A method of performing a catheter-based procedure can include introducing a delivery sheath inside a patient's body and advancing a secondary sheath through the delivery sheath, toward a treatment site inside the patient's body. The secondary sheath can be distinct from the delivery sheath, coaxial to the delivery sheath along at least a portion of a length of the delivery sheath, and can have a default linear shape that is substantially free of radial bias. The method can further include introducing a catheter through the delivery sheath and secondary sheath, to the treatment site, and performing a procedure at the treatment site with the catheter. Performing the procedure can include performing the procedure while maintaining at a relatively fixed position the secondary sheath.