CARDIAC-OUTPUT IN SINGLE-LEAD VDD PACING VERSUS RATE-MATCHED VVIR PACING

The importance of atrioventricular synchronous pacing compared with si ngle-chamber rate-responsive pacing is still under discussion, especia lly 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 of 1 to 2.5 mp h with a gradient of 2% to 4% was performed. Cardiac output was determ ined using a standard carbon dioxide rebreathing technique. initially, the VDD mode was programmed, and after 5 minutes of exercise, cardiac output wets measured in steady-state conditions. The pacemaker was th en reprogrammed to the WI mode at a rate 5 to 10 beats above the maxim al atrial tracking rate to simulate rate-matched VVIR pacing (VVIRm). After 5 additional minutes of steady-state exercise, cardiac output wa s 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 outp ut than VVIRm pacing (10.6 +/- 1.9 vs 9.2 +/- 1.4 L/min; p <0.002), wi th 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 pace maker patients with normal left ventricular function, atrioventricular synchronous pacing, compared with single-chamber rate-responsive paci ng, offers superior hemodynamics for everyday activities.