Reducing Heart Rate of the Dog by Electrical Stimulation

1) The frequency of effective ventricular contractions could be reduced by almost 50% in dogs by stimulating the ventricles (or atria) with electrical impulses of long duration (2 volts, 200 to 350 msec). 2) A similar result was obtained when pairs of impulses (2 volts), each 3 msec in duration, were used, with the time interval between the two impulses of the pair similar to that between the make and break of the long impulses (noted above). 3) The dogs were under general anesthesia and positive pressure breathing was maintained. After thoracotomy, platinum electrodes were implanted in the epicardial surface of the right ventricle or atrium. Pressures were measured in all heart chambers and the unipolar electrocardiogram was recorded from the right atrium with a catheter electrode. Several frequencies of stimulation, below the inherent sinus rate, were tested and at each frequency the time interval between pairs of stimuli was progressively increased from 100 to 350 msec. 4) In all dogs reduction of the ...