Patent Publication Number: US-2022218385-A1

Title: Atherectomy system adapted to free a stuck atherectomy burr

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/444,789, filed Jun. 18, 2018, now U.S. Pat. No. 11,291,468, the entire contents of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to medical devices, and methods for manufacturing and using medical devices. More particularly, the disclosure is directed to devices and methods for removing occlusive material from a body lumen. Further, the disclosure is directed to an atherectomy device for forming a passageway through an occlusion of a body lumen, such as a blood vessel. 
     BACKGROUND 
     Many patients suffer from occluded arteries and other blood vessels which restrict blood flow. Occlusions can be partial occlusions that reduce blood flow through the occluded portion of a blood vessel or total occlusions (e.g., chronic total occlusions) that substantially block blood flow through the occluded blood vessel. In some cases a stent may be placed in the area of a treated occlusion. However, restenosis may occur in the stent, further occluding the vessel and restricting blood flow. Revascularization techniques include using a variety of devices to pass through the occlusion to create or enlarge an opening through the occlusion. Atherectomy is one technique in which a catheter having a cutting element thereon is advanced through the occlusion to form or enlarge a pathway through the occlusion. A need remains for alternative atherectomy devices to facilitate crossing an occlusion. 
     SUMMARY 
     This disclosure provides design, material, manufacturing method, and use alternatives for medical devices. For example, an atherectomy system includes an atherectomy burr and a drive mechanism that is adapted to rotatably actuate the atherectomy burr. A controller is adapted to operate the drive mechanism in a first operating mode in which the atherectomy burr is operated at a speed reference and with a predetermined torque limit. The controller is adapted to determine when the atherectomy burr becomes stuck while in the first operating mode. When the atherectomy burr becomes stuck, the controller is further adapted to operate the drive mechanism in a second operating mode that is different from the first operating mode. 
     Alternatively or additionally, the second operating mode may include operating the atherectomy burr at a position reference instead of the speed reference. 
     Alternatively or additionally, when in the second operating mode, the controller may be further adapted to alternate between driving the drive mechanism in a first rotational direction and driving the drive mechanism in a second rotational direction opposite that of the first rotational direction. 
     Alternatively or additionally, when in the second operating mode, the controller may be further adapted to drive the drive mechanism in the first rotational direction for a first distance and to drive the drive mechanism in the second rotational direction for a second distance that is different from the first distance. 
     Alternatively or additionally, the first distance and the second distance may be selected based on a known spring constant of the drive mechanism. 
     Alternatively or additionally, when in the second operating mode, the controller may be further adapted to periodically adjust the first distance and/or the second distance. 
     Alternatively or additionally, when in the second operating mode, the controller may be further adapted to periodically adjust a time period between driving the drive mechanism in the first rotational direction and driving the drive mechanism in the second rotational direction. 
     Alternatively or additionally, the second operating mode may include operating the atherectomy burr at low speed at a temporary torque value that exceeds the predetermined torque limit of the first operating mode while the atherectomy burr is not moving. 
     Alternatively or additionally, the temporary torque value may exceed the predetermined torque limit of the first operating mode by ten percent. 
     Alternatively or additionally, the temporary torque value may exceed the predetermined torque limit of the first operating mode by twenty percent. 
     Alternatively or additionally, when in the second operating mode, the controller may revert back to the first operating mode as soon as the atherectomy burr begins to move. 
     Alternatively or additionally, the second operating mode may further include temporarily exceeding the predetermined torque limit of the first operating mode while alternating driving the drive mechanism in a first rotational direction and driving the drive mechanism in a second rotational direction opposite that of the first rotational direction. 
     As another example, an atherectomy system includes an atherectomy burr and a drive mechanism that is adapted to rotatably actuate the atherectomy burr. A controller is adapted to operate the drive mechanism using a speed reference, and is adapted to determine when the atherectomy burr becomes stuck. The controller is further adapted to, when the atherectomy burr becomes stuck, switch to a stuck burr mode in which the controller uses a position reference in alternating between driving the drive mechanism in a first rotational direction and driving the drive mechanism in a second rotational direction opposite that of the first rotational direction. 
     Alternatively or additionally, when in the stuck burr mode, the controller may be further adapted to drive the drive mechanism in the first rotational direction for a first distance and to drive the drive mechanism in the second rotational direction for a second distance that is different from the first distance. 
