A medical device and associated method for discriminating cardiac events includes determining whether a first match score is within a first match zone having a first correlation with a non-treatable cardiac event, a second match zone having a second correlation with the non-treatable cardiac event less than the first correlation with the non-treatable event, a third match zone having a first correlation with a treatable cardiac event, and a fourth match zone having a second correlation with the treatable cardiac event greater than the first correlation with the treatable cardiac event. A determination is made as to whether a second match score and a third match score are within the first match zone, the second match zone, the third match zone and the fourth match zone to generate a first adjusting factor, and cardiac event evidence is accumulated in response to the first adjusting factor for discriminating cardiac events.