A method and apparatus for morphologic analysis of an electrical signal, implementable in an implantable device such as a pacemaker, cardioverter, defibrillator or the like. The morphologic analysis uses a phase plane representation of the signal, where the signal and its first derivative are plotted along orthogonal axes. A magnitude signal corresponding to the magnitude component of the trajectory of the phase plane representation is generated and applied to a comparator. The comparator produces an activation signal when the magnitude signal exceeds a predetermined threshold. In response to the activation signal, a quadrant detector selectively applies the magnitude signal to one of four integrators, the selection of one integrator over the others being based at all times upon which quadrant of the phase plane the trajectory is in. When the magnitude decreases below a predetermined threshold, the activation signal is deasserted, whereupon the respective outputs from the four integrators may be interpreted as reflecting of the trajectory of the phase plane representation of the signal. In operation, a particular cardiac event to be detected is induced in a patient, and the resultant phase plane signals are examined to determine particular aspects of the phase plane signals which can be used as an indication that the particular event has occurred. The apparatus is then conditioned to recognize such aspects in subsequent phase plane signals, in order to provide an indication when such aspects are again present in the signals.