Objective-To study the pattern of innervation of the conduction system
of the neonatal heart in humans. Design-A prospective analysis based
on immunohistochemical and enzyme histochemical examination of newborn
human hearts. Setting-A general district hospital. Main outcome measu
res-Fresh necropsy tissue. Material-Hearts of three neonatal humans wi
th no cardiac anomaly, freshly taken at necropsy. Methods-Serial secti
oning to obtain a three dimensional reconstruction of the cardiac cond
uction system, followed by identification of the pattern of innervatio
n by immunohistochemical and enzyme histochemical techniques; with a p
anel of antisera against protein gene product (PGP) 9-5 as a general n
eural indicator; dopamine beta-hydroxylase (DBH) and tyrosine hydroxyl
ase (TH) as indicators for sympathetic neural tissue; and selected neu
ropeptides-namely, neuropeptide Y (NPY), vasoactive intestinal polypep
tide (VIP), calcitonin gene related peptide (CGRP), and substance P (S
P). Gomori's technique was used for locating cholinesterase activity.
Results-PGP immunoreactive (PGP-IR) nerves were present in large numbe
rs in the sinus node, atrioventricular (AV) node, and penetrating atri
oventricular bundle; in moderate numbers in the branching bundle; and
occasionally in the bundle branches. Small numbers of DBH-IR and TH-IR
nerves were seen in the sinus and AV nodes, mainly perivascularly; th
ere were few in the penetrating and branching bundles and none in the
bundle branches. A few perivascular NPY-IR nerves were seen only in th
e sinus node. VIP-IR, CGRP-IR, and SP-IR nerves were not seen. Pseudoc
holinesterase activity was found in the conduction tissue, whereas occ
asional acetylcholinesterase positive nerves were found only in the si
nus and AV nodes. Conclusion-A considerable innervation of the human c
ardiac conduction system is present at birth, although, by comparison
with the results of other studies on adult tissue, the mature pattern
has not yet been established. Thus it is still in the process of matur
ation, especially with regard to the acquisition of various neurotrans
mitters, including the more recently described neuropeptides.