Methods and appartus for crossing occlusions in blood vessels

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

advancing an elongate shaft of a medical device through a lumen of a blood vessel to a location proximate an occlusion in the blood vessel, the medical device including a handle assembly attached to a proximal portion of the elongate shaft;

rotating a housing of the handle assembly in a first direction about a longitudinal axis of the elongate shaft to rotate the elongate shaft and a distal tip of the medical device in the first direction, wherein the rotating applies a torque to the elongate shaft below a first maximum torque; and

advancing the distal tip of the elongate shaft between a location proximal of the occlusion and a location distal of the occlusion while rotating the housing of the handle assembly;

wherein the handle assembly includes a torque control mechanism that transfers torque from the housing to the elongate shaft to rotate the elongate shaft in the first direction when the torque is below the first maximum torque and the torque control mechanism prevents rotation of the elongate shaft in the first direction when the torque is above the first maximum torque.

2. The method of claim 1 , wherein the distal tip of the elongate shaft is advanced between the occlusion and an adventitial layer of the blood vessel.

3. The method of claim 1 , wherein the handle assembly includes a first camming element having a ramped surface and a second element having a recess having an engagement surface in contact with the ramped surface at torques below the first maximum torque.

4. The method of claim 3 , wherein the ramped surface disengages the engagement surface of the recess at torques above the first maximum torque.

5. The method of claim 4 , wherein the first camming element rotates with the second element at torques below the first maximum torque to permit the elongate shaft to rotate as the housing of the handle assembly is rotated.

6. The method of claim 5 , wherein the second element rotates relative to the first camming element at torques above the first maximum torque to prevent the elongate shaft from rotating as the housing of the handle assembly is rotated.

7. The method of claim 1 , further comprising:

rotating the housing of the handle assembly in a second direction about the longitudinal axis of the elongate shaft to rotate the elongate shaft and the distal tip of the medical device in the second direction, wherein the rotating applies a torque to the elongate shaft below a second maximum torque;

wherein the torque control mechanism transfers torque from the housing to the elongate shaft to rotate the elongate shaft in the second direction when the torque is below the second maximum torque and the torque control mechanism prevents rotation of the elongate shaft in the second direction when the torque is above the second maximum torque.

8. The method of claim 7 , wherein the handle assembly includes a first camming element having a ramped surface and a second camming element having a recess having an engagement surface in contact with the ramped surface at torques below the first maximum torque, and the ramped surface disengages the engagement surface of the recess at torques above the first maximum torque.

9. The method of claim 8 , wherein the first camming element rotates with the second camming element at torques below the first maximum torque to permit the elongate shaft to rotate as the housing of the handle assembly is rotated, and the second camming element rotates relative to the first camming element at torques above the first maximum torque to prevent the elongate shaft from rotating as the housing of the handle assembly is rotated.

10. The method of claim 9 , wherein the handle assembly includes a cap having a recess and the second camming element has a ramped surface in contact with an engagement surface of the recess of the cap at torques below the second maximum torque, and the ramped surface of the second camming element disengages the engagement surface of the recess of the cap at torques above the second maximum torque.

11. The method of claim 10 , wherein the first maximum torque is different from the second maximum torque.

12. A method of facilitating treatment of a blood vessel, the method comprising:

providing a medical device shaft having a distal end and a proximal end;

providing a handle assembly attached to the proximal end of the shaft, the handle assembly including a first portion, wherein rotation of the first portion in a first direction about a longitudinal axis of the shaft causes rotation of the shaft in the first direction when a torque applied by the first portion to the shaft is below a first maximum torque, and wherein rotation of the first portion in the first direction about the longitudinal axis of the shaft does not cause rotation of the shaft in the first direction when the torque applied by the first portion is above the first maximum torque; and

rotating the first portion of the handle assembly in the first direction about the longitudinal axis, wherein the rotating applies a torque to the shaft below the first maximum torque, and wherein the rotating causes the shaft to rotate.

13. The method of claim 12 , further comprising:

advancing the shaft within a blood vessel a first amount while rotating the first portion of the handle assembly in the first direction.

14. The method of claim 13 , further comprising:

advancing the shaft within the blood vessel a second amount while rotating the first portion of the handle in a second direction opposite the first direction.

15. The method of claim 12 , wherein the first portion of the handle assembly is rotated in the first direction at a rotational speed of between about 50 revolutions per minute and about 150 revolutions per minute.

16. The method of claim 15 , wherein rotating the first portion of the handle assembly in the first direction is achieved by rolling the handle assembly between a thumb and a forefinger of a hand of a user.

17. The method of claim 12 , wherein the handle assembly includes a second portion, the first portion being rotatable relative to the second portion when the torque applied by the first portion is above the first maximum torque, and the second portion being rotatable with the first portion when the torque applied by the first portion is below the first maximum torque.

18. The method of claim 12 , wherein the handle assembly includes a torque control mechanism including a first camming element and a second camming element, wherein the first camming element couples rotation of the first portion to rotation of a second portion of the handle assembly in the first direction when the torque applied by the first portion to the second portion is below the first maximum torque.

19. The method of claim 18 , wherein the first camming element decouples rotation of the first portion from rotation of the second portion in the first direction when the torque applied by the first portion to the second portion is above the first maximum torque.

20. The method of claim 19 , wherein the handle assembly provides an audible indication when the torque applied by the first portion to the second portion is above the first maximum torque.