302 
SURGERY AND TRANSPLANTATION 
fibers to the LA enter along the left side of the 
main pulmonary artery. 
AV Node Innervation 
Prior to surgical intervention, electrical 
stimulation of each of the cardiac nerves 
resulted in either sinus acceleration or a 
decrement in sinus rate in the majority of 
experiments (see sinus node innervation). 
Since the majority of sympathetic and parasym- 
pathetic nerve pathways to the sinus node en- 
ter the heart along the SVC, AV nodal rhythm 
was demonstrated in the eleven experiments in 
which transection of the SVC was the first 
intervention performed. Following transection 
of the SVC, acceleration of the AV node or 
slowing of the AV node was demonstrated dur- 
ing stimulation independent of neural influence 
on the sinus node. Moreover, in the few experi- 
ments in which sinus node responses persisted 
after SVC transection, neural influences upon 
the AV node were not demonstrated until the 
remainder of sinus node innervation was inter- 
rupted (see Sinus Node Innervation) . 
Sympathetic Innervation 
Following interruption of sympathetic path- 
ways to the sinus node, AV junctional tachy- 
cardia was demonstrated in all eleven animals. 
Average rates were 199/minute (range = 
170 to 240). LAA and VLCN stimulation re- 
sulted in AV tachycardia in 11 animals, while 
LPA did so in 8 experiments, RAA in 7, and 
RPA in 6 experiments. Stimulation of the in- 
nominate nerve, recurrent cardiac nerve and 
craniovagal nerve each produced the response 
in 2 experiments, whereas VMCN resulted in 
AV nodal rhythm in 3 experiments. The 
caudovagal nerve and right thoracic vagus 
nerves each elicited the response in one of the 
eleven animals. 
The AV nodal response to electrical stimula- 
tion of the caudovagal nerve, right thoracic 
vagus nerve, and innominate nerve, was inter- 
rupted after transection of the inferior margin 
of the LA on all occasions, whereas the response 
to stimulation of the recurrent cardiac nerve, 
VMCN and craniovagal nerve was interrupted 
following transection of nerves at the root of 
the great vessels in all cases. The RAA, RPA j 
and LPA each exhibited a bimodal distribution 
to the AV node. Transection of nerves at the 
root of the great vessels interrupted the AV 
nodal tachycardia to RAA and RPA stimulation j 
in 2 experiments, and to LPA stimulation in 4 ' 
experiments. Further abolition of the AV re- | 
sponse occurred after transection of the in- j 
ferior LA to LPA and RPA stimulation in 4 
experiments, while the response to RAA stim- 
ulation was interrupted by this procedure on 5 
occasions. The AV nodal response to LAA stim- 
ulation was interrupted following transection of 
the inferior LA in 6 experiments. In 3 additional 
experiments, transection of the nerves at the 
root of the great vessels was necessary for 
complete abolition of the response. In the re- [ 
maining 2 experiments, the response was not j 
interrupted until transection of the VLCN was ; 
performed. The AV nodal response to stimula- 
tion of the VLCN was interrupted after tran- 
section of the inferior LA in 7 experiments. In ' 
the remaining 4 experiments, both transection 
of the nerves at the root of the great vessels 
and transection of the VLCN were required to L 
completely interrupt the response. Following . 
either of the two latter procedures, the magni- , 
tude of the responses was usually decreased, 
however both procedures were necessary in each | 
instance in order to result in interruption of i 
AV nodal tachycardia. \[ 
Figure 5 depicts cardio-acceleration during ^ 
electrical stimulation of the right anterior ansa f 
from 146 to 250/minute (column-control). Elec- [ 
trical and mechanical activation of the RA (BE f 
[RA] and RAF) precedes electrical and me- ' 
chanical activation of the RV (BE [RV] and 
RVF). Following transection of the SVC (col- ' 
umn-SVC transection), electrical stimulation re- ■ 
suits in increase in HR to 190/minute with [ 
electrical and mechanical activation of the RA j' 
and RV occurring simultaneously. Thus, the i' 
sympathetic fibers from this nerve to the sinus ' 
node enter the heart along the SVC and inter- | 
ruption of these neural elements unmasks AV } 
junctional tachycardia. The sympathetic fibers ■ 
to the AV node are interrupted following tran- <' 
section at the junction of the inferior vena cava I' 
with the inferior margin of the LA (column- ^ 
IVC-ILA junction). Note that in the right i 
1 
I 
