intravascular catheters that include a flexible catheter body , a distal housing secured to the catheter body , a work element disposed within the housing and exposed to the external environment through a side window , and a guiding structure for the work element , are disclosed . an axial path through the housing is defined by the guiding structure . embodiments of the guiding structure include a slot or channel formed in the housing , a coaxial tube attached to the housing , a radially offset ribbon attached to the housing , or the external surface of the housing itself . the work element , such as a rotatable cutting blade in an atherectomy catheter , is coupled to the guiding structure such that the work element is retained within the housing during insertion and operation of the catheter and even when the housing is bent or distorted as a result of bends in the blood vessel .