Background: This study focuses the role of heart rate on cardiac output (CO) at rest and during walk test in patients with dual-chamber pacemaker and depressed or normal left ventricular (LV) function.
Methods and results: In nine patients with ejection fraction (EF) <50% (group A) and in seven with EF 50% (group B) haemodynamics were assessed at rest and during three randomized 6-min walk tests at fixed rate of 70, 90, and 110beats.min(-1). All patients had dual-chamber pacemaker implanted for complete heart block. Left ventricular function was monitored by a radionuclide system. In group A, with increasing pacing-rate from 70 to 110beats.min(-1), CO did not change both at rest and during walk, whereas end-systolic volume (ESV) increased (P<0.05) and stroke volume (SV) decreased from 68+/-6 to 47+/-9ml at rest (P<0.0001) and from 112+/-21 to 76+/-17ml during walk (P<0.005). In group B, with increasing pacing-rate, CO rose from 6.4+/-0.7 to 9.1+/-1.6l.min(-1)at rest (P<0.001) and from 10+/-1.5 to 14.1+/-2.2l.min(-1)during walk (P<0.0001), with no change in ESV and SV.
Conclusions: Increasing heart rate in presence of ventricular asynchrony induced by dual-chamber pacing has negative effect on cardiac contractility and does not improve CO at rest or during physical activity in patients with depressed LV function as occurs in those with normal function.