Cross-stimulation during lead impedance monitoring

At the age of 4 years, a total cavopulmonary connection was performed in a boy with a complex congenital heart defect. On addition, a DDDR pacemaker w as implanted for sick sinus syndrome. Atrial and ventricular leads were epi cardially placed at the left atrium and left ventricle. At the age of 10 ye ars, a new epicardial ventricular lead was placed because of malfunction of the existing lead. At the some operation the pulse generator was replaced by a Medtronic Kappa DR 731. After replacement, the boy experienced episode s of phrenic nerve stimulation associated with feelings of discomfort. Holt er recordings revealed ventricular stimulation from the atrial stimulus for 2 consecutive beats. This phenomenon repeated exactly every 3 hours and wa s caused by the automatic lead impedance measurement that used a 5-V, 1-ms stimulus output.