     Alternatively or additionally, the first distance and the second distance may be selected based on a known spring constant of the drive mechanism. 
     Alternatively or additionally, when in the stuck burr mode, the controller may be further adapted to periodically adjust the first distance and/or the second distance. 
     Alternatively or additionally, when in the stuck burr mode, the controller may be further adapted to periodically adjust a time period between driving the drive mechanism in the first rotational direction and driving the drive mechanism in the second rotational direction. 
     As another example, an atherectomy system includes an atherectomy burr and a drive mechanism that is adapted to rotatably actuate the atherectomy burr. A controller is adapted to operate the drive mechanism using a speed reference and with a predetermined torque limit, and is adapted to determine when the atherectomy burr becomes stuck. The controller is further adapted to, when the atherectomy burr becomes stuck, to operate the drive mechanism at low speed at a temporary torque value that exceeds the predetermined torque limit while the atherectomy burr is not moving. 
     Alternatively or additionally, the temporary torque value may exceed the predetermined torque limit up to twenty percent. 
     Alternatively or additionally, the controller may revert to operating the drive mechanism in accordance with the speed reference and the predetermined torque limit as soon as the atherectomy burr begins to move. 
     The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of an example atherectomy system; 
         FIG. 2  is a schematic block diagram of an example atherectomy system; 
         FIG. 3  is a schematic block diagram of an example atherectomy system; 
         FIG. 4  is a schematic block diagram of an example atherectomy system; 
         FIG. 5  is a schematic block diagram of an example atherectomy system; 
         FIG. 6  is a schematic diagram of an example PID controller usable in the example atherectomy systems of  FIGS. 1 through 5 ; and 
         FIG. 7  is a graphical representation of an example motor position reference usable while the atherectomy burr may be jammed. 
     
    
    
     While the 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. 
     DETAILED DESCRIPTION 
     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 numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
     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 employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The following detailed description should be read with reference to the drawings in which similar 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. 
     Many patients suffer from occluded arteries, other blood vessels, and/or occluded ducts or other body lumens which may restrict bodily fluid (e.g. blood, bile, etc.) flow. Occlusions can be partial occlusions that reduce blood flow through the occluded portion of a blood vessel or total occlusions (e.g., chronic total occlusions) that substantially block blood flow through the occluded blood vessel. Revascularization techniques include using a variety of devices to pass through the occlusion to create or enlarge an opening through the occlusion. Atherectomy is one technique in which a catheter having a cutting element thereon is advanced through the occlusion to form or enlarge a pathway through the occlusion. Ideally, the cutting element excises the occlusion without damaging the surrounding vessel wall and/or a previously implanted stent where restenosis has occurred. However, in some instances the cutting element may be manipulated and/or advanced such that it contacts the vessel wall and/or the stent. Therefore, it may be desirable to utilize materials and/or design an atherectomy device that can excise an occlusion without damaging the surrounding vessel and/or a previously implanted stent where restenosis has occurred. Additionally, it may be desirable that a cutting element be useful in removing hard occlusive material, such as calcified material, as well as softer occlusive material. The methods and systems disclosed herein may be designed to overcome at least some of the limitations of previous atherectomy devices while effectively excising occlusive material. For example, some of the devices and methods disclosed herein may include cutting elements with unique cutting surface geometries and/or designs. 
       FIG. 1  is a schematic block diagram of an example atherectomy system  10  that includes a drive mechanism  12  that is adapted to rotatably actuate an atherectomy burr  14 . The atherectomy system  10  includes a controller  16  that is 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 coupled to the controller  16  such that the controller  16  is able to display information regarding the performance of the drive mechanism  12 . This information may, for example, include one or more of an instantaneous speed of the drive mechanism  12 , an instantaneous torque being experienced by the atherectomy burr  14 , and the like. In some instances, the atherectomy system  10  may not include the user interface  18 . In some cases, the atherectomy burr  14  may also be referred to as being or including a cutting head or a cutting member, and these terms may be used interchangeably. 
