A novel screening test for inappropriate shocks due to myopotentials from the subcutaneous implantable cardioverter–defibrillator

BACKGROUND: The subcutaneous implantable cardioverter-defibrillator (S-ICD) is effective in preventing sudden cardiac death. Compared with transvenous ICDs, S-ICDs have a lower rate of inappropriate shocks (IASs) for supraventricular arrhythmias, but such shocks for T-wave oversensing (TWO) and extracardiac myopotentials are more common. No screening tests to identify patients at risk for IAS due to myopotential interference (MPI) currently are available. OBJECTIVE: The purpose of this study was to assess the efficacy of a tube exercise test (TET) developed to detect MPI post S-ICD implantation. METHODS: TET includes 3 different maneuvers using an exercise tube. S-ICD electrograms were recorded to assess MPI while patients performed each of the maneuvers. RESULTS: TET was performed in 43 patients, and MPI was observed in 12 patients (28%). In 10 of the 12 TET-positive patients, the positive vector corresponded with a vector that did not show TWO on standard S-ICD preoperative screening. During median follow-up of 672 days (interquartile range 465-805 days), 3 patients (7%) experienced IAS due to MPI. Importantly, the vector at the time of IAS in all 3 patients passed standard preoperative screening for TWO but was positive with TET. Sensitivity and specificity of TET were 100% and 78%, respectively, and positive and negative predictive values were 25% and 100%, respectively. CONCLUSION: Postimplant screening for MPI identified patients at increased risk for IAS. TET may be helpful for guiding optimal programming to prevent IAS.