A system for detecting arrhythmias in cardiac activity, comprising: memory configured to store specific executable instructions; and one or more processors configured, when executing the specific executable instructions, to: obtain a far field cardiac activity data set that includes far field CA signals for a series of beats detected by sense electrodes (114, 126) of an implantable cardiac monitoring device; calculate a P-wave segment ensemble from the an ensemble of candidate beats; perform a morphology-based comparison between the P-wave segment ensemble and at least one of a monophasic or biphasic template; declare a valid P-wave to be present within the CA signals based on the morphology-based comparison; and utilize the valid P-wave in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence or arrhythmia exit, characterized in that the one or more processors configured, when executing the specific executable instructions, to: determine whether the current beat satisfies a rate based selection criteria; declare a current beat, from the CA signals, to be a candidate beat or an ineligible beat based on whether the current beat satisfies the rate based selection criteria; and repeat the determining and declaring operations for multiple beats to form the ensemble of candidate beats. memory configured to store specific executable instructions; and one or more processors configured, when executing the specific executable instructions, to: obtain a far field cardiac activity data set that includes far field CA signals for a series of beats detected by sense electrodes (114, 126) of an implantable cardiac monitoring device; calculate a P-wave segment ensemble from the an ensemble of candidate beats; perform a morphology-based comparison between the P-wave segment ensemble and at least one of a monophasic or biphasic template; declare a valid P-wave to be present within the CA signals based on the morphology-based comparison; and utilize the valid P-wave in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence or arrhythmia exit, characterized in that the one or more processors configured, when executing the specific executable instructions, to: obtain a far field cardiac activity data set that includes far field CA signals for a series of beats detected by sense electrodes (114, 126) of an implantable cardiac monitoring device; calculate a P-wave segment ensemble from the an ensemble of candidate beats; perform a morphology-based comparison between the P-wave segment ensemble and at least one of a monophasic or biphasic template; declare a valid P-wave to be present within the CA signals based on the morphology-based comparison; and utilize the valid P-wave in an arrhythmia detection process to determine at least one of an arrhythmia entry, arrhythmia presence or arrhythmia exit, characterized in that the one or more processors configured, when executing the specific executable instructions, to: determine whether the current beat satisfies a rate based selection criteria; declare a current beat, from the CA signals, to be a candidate beat or an ineligible beat based on whether the current beat satisfies the rate based selection criteria; and repeat the determining and declaring operations for multiple beats to form the ensemble of candidate beats.