination of quantity, position and pitch of various sliced segments within a catheter in order to impart different characteristics into the catheter. For example, a first spirally sliced tube 10 with a pitch angle θ1 and a second spirally sliced tube 10 with a different pitch angle θ2, wherein θ1>θ2, could be placed in a catheter so that the first tube is distal to the second. This arrangement would provide a catheter with more flexure at the distally than proximally. Myriad combinations of tubes with different angles and spirally sliced portions can be created in order to customize catheter flexure.
As shown in
The overall length of the length of the catheter will vary according to its application for use but a preferred length is between approximately 90 and 120 cm and more preferably between approximately 100 and 110 cm. The outer diameter of the proximal section 32 is also a design characteristic that varies according to the application of the catheter but is preferably less than approximately 8 French (Fr). Inner wall 18 comprises a spirally-sliced tube (also referred to as a spirally-sliced tubular member) 10 and is sized so that the outer diameter is about the same size or slightly smaller than the inner diameter of outer wall 30 thereby providing additional stiffness which can be controlled by the pitch angle of the cut as described above.
In an RF ablation catheter, tip electrode 38 and ring electrode 40 are each electrically connected to a separate lead wire 60. Each lead wire 60 extends from the control handle 36 through the lumen 58 in the proximal section 32 and through lumen 56 in distal section 34 to tip electrode 38 and ring electrode 40. The proximal end of each lead wire 60 is connected to an appropriate connector (not shown) in the control handle 36 which can be plugged into a suitable source of rf energy.
In a bi-directional rf ablation catheter a pair of puller wires 44a and 44b extend through the through the lumen 58 in the proximal section 32 and through lumen 56 in distal section 34. The puller wires are made of any suitable material such as stainless steel or Nitinol. Preferably, each puller wire 44 is covered with a lubricious coating such as PTFE or a similar material. Each puller wire 44 extends from the control handle 36 to near the tip of distal section 34. Puller wires 44 may be slidably mated to each other along a portion of their length in various manners such as that depicted in
A sleeve 50 is provided that surrounds the puller wires to keep them in a closely adjacent relationship. Sleeve 50 may be made of any suitable material, e.g., polyamide or polyurethane or comprise a compression coil. Alternatively, sleeve 50 may also comprise one or more a spirally sliced tubes 10, 12 and 14 that provides the catheter designer with an ability to change the characteristics of the response of the catheter to the puller wires 44a and 44b by replacing the compression coil with a spirally-sliced tube or tubes 10, 12, or 14.
Examples of other suitable control handles that can be used with the present invention are described in U.S. Pat. No. 6,123,699, 6,171,277, 6,183,463 and 6,198,974 the disclosure of which are hereby incorporated by reference. Additional configurations of puller wires 44 and gearing within the control handle may be used such as those disclosed in U.S. Pat. No. 7,077,823 which is also hereby incorporated by reference.
An alternative embodiment of a catheter in accordance with the present invention would provide a standard (non-spirally sliced) stiffening tube in place of the spirally-sliced tube 10 for inner wall 18. The only spirally-sliced tube would be used for the sleeve 50. The stiffening tube for inner wall 18 could be made of could be made of any suitable material, but would preferably be made of polyimide or nylon.
The spirally-sliced tube 10, 12 or 14 may also be used to inside and/or outside an irrigation lumen. Placement outside an irrigation lumen would increase the hoop strength of a low durometer polymer tubing used as an irrigation lumen while also being flexible.
The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention.
Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.
