Cardiac output in single-lead VDD pacing versus rate-matched VVIR pacing

The importance of atrioventricular synchronous pacing compared with single-chamber rate-responsive pacing is still under discussion, especially for low-intensity workload representing daily life activities. We evaluated hemodynamics in single-lead VDD pacing versus VVIR pacing in 11 patients (8 men and 3 women, aged 58.6 ± 13.8 years) with normal left ventricular function and a previously implanted single-lead VDDR pacemaker. A low-intensity steady-state treadmill test at 1 to 2.5 mph with a gradient of 2% to 4% was performed. Cardiac output was determined using a standard carbon dioxide rebreathing technique. Initially, the VDD mode was programmed, and after 5 minutes of exercise, cardiac output was measured in steady-state conditions. The pacemaker was then reprogrammed to the VVI mode at a rate 5 to 10 beats above the maximal atrial tracking rate to simulate rate-matched VVIR pacing (VVIRm). After 5 additional minutes of steady-state exercise, cardiac output was measured again. The maximal atrial rate in the VDD mode was 119 ± 19 beats/ min versus a programmed rate of 129 ± 18 beats/min in the VVIRm mode. VDD pacing resulted in a significantly higher cardiac output than VVIRm pacing (10.6 ± 1.9 vs 9.2 ± 1.4 L/min; p < 0.002), with a mean difference of 1.6 ± 1.2 L/min between the 2 modes. In the VDD mode, stroke volume (90.7 ± 20.1 vs 71.6 ± 13.0 ml; p < 0.001) and maximal oxygen uptake (1,183 ± 264 vs 1,076 ± 289 ml/min, p < 0.01) were also higher than in VVIRm. It is concluded that in most pacemaker patients with normal left ventricular function, atrioventricular synchronous pacing, compared with single-chamber rate-responsive pacing, offers superior hemodynamics for everyday activities.