Abstract

A method and apparatus are disclosed for telemetering both analog and digital data from an implantable medical device to an external receiver, such as between an implanted cardiac pacer and its external programming equipment. Analog data is first converted to digital format by an analog-to-digital converter, such that the transmission is digital data. A damped carrier at 175 kilohertz is pulse position modulated by the data. The modulation scheme defines a frame of slightly less than 2 milliseconds. The frame is divided into 64 individual time periods using a crystal clock. The data, along with synchronization and identification codes, are positioned into predefined ranges within each frame as measured by the individual time periods. The data is uniquely identified by the position of a burst of the carrier within the predetermined range. This modulation scheme enables necessary data to be transmitted at sufficiently high rates with reduced power requirements thereby conserving the internal battery of the implantable device. This modulation scheme provides flexibility of use, for example, with complex medical devices where transmission of increased volumes of data is desirable, such as cardiac devices having dual-chamber or multisensor capabilities, and for controlling particular conditions, such as tachyarrhythmia.