Chemodectoma in a patient with a single ventricle.

found in the bipolar pacing system of our patient, probably because the insulation break was a tiny one confined to the outer insulation coating and allowing just a small amount of fluid intrusion during the two month period postimplant, and minimal leakage of current. Additionally, the impedance of the anode and the external wire, over which the fluid was accumulated, was not very low since an impedance lower than 250 ohms is considered to be definite evidence of a lead failure.2 However, this invisible insulation defect resulted in the described erratic pacing spike interval prolongation or "pacemaker pauses" similarly to the sinus pauses of sick sinus syndrome before the pacemaker implantation and with the same symptoms.