A cardiac rhythm management device is configured to discriminate between ventricular and supraventricular tachycardias (referred to as SVT/VT discrimination) by utilizing a morphology criterion in which the morphology of electrogram waveforms during ventricular beats are analyzed to determine if the beats are normally conducted. After the delivery of a cardioversion/defibrillation shock, however, the intraventricular conduction system is left in a modified state which alters the subsequently generated electrogram signal. Use of the morphology criterion for to SVT/VT discrimination is discontinued after delivery of such a shock and resumed after a predetermined minimum number of normally conducted ventricular beats has been detected.