A system for detecting arrhythmias in cardiac activity, comprising: memory to store specific executable instructions; one or more processors configured to execute the specific executable instructions for: obtaining far field cardiac activity signals for a series of beats; for at least a portion of the beats in the CA signal, performing the following on a beat by beat basis: a) identifying first and second feature of interests from a segment of the CA signal that corresponds to a current beat; and b) classifying the current beat into one of first and second groups based on a relation between the first and second FOls for the current beat; designating one of the first and second groups to be a primary group based on a relation between the first and second groups; for the beats in the primary group, marking a select one of the first and second FOls as the R-wave FOI; positioning a P-wave detection window over the CA signal in connection with at least a portion of the beats based on the R-wave FOI for the corresponding beat; detecting P-waves in the P-wave detection window over the CA signals; and rejecting arrhythmia detections based on the P-waves detected. memory to store specific executable instructions; one or more processors configured to execute the specific executable instructions for: obtaining far field cardiac activity signals for a series of beats; for at least a portion of the beats in the CA signal, performing the following on a beat by beat basis: a) identifying first and second feature of interests from a segment of the CA signal that corresponds to a current beat; and b) classifying the current beat into one of first and second groups based on a relation between the first and second FOls for the current beat; designating one of the first and second groups to be a primary group based on a relation between the first and second groups; for the beats in the primary group, marking a select one of the first and second FOls as the R-wave FOI; positioning a P-wave detection window over the CA signal in connection with at least a portion of the beats based on the R-wave FOI for the corresponding beat; detecting P-waves in the P-wave detection window over the CA signals; and rejecting arrhythmia detections based on the P-waves detected. obtaining far field cardiac activity signals for a series of beats; for at least a portion of the beats in the CA signal, performing the following on a beat by beat basis: a) identifying first and second feature of interests from a segment of the CA signal that corresponds to a current beat; and b) classifying the current beat into one of first and second groups based on a relation between the first and second FOls for the current beat; a) identifying first and second feature of interests from a segment of the CA signal that corresponds to a current beat; and b) classifying the current beat into one of first and second groups based on a relation between the first and second FOls for the current beat; designating one of the first and second groups to be a primary group based on a relation between the first and second groups; for the beats in the primary group, marking a select one of the first and second FOls as the R-wave FOI; positioning a P-wave detection window over the CA signal in connection with at least a portion of the beats based on the R-wave FOI for the corresponding beat; detecting P-waves in the P-wave detection window over the CA signals; and rejecting arrhythmia detections based on the P-waves detected.