Abstract: Methods, devices, and program products are provided under control of one or more processors within an implantable medical device (IMD) that senses far field (FF) signals between a combination of electrodes coupled to the IMD. Correlation scores are determined by comparing the FF signals associated with a number of beats to a template. The correlation scores of the number of beats are compared to a correlation threshold, and correlation variability scores are determined for the number of beats. Shock delivery, by a pulse generator within the IMD, is postponed in response to i) a first number of beats within the number of beats having the correlation scores that are less than the correlation threshold, and ii) a second number of beats within the number of beats having correlation variability scores that are less than a correlation variability threshold.