The present disclosure relates generally to various force sensing catheter features.
In ablation therapy, it may be useful to assess the contact between the ablation element and the tissue targeted for ablation. In interventional cardiac electrophysiology (EP) procedures, for example, the contact can be used to assess the effectiveness of the ablation therapy being delivered. Other catheter-based therapies and diagnostics can be aided by knowing whether a part of the catheter contacts targeted tissue, and to what degree the part of the catheter presses on the targeted tissue. The tissue exerts a force back on the catheter, which can be measured to assess the contact and the degree to which the catheter presses on the targeted tissue.
The present disclosure concerns, among other things, systems for measuring a force with a catheter.
The present disclosure relates to devices, systems, and methods for measuring a force experienced by a catheter.
Example 1 is a system for measuring a force on a catheter, the system including a catheter and control circuitry. The catheter includes a proximal segment, a distal segment, and an intermediary segment. The intermediary segment includes at least one strut. Each strut extends from the proximal segment to the distal segment. Each strut formed from a super-elastic metal alloy material. The at least one strut is configured to resiliently support the distal segment with respect to the proximal segment while permitting relative movement between the distal segment and the proximal segment. The control circuitry is configured to measure, for each of the at least one strut, a change in an electrical property of the super-elastic metal alloy material of the strut when the distal segment moves relative to the proximal segment.
Example 2 is the system of Example 1, wherein the control circuitry is configured to calculate a magnitude and a direction of the force based on the changes in the electrical property of the super-elastic metal alloy material of the at least one strut.
Example 3 is the system of Example 2, further comprising a display, wherein the control circuitry is configured to graphically indicate on the display the magnitude and the direction of the force.
Example 4 is the system of any of Examples 1-3, wherein the change in the electrical property comprises an increase or a decrease in electrical resistance.
Example 5 is the system of any of Examples 1-4, wherein the electrical property is the electrical resistance of the super-elastic metal alloy material.
Example 6 is the system of any of Examples 1-5, wherein the super-elastic metal alloy material is a nickel-titanium alloy.
Example 7 is the system of any of Examples 1-5, wherein the super-elastic metal alloy material is a copper-aluminum-nickel alloy.
Example 8 is the system of any of Examples 1-7, wherein the change in the electrical property of the super elastic metal alloy material is due to the super elastic metal alloy material changing phases during elastic deformation.
Example 9 is the system of Example 8, wherein the changing phases comprising transitioning one or both of into and out of an intermediary phase between austenite and martensite.
Example 10 is the system of any of Examples 1-9, wherein the catheter further comprises a proximal hub located in the proximal segment and a distal hub located in the distal segment, wherein each strut comprises a proximal end that is attached to the proximal hub and a distal end that is attached to the distal hub.
Example 11 is the system of any of Examples 1-10, wherein the at least one strut comprises a plurality of struts.
Example 12 is the system of Example 11, wherein the plurality of struts are configured to mechanically support the distal segment in a base orientation with respect to the proximal segment, flex when the distal segment moves relative to the proximal segment in response to the application of the force and exhibit the change in the electrical property of the super elastic metal alloy material in response to said flexing, and resiliently return the distal segment to the base orientation with respect to the proximal segment once the force has been removed.
Example 13 is the system of any of Examples 11-12, wherein the plurality of struts are arrayed around a longitudinal axis, the longitudinal axis extending through the centers of the proximal segment and the distal segment when the distal segment is in the base orientation with respect to the proximal segment.
Example 14 is a method of measuring an applied force on a catheter within a patient. The catheter includes a proximal segment, a distal segment, and at least one strut that mechanically supports the distal segment with respect to the proximal segment. The method includes measuring an electrical property of each of the at least one strut as the catheter is advanced within the body, detecting a change in the electrical property of each of the at least one strut indicative of the force deflecting the distal segment with respect to the proximal segment, and outputting an indication via a user interface of the force, wherein each of measuring, detecting, and outputting are performed at least in part by control circuitry.
Example 15 is the method of Example 14, wherein each of the at least one strut is formed from nitinol.
Example 16 is a system for measuring a force on a catheter, the system including a catheter and control circuitry. The catheter includes a proximal segment, a distal segment, and an intermediary segment. The intermediary segment includes at least one strut. Each strut extends from the proximal segment to the distal segment. Each strut formed from a super-elastic metal alloy material. The at least one strut is configured to resiliently support the distal segment with respect to the proximal segment while permitting relative movement between the distal segment and the proximal segment. The control circuitry is configured to measure, for each of the at least one strut, a change in an electrical property of the super-elastic metal alloy material of the strut when the distal segment moves relative to the proximal segment.
