A monitoring device for implant in a patient's body and a method of its use. The monitoring device is provided with an electrogram amplifier, a sensing electrode coupled to the amplifier, and a memory for storing electrogram signals sensed by the electrogram amplifier. Responsive to detection of an arrhythmia, the monitor generates an internal electrogram storage trigger signal and initiates a patient trigger confirmation period. In response to receiving a patient trigger signal within the confirmation period, the monitor stores electrogram signals. The monitor preferably also defines an internal trigger confirmation period following a patient trigger signal and in response to an internal electrogram storage trigger signal within the internal trigger confirmation period, also stores electrogram signals.