Patent Application
20150126895
The present invention relates generally to catheter sheaths, and particularly to catheter location tracking in sheaths.
A wide range of medical procedures involve inserting sensors, catheters, implants, and other medical devices in the human body and guiding them to a particular position within the body. When a catheter is inserted into the body, impedance-based position sensing is one method used to guide the tip of the catheter to the target position in which the medical procedure is to be performed. In some procedures, catheters are guided in the human body within the lumen of a sheath.
U.S. Pat. 7,869,865, whose disclosure is incorporated herein by reference, describes a method for position sensing includes inserting a probe comprising at least one electrode into a body of a subject, and passing electrical currents through the body. between the at least one electrode and a plurality of locations on a surface of the body. Respective characteristics of the currents passing through the plurality of the locations are measured in order to determine position coordinates of the probe.
U.S. Pat. 6,582,536, whose disclosure is incorporated herein by reference, describes a method for manufacturing a steerable catheter having a distal end, proximal end, an outer jacket, a pull wire and a central lumen. The central lumen is maintained in a circular shape without bulges diminishing the useful inter-diameter by using an outer jacket with an elliptical shape and uneven thickness to encase a pull wire.
An embodiment of the present invention that is described herein provides a sheath including an elongate tube, which has an outer wall that surrounds an inner lumen and has multiple holes along the tube penetrating the outer wall. Multiple electrically-conducting elements are inserted in the respective holes, so as to allow transmission of electrical current between the inner lumen and an exterior of the outer wall.
In some embodiments, the electrically-conducting elements include metallic beads filling the multiple holes. In other embodiments, the electrically-conducting elements include metallic rivets filling the multiple holes. In yet other embodiments, the electrically-conducting elements include metallic springs threaded through the multiple holes. In some embodiments, the elongate tube includes metallic filaments forming a braid, and the sheath includes an insulating material that insulates the elements from the metallic filaments of the braid.
There is also provided, in accordance with an embodiment of the present invention, a method including producing an elongate tube, which includes an outer wall that surrounds an inner lumen and has multiple holes along the tube penetrating the outer wall. Multiple electrically-conducting elements are inserted into the respective holes so as to allow transmission of electrical current between the inner lumen and an exterior of the outer wall.
In other embodiments, producing the tube and inserting the electrically-conducting elements include mixing metallic objects in an insulating material used for producing the tube, and then forming the tube by extrusion. In yet other embodiments, producing the tube includes drawing insulating material over a mold having multiple openings, and inserting the electrically-conducting elements includes injecting metal through the openings.
There is also provided, in accordance with an embodiment of the present invention, an apparatus including a plurality of body surface electrodes, a sheath, a probe, and a processor. The body surface electrodes are fixed at respective locations on a surface of a living body. The sheath is inserted into the living body and includes an elongate tube. The elongate tube includes an outer wall that surrounds an inner lumen and has multiple holes along the tube penetrating the outer wall. Multiple electrically-conducting elements are inserted in the respective holes so as to allow transmission of electrical current between the inner lumen and an exterior of the outer wall. The probe includes at least one probe electrode, and is guided through the inner lumen of the sheath. The processor is configured to measure the electrical current that flows via the elements between the at least one probe electrode and the body surface electrodes, and to estimate a position of the at least one probe electrode based on the measured electrical current.
There is also provided, in accordance with an embodiment of the present invention, a method including fixing a plurality of body surface electrodes at respective locations on a surface of a living body. A sheath inserted into the living body includes an elongate tube. The elongate tube includes an outer wall that surrounds an inner lumen and has multiple holes along the tube penetrating the outer wall. Multiple electrically-conducting elements are inserted in the respective holes so as to allow transmission of electrical current between the inner lumen and an exterior of the outer wall. A probe including at least one probe electrode is guided through the inner lumen of the sheath. The electrical current that flows via the elements is measured between the at least one probe electrode and the body surface electrodes. A position of the at least one probe electrode is estimated based on the measured electrical current.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
Medical probes, such as catheters, are used in a variety of therapeutic and diagnostic procedures.
