Atherectomy System with Overtorque Protection

Abstract

The atherectomy system includes a drive mechanism adapted to rotatably actuate the atherectomy burr and a controller adapted to regulate operation of the drive mechanism. The controller calculates an estimated load torque on the atherectomy burr based on at least one of an angular velocity of the atherectomy system and an angular acceleration of the atherectomy system. The controller is further adapted to stop or reverse the drive mechanism when the estimated load torque on the atherectomy burr exceeds a torque threshold.

Description

[Technical Field]

[0001] The present invention relates to medical devices and methods for making and using medical devices. More particularly, the present invention relates to devices and methods for removing occlusive material from a body lumen. Furthermore, the present invention relates to atherectomy devices for forming a passageway through an occlusion in a body lumen, such as a blood vessel. [Background technology]

[0002] Many patients suffer from blocked blood vessels, such as blocked arteries, that restrict blood flow. The blockage can be a partial blockage, which reduces blood flow through the blocked portion of the vessel, or a complete blockage (e.g., a chronic complete blockage), which substantially blocks blood flow through the blocked vessel. In some cases, a stent may be placed in the area of the treated blockage. However, restenosis may occur within the stent, further blocking the vessel and restricting blood flow. Revascularization procedures involve using various devices to pass through the blockage and create or enlarge an opening through the blockage. Atherectomy is one technique for advancing a catheter having a cutting element mounted thereon through the blockage to create or enlarge a pathway through the blockage. Summary of the Invention [Problem to be solved by the invention]

[0003] There remains a need for alternative atherectomy devices to facilitate crossing of occlusions. [Means for solving the problem]

[0004] The present invention provides medical device designs, materials, manufacturing methods, and alternative uses. For example, an atherectomy system includes an atherectomy burr and a drive mechanism adapted to rotatably actuate the atherectomy burr. A controller is adapted to coordinate operation of the drive mechanism and to calculate an estimated load torque on the atherectomy burr based on at least one of an angular velocity of the atherectomy system and an angular acceleration of the atherectomy system. The controller is further adapted to stop or reverse the drive mechanism when the estimated load torque on the atherectomy burr exceeds a torque threshold.

[0005] Alternatively or additionally, the controller may be adapted to determine the angular position of the atherectomy system. Alternatively or additionally, the controller may be adapted to determine the angular velocity of the atherectomy system by determining the first derivative of the angular position with respect to time.

[0006] Alternatively or additionally, the controller may be adapted to determine the angular acceleration of the atherectomy system by determining the second derivative of the angular position with respect to time. Alternatively or additionally, the controller may calculate an estimated load torque T on the atherectomy burr according to equation (1): load It can be adapted to calculate

[0007]

number

[0008] where K T is the torque constant of the drive motor. i is the drive motor current. C D is the value of the friction coefficient.

[0009]

number

[0010] is the angular velocity of the atherectomy system. I is the inertia of the atherectomy system.

[0011]

number

[0012] is the angular acceleration of the atherectomy system. Alternatively or additionally, i may be a measured or calculated value. Alternatively or additionally, C D can be a constant.

[0013] Alternatively or additionally, C D can be a calculated value. Alternatively or additionally, the drive mechanism may include a drive cable coupled to the atherectomy burr and a drive motor adapted to rotate the drive cable.

[0014] As another example, an atherectomy system includes a drive mechanism adapted to rotatably actuate an atherectomy burr and a controller adapted to regulate operation of the drive mechanism, the controller calculating an estimated load torque T on the atherectomy burr according to equation (2): load is adapted to calculate:

[0015]

number

[0016] where T motor is the estimated motor torque of the drive motor. T drag is the estimated drag torque of the drive mechanism. I is the inertia value of the system.

[0017]

number

[0018] is the value of the angular acceleration. The controller also load is adapted to stop or reverse the drive mechanism when the torque exceeds a torque threshold. Alternatively or additionally, T motor is calculated by the controller according to equation (3).

[0019]

number

[0020] K T is the torque constant of the drive motor. i is the drive motor current. Alternatively or additionally, i may be a measured or calculated value.

[0021] Alternatively or additionally, T drag is expressed as equation (4).

[0022]

number

[0023] is calculated by the controller according to where C D is the coefficient of friction value.

[0024]

number

[0025] is the angular velocity value. Alternatively or additionally, C D can be a constant. Alternatively or additionally, C D can be a time-varying value.

[0026] Alternatively or additionally, when operating at steady state, T motor is Tdrag Since it is essentially equal to T load is calculated by the controller according to equation (5).

