The present invention generally relates to implantable stimulation devices, such as pacemakers, defibrillators, and cardioverters, and, in particular, to implantable medical devices using atrial based pacing such as an AAI pacing mode and methods for such implantable medical devices for detecting early stages of incipient A-V node malfunction as well as presence of A-V node malfunction. An AV conduction capacity is detected, wherein a sensed ventricular event following an intrinsic or paced atrial event during a predetermined period of time indicates good AV conduction capacity and wherein absence of a ventricular event within the predetermined period of time indicates poor AV conduction capacity. At least one A-V node function parameter indicating a function of the A-V node is determined, wherein the A-V node function parameter includes whether a status of the AV conduction capacity is good or poor. Incipient A-V node malfunction is detected where poor AV conduction capacity indicates incipient A-V node malfunction.
