A medical system including a device head configured to be positioned in an atrium of a heart, an implantable medical device configured to be positioned within a vena cava of the heart, and a lead extending from the device head to the implantable medical device. A fixation element coupled to the device head is configured to engage tissues within the atrium. The device head includes an electrode configured to deliver therapy and/or sensing signals to tissues within the atrium using stimulation signals received from processing circuitry within the implantable medical device. The medical system may include a delivery catheter configured to allow delivery of the device head to the atrium.