Example 17 is the system of Example 16, wherein the control circuitry is configured to calculate a magnitude and a direction of the force based on the changes in the electrical property of the super-elastic metal alloy material of the at least one strut.
Example 18 is the system of Example 17, wherein the control circuitry is configured to graphically indicate on the display the magnitude and the direction of the force.
Example 19 is the system of any of Examples 16-18, wherein the electrical property is the electrical resistance of the super-elastic metal alloy material.
Example 20 is the system of any of Examples 16-19, wherein the super-elastic metal alloy material is a nickel-titanium alloy.
Example 21 is the system of any of Examples 16-19, wherein the super-elastic metal alloy material is a copper-aluminum-nickel alloy.
Example 22 is the system of any of Examples 16-21, wherein the change in the electrical property of the super elastic metal alloy material is due to the super elastic metal alloy material changing phases during elastic deformation.
Example 23 is the system of Example 22, wherein the changing phases comprising transitioning one or both of into and out of an intermediary phase between austenite and martensite.
Example 24 is the system of any of Examples 16-23, wherein the at least one strut comprises a plurality of struts.
Example 25 is a system for measuring a force on a catheter, the system including a catheter and control system. The catheter includes a proximal segment, a distal segment, and a spring segment. The spring segment extends from the proximal segment to the distal segment. The spring segment is configured to permit relative movement between the distal segment and the proximal segment in response to application of the force on the distal segment. The spring segment includes at least one structural element. Each structural element extends from the proximal segment to the distal segment. Each structural element is formed from a super-elastic metal alloy material. The at least one structural element is configured to mechanically support the distal segment in a base orientation with respect to the proximal segment, flex when the distal segment moves relative to the proximal segment in response to the application of the force and exhibit a change in an electrical property of the super elastic metal alloy material in response to said flexing, and resiliently return the distal segment to the base orientation with respect to the proximal segment once the force has been removed. The control circuitry is configured to measure, for each of the at least one structural element, the change in the electrical property when the distal segment moves relative to the proximal segment.
Example 26 is the system of Example 25, wherein the change in the electrical property comprises an increase or a decrease in electrical resistance.
Example 27 is the system of any of Examples 25-26, wherein the at least one structural element comprises a plurality of struts.
Example 28 is the system of Example 27, wherein the plurality of struts are arrayed around a longitudinal axis, the longitudinal axis extending through the centers of the proximal segment, the spring segment, and the distal segment when the distal segment is in the base orientation with respect to the proximal segment.
Example 29 is the system of any of Examples 25-28, wherein the catheter further comprises a proximal hub located in the proximal segment and a distal hub located in the distal segment, wherein each strut comprises a proximal end that is attached to the proximal hub and a distal end that is attached to the distal hub.
Example 30 is the system of any of Examples 25-29, wherein the control circuitry is at least partially located within the catheter.
Example 31 is the system of any of Examples 25-30, wherein the control circuitry is configured to calculate, for each of the at least one structural element, an amount of strain that the structural element experiences when the distal segment moves relative to the proximal segment based at least in part on the change in the electrical property.
Example 32 is the system of any of Examples 25-31, wherein the at least one structural element comprises at least three structural elements, and the control circuitry is configured to calculate a magnitude and a direction of the force based on the changes in the electrical property for the at least three structural elements
Example 33 is the system of Example 32, further comprising a display, wherein the control circuitry is configured to graphically indicate on the display the magnitude and the direction of the force.
Example 34 is a method of measuring an applied force on a catheter within a patient. The catheter includes a proximal segment, a distal segment, and at least one strut that mechanically supports the distal segment with respect to the proximal segment. The method includes measuring an electrical property of each of the at least one strut as the catheter is advanced within the body, detecting a change in the electrical property of each of the at least one strut indicative of the force deflecting the distal segment with respect to the proximal segment, and outputting an indication via a user interface of the force, wherein each of measuring, detecting, and outputting are performed at least in part by control circuitry.
Example 35 is the method of Example 34, wherein each of the at least one strut is formed from nitinol.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes various illustrative embodiments of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
While the scope of the present disclosure is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the scope of the invention to particular embodiments described and/or shown. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.
