INNERVATION OF THE HUMAN CARDIAC CONDUCTION SYSTEM AT BIRTH

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.