[Blocked atrial extrasystole simulating impaired anterograde conduction during atrial stimulation]

In a 72-years-old patient with intermittent bradycardia definitive atrial pacing was considered. Surface ECG was misleading because of demonstrating 2:1 anterograde block during atrial stimulation at a rate of 100 beats per minute. Intracardiac recordings disclosed the bigeminal occurrence of premature atrial contractions. Every second stimuli fall within the premature atrial contraction's refractory period simulating impaired AV-conduction. Our report emphasizes the importance of intracardiac recordings during atrial stimulation in order to evaluate the anterograde conduction before pacemaker implantation.