A medical device having a plurality of electrodes sensing cardiac signals, and a microprocessor operably coupled to the plurality of electrodes and configured to determine a cumulative atrioventricular interval (AVI) burden in response to the sensed cardiac signals, and to switch operation of the device between a minimal biventricular pacing (MBVP) mode and a conditional triple chamber pacing (CTCP) mode in response to the determined AVI burden.