CONTRASTING STRUCTURE OF THE SAPHENOUS-VEIN AND INTERNAL MAMMARY ARTERY USED AS CORONARY-BYPASS VESSELS

Objectives: To report quantitatively on the three-dimensional layered organization of the collagen and smooth muscle component of the two mo st successful vessels for coronary bypass-the internal mammary artery (IMA) and the long saphenous vein (SV). Our aim was to provide an expl anation for the differential structural stiffness of these two vessels (both functioning at arterial pressures in their new environment), an d how they might be susceptible to endothelial thickening. Methods: El even human saphenous veins and 23 internal mammary arteries were fixed at arterial distending pressure of 110 mmHg, and were sectioned in cr oss-section at 7 mu m thickness. A subset of these was also sectioned tangentially. Measurements of the three-dimensional alignment of colla gen and smooth muscle fibers within the vessel wall were made using po larized light microscopy and the universal stage attachment. Data were plotted and analysed using circular statistics. Results: The IMA, str uctured like an elastic artery, is dominated by a media with discrete lamellae of wavy collagen and smooth muscle, aligned nearly circumfere ntially, with a low variability of alignment (mean circular SD 12 degr ees). The SV is more variable in its size and structure, characteristi cally with a narrow circumferential media comprised mostly of collagen which is straightened and highly aligned at arterial pressures (mean circular SD 9 degrees). Circumferential collagen in the vein was often adjacent to longitudinal bundles of smooth muscle and collagen. Concl usions: The strikingly aligned structure of the SV complements the kno wn high mechanical stiffness of this vessel when at arterial distendin g pressure. The high fraction of longitudinal muscle, in addition to t he circumferential muscle cells in the SV make it vulnerable to any pr e-implant surgical preparation, and to the cyclical luminal pressures and longitudinal strains characteristic for epicardial arteries.