W. p. GEIS AND M. P. KAYE 
297 
with the inferior margin of the LA were ex- 
cised after procedures (1), (2) and (3) to 
definitively localize neural pathways to this 
I area. 
RESULTS 
Whenever nerve stimulation resulted in an in- 
crement in heart rate accompanied by electrical 
activity and contraction of the RA and LA pre- 
ceding the RV electrical activity and contrac- 
tion, the interpretation was sinus acceleration 
and sympathetic innervation of the sinus node, 
whereas, if RA contraction and RA electrical 
activity occurred at the same time as or slightly 
following RV electrical activity and contraction, 
the designation was AV junctional rhythm 
and sympathetic innervation of the AV 
I node. When nerve stimulation resulted in a 
: decrement in atrial rate, the interpretation was 
sinus bradycardia or arrest and cholinergic in- 
nervation of the sinus node ; when stimulations 
caused no change in atrial rate but slowing of 
RV rate or complete RV arrest, the response 
was interpreted as cholinergic innervation of 
AV node. 
Sinus Node Sympathetic Innervation 
Prior to ablation procedures, heart rates 
averaged 139/minute (range 128 to 171). Elec- 
trical stimulation of the following nerves re- 
sulted in sinus tachycardia, right anterior ansa, 
right posterior ansa, right stellate cardiac, left 
posterior ansa, left anterior ansa, recurrent car- 
diac nerve, innominate nerve, VMCN and 
VLCN. Following transection of the medial and 
lateral portions of the SVC, stimulation of the 
right anterior and posterior ansae, the recurrent 
I cardiac nerve, the innominate nerve, and the 
j right stellate cardiac nerve no longer produced 
sinus acceleration in all experiments. 
Following transection of the SVC, sinus ac- 
celeration continued to be observed occasionally 
during nerve stimulation but the response was 
of lesser magnitude: left posterior ansa in 2 
experiments (HR = 152 and 160), left anterior 
I ansa in 2 experiments (HR = 140 and 152). 
Following interruption of neural elements at 
the origin of the great vessels the responses no 
longer occurred during stimulation of these 
nerves. Stimulation of the VLCN continued to 
result in sinus acceleration in 2 experiments 
(HR = 152 and 193), and the VMCN did so in 1 
experiment: (HR — 172). The responses in 
these experiments were interrupted following 
interruption of neural elements in the inter- 
atrial groove. 
Figure 2 depicts the response to right stellate 
cardiac nerve stimulation prior to transection 
of the SVC (control) and after transection of 
the SVC (SVC transection). Recordings are 
right atrial contraction (RAF), electrical acti- 
vation of the RA (BE [RA] ), right ventricular 
contraction (RVF) and electrical activation of 
the right ventricle (BE [RV]). Prior to tran- 
section of the SVC, the onset of RA electrical 
and mechanical activity precedes that of the 
RV. During stimulation there is no augmenta- 
tion in contractile force, but heart rate (HR) 
accelerates from 150/minute to 272/minute, 
and RA activity continues to precede RV activa- 
tion. This nerve, therefore, contains sympathe- 
tic fibers to the sinus node only. Following SVC 
transection, no longer is HR increased during 
stimulation. Thus, sympathetic fibers from the 
right stellate cardiac nerve to the sinus node 
enter the heart along the anterior aspect of the 
SVC. 
Sinus Node Cholinergic Innervation 
Initial electrical stimulation of the following 
nerves caused sinus depression in all animals: 
right vagosympathetic trunk, left vagosympa- 
thetic trunk, right thoracic vagus, left thoracic 
vagus and cranio-vagal nerve. Further, recur- 
rent cardiac nerve stimulation resulted in a 
decrement in sinus rate in 8 experiments while 
stimulation of the caudovagal nerve did so in 16 
experiments. Stimulation of the remaining 
nerves did not result in a decrement in sinus 
rate. 
Following transection of the SVC, interrup- 
tion of the sinus slowing response occurred in 
the maority of nerve stimulations. Decrement 
in sinus rate did persist on occasion and the 
response was interrupted as follows: right 
vagosympathetic trunk required inter-atrial 
groove dissection on two occasions; left vago- 
