Initial clinical experience with a single pass VDDR pacing system.

Although ventricular rate adaptive pacing (VVIR) improves exercise capacity and cardiac output compared to constant rate ventricular pacing (VVI), this pacing mode does not provide benefit of atrioventricular (AV) synchrony. We evaluated the use of a custom-built VDDR pacing system using a single pass, ventricular lead, which detects endocavity P wave using a pair of diagonally arranged atrial bipolar (DAB) electrodes. In the VDDR mode, AV synchrony is enabled and the P wave rate is used in conjunction with an accelerometer based activity sensor for rate adaptive pacing. A VDDR pacemaker was implanted in three patients with complete AV block (mean age 63 +/- 1 year) and the mean implantation time was 29 minutes. Mean P wave amplitude was 2.4 mV (1.2-4.2 mV) at implantation and telemetered P wave amplitude was stable over a follow-up of 6 months. At a sensitivity of 0.2 mV, stable P wave sensing was observed during breathing maneuvers, arm swinging, myopotential induction, and Holter recording. Paired exercise tests performed in the VDDR and VVIR modes showed higher cardiac output at rest, during exercise, and in the recovery period in the VDDR pacing mode. Thus VDDR pacing using a single pass lead is superior to VVIR pacing by enabling P synchronous ventricular pacing without adding to the complexity of implantation.