Comparison among arterial grafts and coronary artery. An attempt at functional classification

Various arterial conduits have been used for coronary artery bypass grafting. However, arterial grafts are not uniform either in anatomy or in function. Some conduits are more spastic than others and there may be possible differences in long-term patency rates. The diverse biologic characteristics promote a necessity of classification of arterial grafts, which may facilitate the understanding of surgeons of biologic characteristics of various arterial grafts and provide a scientific basis for searching for new grafts. Another important issue is the comparison of reactivity between arterial grafts and coronary arteries. In this study, we aim to compare the pharmacologic reactivity among the human arteries (grafts and coronary arteries) and to classify arterial grafts. Segments of three arterial grafts (gastroepiploic, internal mammary, and inferior epigastric) taken from patients undergoing coronary artery bypass grafting and coronary arteries taken from explanted hearts were studied in organ baths for the contraction to four vasoconstrictors (endothelin-1, thromboxane A2 mimetic U46619, full adrenoceptor agonist norepinephrine, and depolarizing agent potassium) under physiologic pressure. The diameter of the four arteries at a pressure of 100 mm Hg was similar (p > 0.05). However, the gastroepiploic artery contracted to higher forces (9.41 +/- 2.0 gm for endothelin, 11.79 +/- 1.85 gm for U46619, 13.54 +/- 2.7 gm for norepinephrine, and 11.11 +/- 1.97 gm for potassium) than did the coronary artery and internal mammary artery (p < 0.05) for all the tested vasoconstrictors and higher than the inferior epigastric artery for potassium and norepinephrine (p < 0.05). There was no significant difference among the other three arteries (internal mammary artery, inferior epigastric artery, and coronary artery) regarding the maximal contraction force to any vasoconstrictor. No difference was detected in regard to the sensitivity (effective concentration causing 50% of the maximal response) to the vasoconstrictors among the four arteries. This study reveals that among the arterial grafts and the coronary artery, the gastroepiploic artery has the highest contractility to various vasoconstrictors. On the basis of our findings and physiologic and embryologic knowledge we propose a classification for arterial grafts: type I (somatic arteries), type II (splanchnic arteries), and type III (limb arteries). Types II and III are prone to spasm because of higher contractility whereas type I arteries are usually less spastic. This classification may have important clinical implications for the understanding of arterial graft spasm or patency and may be useful in the search for new grafts.