Relationship between atrioventricular delay and oxygen consumption in patients with sick sinus syndrome: Relevance to rate responsive pacing

To develop a dromotropic-controlled rate adaptive algorithm for patients wi th sick sinus syndrome (SSS) and intact AV conduction, 14 pacemaker patient s with SSS underwent cardiopulmonary exercise testing (CPX). During exercis e; the pacemaker was programmed in an AAT mode without rate adaptation, whe reby 3 patients developed supraventricular arrhythmia and 11 patients kept sinus rhythm. Chronotropic incompetence (CI) at heart rate (HR) < 95 beats/ min at the anaerobic: threshold (AT) was found in five patients. In patient s with chronotropic competence (CC), the HR increase was significantly grea ter than in CI patients (rest: 73.2 +/- 12.6 vs. 64.2 +/- 4.0 beats/min; AT :101.2 +/- 6.2 vs. 82.0 +/- 5.1 beats/min; peak: 135.2 +/- 10.7 vs. 103.2 /- 10.9 beats/min). There was no significant difference in the AVD between CC and CI patients (rest: 167.7 +/- 38.6 vs. 170.8 +/- 22.5 ms, AT: 156.2 /- 30.7 vs. 163.6 +/- 21.6 ms, peak: 144.7 +/- 29.0 vs. 152.4 +/- 15.0 ms). The correlation coefficient between HR increase and (V) over dot O-2 was 1.0 and between AVD decrease and (V) over dot O-2 - 1.0 in both groups. An increase in pacing rate from 75 beats/min to 120 beats/min without exercise (overpacing) led to a prolongation of the AV interval of about 30.6 +/- 24 .2 ms. Based on this closed loop control with negative feedback, a dromotro pic rate adaptive algorithm for patients with SSS and intact AV conduction could be developed.