Atrioventricular block and optimal synchronous pacing on ECG in a single lead VDD pacing population

INTRODUCTION In patients with atrioventricular (AV) block and preserved sinus node function on 12‑leads electrocardiogram (ECG) a single‑lead VDD pacing is today an established alternative to dual-chamber pacing, potentially offering reduced complications. Optimal pacing in AV block should maintain the AV synchrony on ECG in order to maximize cardiac output as well as stroke volume. Therefore in single‑lead VDD pacing population a proper planning of the AV interval is critical, as it allows the atrial contraction to complete before ventricular activation begins. METHODS AND RESULTS We enrolled 67 consecutive patients with complete AV block and preserved sinus node function, with a single‑lead VDD pacemaker indication. According to atrial dipole length patients were divided into a long-dipole group (>20 mm, n = 25) and a short-dipole group (≤20 mm, n = 26), while 16 patients were excluded (8 due to loss at follow-up, 8 for clinical non-eligibility considering atrial fibrillation and/or documented sinus node dysfunction). The mean atrial sensing amplitude was 0.60 ± 0.56 mV in the long-dipole group versus 1.16 ± 0.92 mV in the short-dipole group (p = 0.02) at 6-months follow-up. AV synchrony was significantly higher with long dipoles (95.4 ± 4.6%) compared with short dipoles (84.6 ± 25.5%; p = 0.04) at same follow-up. CONCLUSIONS In a single‑lead VDD pacing population, a longer atrial dipole is associated with a superior AV synchrony on ECG despite lower atrial sensing, supporting the concept that detection stability and electro-geometric consistency may prevail over absolute signal amplitude in preserving AV synchrony.