1. An external medical device, comprising: a telemetry module configured for bidirectional wireless communication with a plurality of implantable medical devices; and a control module configured to: determine an active membership of an implantable medical device (IMD) system, wherein the active membership comprises each one of the plurality of implantable medical devices that is present in a patient and operable, establish programmable parameters for the IMD system based on the active membership, wherein the programmable parameters control at least one of a therapy delivery operation and a physiological signal sensing operation by each of the plurality of implantable medical devices of the active membership; and control the telemetry module to transmit values for the established programmable parameters to the active membership.