Decrease in amplitude of intracardiac ventricular electrogram and inappropriate therapy in patients with an implantable cardioverter defibrillator.

Intracardiac electrograms are important for discrimination of tachyarrhythmia by implantable cardioverter defibrillators (ICD). A low R-wave can cause not only undersensing of ventricular tachyarrhythmia but also inappropriate discharges due to oversensing of unexpected signals because of its characteristic sensing algorithm. Therefore, this study aimed to investigate adverse events associated with R-wave amplitude. We included 115 consecutive patients followed-up over one year after implantation of a transvenous ICD system. The status of the ICD was checked every 3 months and intracardiac ventricular electrograms were analyzed. The decrease in R-wave amplitude was high in arrhythmogenic hypertrophy cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy (ARVC), and sarcoidosis. Low R-waves (< 5.0 mV) were observed in 13 patients at a follow-up of 15 +/- 16 months after implantation, and the mean R-wave was 3.0 +/- 0.8 mV. The frequency of low R-waves was high in ARVC (38%), sarcoidosis (33%), and dilated cardiomyopathy (17%). All of the dilated cardiomyopathy patients with low R-waves had severe left ventricular dysfunction. Inappropriate ICD therapy resulting from T-wave oversensing occurred in 7 patients and the R-wave was < 5.0 mV in 6 of the patients. The frequency of inappropriate therapy was high in patients with sarcoidosis. In 3 patients, inappropriate therapy caused ventricular tachyarrhythmia. In conclusion, decreases in R-wave amplitude occurred in some progressive cardiac disorders and caused inappropriate ICD discharges having arrhythmogenicity. Physicians should attempt to obtain a high R-wave amplitude during ICD implantation and careful follow-up is required, especially in patients with ARVC or sarcoidosis.