An implantable medical device is provided that comprises a pulse generator that provides atrial and ventricular pacing pulses on demand. The pulse generator times delivery of the ventricular pacing pulses based on an AV pacing interval. The device also includes an AV hysteresis module that extends the AV interval from a base AV interval to an extended AV interval to promote intrinsic heart activity. A refractory module establishes a PVARP interval equal to base PVARP interval following at least one of the ventricular pacing pulses. The refractory module lengthens the PVARP interval by adding a PVARP extension to a base PVARP interval to provide an extended PVARP interval. The device further includes a reentrant conduction detector that identifies an intrinsic reentrant tachycardia having a retrograde P wave occurring during the PVARP extension, based on one or more of i) a retrograde P wave, ii) intrinsic R waves sensed over N cardiac cycles at an R to R interval above a rate threshold and iii) one or more of PR and RP intervals that exceed PR and RP thresholds.