Coronary Bypass Surgery Highlights Blood Vessel Biology

Coronary Bypass Surgery Highlights Blood Vessel Biology George E. Green, M.D. In 1972, I [l]reported that early results of internal mammary (1MA)-coronary artery anastomoses were superior to those of aortocoronary saphenous vein grafts (SVGs). In 1983, my colleagues and I [2] reported that late results of IMA grafts were superior to those of SVGs. Nevertheless, it appears that use of the IMA has not become much more general than it was in 1977, when 6% of cardiac surgeons used it (31. This surmise is based on the fact that of 183,859 coronary bypass operations registered by the National Institutes of Health in 1984, single IMA grafts were used in 11%and double IMA grafts, in less than 1%of the operations. Surgical results depend on a combination of technique and judgment. Awareness of the biology of blood vessels is crucial to judgment in vascular surgery. In recent decades, much attention has been paid to the nature of prosthetic grafts, but little to essential differences between veins and arteries. It is as though we expect autogenous tissues to be simply more effective plastics. Such expectation is not warranted by the data. Szylagyi and associates [4] carefully described the shortterm and long-term fate of vein grafts as arterial replacements. Though more effective than plastic prostheses, early failures of vein grafts did occur, and late failures were reported with increasing frequency as years went by. Szylagyi and co-workers [4] believed the most important factor in success to be the quality of the vein itself. That the range in quality of veins is limited was emphasized by Wylie’s preference for arterial autografts in difficult settings [5]. The report by Singh, Beg, and Kay (this issue, p 247) again emphasizes differences between IMA grafts and SVGs. Soon after coronary bypass grafting became a clinical reality, it was demonstrated experimentally that vein grafts in the aortocoronary position were far more vulnerable to atherosclerosis than pedicled IMA grafts [6]. Rather than attracting attention and stimulating discussion, this demonstration was overwhelmingly ignored. SVGs were used at an accelerating rate and with the satisfaction that one surgical doyen expressed when he introduced a pioneer of SVGs at a national meeting as “the great can opener at this surgical picnic.” Reports of early failure of SVGs due to subintimal hyperplasia caused a brief flurry of concern. But as attention was directed to more suitable matching of the size of vein grafts to recipient arteries, the incidence of hyperplastic obstruction diminished and the potential problems of vein grafts ceased to attract attention. It was declared that optimal harvesting of veins would almost eliminate early failure and that after the first postoperative year, From St. Luke‘dRoosevelt Hospital, New York, NY

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Ann Thorac Surg 41:235-236, Mar 1986

failure would be rare because SVGs were relatively resistant to atherosclerosis. Such declarations seem strange in view of the regular yearly incidence with which angina recurred after operation. Surgeons who were evaluating IMA grafts as well as SVGs found that when angina recurred, angiographic evaluation usually showed the cause of failure to be the SVG. Beyond five years following operation, failures of SVGs became increasingly frequent and were clearly due to atherosclerosis of an accelerated nature [7,8]. By 1984, there was no riposte to the statement by Grondin [9] that the future of coronary bypass surgery would depend on wider application of IMA grafts. However, it is an historical fact that demonstration of the superiority of a technique does not lead quickly to its adoption, especially if that technique is comparatively inconvenient. For example, more than a decade passed before SVGs were used more frequently than Dacron grafts in the femoropopliteal position. Emphasizing differences between IMA grafts and SVGs, and reviewing data that bear on the etiology of atherosclerosis, may help to encourage use of IMA grafts. Impairment of arteriolar, venous, or even lymphatic vasa vasorum creates lesions identified as arteriosclerosis [lo, 111. The vasa vasorum of free vein grafts are totally disrupted at the time of implantation. The walls of such grafts are devoid of capillary flow for seventy-two hours, and approximately six weeks are required for maximal reconstitution of arteriolar flow. This flow, regardless of whether the vein is in its native position or grafted into the arterial circulation, does not come from its own lumen. It emanates from neighboring arteries. Reconstitution of the vasa vasorum of free vein grafts is rarely perfect [12]. Deficiency of vasa vasorum makes the development of arteriosclerosis highly probable. As reported by Grondin [9], at ten years, only 21% of SVGs in the aortocoronary position showed no adverse change, whereas 95% of IMA-coronary artery pedicled grafts demonstrated no adverse change. The IMA pedicled graft carries its homeostatic milieu with it. Moreover, the IMA is endowed with an exceptional immunity to atherosclerosis [13]. Part of the immunity of the IMA to atherosclerosis appears to be the thinness of its wall [13]. This is the same factor cited as the drawback to its surgical use and as underlying the need for magnification when handling it [14]. If IMA grafts are to be used, handling of thin, friable walls will have to be accepted and an appropriate technique adopted. Such technique becomes particularly compelling when use of the IMA is extended to bilateral and sequential grafts. Extended use means longer pedicles and smaller, thinner walls. The difficulty of surgical handling seems warranted, because, as epitomized in

