A telemetry system for data transmission between an implantable medical device and an external system includes a plurality of channels each representing a frequency band within a predetermined frequency range. The data transmission is performed using at least one active channel at any instant. Channel hopping is performed upon detecting an interruption of communication, such that a scan is performed through an array of channels selected from the plurality of channels. If a data frame is not successfully transmitted, it is repeatedly re-transmitted using the current and/or the next active channels until its transmission becomes successful.