Typically, a catheter is inserted percutaneously into the patient, and an operator guides the catheter to a target region in the body cavity where the procedure is to be performed. In some procedures, the operator first inserts a sheath into the patient body and guides the sheath's distal end to the target region. The operator then inserts the catheter into the lumen of the sheath and guides the catheter distal tip through the sheath to the target region.
A position sensing system may be used for detecting the position of the catheter's distal tip as the operator manipulates the catheter in the patient's body cavity, for example in a chamber of the heart. In impedance-based position sensing systems, for example, the system generates and then measures a plurality of currents between at least one electrode disposed near the catheter distal tip and a plurality of body surface electrodes, fixed at respective locations on a surface of the patient body. The system then computes a plurality of impedances based on the measured currents and detects the position of the catheter's distal tip using the computed impedances.
If, however, the catheter is guided via an electrically-insulating sheath, the position of the catheter's distal tip cannot be measured correctly using impedance-based location sensing while the tip is inside the sheath. Since the insulating sheath prevents current from flowing between the catheter and the body surface electrodes, the system is essentially “blind” to the catheter's position within the insulating sheath until the catheter's distal tip emerges from the sheath close to the target region.
Embodiments of the present invention that are described herein provide sheathes and associated methods which enable impedance-based position sensing systems to detect the position of the catheter's distal tip even while the catheter is within the lumen of the sheath.
In order to make the sheath suitable for accurate impedance-based position measurements, a plurality of discrete, electrically-conducting elements are disposed either randomly or at predefined positions along the length of the sheath. The electrically-conducting elements pass through the sheath wall into the inner lumen of the sheath, and thus allow current to flow outward locally from the electrode at the catheter's distal tip to the body surface electrodes.
Typically, the electrically-conducting elements are small and isolated from one another. As such, current cannot flow along the sheath—Current can only traverse the sheath wall locally through the sheath wall via the elements. Adjacent elements are close enough to one another so as to allow current to traverse the wall locally near the position of the catheter tip in the sheath. As a result, the impedances or currents measured between the catheter electrode via the electrically-conducting elements and the body surface electrodes remain indicative of the catheter tip position.
In some embodiments, the sheath comprises an elongate electrically-insulating tube. Multiple holes are formed along the length of the insulating tube. The holes penetrate the outer wall, between the exterior of the tube and the internal lumen of the sheath. Multiple discrete, electrically conducting elements are then inserted into the respective holes to realize discrete localized electrically conducting paths through the sheath wall. In this manner, the sheath allows the impedance-based position sensing system to locate the distal tip of the catheter in the sheath in real time as the operator pushes the catheter through the lumen of the sheath.
The electrically conducting (typically metallic) elements may be implemented in various ways. In some embodiments, metal beads are mixed into insulating material, such as a polymer, which is pushed through a die to form the electrically transparent sheath by extrusion. In other embodiments, the polymer material is drawn over a tubular mold with openings, and metal is injected through the openings into the polymer to form an array of metal elements.
In yet other embodiments, holes are drilled into the tube and metal rivets are inserted into the holes so as to form the metal inserts along the length of the sheath. In other embodiments, springs are threaded through holes drilled in the tubing so as to form the metal inserts along the length of the sheath.
In some embodiments, the sheath comprises an internal layer that comprises a metallic braid, e.g., a braid of interwoven metallic filaments. In such embodiments, an insulating material may be disposed between the electrically conducting elements (e.g., the metal rivets or springs) and the braid, so as to prevent electrical shorting of the current traversing the metal element to the metal braid.
When using the disclosed sheaths, the operator can guide and maneuver the catheter through the sheath to the target region as the position of the distal tip is tracked within the sheath in real time. As a result, the electrically transparent sheath formed using the methods taught herein significantly enhances the control of the operator over the medical procedure.
