A medical device implanted within a lumen of a patient, such as the esophagus, stomach, or another portion of the gastrointestinal tract, includes a device housing and a lead that extends from the device housing. An anchor member is located at a distal portion of the lead, and the lead includes one or more electrodes located between the device housing and the anchor member. A delivery system for implanting the medical device within the lumen includes an elongated delivery device and a needle. The needle includes a bore to receive the anchor member of the medical device. The delivery system inserts the anchor member through a passageway from the lumen, through the tissue, and back into the lumen.