Histological Study Of The Myocardial Sleeve Of The Superior Vena Cava In Human

Background: Atrial fibrillation is the most common sustained cardiacarrhythmia. Rapid discharges from the myocardium extending from theatrium into the thorax vein have been shown to initiate atrial fibrillation.Pulmonary vein as a triggered site has been studied broadly in anatomy andhistology. However, little is known about the superior vena cava (SVC). Objective: To investigate the anatomic and histological features ofSVC. Methods: The samples were obtained from 20 patients dying fromnoncardiac causes. They were from 18 men and 2 women aged 48±15years at the time of death (range, 22 to 72 years). The specimens were fixedusing 4% formalin. The SVCs were removed and then were dehydrated byethanol and embedded in paraffin. The specimens were cut alonglongitudinal and transverse direction at 3 to 5μm in the thickness, and werestained with hematoxylin and eosin(HE). Selected sections were stainedwith Masson-Trichrome or with general neural marker protein gene product9.5(PGP9.5) according to instruction. The morphologic characteristics andthe arrangement of the cardiomyocytes of the sleeves in SVC wereevaluated by light microscope. Results: (1)The morphologic characteristics of the cardiomyocytesin the sleeves were similar to those in the right atrium. The cardiac musclefibers extended from the atrium into the SVC with mean extensions of26.6±6.5 mm. The mean thickness of myocardium at the proximal SVCwas 2.5±0.5 mm. The cross sections of the SVC showed that the thicknessof the cardiac muscle varies at different levels from the anterior wall to theposterior wall and the lateral wall. The longitudinal sections showed thatthe arrangement of myocardial fibers was longitudinal, circular or oblique,even more disorganized at some sites. Gaps between the fibers wereobserved in the manner of fatty tissues, fibrous tissue, nerves, and bloodvessels.(2)Sections stained by Masson-Trichrome showed that theadventitia were blue, the myocardial cells and the nerve fibers andganglions were red. At the proximal SVC, myocardial fibers generally ranin the circular direction. From the atrial myocardium towards the vein, thethickness of myocardial sleeves gradually decreased.(3)Immunolabelingshowed that nerve fibers and nerve ganglions distributed in the epicardiumof the SVC. Conclusions: (1)Histology showed that myocardium of the rightatrial extended into the SVC at varied length may contributed to thesubstrate of arrhythmia.(2)The abundant autonomic nerves distributed inthe venous walls of SVC may have an effect on the electrophysiologicalcharacteristics of the cardiomyocytes.