Various cardiac abnormalities can be attributed to improper electrical activity of cardiac tissue. Such improper electrical activity can include, but is not limited to, generation of electrical signals, conduction of electrical signals, and/or mechanical contraction of the tissue in a manner that does not support efficient and/or effective cardiac function. For example, an area of cardiac tissue may become electrically active prematurely or otherwise out of synchrony during the cardiac cycle, thereby causing the cardiac cells of the area and/or adjacent areas to contract out of rhythm. The result is an abnormal cardiac contraction that is not timed for optimal cardiac output. In some cases, an area of cardiac tissue may provide a faulty electrical pathway (e.g., a short circuit) that causes an arrhythmia, such as atrial fibrillation or supraventricular tachycardia. In some cases, inactivated tissue (e.g., scar tissue) may be preferable to malfunctioning cardiac tissue.
Cardiac ablation is a procedure by which cardiac tissue is treated to inactivate the tissue. The tissue targeted for ablation may be associated with improper electrical activity, as described above. Cardiac ablation can lesion the tissue and prevent the tissue from improperly generating or conducting electrical signals. For example, a line, a circle, or other formation of lesioned cardiac tissue can block the propagation of errant electrical signals. In some cases, cardiac ablation is intended to cause the death of cardiac tissue and to have scar tissue reform over the lesion, where the scar tissue is not associated with the improper electrical activity. Lesioning therapies include electrical ablation, radio frequency ablation, cyroablation, microwave ablation, laser ablation, and surgical ablation, among others. While cardiac ablation therapy is referenced herein as an exemplar, various embodiments of the present disclosure can be directed to ablation of other types of tissue and/or to non-ablation diagnostic and/or catheters that deliver other therapies.
Ideally, an ablation therapy can be delivered in a minimally invasive manner, such as with a catheter introduced to the heart through a vessel, rather than surgically opening the heart for direct access (e.g., as in a maze surgical procedure). For example, a single catheter can be used to perform an electrophysiology study of the inner surfaces of a heart to identify electrical activation patterns. From these patterns, a clinician can identify areas of inappropriate electrical activity and ablate cardiac tissue in a manner to kill or isolate the tissue associated with the inappropriate electrical activation. However, the lack of direct access in a catheter-based procedure may require that the clinician only interact with the cardiac tissue through a single catheter and keep track of all of the information that the catheter collects or is otherwise associated with the procedure. In particular, it can be challenging to determine the location of the therapy element (e.g., the proximity to tissue), the quality of a lesion, and whether the tissue is fully lesioned, under-lesioned (e.g., still capable of generating and/or conducting unwanted electrical signals), or over-lesioned (e.g., burning through or otherwise weakening the cardiac wall). The quality of the lesion can depend on the degree of contact between the ablation element and the targeted tissue. For example, an ablation element that is barely contacting tissue may not be adequately positioned to deliver effective ablation therapy. Conversely, an ablation element that is pressed too hard into tissue may deliver too much ablation energy or cause a perforation.
The present disclosure concerns, among other things, methods, devices, and systems for assessing a degree of contact between a part of a catheter (e.g., an ablation element) and tissue. Knowing the degree of contact, such as the magnitude and the direction of a force generated by contact between the catheter and the tissue, can be useful in determining the degree of lesioning of the targeted tissue. Information regarding the degree of lesioning of cardiac tissue can be used to determine whether the tissue should be further lesioned or whether the tissue was successfully ablated, among other things. Additionally or alternatively, an indicator of contact can be useful when navigating the catheter because a user may not feel a force being exerted on the catheter from tissue as the catheter is advanced within a patient, thereby causing vascular or cardiac tissue damage or perforation.
As shown in
The proximal segment 111, the spring segment 112, and the distal segment 113 can be coaxially aligned with each other in a base orientation as shown in
The proximal segment 111, the spring segment 112, and the distal segment 113 can be mechanically biased to assume the base orientation. Specifically, a structural element 108 can reside within the distal end 116 of the catheter 110. The structural element 108 can extend from the proximal segment 111, through the spring segment 112, to the distal segment 113. While a single structural element 108 is shown in
The structural element 108 can be formed from a super-elastic metal alloy, such as a nickel-titanium alloy (e.g., nitinol), a copper-zinc-aluminum alloy, a copper-aluminum alloy, or a copper-aluminum-nickel alloy. Super-elastic metal alloys can be useful in catheters because of such metals exhibit large elastic deformation ranges and therefore are resilient. Such resiliency can return the shape of the distal end 116 of the catheter 110 to its nominal base orientation after deflection.