       FIG. 2  is a schematic block diagram of an example atherectomy system  20  in which the drive mechanism  12  may include a drive motor  22  and a drive cable  24  that is operably coupled with the drive motor  22  as well as the atherectomy burr  14 . In some cases, features of the atherectomy system  20  may be combined with features of the atherectomy system  10 . In some cases, the atherectomy system  20  may also include a handle (not shown). 
       FIG. 3  is a schematic block diagram of an example atherectomy system  40  that includes a control system  42  that is adapted to regulate operation of the drive mechanism  12  in order to rotatably actuate the atherectomy burr  14 . In some cases, features of the atherectomy system  40  may be combined with one or more of the atherectomy system  10  and the atherectomy system  20 . The control system  42  may include a reference block  32  as well as a Proportional Integral Derivative (PID) controller  44  that is operably coupled to the reference block  32 . In some cases, the reference block  32  may determine a speed reference  46  that is selectable between a nominal value, a negative value and zero. In some instances, the PID controller  44  may be further adapted to add an offset value to the speed reference  46  received from the reference block  32 , although in some cases, the reference block  32  may add the offset value. The PID controller  44  may be further adapted to provide a reduction in motor speed of the drive mechanism  12  that is greater than what would otherwise normally occur in response to an increasing torque experienced at the atherectomy burr  14 . 
       FIG. 4  is a schematic block diagram of an example atherectomy system  50  that includes a control system  52  that is adapted to regulate operation of the drive motor  22  in order to rotatably actuate the atherectomy burr  14 . In some cases, features of the atherectomy system  50  may be combined with one or more of the atherectomy system  10 , the atherectomy system  20  or the atherectomy system  40 . The control system  52  is operably coupled to the drive motor  22  and includes a feedback loop  54  that is adapted to monitor performance of the drive motor  22  and to output a control effort signal  56 . A drive circuit  58  is adapted to receive the control effort signal  56  and to regulate operation of the drive motor  22  in accordance with the control effort signal  56 . 
     In some cases, the feedback loop  54  may include a reference block for determining a speed reference and a Proportional Integral Derivative (PID) controller that is operably coupled to the reference block for receiving the speed reference, the PID controller 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 signal. In some cases, the feedback loop  54  may be adapted to add an offset value to a reference signal provided to the reference loop  54  in order to accurately hold speed of the drive motor  22  during a no-load situation. In some instances, for example if the atherectomy burr  14  becomes stuck, the control system  52  may be further adapted to increase the torque provided by the drive motor  22  until a torque threshold is reached for a brief period of time, and to subsequently direct the drive motor  22  to reverse at a slow speed in order to unwind energy in the drive mechanism. 
       FIG. 5  is a schematic block diagram of an example atherectomy system  300 . In some cases, the atherectomy system  300  may be considered as being an example of the atherectomy system  10 ,  20 ,  40  or  50 . In some instances, features of the atherectomy system  300  may be combined with features of any of the atherectomy systems  10 ,  20 ,  40  or  50 , for example. The atherectomy system  300  includes a motor  302  that drives a drive cable  304  which itself engages a load  306 . The load  306  represents an atherectomy burr, for example. The motor  302  is controlled by a drive circuitry  308  which may be considered as being an example of or otherwise incorporated into the drive motor  22  ( FIG. 2 ) and/or the controller  16  ( FIGS. 1-2 ), for example. In some cases, the motor  302  may be sized, relative to the weight and other dimensions of the atherectomy system  300 , to be capable of accelerating the atherectomy burr to full speed in less than 3 seconds, or in some cases in less than 2 seconds. As an example, the motor  302  may be rated for at least 60 watts. In a particular example, the motor  302  may be rated for about 80 watts. These are just examples. 
     The drive circuitry  308  receives an input from a feedback portion  310 . In some cases, the feedback portion  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  may be configured to accept additional inputs, such as from a user and/or from additional sensors not illustrated. As an example, if the device has been running for too long of a period of time, the reference schedule block  314  may reduce the speed reference in order to prevent overheating. A PID controller is a controller that includes a (P) proportional portion, an (I) integral portion and a (D) derivative portion. The PID controller  316  outputs a control effort value or reference current  318  to the drive circuitry  308 . A motor state estimation block  320  receives a current/voltage signal  322  and a motor position signal  323  from the drive circuitry  308  and receives state feedback  324  from the PID controller  316 . The motor state estimation block  320  provides a state feedback signal  325  back to the PID controller  316 . 