[0027]

number

[0028] Alternatively or additionally, the drive mechanism may include a drive cable coupled to the atherectomy burr and a drive motor adapted to rotate the drive cable. As another example, an atherectomy system includes a drive mechanism adapted to rotatably actuate an atherectomy burr and a controller adapted to regulate operation of the drive mechanism. The controller determines an estimated torque value T load The controller is adapted to stop or reverse the drive mechanism when T exceeds a torque threshold. When the atherectomy system is in steady state, the controller calculates T according to equation (5). load is adapted to calculate

[0029]

number

[0030] I is the inertia of the atherectomy system.

[0031]

number

[0032] is the angular acceleration of the atherectomy system. Here, when the atherectomy system is accelerating, the controller calculates T according to equation (1). load is adapted to calculate

[0033]

number

[0034] where K T is the torque constant of the drive motor. i is the drive motor current. C D is the coefficient of friction value.

[0035]

number

[0036] is the angular velocity of the atherectomy system. Alternatively or additionally, the drive mechanism may be adapted to accelerate the atherectomy burr to full speed in less than 2 seconds.

[0037] Alternatively or additionally, the drive mechanism may include a drive motor having a power rating of at least about 60 watts. The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The following figures and detailed description more particularly exemplify these embodiments.

[0038] The present invention may be more fully understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings. [Brief explanation of the drawings]

[0039] [Figure 1] 1 is a block diagram illustrating a schematic of an exemplary atherectomy system. [Figure 2] 1 is a block diagram illustrating a schematic of an exemplary atherectomy system. [Figure 3] 1 is a block diagram illustrating a schematic of an exemplary atherectomy system. [Figure 4] 1 is a block diagram illustrating a schematic of an exemplary atherectomy system. [Figure 5] 1 is a block diagram illustrating a schematic of an exemplary atherectomy system. [Figure 6]6 is a schematic diagram of an example PID controller that can be used in the example atherectomy system of Figures 1-5. DETAILED DESCRIPTION OF THE INVENTION

[0040] While the present disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

[0041] For the following defined terms, these definitions shall be applied unless a different definition is given in the claims or elsewhere in this specification. All numerical values herein are assumed to be modified by the term "about," whether explicitly stated or not. The term "about" generally refers to a range of numbers that one of ordinary skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term "about" may include numbers that are rounded to the nearest significant figure.

[0042] The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally used in its sense including "and / or" unless the content clearly dictates otherwise.

[0043] The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

[0044] Many patients suffer from blocked arteries, other blood vessels, and / or occluded ducts or other body cavities that may restrict the flow of bodily fluids (e.g., blood, bile, etc.). The blockage may be a partial blockage, which reduces blood flow through the blocked portion of the vessel, or a complete blockage (e.g., a chronic complete blockage), which substantially blocks blood flow through the blocked vessel. Revascularization procedures involve using various devices to open the blockage and create or enlarge an opening through the blockage. Atherectomy is a technique in which a catheter having a cutting element mounted thereon is advanced through the blockage to form or enlarge a pathway through the blockage. Ideally, the cutting element ablates the blockage without damaging the surrounding vessel wall and / or a previously implanted, restenotic stent. However, in some cases, the cutting element may be manipulated and / or advanced so that it contacts the vessel wall and / or stent. Therefore, it may be desirable to utilize materials and / or design an atherectomy device that can ablate the blockage without damaging the surrounding vessel and / or a previously implanted, restenotic stent. Additionally, it may be desirable for the cutting element to be useful in removing hard occlusive material, such as calcified material, as well as softer occlusive material. The methods and systems disclosed herein can be designed to overcome at least some of the limitations of previous atherectomy devices while effectively ablating occlusive material. For example, some of the devices and methods disclosed herein can include cutting elements with unique cutting surface shapes and / or designs.

[0045] FIG. 1 is a schematic block diagram illustrating an exemplary atherectomy system 10 having a drive mechanism 12 adapted to rotatably actuate an atherectomy burr 14. The atherectomy system 10 includes a controller 16 adapted to regulate operation of the drive mechanism 12. In some cases, the atherectomy system 10 may include a user interface 18 that may be operably connected to the controller 16 to enable the controller 16 to display information regarding the performance of the drive mechanism 12. This information may include, for example, one or more of the instantaneous speed of the drive mechanism 12, the instantaneous torque experienced by the atherectomy burr 14, etc. In some cases, the atherectomy system 10 may not have a user interface 18. In some cases, the atherectomy burr 14 may be referred to as being or including a cutting head or cutting element, and these terms may be used interchangeably.

