Inappropriate discharges from an intravenous implantable cardioverter defibrillator due to T-wave oversensing

This report describes the clinical management of 2 patients with ventricula r fibrillation (VF) who received inappropriate shocks from an implantable c ardioverter defibrillator (ICD) due to T-wave oversensing. Cardiac sarcoido sis was confirmed as the underlying heart disease in 1 patient and idiopath ic dilated cardiomyopathy in the other. Within 2 months after ICD implantat ion, both patients received several inappropriate shocks during sinus rhyth m. Stored electrograms showed decreased R-wave amplitudes and increased T-w ave amplitudes. The ICD sensed both R- and T-waves as ventricular activatio n, which met the rate criteria for VF treatment. Reprogramming the sensing threshold in association with administration of a drug to slow the heart ra te decreased the incidence of the inappropriate shocks in both patients, bu t these palliative measures did not completely suppress the inappropriate s hocks. To avoid T-wave oversensing, the repositioning or adding of a sensin g lead is required. The potential risk of T-wave oversensing in ICD patient s who have small R-wave amplitudes should be recognized.