Influence of the pacing rate on the atrioventricular conduction time during aerobic and anaerobic exercise: Basic concepts for a dromotropically controlled rate responsive pacemaker

The dromotropic pacemaker concept needs a rate responsive algorithm in whic h the pacing rate is controlled by the atrioventricular conduction time (AV CT). To develop basic concepts for such a rate responsive algorithm, the in fluence of the pacing rate on the AVCT was investigated. Seven patients (62 +/- 7.8 years) with sick sinus syndrome and intact atrioventricular conduc tion underwent two cardiopulmonary exercise tests (CPX) on a treadmill. Acc ording to the determination of the anaerobic threshold (AT) and the patient s maximum capacity in the first incremental CPX the work rate for two exerc ise levels below and above the AT were chosen for the second constant workl oad CPX. The calculation of the optimal pacing rate (HRopt) was based on th e oxygen uptake ((V) over dot O-2) during exercise after reaching steady-st ate conditions. According to the increase of the (V) over dot O-2 from 14.8 +/- 2.3 mL/min per kilogram during aerobic work 38.3 +/- 16.0 W) to 19.4 /- 4.7 mL/min per kilogram during anaerobic work (80.6 +/- 32.3 W), the HRo pt was calculated to be 98.6 +/- 6.9 beats/min and 116.4 +/- 4.7 beats/min. Starting from HRopt, the pacing rate was increased (overpacing) and decrea sed (underpacing) by about 5 beats/min every minute. At optimal pacing rats the AVCT decreased significantly from 233.0 +/- 30.5 ms during aerobic wor k and to 226.4 +/- 27.3 ms during anaerobic work (P < 0.05), Whereas overpa cing induced a significant prolongation of the AVCT during aerobic work (4. 17 +/- 1.78 ms per 10 beats/min) and anaerobic work (3.84 +/- 1.60 ms per 1 0 beats/min), underpacing yielded a significant shortening of the AVCT by a bout 4.49 +/- 2.64 ms per 10 beats/min during aerobic work and 4.75 +/- 1.8 7 ms per 10 beats/min during anaerobic work (P < 0.01). The slopes of the r egression lines of the relationship between AVCT and pacing rate were not s ignificantly different. Based on the reciprocal relationship of heart rate (HR) and AVCT, basic concepts may be established for a dromotropic rate res ponsive algorithm.