1. Within an implantable medical device, a method of confirming a ventricular tachycardia sense event declared when the apparent ventricular heart rate exceeds a tachycardia rate comprising: sensing the PQRST electrogram of the heart across an internal lead vector defined by a pair of vectorcardiogram sense electrodes implanted in the body and defining an internal lead vector in the body having a vector orientation in relation to reference sagittal, horizontal, and frontal planes of the body; declaring a ventricular tachycardia sense event when a feature of the PQRST electrogram satisfies ventricular sense event detection criteria characteristic of an R-wave, and is therefore an apparent R-wave, and the interval between successive ventricular sense events satisfies tachycardia rate criteria; deriving a QRS vectorcardiogram of the QRS segment of the sensed QRST electrogram quantifying the orientation and magnitude of the vector of the QRS wave; deriving a T-wave vectorcardiogram of the T-wave of the sensed QRST electrogram quantifying the orientation and magnitude of the vector of the T-wave; determining that the apparent R-wave is a true depolarization R-wave or a re-polarization T-wave satisfying the sense event detection criteria from characteristic features of one or both of the derived QRS vectorcardiogram and T-wave vectorcardiogram; and confirming the declaration of the ventricular tachycardia sense event when the apparent R-wave is determine to be a true depolarization R-wave.