1. An implantable medical device (IMD) comprising: a controller; a pulse generator operably coupled to the controller to deliver pacing stimuli; an atrial lead coupled with the pulse generator; a ventricular lead coupled with the pulse generator; a QT detection module operably coupled with the controller to provide a QT interval to the controller; and a calculation module operably coupled with the controller to determine an AV interval for the IMD that is equal to the current cardiac cycle length (CL) minus the QT interval, wherein the controller implements the determined AV interval in a pacing mode; and wherein the AV interval determined by the calculation module includes: a non-encroaching AV interval for sensed atrial events (SAVmax) wherein SAVmax=CL−EMSs+IAEMDs−PSO, where EMSs is the QT interval during a cardiac cycle with intrinsic ventricular activity, IAEMDs is a value for an interatrial electromechanical conduction delay for intrinsic atrial events and PSO is a value for a P wave sense offset; and a non-encroaching AV interval for paced atrial events (PAVmax) wherein PAVmax=CL−EMSp+IAEMDp, where EMSp is the QT interval during a cardiac cycle with ventricular pacing and IAEMDp is a value for an interatrial electromechanical conduction delay for paced atrial events.