     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 being 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 the derivative or integral of any of these values. In some cases, the motor state estimation block  320  may instead receive a signal  323  that represents speed, instead of position (as illustrated). The motor position signal  323  may be an indication of relative rotational position of an output shaft of the motor  302 , and thus an indication of relative rotational position of the load  306 , which if tracked over time may provide an indication of speed. 
     In some cases, the drive circuitry  308  and the feedback loop  310  may in combination be considered as forming a controller  350  that is adapted to determine an estimated torque at the atherectomy burr (the load  306  as shown in  FIG. 5 ). The controller  350  may be considered as being an example of the controller  16  ( FIG. 1 ). In some cases, the controller  350  may be considered as including only some elements of the drive circuitry  308  and the feedback loop  310 . In some instances, some of the features and functions of the controller  350  may take place in the motor state estimation block  320 . It will be appreciated that while  FIG. 5  shows various components as standalone components, in some cases the functions of one or more of the components may actually be spread between separate components. In some instances, the functions of one or more of the components may be combined into one or more components. 
     If the estimated torque at the load  306  becomes too high, this may be an indication that the burr is getting stuck. In order to protect against possible damage to the drive cable  304 , and to protect against possible injury to the patient, the atherectomy system  300  may be adapted to stop or even reverse operation of the atherectomy system  300  if the estimated torque meets or exceeds a predetermined torque threshold. It will be appreciated that the actual value of the predetermined torque threshold may vary, depending on the mechanics of the atherectomy system  300 , but may be set at a level low enough to prevent damage and injury, but not set so low as to engender too many false alarms caused by minor and/or temporary torque increases that are not caused by the load  306  becoming stuck. For example, the instantaneous torque may vary by small amounts as the atherectomy system  300  progresses through the patient&#39;s vasculature. Accordingly, the controller  350  may be adapted to calculate an estimated torque at the load  306  and to compare the estimated torque at the load  306  to the torque threshold. If the estimated torque meets or exceeds the torque threshold, the atherectomy system  300  may stop or even reverse the drive mechanism (the drive motor  302  and the drive cable  304 , for example). 
       FIG. 6  is a schematic block diagram of the PID controller  316 , which may be considered as being an example of the PID controller  44  shown in  FIG. 3 . An error signal  312 , which is representative of an error between a desired value and an actual value, enters the PID controller  316 . The PID controller  316  calculates a P term  340 , which is proportional to the error. The PID controller  316  calculates an I term  342 , which is an integral of the error and a D term  344 , which is a derivative of the error. These terms are added together at a summation point  346 , resulting in an output of the control effort signal  318 . 
     In some instances, the atherectomy system  300  may be considered as having a first operating mode and a second operating mode. The first operating mode may be considered as a normal operating mode, in which the atherectomy system  300  operates using a speed reference, and with a predetermined torque threshold or limit. As long as the load  306  (the atherectomy burr) is not stuck, i.e., seems to be rotating at a speed close to that expected in response to the rotation of the drive cable  304 , the controller  350  will operate in the first operating mode. However, if the controller  350  determines that the load  306  (the atherectomy burr) has become stuck, the controller  350  may instead operate in a second operating mode. In the second operating mode, the atherectomy system  300  may operate differently than in the first operating mode. In some instances, the second operating mode may correspond to a “stuck burr” mode in which the controller  350  is trying to facilitate freeing the stuck burr. 
     In some cases, the controller  350  will switch to using a position reference instead of a speed reference. In this situation, the controller  350  may alternate between driving the drive mechanism (the drive motor  302  and the drive cable  304 , for example) in a first rotational direction and driving the drive mechanism in a second rotational direction that is opposite that of the first rotational direction. In some cases, the controller  350  may drive the drive mechanism in the first rotational direction for a first distance and to drive the drive mechanism in the second rotational direction for a second distance that is different from the first distance. It will be appreciated that the relative distance, or number of rotations of the drive motor  302  in each direction may be different in order to accommodate the spring constant of the drive cable  304 . As noted previously, the drive cable  304  may be modeled as a spring. As such, it will be appreciated that rotating the drive cable  304  in one direction may tend to “wind” the spring while rotating the drive cable  304  in the opposing direction will tend to “unwind” the spring. In some cases, for example, the first distance and the second distance may be selected based upon a known spring constant of the drive mechanism. 
