Rotational atherectomy device with electric motor

Abstract

An atherectomy device is disclosed, which is rotationally driven by an electric motor. In some designs, the device includes features unavailable on gas turbine-driven systems, such as the storing in memory of low/medium/high preset rotation speeds for particular models of handle, calculations of the amount of saline left in the IV and associated warnings when it gets sufficiently low, and automatic adjustment of the IV pump rate to a predetermined or calculated level when the rotational speed of the motor is changed. The electric motor has far more rotational inertia than a comparable gas turbine, so the system includes a control mechanism that helps prevent damage from excessive torque being applied to the distal end of the drive shaft. When an obstruction at the distal end is detected, by a drop in the motor rotational speed, the motor is released and is allowed to spin freely as a flywheel. The freely-spinning motor allows the large angular momentum of the system to dissipate rapidly and safely, without excessive torque to the drive shaft.

What is claimed is: 
     
         1 . A device, comprising:
 an elongated flexible drive shaft comprising:
 a proximal end; 
 a distal end; and 
 an abrasive element fixedly attached proximate the distal end thereof; 
   an electric motor;   a coupler rotatably coupling the electric motor and the drive shaft at the proximal end thereof; and   a controller configured for:
 rotating the drive shaft by operating the electric motor; 
 inhibiting a torque at the abrasive element from exceeding a predetermined torque; 
 monitoring a rotational speed of the electric motor; 
 monitoring a current flowing through the electric motor; and 
 interrupting electrical power to the electric motor such that the electric motor is allowed to spin freely as a flywheel and no current or current-induced torque is supplied by the electric motor to the drive shaft when:
 a change in the rotational speed is greater than a first predetermined threshold or the rotational speed drops below a predetermined speed; and 
 a change in the current is greater than a second predetermined threshold or the current increases above a predetermined current. 
 
   
     
     
         2 . The device of  claim 1 , wherein:
 the first predetermined threshold is a percentage change in the rotational speed, a time rate of change in the rotational speed, or an absolute change in the rotational speed; and   the second predetermined threshold is a percentage change in the current, a time rate of change in the current, or an absolute change in the current.   
     
     
         3 . The device of  claim 1 , wherein inhibiting the torque from exceeding the predetermined torque comprises de-coupling the electric motor and the drive shaft instead of or in combination with interrupting electrical power to the electric motor. 
     
     
         4 . The device of  claim 1 , wherein the controller is configured for:
 operating the electric motor at one of a plurality of rotational speeds or at a variable rotational speed between a maximum speed and a minimum speed; and   operating a pump for supplying a fluid along the drive shaft at one of a plurality of pump speeds or at a variable pump speed between a maximum speed and a minimum speed.   
     
     
         5 . The device of  claim 1 , wherein the controller is configured for monitoring a voltage applied to the electric motor. 
     
     
         6 . The device of  claim 1 , wherein the predetermined torque is approximately zero. 
     
     
         7 . A device, comprising:
 an elongated flexible drive shaft comprising:
 a proximal end; 
 a distal end; and 
 an abrasive element fixedly attached proximate the distal end thereof; 
   an electric motor;   a coupler rotatably coupling the electric motor and the drive shaft at the proximal end thereof; and   a controller configured for:
 rotating the drive shaft by operating the electric motor; 
 inhibiting a torque at the abrasive element from exceeding a predetermined torque; and 
 monitoring a rotational speed of the electric motor and interrupting electrical power to the electric motor when the rotational speed drops below a predetermined speed, the rotational speed changes by a predetermined value, a percentage change in the rotational speed deviates from a predetermined permitted percentage, or a time rate of change in the rotational speed deviates from a predetermined permitted rate or 
 monitoring a current flowing through the electric motor and interrupting electrical power to the electric motor when the current is greater than a predetermined current, the current changes by a predetermined value, a percentage change in the current deviates from a predetermined permitted percentage, or a time rate of change in the current deviates from a predetermined permitted rate, 
 wherein interrupting electrical power to the electric motor comprises allowing the electric motor to spin freely as a flywheel and inhibiting current or current-induced torque from being supplied by the electric motor to the drive shaft. 
   
     
     
         8 . The device of  claim 7 , wherein inhibiting the torque from exceeding the predetermined torque comprises de-coupling the electric motor and the drive shaft instead of or in combination with interrupting electrical power to the electric motor. 
     
     
         9 . The device of  claim 7 , wherein the controller is configured for:
 operating the electric motor at one of a plurality of rotational speeds or at a variable rotational speed between a maximum speed and a minimum speed; and   operating a pump for supplying a fluid along the drive shaft at one of a plurality of pump speeds or at a variable pump speed between a maximum speed and a minimum speed.   
     
     
         10 . The device of  claim 7 , wherein the controller is configured for monitoring a voltage applied to the electric motor. 
     
     
         11 . The device of  claim 7 , wherein the predetermined torque is approximately zero. 
     
     
         12 . A method, comprising:
 rotatably coupling an electric motor and an elongated flexible drive shaft at a proximal end thereof, the drive shaft comprising an abrasive element fixedly attached proximate a distal end thereof;   rotating the drive shaft by operating the electric motor;   inhibiting a torque at the abrasive element from exceeding a predetermined torque;   monitoring a rotational speed of the electric motor;   monitoring a current flowing through the electric motor; and   interrupting electrical power to the electric motor such that the electric motor is allowed to spin freely as a flywheel and no current or current-induced torque is supplied by the electric motor to the drive shaft when:
 a change in the rotational speed is greater than a first predetermined threshold or the rotational speed drops below a predetermined speed; and 
 a change in the current is greater than a second predetermined threshold or the current increases above a predetermined current. 
   
     
     
         13 . The method of  claim 12 , wherein:
 the first predetermined threshold is a percentage change in the rotational speed, a time rate of change in the rotational speed, or an absolute change in the rotational speed; and   the second predetermined threshold is a percentage change in the current, a time rate of change in the current, or an absolute change in the current.   
     
     
         14 . The method of  claim 12 , comprising:
 not monitoring the current flowing through the electric motor; and   interrupting electrical power to the electric motor when the rotational speed drops below a predetermined speed, the rotational speed changes by a predetermined value, a percentage change in the rotational speed deviates from a predetermined permitted percentage, or a time rate of change in the rotational speed deviates from a predetermined permitted rate.   
     
     
         15 . The method of  claim 12 , comprising:
 not monitoring a rotational speed of the electric motor; and   interrupting electrical power to the electric motor when the current is greater than a predetermined current, the current changes by a predetermined value, a percentage change in the current deviates from a predetermined permitted percentage, or a time rate of change in the current deviates from a predetermined permitted rate.   
     
     
         16 . The method of  claim 12 , wherein inhibiting the torque from exceeding the predetermined torque comprises de-coupling the electric motor and the drive shaft instead of or in combination with interrupting electrical power to the electric motor. 
     
     
         17 . The method of  claim 12 , comprising:
 operating the electric motor at one of a plurality of rotational speeds or at a variable rotational speed between a maximum speed and a minimum speed; and   operating a pump for supplying a fluid along the drive shaft at one of a plurality of pump speeds or at a variable pump speed between a maximum speed and a minimum speed.   
     
     
         18 . The method of  claim 12 , comprising monitoring a voltage applied to the electric motor. 
     
     
         19 . The method of  claim 12 , wherein the predetermined torque is approximately zero.