A medical device system and method for monitoring a cardiovascular pressure signal to identify an atrial arrhythmia that includes a sensor sensing a cardiovascular pressure signal and a pressure analysis module that is configured to determine at least one of an interval dispersion and an amplitude dispersion of the sensed pressure signal, compare the at least one of an interval dispersion and an amplitude dispersion of the sensed pressure signal to a dispersion threshold, and determine whether the atrial arrhythmia is occurring in response to the comparing