Harris, A. S., Estandia, A., and Tillotson, R. F.:
Ventricular Ectopic Rhythms and Ventricular
Fibrillation following Cardiac Sympathectomy and
Coronary Occlusion. Am. J. Physiol. 165: 505
(June), 1951.
Abrupt coronary artery occlusion in dogs with
open chest is followed by a 10 minute period (phase
I) of ectopic discharges of increasing frequency which
either pass through a maximum and then decrease
or end in fibrillation. A two stage occlusion avoids
the danger of fibrillation in this phase. During the
next four and one-half to eight hours the ectopic
frequency is no more than 5 per minute (phase II)
in those animals which survive. Following this there
is a rapid increase in ectopic frequency (phase III)
which reaches a maximum in 10 to 20 hrs. after the
artery has been tied. This ectopic activity usually
lasts two to four days. Experiments were devised to
obtain evidence concerning the effects of upper
thoracic sympathectomy upon the occurrence of
ectopic ventricular complexes during each of these
three phases. The authors, as a result of their ex-
periments, came to the point of view that "multiple
excitatory factors contribute to the production of
ectopic impulses following coronary occlusion during
all three phases and that sympathetic nerve excitation is one of these factors.