An operator 30 of the medical procedure manipulates catheter 22 in the vascular system of patient 28 with a hand 35 of operator 30, and guides a distal tip 40 of catheter 22 to the target region in the chamber of heart 26 to perform the medical procedure. Operator 30 can view an image 44 of the heart while monitoring the medical procedure on a display 46.
Control console 24 comprises a probe interface/control unit 50 for relaying signals to the at least one electrode disposed on the body of catheter 22 near distal tip 40. Usually the signals are relayed between the at least one electrode at distal tip 40 and probe interface/control unit 50 through multiple wires placed in the internal lumen of the catheter, which are not shown in
Control units 50 and 60 generate the plurality of currents and relay the measured currents to a processor 70. Processor 70 computes a plurality of respective impedances between the at least one electrode at the catheter distal tip and the plurality of the body surface electrode based on the measured currents. Processor 70 then computes the location of probe 22 in the patient's body based on the computed impedances. Processor 70 outputs the position of the catheter to operator 30 on display 46, which is typically visually mapped within image 44 of heart 26.
Probe 22 may comprise a catheter with one or more probe electrodes disposed near the distal tip. System 20 then computes a plurality of impedances between each of the multiple probe electrodes and the plurality of body surface electrodes at respective locations on the body of the patient.
As will be explained in detail below, the sheath used for guiding catheter 22 comprises multiple electrically-conducting elements (e.g., metal inserts) that allow electrical current to pass locally through the sheath wall. These elements enable system 20 to measure the position of the catheter distal tip using impedance measurements, even though the tube of the sheath is electrically insulating. In the present context, the term “metallic” means comprising metal so as to facilitate conduction of electrical current. A metallic element may be entirely made of metal, covered or plated with metal, or filled with metal, for example.
The position sensing system shown in
Any suitable parameters may be measured and/or processed by system 20, and output to a display 46. For example, a mapping of an image 44 of heart 26 with multiple local electro-cardiac signals measured by multiple electrodes near distal tip 40 of catheter 22 which contact multiple points in the heart cavity. The mapping may be output to display 46.
Processor 70 typically comprises a general-purpose computer, with suitable front end and interface circuits for transmitting and receiving signals from probe 22, and for controlling the other components of system 20 described herein. Processor 70 may be programmed in software to carry out the functions that are used by the system, and the processor may store data for the software in a memory. The software may be downloaded to console 24 in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of processor may be carried out by dedicated or programmable digital hardware components.
In many catheter-based medical procedures, a sheath is first inserted into the vascular system of patient 28, until reaching the target region. The catheter itself is then guided through the sheath. Typically, the sheath is formed from lubricous polymer materials such as polypropylene, polyethylene, FEP (fluorinated ethylene propylene), and ETFE (ethylene tetrafluoroethylene), which are electrically insulating. Alternatively, however, the sheath may be fabricated from any other suitable material.
When using an electrically insulating sheath, current flow between the catheter electrodes and the body surface electrodes is blocked. As a result, the position of the distal tip of the catheter cannot be measured correctly by system 20 while in the sheath. In such a case, system 20 can detect and visualize the position of the catheter distal tip only when the distal tip emerges from the sheath. This obstruction slows and complicates the catheter guidance.
In the embodiments described herein, holes are formed in the sheath either randomly or at predefined locations along the length of the sheath. Electrically-conducting elements, e.g., metal inserts, are inserted into the holes. With the metal inserts in place, as the catheter moves within the sheath, electrical current is able to flow between the catheter tip electrode and the body surface electrodes, thus facilitating the impedance-based position measurements of system 20.
As a result, operator 30 can now quickly navigate the catheter through the lumen of the sheath into position at the target region since system 20 computes and displays the position of the sheath to the operator in real time. This feature significantly reduces the duration of the medical procedure.
In the embodiments presented herein, there are a number of methods for forming electrically transparent sheaths and particularly, the electrically-conducting elements. Several example implementations of electrically conducting elements are described below. Generally, however, these elements can be implemented in any other suitable way.
