REGIONAL DENERVATION OF THE CANINE HEART 
Gels, W, P. and Kaye, M. P. 
If implantation of cardiac and paracardiac devices 
interferes with autonomic cardiac innervation, neural 
control of cardiovascular events is altered. Accordingly, 
the sites of entry onto the heart of cardiac efferent 
nerves must be well defined. Cardiac inotropic and 
chronotropic innervation was evaluated using electrical 
stimulation of efferent cardiac nerves. Stimulations 
were repeated following localized transection of para- 
cardiac tissue. Results indicate that efferent nerves enter 
the heart along the superior vena cava, subjacent to the 
adventia of the pulmonary artery and aorta, along the 
superior and lateral margins of the left atrium, and at 
the junction of the inferior vena cava with the left 
atrium. These areas must be assiduously avoided during 
paracardiac and cardiac manipulation and/or instru- 
mentation during experimental investigations. 
INTRODUCTION 
In recent years, investigators studying car- 
diovascular hemodynamics, ventricular me- 
chanics, atrioventricular conduction and myo- 
cardial excitability, as well as cardiovascular 
reflex phenomena have made concerted efforts 
to assidously avoid the alterations in cardio- 
vascular physiology which occur during anesthe- 
sia. Anesthetic agents have been well-known to 
suppress autonomic responses ^ and to depress 
myocardial contractility directly.- To this end, a 
variety of invasive techniques have been utilized 
to implant blood flow devices, pressure gauges, 
venous and arterial occlusion cuffs, and various 
infusion and sampling instruments. The experi- 
mental animals — chronically instrumented — 
are later subjected to experimental procedures, 
and investigations are carried out with animals 
in the awake state. These investigational data 
are not only unmodified by anesthetic agents but 
physiological alterations induced by the open- 
chest state and positive pressure respiration 
are avoided. 
The criticism of chronic cardiac and para- 
cardiac instrumentation is subtle but very real. 
♦Illinois Institute of Technology Eesearch Institute Chicago, Illinois 
and Loyola Univei-sity Medical Center, Maywood, Illinois 
Since reflex phenomena determine the modula- 
tion of cardiovascular events during stress and 
during investigational interventions, it is of 
paramount importance that implantation of 
paracardiac devices does not interfere with 
neural control of the heart and vascular sys- 
tems. It is, therefore, appropriate in the re- 
search setting to be acutely aware of the paths 
which cardiac autonomic efferent nerves travel 
to enter the heart. Overzealous dissection 
in areas which have high concentration of nerve 
fibers will certainly result in inadvertant de- 
nervation of myocardium and/or nodal tissue. 
Detailed anatomical descriptions of paracardiac 
and cardiac autonomic nerve pathways have 
been published.'' However, until recently, there 
has been no correlation from the anatomical to 
the physiological. Randall has provided a phys- 
iological demonstration of the segmental nature 
of myocardial innervation,"* implying that a por- 
tion of the myocardium might be denervated 
while the innervation to the remainder of the 
ventricular chambers remains intact. Kaye et al. 
have interrupted efferent sympathetic nerves 
which enter the heart subjacent to the ad- 
ventitia of the great vessels and have obtained 
functional evidence for sympathetic denervation 
of the anterior and lateral walls of the ventric- 
ular chambers as well as significant depression 
of myocardial catecholamine content in the cor- 
responding areas. ^ Their co-workers have pro- 
vided evidence for depression of left ventricular 
function following acute partial denervation of 
the left ventricular chamber.® 
The total hemodynamic impact of inadvertant 
or purposeful interruption of a portion of the 
cardiac nerve pathways as they enter or exit 
the heart is not known. Accordingly, it is the 
purpose of this presentation: (1) to elucidate 
the sites of entry of efferent nerves onto the 
heart along with their corresponding distribu- 
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