The catheter 110 includes force sensing capabilities. For example, the catheter 110 is configured to sense a force due to engagement with tissue 117. The distal segment 113 can be relatively rigid while segments proximal of the distal segment 113 can be relatively flexible. In particular, the spring segment 112 may be more flexible than the distal segment 113 and the proximal segment 111 such that when the distal end 116 of the catheter 110 engages tissue 117, the spring segment 112, as shown in
The structural element 108 can be used to determine the magnitude and the direction of the force due to engagement with the tissue 117. Super-elastic metal alloys can be induced to transition between martensite and austenite phases based on a change in temperature, thus providing shape memory effects. Super-elastic metal alloys have slip planes such that the material changes phases under elastic deformation. Super-elastic metal alloys can be forced to transition between martensite and austenite phases by induction of stress in the material. For example, a super-elastic metal alloy material may be in the austenite phase when unstressed but will transform to the martensite phase above a critical stress (e.g., during deformation). The material can transition back to the austenite phase once the stress is released. Between the martensite and austenite phases is an unstable transition area phase which is referred to as the “R” phase herein. One remarkable aspect of the R phase is an electrical property of the super-elastic metal alloy material changes as it transitions through the R phase. Specifically, the resistivity of the super-elastic metal alloy material increases as it transitions through the R phase under increasing stress. Various embodiments of the present disclosure capitalize on this phenomenon by measuring an electrical property of a structural element formed by a super-elastic metal alloy to determine the strain that the structural element is undergoing. As such, the structural element can serve multiple purposes including mechanically supporting parts of the distal end 116 of the catheter 110 while also functioning as a strain sensor.
As shown in
The control unit 120 of the system 100 includes a display 121 (e.g., LCD) for displaying information. The control unit 120 further includes a user input 122 which can comprise one or more buttons, toggles, a track ball, a mouse, touchpad, or the like for receiving user input. The user input 122 can additionally or alternatively be located on the handle 114. The control unit 120 can contain control circuitry for performing the functions referenced herein. Some or all of the control circuitry can alternatively be located within the handle 114.
The control unit 120 can include a catheter interface 123. The catheter interface 123 can include a plug which receives a cord from the handle 114. The catheter 110 can include multiple conductors (not illustrated but known in the art) to convey electrical signals between the distal end 116 and the proximal end 115 and further through the handle 114 to the catheter interface 123. It is through the catheter interface 123 that the control unit 120 (and/or the handle 114 if control circuitry is included in the handle 114) can send electrical signals to any element within the catheter 110 and/or receive an electrical signal from any element within the catheter 110. The catheter interface 123 can conduct signals to or from any of the components of the control unit 120.
The control unit 120 can include an ultrasound subsystem 124 which includes components for operating the ultrasound functions of the system 100. While the illustrated example of control circuitry shown in
The control unit 120 can include an ablation subsystem 125. The ablation subsystem 125 can include components for operating the ablation functions of the system 100. While the illustrated example of control circuitry shown in
The control unit 120 can include a force sensing subsystem 126. The force sensing subsystem 126 can include components for measuring a force experienced by the catheter 110. The force sensing subsystem 126 can include some of the components shown in
Each of the ultrasound subsystem 124, the ablation subsystem 125, and the force sensing subsystem 126 can send signals to, and receive signals from, the processor 127. The processor 127 can be any type of processor for executing computer functions. For example, the processor 127 can execute program instructions stored within the memory 128 to carry out any function referenced herein, such as determine the magnitude and direction of a force experienced by the catheter 110.
The control unit 120 further includes an input/output subsystem 129 which can support user input and output functionality. For example, the input/output subsystem 129 may support the display 121 to display any information referenced herein, such as a graphic representation of tissue, the catheter 110, and a magnitude and direction of the force experienced by the catheter 110, among other options. Input/output subsystem 129 can log key and/or other input entries via the user input 122 and route the entries to other circuitry.
A single processor 127, or multiple processors, can perform the functions of one or more subsystems, and as such the subsystems may share control circuitry. Although different subsystems are presented herein, circuitry may be divided between a greater or lesser numbers of subsystems, which may be housed separately or together. In various embodiments, circuitry is not distributed between subsystems, but rather is provided as a unified computing system. Whether distributed or unified, the components can be electrically connected to coordinate and share resources to carry out functions.