In a first embodiment, metal beads are mixed in the polymer material and the sheath is formed by extrusion. In a second embodiment, the polymer is drawn over a mold with openings along the length of the mold. Metal is injected through the openings into the polymer to form the metal elements in the sheath. In a third embodiment, holes are drilled into a multilayered polymer-based tube forming the sheath, and metal rivets are inserted into the holes to form the metal elements in the sheath. In a fourth embodiment, holes are drilled into a multilayered polymer-based tube forming the sheath, and spring coils are inserted through a hole formed in the tubing so as to form the metal elements in the sheath.
As electrode 125 disposed on the distal tip moves through sheath 100, current driven by system 20 through catheter electrode 125 is transmitted through the multiple metal holes typically closest to the distal tip, and through the body of patient 28 to the plurality of body surface electrodes 42, such that system 20 can detect the position of the catheter distal tip in sheath 100 based on the currents. Each of the multiple metal filled holes is electrically isolated one from another. The metal filled holes are typically 1 mm in diameter with a 0.5 mm spacing between adjacent holes, but may be any suitable geometry. Alternatively, however, any other suitable hole dimensions and spacing can be used.
In some embodiments, metal filled holes 110 are arranged in an array with a fixed spacing S along the length of sheath 100. In other embodiments, metal filled holes 110 are arranged in an arbitrary or random fashion along the length of sheath with a random spacing S. The spacing S between adjacent metal filled holes can be oriented in any arbitrary direction along the length of the catheter. The spacing parameter S is used here for conceptual clarity, and not by way of limitation of the embodiments of the present invention.
The embodiment with multiple filled metal holes 110 arranged in a random fashion is shown in
Similarly, the embodiment with multiple filled metal holes 110 arranged in a well-defined array pattern can be formed by drawing the polymer material over a tubular mold with openings in the mold arranged along the length of the mold with the desired well-defined array pattern. After the polymer is drawn over the mold, metal is injected through the openings and into the polymer, so as to form multiple filled metal holes 110 in the desired well-defined array pattern.
The embodiments described herein refer mainly to an electrode fitted at or near the distal end of catheter 22. Alternatively, however, the disclosed techniques can be used for measuring the positions of electrodes fitted at any desired position along the catheter. In some embodiments, an electrode may be fitted at a position along the catheter that is always inside the sheath. The disclosed techniques are especially valuable for locating such electrodes.
Holes are drilled through sheath 200 from the outer jacket into the sheath lumen at predefined locations along the length of the sheath. Metal rivets 240 are inserted into the drilled holes. The metal rivets are the metal elements needed to transmit the current to body surface electrodes 42 for detecting the position of a catheter 230 in sheath 200. The holes can be formed by any suitable method, such as drilling, and the metal rivets fastened in the holes.
However, after the holes are formed and metal rivets 240 inserted, the metal filaments 217 may electrically short the metal rivets to the metal braid over the length of the sheath in metal braid layer 215, which degrades position detection accuracy of the catheter's distal end. Position accuracy is maintained by using discrete current transmission points for detecting the position of catheter electrode 235 near the distal tip of catheter 230. To circumvent this, any suitable insulating material 245 is applied to the shaft of the metal rivet or to the sidewalls of the drilled holes so as to electrically isolate the metal rivets from the metal filaments in the metal braid layer.
Holes are drilled from the outer wall of sheath 300 into the sheath lumen at predefined locations along the length of the sheath. Metal springs 310 are then threaded through the drilled holes. The metal springs transmit the current to body surface electrode 42 for detecting the position of a catheter 330 in sheath 300. The holes can be formed by any suitable method. Typically, the metal springs threaded into the holes such that a portion of the spring coils remain wrapped around outer jacket 302, and a portion coil around inner liner layer 306 in inner lumen 308.
As explained above with reference to
In the embodiments shown in
Although the embodiments described herein mainly address position sensing of catheters in an insulating sheath, the methods and systems described herein can also be used for location measurement of an intra-body probe in any suitable intra-body procedure.
It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.
