An implantable medical device includes a lead, a pulse generator, an autothreshold module and a control module. The lead includes electrodes positioned within a heart. At least one of the electrodes senses cardiac signals. The pulse generator delivers a stimulus pulse through at least one of the electrodes. The autothreshold module performs a threshold search when operating in an autothreshold mode and causes atrial stimulus pulses to be delivered in an atrium of the heart at an overdrive rate during the threshold search. The control module determines an AV conduction time and applies an overdrive AV adjustment to the AV conduction time to generate an AV delay. The autothreshold module uses the AV delay in connection with delivering ventricular stimulus pulses to a ventricle of the heart.