COMPARATIVE-EVALUATION OF ACUTE AND LONG-TERM CLINICAL-PERFORMANCE OF2 SINGLE-LEAD ATRIAL SYNCHRONOUS VENTRICULAR (VDD) PACEMAKERS - DIAGONALLY ARRANGED BIPOLAR VERSUS CLOSELY SPACED BIPOLAR RING ELECTRODES

Floating P wave sensing can be derived from bipolar atrial electrodes with different electrode configurations, although the relative clinica l efficacy of these methods of atrial sensing has not bee studied. We evaluated 32 sex and age matched patients with advanced AV block who r eceived AV synchronous pacers using wither a single lead with diagonal ly arranged bipole (Unity VDDR, Model 292, Intermedics Inc.) or closel y spaced bipolar complete ring electrodes (Thera VDD, Model 8948, Medt ronic Inc.). The total surface area of the atrial electrodes were 17.2 and 25mm(2), and the highest programmable atrial sensitivities were 0 .1 and 0.25 mV, respectively. Atrial electrogram amplitude and sensing threshold were evaluated at implant and at each follow-up clinic visi t (1, 3, and 6 months). Stability of atrial sensing was assessed durin g physical maneuvers, treadmill exercise test, and Holter recording. A trial electrogram amplitude at implantation was higher in the Thera VD D (2.08 +/- 0.79 vs 1.45 +/- 0.59 mV in Unity VDDR; P < 0.05), but the value of atrial sensing threshold was lower during follow-up than Uni ty VDDR. P wave undersensing was additionally observed with both pacem akers during physical maneuvers and exercise testing (6%-19% of patien ts). Two and four patients had atrial undersensing on Holter in the Un ity VDDR and Thera VDD, respectively, and the percentage P wave unders ensing were 0.88% +/- 2.41% versus 3.63% +/- 8.16%, respectively. Repr ogramming of the atrial sensitivity it the Unity VDDR and the use of i nvestigational software allowing 0.18 mV atrial sensitivity to be prog rammed in the Thera VDD substantially reduced the percentage of P wave undersensing on Holter to 0.46% +/- 1.67% and 0.19% +/- 0.24%, respec tively. Beginning at discharge with a programmed atrial sensitivity le vel at least twice the sensing margin, the mean atrial sensitivity lev el was reprogrammed from 0.29 to 0.26 mV for Unity VDDR and 0.33 to 0. 24 mV for Thera VDD at 6 months. There was no incidence of atrial over sensing. Despite differences in atrial amplitudes at implantation betw een the diagonally arranged bipole and closely spaced full ring single lead systems, the clinical performances of atrial sensing were simila r at an appropriately high atrial sensitivities. The absence of atrial oversensing suggests that single pass VDD pacemakers should probably be programmed at the highest available atrial sensitivity to ensure ad equate P wave sensing as guided by physical maneuvers and Holter recor ding to minimize the need of subsequent reprogramming.