[0046] 2 is a block diagram illustrating a schematic of an exemplary atherectomy system 20, in which drive mechanism 12 may include drive motor 22 and drive cable 24 operably connected to drive motor 22 and atherectomy burr 14. In some cases, features of atherectomy system 20 may be combined with features of atherectomy system 10. In some cases, atherectomy system 20 may also include a handle (not shown).

[0047] 3 is a schematic block diagram of an exemplary atherectomy system 40 including a control system 42 adapted to regulate operation of the drive mechanism 12 to rotatably actuate the atherectomy burr 14. In some cases, features of the atherectomy system 40 can be combined with one or more of the atherectomy systems 10 and 20. The control system 42 can include a reference block 32 and a proportional-integral-derivative (PID) controller 44 operably coupled to the reference block 32. In some cases, the reference block 32 can determine a speed reference 46 selectable between a nominal value, a negative value, and zero. In some cases, the PID controller 44 can be further adapted to add an offset value to the speed reference 46 received from the reference block 32, or in some cases, the reference block 32 can add the offset value. The PID controller 44 may further be adapted to provide a greater reduction in the motor speed of the drive mechanism 12 than would normally occur in response to an increase in torque experienced by the atherectomy burr 14 .

[0048] 4 is a schematic block diagram of an exemplary atherectomy system 50 including a control system 52 adapted to regulate operation of drive motor 22 to rotatably actuate atherectomy burr 14. In some cases, features of atherectomy system 50 can be combined with one or more of atherectomy system 10, atherectomy system 20, or atherectomy system 40. Control system 52 includes a feedback loop 54 operably connected to drive motor 22 and adapted to monitor performance of drive motor 22 and output a control effort value signal 56. A drive circuit 58 is adapted to receive control effort value signal 56 and regulate operation of drive motor 22 in accordance with control effort value signal 56.

[0049] In some cases, the feedback loop 54 may comprise a reference block for determining a speed reference and a proportional-integral-derivative (PID) controller operatively connected to the reference block to receive the speed reference, where the PID controller may be adapted to utilize the speed reference, a proportional (P) gain value, an integral (I) gain value, and a derivative (D) gain value in determining the control effort value signal. In some cases, the feedback loop 54 may be adapted to add an offset value to the reference signal provided to the reference loop 54 to accurately maintain the speed of the drive motor 22 during unloaded conditions. In some cases, for example, if the atherectomy burr 14 becomes stuck, the control system 52 may increase the torque provided by the drive motor 22 until a torque threshold is reached for a short period of time, and then reverse the motor 22 at a slow speed to rewind energy from the drive mechanism.

[0050] FIG. 5 is a schematic block diagram of an exemplary atherectomy system 300. In some cases, atherectomy system 300 may be considered an example of atherectomy system 10, 20, 30, 40, or 50. In some cases, features of atherectomy system 300 may be combined with features of any of atherectomy systems 10, 20, 30, 40, or 50, for example. Atherectomy system 300 includes a motor 302 that drives a drive cable 304 that itself engages a load 306. Load 306 may be, for example, an atherectomy burr. Motor 302 is controlled by a drive circuit 308, which may be, for example, an example of, or otherwise be considered incorporated into, drive module 22 and / or control system 16. In some cases, motor 302 may be sized, relative to the weight and other dimensions of atherectomy system 300, to accelerate the atherectomy burr to full speed in less than three seconds, or in some cases, less than two seconds. As an example, the motor 302 may be rated at least 60 watts. In a particular example, the motor 302 may be rated at approximately 80 watts. These are merely examples.

[0051] The drive circuit 308 receives input from a feedback section 310. In some cases, the feedback section 310 begins with a reference input 312 from a reference schedule block 314, which provides the reference input 312 to a PID controller 316. In some cases, the reference schedule block 314 can be configured to accept additional inputs, such as from a user and / or from additional sensors not shown. As an example, if the device is running for a very long period of time, the reference schedule block 314 can reduce the speed reference to prevent overheating. A PID controller is a controller that includes a (P) proportional part, an (I) integral part, and a (D) derivative part. The PID controller 316 outputs a control effort value or reference current 318 to the drive circuit 308. A motor state estimation block 320 receives a current / voltage signal 322 and a motor position signal 323 from the drive circuit 308 and a state feedback 324 from the PID controller 316. The motor state estimation block 320 returns a state feedback signal 325 to the PID controller 316 .

