LONG-TERM STABILITY OF P-WAVE SENSING IN SINGLE-LEAD VDDR PACING - CLINICAL VERSUS SUBCLINICAL ATRIAL UNDERSENSING

Optimal function of a single lead P wave synchronous rate adaptive ven tricular pacing system (VDDR) requires reliable P wave sensing over ti me and during daily activities. The stability of P wave sensing and th e incidence of sensitivity reprogramming in a single pass lead with a diagonally arranged bipole wa:; assessed in 30 patients with complete atrioventricular block over a follow-up period of 12 +/- 1 months (ran ge 6 months to 3 years). Atrial sensing was assessed during clinic vis its, by physical maneuvers (postural changes, breathing, Valsalva mane uver, walking and isometric exercise), maximum treadmill exercise and Holter recordings. P wave amplitude at implantation was 1.21 +/- 0.09 (0.5-3.6) mV, and the atrial sensing threshold remained stable over th e entire period of follow-up. Using an atrial sensitivity based on twi ce the sensing threshold at 1 month, P wave undersensing was found in 2, 4, 3, and 7 patients during clinic visit, physical maneuvers, exerc ise, and Holter recordings, respectively. Atrial sensitivity reprogram ming was performed in three patients based on the correction of unders ensing during physical maneuvers. Although eight patients had atrial u ndersensing on Holter recordings, the number of undersensed P waves wa s small (total 101 beats or 0.013% +/- 0.001% of total ventricular bea ts) and no patient was symptomatic. One patient had intermittent atria l undersensing at the highest sensitivity, but the VDDR mode was still functional most of the time. No patient had myopotential interference at the programmed sensitivity. One patient developed chronic atrial f ibrillation and was programmed to the VVIR mode. Thus, single lead VDD R pacing is a stable pacing mode in 97% of patients. Because of the la rge variability of P wave amplitude, the use of a sensitivity margin a t least three times the atrial sensitivity threshold will maximize atr ial sensing and minimize the need for atrial sensitivity reprogramming (1/30 patients). Physical maneuvers and exercise tests are effective means for rapid assessment of the adequacy of P wave sensing.