Cardiovascular responses to time delays of electrocardiogram-coupled electrical stimulation of carotid sinus nerves in dogs.

In search of improved patterns for electrical stimulation of the carotid sinus nerves (CSNs), which is applied therapeutically in patients with previous therapy refractory hypertension or angina pectoris, the timing of stimulation trains within the cardiac cycle was investigated in anesthetized dogs. Blood pressure responses and prolongations of heart beat intervals upon CSNs were analyzed. Electrocardiogram (ECG)-coupled trains of electrical stimuli were applied to bilateral intact CSNs. Pulses of 1 ms duration and the maximal (5-10 V) and 50% maximal stimulus amplitude were applied. The onset of stimulation trains (150 ms long, 15 impulses/train) was delayed from ECG-R-wave synchronous periods in units of 30 ms to maximally 150 ms. The timing of stimulus trains within the cardiac cycle did not influence the responses. Heart rate and blood pressure reductions upon CSNs were entirely dependent on the amplitudes of stimuli. In conclusion, a phase-dependency of such responses to CSNs, supposedly due to coincidence of electrically induced carotid sinus nerve activity with endogenous signals centrally converging from other cardiovascular afferents, could not be supported, using such stimulation trains. The observed responses did not show the known phase-dependency of sensitivity of the sino-atrial node to changes in effernt vagal activity. In experimental and therapeutic electrical CSNs (baropacing) for obtaining stronger cardiovascular responses with similar parameters, a preferential timing of stimuli relative to the cardiac cycle cannot be recommended.