As shown, the proximal segment 211 can be proximal and adjacent to the spring segment 212. The length of the proximal segment 211 can vary between different embodiments, and can be five millimeters to five centimeters, although different lengths are also possible. The length of the spring segment 212 can also vary between different embodiments, and can be dependent on the length of underlying struts as will be further discussed herein. The spring segment 212 is adjacent to the distal segment 213. As shown in
The proximal hub 241 and the distal hub 242 can be coaxially aligned with respect to the longitudinal axis 209. For example, the longitudinal axis 209 can extend through the respective radial centers of each of the proximal hub 241 and the distal hub 242. One or more inner tubes 240 (one shown) can extend through the catheter 210 (e.g., to the handle 114), through the proximal hub 241 and the distal hub 242. The inner tube 240 can include one or more lumens within which one or more conductors (e.g., conductors 261) can extend from the proximal end 215 to the distal segment 213, such as for connecting with one or more electrical elements (e.g., ultrasound transducer, electrode, struts 251-253, or other component). Coolant fluid can additionally or alternatively be routed through the inner tube 240, or through an additional inner tube 240. In various embodiments, the catheter 210 is open irrigated (e.g., through the plurality of ports 231) to allow the coolant fluid to flow out of the distal segment 213. Various other embodiments concern a non-irrigated catheter 210.
A tether 243 can attach to a proximal end of the proximal hub 241. The tether 243 can attach to a deflection mechanism within a handle to cause deflection of the distal end 216. A knob, slider, or plunger on a handle may be used to create tension or slack in the tether 243.
As shown in
The proximal hub 241 includes an attachment portion 246. The attachment portion 246 can be on a distal side of the proximal hub 241. Proximal portions of the plurality of struts 251-253 can be attached to the attachment portion 246. For example, a proximal portion 272 of the strut 251 can be attached to the attachment portion 246 of the proximal hub 241. The distal hub 242 can include an attachment portion 247. The attachment portion 247 can be on a proximal side of the distal hub 242. Distal ends of the plurality of struts 251-253 can be attached to the attachment portion 247. For example, a distal portion 273 of the strut 251 can be attached to the attachment portion 247 of the distal hub 242. The length of the spring segment 212 may be defined as the length of the plurality of struts 251-253 that is not overlapped by either of the proximal hub 241 or the distal hub 242 because this is the portion of the distal end 216 which is configured to bend due to a force.
Each of the plurality of struts 251-253 can be similar to the structural element 108 in form and/or function. Each strut 251-253 can be a respective unitary piece of metal formed from a super-elastic metal alloy material, such as a nickel-titanium alloy (e.g., nitinol), a copper-zinc-aluminum alloy, a copper-aluminum alloy, or a copper-aluminum-nickel alloy. The plurality of struts 251-253 can therefore be formed of a super-elastic metal alloy material and can exhibit the mechanical and electrical character characteristics discussed herein. For example, the plurality of struts 251-253 can mechanically support the distal segment 213 relative to proximal segment 211 while also functioning as individual strain sensors by changing in an electrical property under strain. Conductors 261 can be attached to opposite proximal and distal ends of the struts 251-253, respectively, to run current through the struts 251-253 to measure the change in the electrical property. For example, a conductor 261 can connect to the proximal portion 272 of the strut 251 while another conductor 261 can connect to the distal portion 273 of the strut 251. The conductors can be routed through holes in the proximal hub 241 and the distal hub 242 and into the inner tube 240 then extend within a lumen of the inner tube 240 to a proximal end of the catheter 210 for delivering signals to and/or from control circuitry. The conductors 261 can be copper wires insulated by a polymer coating.
The plurality of struts 251-253 are circumferentially arrayed around the longitudinal axis 209 such that one or more of the struts will be compressed when the distal segment 213 moves relative to the proximal segment 211 while one or more of the other struts will be stretched when the distal segment 213 moves relative to the proximal segment 211. Which struts elongate or compress depends on the direction of the force. If the force had a different direction, a different one or more of the struts will be compressed while a different one or more of the struts will be stretched. Based on the different amounts of stretching and compressing of the struts 251-253, and which struts 251-253 compress and which struts 251-253 elongate, the magnitude and direction of force can be determined by the force sensing subsystem 126. In particular, each of the plurality of struts 251-253 can undergo a phase change to exhibit a measurable change in electrical resistivity indicative of bending of the strut. Each strut 251-253 can sense the strain (compression or stretching) in the struts itself to determine the magnitude and direction of the force.
