Methods and appartus for crossing occlusions in blood vessels

1. A device for facilitating treatment of a blood vessel, the device comprising:

a shaft having a distal end and a proximal end, wherein the shaft is configured for advancement through a blood vessel lumen; and

a handle assembly disposed about the shaft;

wherein the handle assembly includes a first portion and a torque limiting mechanism coupling the first portion to the shaft;

wherein the torque limiting mechanism includes a first ramp that allows relative movement between the first portion and the shaft when the first portion is being rotated in a first direction and a torque applied to the shaft is greater than a first maximum torque; and

wherein the torque limiting mechanism allows relative movement between the first portion and the shaft when the first portion is being rotated in a second direction and a torque applied to the shaft is greater than a second maximum torque.

2. The device of claim 1 , wherein the second maximum torque is different than the first maximum torque.

3. The device of claim 1 , wherein:

the shaft includes a left hand wound coil;

the first direction is a clockwise direction; and

the first maximum torque is greater than the second maximum torque.

4. The device of claim 1 , wherein:

the shaft includes a right hand wound coil;

the second direction is a counterclockwise direction; and

the second maximum torque is greater than the first maximum torque.

5. The device of claim 1 , wherein:

the shaft comprises a coil and the device further comprises a distal tip fixed to a distal end of the coil and a proximal hub fixed to a proximal end of the coil.

6. The device of claim 1 , wherein the torque limiting mechanism comprises a first camming element, the first camming element having a first ramp, the first ramp having a first ramped surface and a first face.

7. The device of claim 6 , wherein the first camming element is coupled to the shaft so that the first camming element is not free to rotate relative to the shaft.

8. The device of claim 6 , wherein the torque limiting mechanism comprises a second camming element having a first ramp engaging surface and a second ramp, the second ramp having a second ramped surface and a second face.

9. The device of claim 8 , wherein the torque limiting mechanism comprises a cap fixed to the first portion, the cap comprising a second ramp engaging surface.

10. The device of claim 9 , wherein:

the first ramp engaging surface engages the first ramped surface when the first portion is rotated in the first direction; and

the second ramp engaging surface engages the second ramped surface when the first portion is rotated in a second direction.

11. The device of claim 10 , wherein:

the first face contacts a first stop when the first portion is rotated in the second direction; and

the second face contacts a second stop when the first portion is rotated in the first direction.

12. The device of claim 8 , wherein:

the first ramped surface has a first pitch;

the second ramped surface has a second pitch; and

the second pitch is different from the first pitch.

13. The device of claim 8 , wherein:

the first ramp has a first maximum height;

the second ramp has a second maximum height; and

the second maximum height is different than the first maximum height.

14. A device for facilitating treatment of a blood vessel, the device comprising:

a shaft having a distal end and a proximal end, wherein the shaft is configured for advancement through a blood vessel lumen;

a handle assembly disposed about the shaft; and

the handle assembly comprising a handle housing and a torque limiting mechanism coupling the handle housing to the shaft;

wherein the torque limiting mechanism allows relative movement between the handle housing and the shaft when the handle housing is being rotated in a first direction and a torque applied to the shaft has exceeded a first maximum torque;

wherein the torque limiting mechanism comprises a first camming element, wherein the first camming element is free to rotate relative to the handle housing;

wherein the torque limiting mechanism comprises a second camming element, wherein the second camming element is free to rotate relative to the handle housing;

wherein the torque limiting mechanism comprises a distal cap, wherein the distal cap is not free to rotate relative to the handle housing.

15. The device of claim 14 , wherein the torque limiting mechanism allows relative movement between the handle housing and the shaft when the handle housing is being rotated in a second direction and the torque applied to the shaft has exceeded a second maximum torque, wherein the second maximum torque is different than the first maximum torque.

16. The device of claim 14 , wherein, the first camming element has a first ramp, the first ramp having a first ramped surface and a first face.

17. The device of claim 16 , wherein the first camming element is coupled to the shaft so that the first camming element is not free to rotate relative to the shaft.

18. The device of claim 16 , wherein the second camming element has a first ramp engaging surface and a second ramp, the second ramp having a second ramped surface and a second face.

19. The device of claim 18 , wherein the cap comprises a second ramp engaging surface.

20. The device of claim 19 , wherein:

the first ramp engaging surface engages the first ramped surface when the handle housing is rotated in the first direction; and

the second ramp engaging surface engages the second ramped surface when the handle housing is rotated in a second direction.