Ventricular Fibrillation Masked by the Implanted Unipolar Pacemaker

¹ Departments of Pediatrics and Surgery, Children's Medical Center, The University of Texas Southwestern Medical School at Dallas

Unipolar pacemakers, such as the synchronous pacemaker, often produce biphasic signals which may be of considerable magnitude. Overshoot, a function of the voltage of the pacemaker, as recorded by an amplifying system, may be of sufficient length to completely conceal the QRS complex. Development of ventricular fibrillation may be masked, when prominent unipolar stimulus artifacts with overshoots produce essentially no change in the monitored electrocardiogram. The pacemaker signal artifact may be minimized, and the clinical danger reduced, by monitoring with lead I with an abdominal pacemaker implantation, or with lead II, III, or AVF, when the unit is placed in the axilla.