Impact of programmed sensitivity safety factor on atrial sensing in children

The relationship between the pacemaker sensitivity safety factor (PSSF) and atrial under- or oversensing as documented by 24-hour Holter monitoring was examined. Our study comprised 78 transvenous fixed atrial leads implanted between 1983-1995 in 71 children. Overall, 210 Holter reports identified 143 (68%) Holters with normal atrial sensing function, 31 (15%) with undersensing, 32 (15%) with oversensing, and 4 (2%) with both problems. From 161 Holter reports in which the PSSF was available, the incidence of undersensing at a PSSF of 2.0 (range 1.5-2.4) was 25% (14/57). There was a dramatic decline in undersensing when the PSSF was > or = 3 (3%) compared to a PSSF < 3 (21%) (P < 0.001). A PSSF cut-off point of 2.0 best predicted occurrence of undersensing with a sensitivity of 79% and a specificity of 67%. Other variable were also examined by multiple logistic regression analysis, but only PSSF remained highly associated with undersensing (odds ratio [OR] = 0.6, P = 0.03). In contrast, PSSF did not have a significant role in predicting oversensing, but presence of sick sinus syndrome (OR = 10.5) or unipolar lead (OR = 5.6) were significantly associated with oversensing (P = 0.0001). The majority of undersensing problems can be avoided by routinely allowing for at least a threefold or more programmed sensitivity margin. Other factors may increase the risk of oversensing, regardless of the PSSF.