Fusion or confusion on Holter recording.

Holter recording of a patient with an implanted dual chamber rate responsive pacemaker revealed an electrocardiogram, where ventricular depolarization seemed to be initiated by the atrial stimulus. In a second patient with a VVI pacemaker, Holter recording showed delay of the pacemaker impulse that was registered after the onset of ventricular depolarization. Misalignment in one of the recorder heads of the display system was responsible for this phenomenon, which in case of dual chamber pacing could have been easily misinterpreted as pacemaker malfunction.