1. A method of cardiac signal analysis in an implantable cardiac stimulus device comprising: implanting, into the patient, cardiac stimulus system comprising a canister and a lead assembly, the lead assembly including a plurality of electrodes thereon and the canister including at least one electrode thereon for use in cardiac activity sensing; identifying a first electrode pair defining a first sensing vector by observing a cardiac signal metric for a plurality of available sensing vectors and using the first electrode pair as a default electrode pair when observing cardiac activity of the patient; determining whether cardiac signals captured using the default electrode pair enable formation of a template representative of normal sinus rhythm for the patient; and, if not, changing the default electrode pair to a different pair of electrodes defining a sensing vector other than the first sensing vector.