The distal hub 242 includes a plurality of attachment surfaces 281. Each attachment surface 281 can be flat while the rest of the attachment portion 247 can be relatively round. As such, the attachment portion 247 can comprise alternating flat and round sections that extend around the circumference of the distal hub 242. Each attachment surface 281 can serve as a surface to interface with a flat, distal portion of a respective one of the struts 251-253. The struts 251-253 can be attached to the attachment portion 247 at such attachment surfaces 281. The struts 251-253 can be attached to the distal hub 242 by an adhesive (e.g., epoxy), welding, and/or riveting. In some embodiments, a collar may be placed over the distal ends of the struts 251-253 to pinch the distal ends of the struts 251-253 between the collar and the distal hub 242 to attach the struts 251-253 to the distal hub 242. The proximal hub 241 and the distal hub 242 in the form from electrically insulative material to electrically isolate the plurality of struts 251-253 from each other to maintain signaling integrity for each strut.
The struts 251-253 can be circumferentially arrayed around each of the proximal hub 241 and the distal hub 242. The circumference (or diameter) of the attachment portion 246 of the proximal hub 241 can be equal to the circumference (or diameter) of the attachment portion 247 of the distal hub 242. The attachment of the struts 251-253 to the proximal hub 241 and the distal hub 242 can secure the distal hub 242 to the proximal of 241 while allowing movement of the distal hub 242 relative to the proximal hub 241. Furthermore, the struts 251-253 can be structurally resilient to return the distal hub 242 back to the base orientation (e.g., coaxial with longitudinal axis 209) with respect to the proximal hub 241 once an external force to the catheter has been removed.
The proximal portion 272 can be flat, the distal portion 273 can be flat, and the bend 254 can be in a nonplanar configuration. The bend 254 of the strut 251 can extend proximally to the proximal portion 272 and distally to the distal portion 273. For example, the proximal portion 272 can be coplanar with the distal portion 273, while the bend 254 can be curved therebetween.
Considering
It is noted that the first side 271 is radially inward facing while the second side 270 is radially outward facing in
If the force exerted on the distal segment 213 is coaxial with the longitudinal axis 209, then each of the struts 251-253 will compress in equal amounts. The struts 251-253 will exhibit equal amounts of dimensional change in the bends of the struts 251-253. Based on these equal changes, the control circuitry can determine a magnitude and direction of the force. The magnitude of the force can be calculated using Hooke's law, wherein the displacement of a spring element (e.g., strut 251) is proportional to the force placed on the element, based on a predetermined constant. Being that the displacements are equal for each of the struts 251-253, the control circuitry can determine that the force is coaxial with the longitudinal axis 209. If the force is not coaxial with the longitudinal axis 209, then one or more of the struts will be in compression (e.g., by as shown in
The pre-bending of the strut 251 ensures that the bend 254 will experience much if not all of the overall bending of the strut 251. This results in improved predictable and consistent bending profile, ideal for measuring. The bend 254 may be the only portion of the strut 251 that bends, therefore the change in resistivity of the material of the strut 251 may be limited to the bend 254. As noted previously, the respective bends of the struts 251-253 can be coextensive with the spring segment 212 such that most or all of the bending in the distal end 216 is captured by the bends and measured by the change in electrical property discussed herein.
Once assembled, the catheter 210 may undergo a calibration step, either at a factory or just before use by a physician. In such a step, a plurality of forces of known magnitude and direction can be placed, in sequence, on the distal segment 213 to move the distal segment 213 relative to the proximal segment 211 while the struts 251-253 output signals or otherwise exhibit changes in on electrical property indicative of the bending of the struts 251-253. A table can be generated indicating a separate entry for each force. Thereafter, a force of unknown magnitude and/or direction can be analyzed by comparing signals output from the struts 251-253 to the values of the table to identify the best match. An algorithm can identify which entry from the calibration data has three (or other number depending on the number of struts) change-in-resistance values best matching the current change-in-resistance values. The magnitude and direction of the known force from the calibration step can be indicated as the magnitude and direction currently being experienced. In some cases, a mathematical relationship can be generated based on the linearity of Hooke's law, wherein a limited number of calibration steps are performed to determine the change-in-resistance, or other parameter, and interpolation and/or extrapolation can be computed based on these calibration values. For example, the spring constant can be determined for a strut such that a subsequent elongation or contraction amount can be multiplied by the spring constant to determine the magnitude of the force acting on the distal segment 213 (and thus the strut). The deflection of multiple struts can be factored for determining an overall magnitude and direction for the force.
