Abstract: Inventive catheters are disclosed which employ a variety of devices for preventing unwanted motion of the catheter tip. These methods include the use of a slidably mounted annular shim located in the tip of the catheter which may frictionally engage the guidewire element, and an annular brush with bristles. In the later case, the extent of the frictional engagement between the tip and the guidewire is determined by the orientation of the bristles. The present invention is also directed to a catheter in which unwanted motion is prevented by the presence of a tension/compression cable extending from the proximal end of the catheter shaft to the distal end of the catheter shaft. In the unlocked position, the tension/compression cable has slack in it while in the engaged position, the cable is either under tension or under compression.