VDD(R) Pacing: Short- and Long-Term Stability of Atrial Sensing with a Single Lead System

Background: Recent studies have shown that the atrial signal can reliably be sensed for VDD(R) pacing via atrial floating electrodes incorporated in a single-pass lead. However, there remains concern about the long-term stability of atrial sensing and proper VDD function under real-life conditions. This study investigated the long-term reliability of atrial sensing and atrioventricular synchronous pacing using a new single lead VDD(R) pacing system. Methods and Results: In 20 consecutive patients (ages 71 ± 14 years) with normal sinus node function and high-degree heart block, a single lead VDD(R) pacemaker (Unity(tm), Intermedics) was implanted, Atrial sensing was studied at implantation, at discharge, and at 1, 3, 6, 12, and 18 months of follow-up. At implant, the measured P wave amplitude was 2.3 ± 1.2 mV. By telemetry, the atrial sensing threshold was 0.79 ± 0.41 mV at discharge, 0.75 ± 0.43 mV at 1 month, 0.73 ± 0.43 mV at 3 months, 0.76 ± 0.41 mV at 6 months, 0.79 ± 0.41 mV at 12 months, and 0.77 ± 0.35 mV at 18 months of follow-up (P = NS). Appropriate VDD pacing was assessed by the percentage of correct atrial synchronization (PAS = atrial triggered ventricular paced complexes ± total number of ventricular paced complexes) during repeated Holters. PAS was 99.99%± 0.01 % at 1 month, 99.99%± 0.02% at 3 months, and 99.98%± 0.05% at 12 months of follow-up (P = NS). No atrial oversensing with inappropriate ventricular pacing was observed, neither during isometric arm exercise testing nor spontaneously during Holier monitoring. Conclusion: The long-term stability of atrial sensing with almost 100% correct atrial synchronous tracking and the lack of inappropriate pacing due to atrial oversensing make the new Unity VDD(R) system a highly reliable single lead pacing system. In view of the lower costs and the ease of single lead implantation, this system may offer an interesting alternative to DDD pacemakers in patients with normal sinus node function.