The magnitude can be represented in grams or another measure of force. The magnitude can be presented as a running line graph that moves over time to show new and recent force values. The direction can be represented as a unit vector in a three dimensional reference frame (e.g., relative to an X, Y, and Z axes coordinate system). In some embodiments, a three dimensional mapping function can be used to track the three dimensional position of the distal end 216 of the catheter 210 in the three dimensional reference frame. Magnetic fields can be created outside of the patient and sensed by a sensor that is sensitive to magnetic fields within the distal end 216 of the catheter 210 to determine the three dimensional position of the distal end 216 of the catheter 210 in the three dimensional reference frame. The direction can be represented relative to the distal end 216 of the catheter 210. For example, a line projecting to, or from, the distal segment 213 can represent the direction of the force relative to the distal segment 213. Such representations can be made on a display as discussed herein.
In some embodiments, the magnitude and direction of the force that are indicated to the user indicates the magnitude and the direction of a force that acts on the distal segment 213. This force typically results from the distal segment 213 pushing against tissue. Therefore, the force acting on the distal segment 213 may be a normal force resulting from the force that the distal segment 213 exerts on the tissue. In some embodiments, it is the force acting on the distal segment 213 that is calculated and represented to a user. Additionally or alternatively, it is the force that the distal segment 203 applies to tissue that is calculated and represented to the user.
The magnitude and direction of the force can be used for navigation by providing an indicator when the catheter encounters tissue and/or for assessing the lesioning of tissue by determining the degree of contact between the lesioning element and the tissue, among other options. In some embodiments, a force under 10 grams is suboptimal for lesioning tissue (e.g., by being too small) while a force over 40 grams is likewise suboptimal for lesioning tissue (e.g., by being too large). Therefore, a window between 10 and 40 grams may be ideal for lesioning tissue and the output of the force during lesioning may provide feedback to the user to allow the user to stay within this window. Of course, other force ranges ideal for lesioning may be used.
The techniques described in this disclosure, including those attributed to a system, control unit, control circuitry, processor, or various constituent components, may be implemented wholly or at least in part, in hardware, software, firmware or any combination thereof. A processor, as used herein, refers to any number and/or combination of a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), microcontroller, discrete logic circuitry, processing chip, gate arrays, and/or any other equivalent integrated or discrete logic circuitry. As part of control circuitry, at least one of the foregoing logic circuitry can be used, alone or in combination with other circuitry, such as memory or other physical medium for storing instructions, to carry about specified functions (e.g., a processor and memory having stored program instructions executable by the processor for determining a magnitude and a direction of a force exerted on a catheter). The functions referenced herein may be embodied as firmware, hardware, software or any combination thereof as part of control circuitry specifically configured (e.g., with programming) to carry out those functions, such as in means for performing the functions referenced herein. The steps described herein may be performed by a single processing component or multiple processing components, the latter of which may be distributed among different coordinating devices. In this way, control circuitry may be distributed between multiple devices. In addition, any of the described units, modules, subsystems, or components may be implemented together or separately as discrete but interoperable logic devices of control circuitry. Depiction of different features as modules, subsystems, or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized as hardware or software components and/or by a single device. Rather, specified functionality associated with one or more module, subsystem, or units, as part of control circuitry, may be performed by separate hardware or software components, or integrated within common or separate hardware or software components of control circuitry.
When implemented in software, the functionality ascribed to the systems, devices, and control circuitry described in this disclosure may be embodied as instructions on a physically embodied computer-readable medium such as RAM, ROM, NVRAM, EEPROM, FLASH memory, magnetic data storage media, optical data storage media, or the like, the medium being physically embodied in that it is not a carrier wave, as part of control circuitry. The instructions may be executed to support one or more aspects of the functionality described in this disclosure.
Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as falling within the scope of the claims, together with all equivalents thereof.
This application claims priority to Provisional Application No. 62/202,673, filed Aug. 7, 2015, which is herein incorporated by reference in its entirety.
Number | Date | Country | |
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62202673 | Aug 2015 | US |