Aerobic Capacity in Rate Modulated Pacing

Whether heart rate or AV synchrony is the most important factor for an increase in aerobic capacity was evaluated in a comparative study between sinus bradycardia, VVIR, DDD, and DDDR stimulation. Sixteen patients (mean age 67 years) with chronotropic incompetence and implanted DDDR pacemaker (Telectronics META 1250) were randomly studied by cardiopulmonary exercise testing. All patients were exercised to their anaerobic threshold (AT) with the following heart rates: DDD 84 +/- 3, VVIR 110 +/- 5, and DDDR 116 +/- 6 beats/min. Mean oxygen uptake (VO2, mL/kg per min) at AT was 7.4 +/- 0.3 in DDD and VVIR modes. A 12% increase was measured in DDDR mode (8.3 +/- 0.4). Compared to VVIR work capacity in the DDDR mode was improved by 17% (41 vs 48 W/min). In patients with isolated sinus node disease (n = 9) the increase of VO2 and work capacity at AT during DDDR mode was more pronounced (16% and 20%, respectively, compared to VVIR). In patients with intermittent second or third degree AV block (n = 7) the differences between the pacing modes were not significant. This might partly be due to a lesser degree of chronotropic incompetence in this subgroup. In conclusion only the conjunction of heart rate increase and preservation of AV synchrony provides a significant improvement in aerobic capacity during exercise.