     This is illustrated for example in  FIG. 7 , which is a graphical representation of using a position reference instead of a speed reference. The X axis represents time while the Y axis represents position. As shown, the Y axis represents a number of motor rotations, with positive numbers representing motor rotations in one direction and negative numbers representing motor rotations in a second, opposing direction. It will be appreciated that by alternating between rotating in a first direction and rotating in a second direction, an oscillation may be achieved. In some cases, an oscillation may assist in freeing a stuck burr. The graph also illustrates how the drive motor  302  may drive further (more turns) in one direction than in the other direction. 
     In some cases, the distances (number of rotations) traveled in each direction may remain constant. In some instances, it is contemplated that the controller  350  may periodically adjust the first distance (number of rotations) and/or the second distance (number of rotations). In some instances, it is contemplated that the controller  350  may periodically adjust a time period between driving the drive mechanism in the first rotational direction and driving the drive mechanism in the second rotational direction. For example, as shown, the controller  350  is driving the drive mechanism a little over 200 rotations in a first direction, and perhaps about 125 rotations in the second opposing direction. In some cases, the zero point may be chosen such that at the zero point, the drive motor  304  needs zero torque in order to maintain position. As illustrated, the time period between driving in the first direction and driving in the second direction is about 5 seconds. The controller  350  could, for example, vary the distance (number of rotations) in the positive direction between 150 and 250 rotations and perhaps vary the distance (number of rotations) in the negative direction between 75 and 150 rotations. The controller  350  could vary the time period from perhaps about 2 seconds to about 10 seconds. These are just examples, and are not intended to be limiting in any fashion. 
     As illustrated, the graphed motor position shown in  FIG. 7  represents an asymmetric sine wave. As will be appreciated, this may be achieved by operating the drive motor  302  at a constant or largely constant rotational speed when driving in the first direction and in the second direction. In some cases, it is contemplated that the drive motor  302  may operate at a varying speed when driving in the first direction and in the second direction. For example, the drive motor  304  may operate faster when initially driving in a particular direction in order to save time, and may operate slower when approaching the desired number of rotations. 
     In some cases, using a position reference limits speed. As position is controlled by the controller  350 , there is no risk of breaking anything by overwinding the system in attempting to clear a jam. In some instances, by limiting the number of turns in either the first direction or the second direction, it will be appreciated that torque limits of the system may be maintained. In some cases, the frequency at which the drive motor  302  operates may be selected in order to maintain low speed limits once the burr becomes un-stuck and is able to once again rotate. 
     As noted, the atherectomy system  300  has a predetermined torque limit. It will be appreciated that the torque experienced at the atherectomy burr is a combination of the torque applied by the drive motor  302 , dynamic effects of the drive cable  304  as well as the inertia of the atherectomy system  300 . The predetermined torque limit has to be set in order to accommodate dynamic effects. When the atherectomy burr is jammed, i.e., not moving, the dynamic effects and the inertia are much reduced, if not substantially zero. Accordingly, when the atherectomy burr is not moving because it is jammed, the torque applied by the drive motor  302  may be temporarily increased above the predetermined torque limit. 
     In some cases, the second operating mode includes operating the atherectomy system  300  at low speed at a temporary torque value that exceeds the predetermined torque limit of the first operating mode while the atherectomy burr is not moving. For example, the temporary torque value may exceed the predetermined torque limit of the first operating mode by five percent, or by ten percent. In some cases, the temporary torque value may exceed the predetermined torque limit by twenty percent, or by thirty percent, or forty percent or fifty percent or more. In some instances, the controller  350  may pulse the drive motor  302  for a brief period of time, perhaps five seconds, ten seconds or twenty seconds, and then briefly stop before pulsing the drive motor  302  again. In some cases, the second operating mode may include temporarily exceeding the predetermined torque limit of the first operating mode while alternating driving the drive mechanism in a first rotational direction and driving the drive mechanism in a second rotational direction opposite that of the first rotational direction. As soon as the atherectomy burr begins to move, the controller  350  would revert back to the first operating mode in which the predetermined torque value is honored. 
     It should 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 exceeding the scope of the disclosure. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.