Inappropriate Ventricular Blanking in a DDI Pacemaker

The DDI mode is a new pacing mode with potential advantages over DVI pacing. We describe anomalous post R wave ventricular pacing due to the presence of inappropriate ventricular blanking periods in a pacemaker programmed to the DDI mode. Although no adverse consequences were seen in our patients, potentially dangerous R-on-T pacing could occur, particularly if long atrioventricular delays are programmed. A method for eliminating this pacing anomaly is described. Patients programmed to the DDI mode with the pacemaker model described should be evaluated for post R wave ventricular pacing and corrective measures should be taken.