[Cardiac stimulation: intermittent capture and loss of control, immediate lowering of the threshold]

The threshold for pacemaking by electrical stimulation is always above the threshold of excitation; it is possible to observe a progression, with intermittent capture and then loss of control, if the amplitude of the stimulus is progressively increased and then decreased. It has also been shown that, after a few minutes of stimulation, it is possible to reduce the amplitude of the impulse slightly without losing control, which is evidence of an immediate reduction in the threshold for electrical stimulation. Permanent loss of all response has been shown to occur at a lower level than that at which the original intermittent capture occurred. The threshold of excitation itself is therefore also lowered. These phenomena occur within the electrical levels, for which the titles "gradients of resistance" and "gradients of facilitation" have already been proposed. The present study, using bipolar intracavity stimulation of the right side, shows how easily the investigation was carried out in 20 patients, and their individual variations. These gradients are the expression of a constant inherent quality of the heart, and form new parameters of myocardial excitability; they open up new horizons for electrophysiological research, for cardiac stimulation, and for study of disorders of rhythm.