Background: Rate adaptive pacing (RAP) during cardiac resynchronisation therapy (CRT) in patients with chronic heart failure (CHF) might improve exercise capacity through enhanced cardiac output (CO). Conversely, higher heart rates (HR) might set off a blunted force-frequency response (FFR).
Methods: Fourteen CRT-treated patients (62+/-3 years, left ventricular ejection fraction 30.8+/-2.7%) underwent two cardiopulmonary exercise tests (CPET). CPET1: rate response off; CPET2: rate response on. Conventional and tissue doppler echocardiography were obtained at rest and at peak exercise.
Results: Peak values for HR (106+/-5 vs. 127+/-3 bpm; P=0.001) and CO (6.4+/-0.4 vs. 7.4+/-0.4 l/min/m; P=0.001) increased significantly comparing CPET1 and CPET2. Stroke volume index (28.8+/-1.4 vs. 27.9+/-1.2 ml/m, P=0.2) and peak oxygen consumption (17.8+/-0.9 vs. 17.4+/-0.7 ml/kg/min, P=0.6), however, did not differ. Longitudinal systolic velocities of the basal septum (SSm: 6.9+/-0.9 vs. 6.1+/-0.8 cm/s, P=0.07), basal left lateral (LSm: 6.1+/-1.3 vs. 5.9+/-0.8 cm/s, P=0.3) and basal right ventricular free wall (RVSm: 11.7+/-0.9 vs. 10.1+/-0.7 cm/s, P<0.01) remained unchanged or decreased. Inter-ventricular (Deltat LSm-RVSm) (10+/-18 vs. 15+/-9 ms) and intra-ventricular mechanical delay (Deltat SSm-LSm) (10+/-15 vs. 9+/-6 ms) did not change.
Conclusion: RAP resulted in a net increase in CO, without an acute favourable effect on exercise capacity. This finding underscores the importance of peripheral factors (endothelial and skeletal muscle dysfunction) as determinants of exercise capacity in CHF. The fact that longitudinal systolic myocardial velocities at higher HR did not change or even decreased suggests that a blunted FFR still occurs, despite CRT. RAP had no effect on mechanical synchrony.