Aims: Mechanical stimulation (MS) represents a readily available, non-invasive means of
pacing the asystolic or bradycardic heart in patients, but benefits of MS at higher heart rates
are unclear. Our aim was to assess the maximum rate and sustainability of excitation by MS
versus electrical stimulation (ES) in the isolated heart under normal physiological conditions.
Methods and results: Trains of local MS or ES at rates exceeding intrinsic sinus rhythm
(overdrive pacing; lowest pacing rates 2.50.5 Hz) were applied to the same mid-left
ventricular free-wall site on the epicardium of Langendorff-perfused rabbit hearts. Stimulation
rates were progressively increased, with a recovery period of normal sinus rhythm between
each stimulation period. Trains of MS caused repeated focal ventricular excitation from the
site of stimulation. The maximum rate at which MS maintained 1:1 capture was lower than
during ES (4.20.2 vs. 5.90.2 Hz, respectively). At all overdrive pacing rates for which
repetitive MS was possible, 1:1 capture was reversibly lost after a finite number of cycles,
even though same-site capture by ES was maintained. The number of MS cycles until loss of
capture decreased with rising stimulation rate. If interspersed with ES, the number of MS to
failure of capture was lower than for MS only.
Conclusion: In this study, we demonstrate that the maximum pacing rate at which MS can be
sustained is lower than that for same-site ES in isolated heart, and that, in contrast to ES, the
sustainability of successful 1:1 capture by MS is limited. The mechanism(s) of differences in
MS versus ES pacing ability, potentially important for emergency heart rhythm management,
are currently unknown, warranting further investigation.