[0052] The motor state estimation block 320 outputs a speed value 326 back to the reference schedule block 314. While the feedback from the motor state estimation block 320 to the reference schedule block 314 is shown as a speed value, in some cases the feedback may additionally or alternatively include one or more of position, torque, voltage, or current, and in some cases may include a derivative or integral of any of these values. In some cases, the motor state estimation block 320 may instead receive a signal 323 representing speed rather than position (as shown). The motor position signal 323 may be an indication of the relative rotational position of the output shaft of the motor 302, and therefore of the relative rotational position of the load 306, which, when tracked over time, may provide an indication of speed.

[0053] In some cases, the drive circuit 308 and feedback loop 310 may be considered to combine to form a controller 350 adapted to determine an estimated torque on an atherectomy burr (load 306 shown in FIG. 5 ). The controller 350 may be considered to be an example of the controller 16 ( FIG. 1 ). In some cases, the controller 350 may be considered to include only some elements of the drive circuit 308 and feedback loop 310. In some cases, some of the features and functions of the controller 350 may be performed in the motor state estimation block 320. While FIG. 5 depicts various components as stand-alone components, it will be understood that in some cases, the functionality of one or more components may actually be distributed among separate mechanical components. In some cases, the functionality of one or more components may be combined into one or more mechanical components.

[0054] If the estimated torque at the load 306 becomes too high, this may indicate a clogged burr. To protect the drive cable 304 from possible damage and the patient from potential injury, the atherectomy system 300 may be adapted to stop or reverse operation of the atherectomy system 300 if the estimated torque equals or exceeds a predetermined torque threshold. The actual value of the predetermined torque threshold may vary depending on the mechanism of the atherectomy system 300, but it will be understood that it may be set at a level low enough to prevent breakage and damage, while not so low as to generate too many false alarms caused by minor and / or momentary torque increases not caused by the load 306 being clogged. For example, the instantaneous torque may change slightly as the atherectomy system 300 advances through the patient's vasculature.

[0055] Accordingly, controller 350 may be adapted to calculate an estimated torque at load 306 and compare the estimated torque at load 306 to a torque threshold. If the estimated torque is equal to or greater than the torque threshold, atherectomy system 300 may stop or even reverse the drive mechanism (e.g., drive motor 302 and drive cable 304). In some cases, atherectomy system 300 may be adapted to calculate the estimated torque at load 306 based on at least one of an angular velocity of atherectomy system 300 and an angular acceleration of atherectomy system 300.

[0056] In some cases, controller 350 may be adapted to determine the angular position of atherectomy system 300. This may mean determining the angular position of motor 302 or the angular position of cable 304. It will be appreciated that controller 350 may be adapted to determine the angular velocity of atherectomy system 300 by determining the first derivative of the angular position with respect to time. Controller 350 may be adapted to determine the angular acceleration of atherectomy system 300 by determining the second derivative of the angular position with respect to time. In some cases, for example, controller 350 may determine T according to equation (1): load The load 306 may be adapted to calculate an estimated torque at the load 306, denoted by:

[0057]

number

[0058] where K T is the torque constant of the drive motor. i is the drive motor current. C D is the value of the friction coefficient.

[0059]

number

[0060] is the angular velocity of the atherectomy system 300. I is the inertia of the atherectomy system 300;

[0061]

number

[0062] is the angular acceleration of the atherectomy system 300. In some cases, i may be a measured or calculated value. In some cases, the drive motor current i may be estimated within the motor state estimation block 320. For example, the reference current 318 may be provided to the motor state estimation block 320 via path 319, which may allow the motor state estimation block 320 to predict the drive motor current i more quickly than the drive motor current i may be measured. In some cases, the friction coefficient C D can be constant. In some cases, C D is a calculated or even time-varying value. In some cases, C D may be a function of one or more of the following: the amount of current being commanded, the system speed, and the elapsed time (total running time of the system). The controller 350 may, for example, determine C based on one or more of these factors. D In some cases, the controller 350 may calculate, for example, C for each of several rotational speed ranges. D This is just one example.

[0063]

number

[0064] represents the angular velocity of the atherectomy system 300 and may be determined by taking the first derivative of the angular position of the atherectomy system 300 with respect to time, as shown.

[0065]

number

[0066] represents the angular acceleration of the atherectomy system 300 and can be determined by taking the second derivative with respect to time of the angular position of the atherectomy system 300, as shown. The inertia I of the system can be easily calculated based on the mass and geometry of the system.

[0067] In some cases, the controller 350 may be adapted to calculate the estimated torque at the load 306 according to equation (2).

[0068]

number

[0069] where T motor is the estimated motor torque of the drive motor 302. T drag is the estimated drag torque of the drive mechanism. In some cases, the controller 350 calculates the estimated motor torque T according to equation (3): motor and may be adapted to calculate an estimated drag torque T drag can be calculated by the controller according to equation (4).

