( A ) Dose–response curve for neurostimulation. The negative dromotropic effect during AF and PS at 20 Hz and an impulse duration of 0.5 ms is presented as a ratio of the CL during PS to CL prior to PS (CL _PS /CL). CL _PS /CL significantly increased with increasing stimulation voltage ( P < 0.001, ANOVA). ( B ) Influence of stimulation frequency on the negative dromotropic effect: CL _PS /CL significantly increases with higher stimulation frequencies at constant stimulation voltage and an impulse duration of 0.5 ms. The most distinct prolongation in ventricular cycle length occurs between 10 and 20 Hz, whereas an additional cycle length prolongation between 20 and 50 Hz is moderate. At higher stimulus strength of 4 V, a significant increase of the negative dromotropic effect was observed ( P < 0.05 all besides 10 Hz). ( C ) Weekly intermittent neurostimulation reveals a sustained negative dromotropic effect over 3 months: during PS (stimulation voltage 1 V; impulse duration 1 ms), ventricular cycle length during AF remains longer than without PS (CL _PS /CL) by a factor of ∼2. During the first 4–6 weeks, there was a non-significant trend towards a further increase in the rate slowing effect until the effect reached a plateau.