Long-term evaluation of sensing variability of a floating atrial dipole in a single‑lead defibrillator: The mechanistic basis of long-term stability of amplified atrial electrogram

Background: A single‑lead implantable cardioverter-defibrillator (ICD) with a floating atrial dipole has been developed to enhance the diagnostic capability of atrial arrhythmias and to facilitate adjudication of arrhythmic events without the additional effort required for atrial lead insertion. However, there have been concerns about the long-term reliability of atrial sensing. Methods: We enrolled patients with the single-chamber ICD with atrial-sensing electrodes from 4 tertiary university hospitals in Korea. Minimal, maximal, and mean P wave amplitudes were collected at 3–6 months, 6–12 months, and 12–24 months after implantation. The difference between the minimal and maximal sensing amplitudes was calculated as an indicator of the variability of atrial sensing, while the atrial sensing stability was assessed using the mean amplitude. Results: A total of 86 patients were included for analysis. The variability of atrial sensing amplitudes significantly decreased at 12–24 months compared to 3–6 months (p = 0.01), while mean atrial amplitudes were stable throughout the mean follow-up duration of 17.4 months. Nine patients (10.5%) experienced inappropriate ICD therapy mostly due to misclassification of supraventricular tachycardia. Conclusions: Under the hypothesis that sensing stability can be guaranteed as the variability decreases with time, we suggest that the concern about long-term sensing stability of a floating dipole can be abated with an ICD that has been implanted for over 2 years.