Methods and devices are provided comprising an implantable lead having electrodes configured to be located proximate to a heart, the electrodes defining a sensing vector through a region of interest in the heart. The method and system collect an intra-cardiac electrogram (EGM) signal associated with an event of interest and determining an global amplitude characteristic (GAC) and a global slope characteristic (GSC) from the EGM signal under control of one or more processors within an implantable medical device (IMD). A QRS start time is defined, within the EGM signal, based on the GSC and determining a local amplitude characteristic (LAC) for a segment of the EGM signal within a search window of the GAC under control of one or more processors within an implantable medical device (IMD) A QRS end time is defined, within the EGM signal, based on the LAC; and calculating a QRS duration based on the QRS start time and QRS end time under control of one or more processors within an implantable medical device (IMD).