An implantable medical device includes a device housing, a fixation device, a first prong projecting from a proximal end of the device housing and a second prong projecting from the proximal end of the device housing. The second prong is spaced apart from the first prong. The first prong includes a first flange projecting away from a longitudinal axis of the device housing. The second prong includes a second flange projecting away from the longitudinal axis. The first prong and the second prong are configured to extend to a first flange diameter in a relaxed configuration and to extend to a second flange diameter in an expanded configuration.