Incidence and significance of far-field R wave sensing in a VDD-implantable cardioverter defibrillator.

Background: A VDD-implantable cardioverter-defibrillator (ICD) provides atrioventricular (AV) synchronous stimulation when necessary and incorporates the advantages of dual chamber arrhythmia discrimination algorithms both at potentially lower costs and less periprocedural complications than a DDD-ICD system. A prerequisite for correct dual chamber ICD function is reliable atrial sensing. Methods: We evaluated atrial near- and ventricular far-field sensing and its impact on the dual-chamber detection algorithm in 106 patients with a single-lead VDD-ICD during a 12-month follow-up period. Results: Six hundred and thirty-nine follow-ups were included. Mean near-field amplitude was 3.82 ± 1.76 mV; mean far-field amplitude was 0.31 ± 0.15 mV. 46% of patients had far-fields >0.35 mV and 35% of patients showed atrial EGM markers corresponding to a ventricular far-field in at least one follow-up. Six hundred and forty-five tachycardia episodes were evaluated. Due to far-field sensing, three of 66 episodes (4.5%) of sinus tachycardia were misclassified as ventricular tachycardia (VT), leading to antitachycardia therapies. Delayed detection of VT was seen in a 12 of 323 episodes (3.7%) in five of 62 patients (8%) having VT events (delay 6.4 ± 6.0 seconds (range 2–24 seconds)). Stable far-field amplitudes <0.2 mV in a follow-up had a high negative predictive value for the occurrence of malfunction during tachycardia—conversely, high far-field amplitudes or a high incidence of far-field markers are only moderately correlated with malfunction. Conclusions: Ventricular far-field sensing in a VDD-ICD is not uncommon, however, tachycardia detection by the dual chamber algorithm is not seriously impaired by far-field sensing.