In some examples, a catheter may include an elongate body and a push assembly. The elongate body may include an inner liner defining an entry port into a lumen, and an outer jacket. The push assembly may an elongate member extending from a proximal portion to a distal portion, where a cross-section of the distal portion is D-shaped and tapers in a distal direction. Distal to a proximal end of the elongate body, a first portion of the elongate member may be positioned between a portion of the inner liner and a portion of the outer jacket, and proximal to the proximal end of the elongate body, a second portion of the elongate member may be positioned outside of the outer jacket and the inner liner.