[0070]

number

[0071] In some cases, when the atherectomy system 300 is operating at steady state and therefore not accelerating, T motor is T drag and therefore, at steady state, T load It will be appreciated that can be calculated by the controller 350 according to equation (5):

[0072]

number

[0073] Therefore, and in some cases, when the atherectomy system 300 is in steady state, the controller 350 may calculate T load and

[0074]

number

[0075] When the atherectomy system 300 is accelerating, the controller 350 calculates T according to equation (1). load can be adapted to calculate:

[0076]

number

[0077] 6 is a schematic block diagram of a PID controller 316, which can be considered an example of the PID controller 44 shown in FIG. 4. An error signal 312, representing the error between a desired value and an actual value, enters the PID controller 316. The PID controller 316 calculates a P term 340 that is proportional to the error. The PID controller 316 calculates an I term 342, which is the integral of the error, and a D term 344, which is the derivative of the error. These terms are added together at a summation point 346 to provide an output control effort signal 318.

[0078] It will be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps, without departing from the scope of the disclosure. This may include, to the extent appropriate, the use of any of the features of one example embodiment used in other embodiments. The scope of the invention will, of course, be defined in the language in which the appended claims are expressed.

Claims

1. atherectomy burr and a drive mechanism for rotatably actuating the atherectomy burr; a controller for regulating operation of the drive mechanism; The controller is configured to: [Equation 1] According to the estimated load torque T ｌｏａｄ Calculate Here, K Ｔ is the torque constant of the drive motor, i is the measured drive motor current; C Ｄ is the value of the friction coefficient, which is a constant, [Equation 2] is the angular velocity of the atherectomy system, calculated by determining the first derivative with respect to time of the measured angular position; I is the calculated inertia of the atherectomy system; [Equation 3] is the angular acceleration of the atherectomy system calculated by determining the second derivative with respect to time of the measured angular position; The atherectomy system further includes the controller stopping or reversing the drive mechanism when an estimated load torque on the atherectomy burr exceeds a torque threshold.

2. The atherectomy system of claim 1 , wherein the controller determines the measured angular position of the atherectomy system.

3. The drive mechanism includes: a drive cable connected to the atherectomy burr; 3. The atherectomy system of claim 1 or 2, further comprising a drive motor for rotating the drive cable.

4. In the atherectomy system, a drive mechanism actuating the atherectomy burr to rotate; a controller for regulating operation of the drive mechanism; The controller is configured to: [Equation 4] The estimated load torque T of the atherectomy burr according to ｌｏａｄ Calculate Here, T ｍｏｔｏｒ is the estimated motor torque of the drive motor, T ｄｒａｇ is the estimated drag torque of the drive mechanism, I is the calculated system inertia value, [Equation 5] is the value of angular acceleration calculated by determining the second derivative with respect to time of the measured angular position; The controller further comprises: ｌｏａｄ and stopping or reversing the drive mechanism when a torque threshold is exceeded.

5. Said T ｍｏｔｏｒ is calculated by the controller according to equation (3), [Equation 6] Here, K Ｔ is the torque constant of the drive motor, 5. The atherectomy system of claim 4, wherein i is the measured drive motor current.

6. Said T ｄｒａｇ is expressed as equation (4). [Equation 7] is calculated by the controller according to Here, C Ｄ is the value of the friction coefficient, which is a constant, [Equation 8] 5. The atherectomy system of claim 4, wherein r is a value of angular velocity calculated by determining the first derivative with respect to time of the measured angular position.

7. The drive mechanism includes: a drive cable connected to the atherectomy burr; and a drive motor that rotates the drive cable.

8. In the atherectomy system, a drive mechanism actuating the atherectomy burr to rotate; a controller for regulating operation of the drive mechanism; The controller calculates the estimated torque value T ｌｏａｄ stopping or reversing the drive mechanism when the torque exceeds a torque threshold; When the atherectomy system is in steady state, the controller calculates the [Equation 9] According to T ｌｏａｄ Calculate I is the calculated inertia of the atherectomy system; [Equation 10] is the angular acceleration of the atherectomy system, calculated by determining the second derivative with respect to time of the measured angular position; When the atherectomy system is accelerating, the controller calculates the velocity of the atherectomy system by: [0011] According to T ｌｏａｄ Calculate Here, K Ｔ is the torque constant of the drive motor, i is the measured drive motor current; C Ｄ is the coefficient of friction value and is a constant, [0012] is the angular velocity of the atherectomy system, calculated by determining the first derivative with respect to time of the measured angular position.

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