A medical device that includes a lead having a lead body extending from a proximal end to a distal end, and a housing having a connector block for receiving the proximal end of the lead body. A fixation mechanism is positioned proximal to an electrode coil located at the distal end of the lead body, and includes a locking sleeve and a mating portion positioned along the lead body proximal to the electrode. The fixation mechanism is capable of being advance from a first state corresponding to a first inner diameter of the locking sleeve and a second state corresponding to a second inner diameter of the locking sleeve greater than the first inner diameter to fixed position the electrode at a target site.