Diverse myocardial extension and autonomic innervation on ligament of Marshall in humans

The ligament of Marshall (LOM) or the oblique vein of Marshall (VOM) in the left atrium (LA) is one of the origins of nonpulmonary vein ectopies causing atrial fibrillation. The distributions of myocardial bundles (Marshall bundles; MBs) and autonomic nerves adjacent to the LOM have not been completely elucidated.

Twenty-eight human hearts were examined postmortem. The inferolateral LA myocardium was dissected en block and cut perpendicularly to the atrioventricular ring. The specimens were sectioned at 1-mm intervals and stained with hematoxylin and eosin, and Azan-Mallory. In addition, S-100 and tyrosine hydroxylase (TH) were employed for the immunohistochemical analysis of the sympathetic and parasympathetic fibers. In 25 cases, MBs were observed. Although the MBs surrounded the VOM at the coronary sinus (CS) juncture, they gradually diminished in density toward the distal venous branch. The connections of the MBs and LA myocardium were frequently observed in the CS juncture and anterior wall of the left pulmonary vein (PV)-LA junctions. TH-stained sympathetic nerve fibers were densely distributed around the PV-LA junctions. On the other hand, non-TH-stained parasympathetic ganglions were mainly observed at the CS juncture.

MB-LA connections were mainly observed at the CS juncture and PV-LA junctions. The association between sympathetic nerve fibers and MBs was distinct at the PV-LA junctions. At the CS juncture, the regression of the sympathetic nerve fibers and the increase of parasympathetic ganglions were observed. The diverse arrangement and autonomic innervation of MBs seem to characterize the LOM region in humans.