An implantable medical device comprising: a sensing module configured to receive a cardiac electrical signal via a plurality of extracardiac electrodes (28, 30) coupled to the implantable medical device; and a control module coupled to the sensing module and configured to: set a first signal analysis segment of the cardiac electrical signal; analyze the first signal analysis segment to determine if shockable rhythm classification criteria are met for the first signal analysis segment; set a plurality of T-wave oversensing (TWOS) analysis windows; analyze cardiac events of the cardiac electrical signal to classify each TWOS analysis window of the plurality of TWOS analysis windows as one of TWOS and no TWOS, each TWOS analysis window being classified as TWOS when cardiac events during the TWOS analysis window satisfy TWOS criteria and classified as no TWOS when the cardiac events during the TWOS analysis window do not satisfy TWOS criteria; determine that TWOS detection criteria are met for the first signal analysis segment when a predetermined number of the plurality of TWOS analysis windows are classified as TWOS; and classify the first signal analysis segment as non-shockable in response to determining that the TWOS detection criteria are met. a sensing module configured to receive a cardiac electrical signal via a plurality of extracardiac electrodes (28, 30) coupled to the implantable medical device; and a control module coupled to the sensing module and configured to: set a first signal analysis segment of the cardiac electrical signal; analyze the first signal analysis segment to determine if shockable rhythm classification criteria are met for the first signal analysis segment; set a plurality of T-wave oversensing (TWOS) analysis windows; analyze cardiac events of the cardiac electrical signal to classify each TWOS analysis window of the plurality of TWOS analysis windows as one of TWOS and no TWOS, each TWOS analysis window being classified as TWOS when cardiac events during the TWOS analysis window satisfy TWOS criteria and classified as no TWOS when the cardiac events during the TWOS analysis window do not satisfy TWOS criteria; determine that TWOS detection criteria are met for the first signal analysis segment when a predetermined number of the plurality of TWOS analysis windows are classified as TWOS; and classify the first signal analysis segment as non-shockable in response to determining that the TWOS detection criteria are met. set a first signal analysis segment of the cardiac electrical signal; analyze the first signal analysis segment to determine if shockable rhythm classification criteria are met for the first signal analysis segment; set a plurality of T-wave oversensing (TWOS) analysis windows; analyze cardiac events of the cardiac electrical signal to classify each TWOS analysis window of the plurality of TWOS analysis windows as one of TWOS and no TWOS, each TWOS analysis window being classified as TWOS when cardiac events during the TWOS analysis window satisfy TWOS criteria and classified as no TWOS when the cardiac events during the TWOS analysis window do not satisfy TWOS criteria; determine that TWOS detection criteria are met for the first signal analysis segment when a predetermined number of the plurality of TWOS analysis windows are classified as TWOS; and classify the first signal analysis segment as non-shockable in response to determining that the TWOS detection criteria are met.