Suppression of pacemaker activity by rapid repetitive phase delay.

Spontaneous activity of pacemaker cells of structures may be suppressed by rapid repetitive stimulation. Conditions are that the oscillator's phase reset curve, characterizing the phase resetting effect of single stimuli, has a phase delay part and that the interval between the stimuli falls within a range of values, determined by the form of the phase reset curve. Under these conditions, which appeared the same as those for stable underdrive pacing, the pacemaker becomes stably entrained to the stimuli without firing, i.e. it is kept within a certain part of its limit cycle because the pulses repeatedly delay the next coming action potential. This rapid stimulation suppression of pacemaker activity is demonstrated experimentally on a simple electronic pacemaker cell model for two types of phase reset curves, a biphasic one for depolarizing and a monophasic one for hyperpolarizing pulses. Computer simulations of coupled pacemaker cells, interacting by phase reset curves, illustrate how this type of pacemaker suppression may protect a population of pacemaker cells like the sinus node in the heart against arrhythmias.