236 The Annals of Thoracic Surgery Vol 41 No 3 March 1986

t h e report of Singh, Beg, a n d Kay, the IMA graft will enlarge in response to demand for flow, provided t h e anastomosis is n o t restrictive. I have found that high magnification, that is, t h e operating microscope, so greatly facilitates s u c h w o r k that t h e need for SVGs be-

7.

comes infrequent. Is there a flag on t h e field? Perhaps not, b u t there is a challenge.

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References

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1. Green GE: Internal mammary artery-to-coronary artery anastomosis: three-year experience with 165 patients. Ann Thorac Surg 14:260, 1972 2. Singh RM, Sosa JA, Green GE: Internal mammary versus saphenous vein graft: comparative performance in patients with combined revascularization. Br Heart J 50:48, 1983 3. Miller DW, Hessel EL, Winterscheid LC: Current practice of coronary bypass surgery. J Thorac Cardiovasc Surg 73:73, 1977 4. Szylagyi DE, Elliot JP, Hageman JH, et al: Biologic fate of autogenous vein implants as arterial substitutes. Surgery 478:232, 1973 5. Stoney RJ: The arterial autograft. In Rutherford RB (ed): Vascular Surgery. Philadelphia, Saunders, 1984, pp 378-381 6. Rossiter SJ, Brody WR, Kosek JC, et al: lnternal mammary

10. 11. 12. 13. 14.

artery versus autogenous vein for coronary artery bypass graft. Circulation 50:1236, 1974 Campeau L, Enjalbert M, Lesperance J, et al: Atherosclerosis and late closure of aorto-coronary saphenous vein grafts: sequential angiographic studies at 2 weeks, 1 year, 5 to 7 years, and 10 to 12 years after surgery. Circulation 68:S~ppl2:l-7, 1983 Okies JE, Page US, Bigelow JC, et al: The left internal mammary artery: the graft of choice. Circulation 7O:Suppl 1:213, 1984 Grondin CM: Late results of coronary artery grafting: is there a flag on the field? (editorial.) J Thorac Cardiovasc Surg 87:161, 1984 Nakata Y, Shinya S: Structure of the lymphatics in the aorta and periaortic tissues and vascular lesions caused by disturbance of the lymphatics. Lymphology 12:18, 1979 Ramsey EM: Nutrition of the blood vessel wall: review of the literature. Yale J Biol Med 9:14, 1936/37 Wyatt AP, Rothnie BG, Taylor GW: The vascularization of vein grafts. Br J Surg 51:378, 1964 Sims FH: A comparison of coronary and internal mammary arteries and implications of the results in the etiology of arteriosclerosis. Am Heart J 105:560, 1983 Carpentier A, Guermonprez JL, Deloche A, et al: The aortato-coronary radial artery bypass graft. Ann Thorac Surg 16:111, 1973