To assess the effect of right ventricular pacing on rate regularity du
ring exercise and daily life activities, 16 patients with sinoatrial d
isease and chronic atrial fibrillation (AF) were studied. Incremental
ventricular pacing was commenced at 40 beats/min until > 95% of ventri
cular pacing were achieved during supine, sifting, and standing. Thirt
een patients also underwent randomized paired submaximal exercise test
s in either a fixed rate mode (VVI) or a ventricular rate stabilizatio
n (VRS) mode in which the pacing rate was set manually at 10 beats/min
above the average AF rate during the last minute of each exercise sta
ge. The pacing interval for rate regularization was shortest during st
anding (692 +/- 26 ms) compared with either supine or sitting (757 +/-
30 and 705 +/- 26 ms, respectively, P < 0.05). During exercise, VRS p
acing significantly increased the maximum rate (119 +/- 5.2 vs 106 +/-
4.2 ms, P < 0.05), percent of ventricular pacing (85% +/- 5% vs 23% /- 7%, P < 0.05), rate regularity index (5.8% +/- 1.6%, vs 13.4% +/- 1
.9%, P < 0.05), and maximum level of oxygen consumption (12.4 +/- 0.5
vs 11.3 +/- 0.5 mL/kg, P < 0.05) compared with VVI pacing. There was n
o change in oxygen pulse or difference in symptom scores in this acute
study between the two pacing modes. If is concluded that right ventri
cular pacing may significantly improve rate regularity and cardiopulmo
nary performance in patients with chronic AF. This may be incorporated
in a pacing device for rate regularization of AF using an algorithm t
hat is rate adaptive to postural and exercise stresses.