A catheter assembly for use in an anatomy can include an elongated body, which can have a proximal end and a distal end. The body can also define a lumen from the proximal end to the distal end. The assembly can include at least one electrode, which can be coupled to the distal end to sense an electrical activity within the anatomy. The assembly can include a core wire, which can be received within the lumen from the proximal end to the distal end. The core wire can be configured to move the distal end from a first configuration to a second configuration. The assembly can also include a necked portion, which can be formed between the proximal end and the distal end to provide increased stiffness to the distal end of the body.