A method of manufacturing a catheter shaft includes extruding an inner polymeric layer having a main lumen and two or more side lumens spaced about the main lumen; forming an outer polymeric layer about the inner polymeric layer; and inserting at least one elongate member, such as a wire, through each side lumen of the inner polymeric layer. The side lumens are less than about ⅕ the size of the main lumen. The method may further include the step of forming a braided layer between the inner polymeric layer and the outer polymeric layer. In an alternate embodiment, the method includes co-extruding an inner polymeric layer and a multi-lumen layer, the multi-lumen layer having two or more side lumens; forming an outer polymeric layer about the multi-lumen layer; and inserting at least one elongate member through each side lumen. Catheter assemblies made according to the described methods are also disclosed.