AJP - Heart and Circulatory Physiology, Vol 238, Issue 3 406-H413, Copyright © 1980 by American Physiological Society
Norepinephrine release by ventricular stimulation: effect on fibrillation thresholds
D. E. Euler
In adult dogs anesthetized with pentobarbital sodium, ventricular
fibrillation thresholds determined by scanning the vulnerable period with a
train of 14 pulses (4 ms, 100 Hz) were significantly less (P less than
0.01) than fibrillation thresholds determined by scanning the vulnerable
period with a single 10-ms stimulus. Following beta-adrenergic blockade
with propranolol, the relative increase in the fibrillation thresholds
measured with trains was about seven times greater than the relative
increase in the single-stimulus threshold (P less than 0.01). In a group of
animals subjected to chronic cardiac denervation, fibrillation thresholds
measured with trains were about three times greater than in a group of
shamthoracotomized animals (P less than 0.01). Furthermore, the train
fibrillation thresholds of the catecholamine-depleted hearts were not
significantly different from the train thresholds of beta-blocked
innervated hearts. These data, coupled with the finding that trains of
stimuli produced a marked augmentation in local myocardial contractile
force, suggest that locally released norepinephrine during a
fibrillation-threshold determination may exert a profound influence on the
level of current necessary to evoke fibrillation.
