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Ann Thorac Surg 2004;77:114-115
© 2004 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, Alfred Hospital, Commercial Rd, PO Box 315, Prahran 3181, Australia
e-mail: f.rosenfeldt{at}alfred.org.au
This elegant laboratory study of preparation technique for saphenous vein graft conduit demonstrated that distention of the vein at uncontrolled pressures of up to 600 mm of mercury caused a severe loss of function in the saphenous vein, manifested by depressed responses to vasoconstrictors and vasodilators.
The authors tested the potency and the duration of action of vasodilators in the saphenous vein. They found that a combination of phenoxybenzamine, nicardipine, and Rho-kinase inhibitor fully dilated nondistended segments of saphenous vein and that the effect was evident for up to 20 hours. However, the capacity of this vasodilator combination to prevent the abnormalities in reactivity caused by forceful distension was not tested. The authors concluded that the abnormalities of endothelium-dependent dilatation were due to dysfunction of endothelial cells rather than to endothelial denudation. This conclusion can be disputed because it was based solely on light microscopy of cross sections of saphenous vein.
We previously reported a study of high pressure distention of human saphenous veins in the operating room and found that pressures of 500–600 mm of mercury resulted in loss of 50% of the endothelial lining of the saphenous vein [1] using en face preparations of the intima. We also found that this loss of endothelium could be largely prevented by using a solution containing a combination of glyceryl trinitrate and verapamil (GV) that relaxed the vein and removed the necessity for high pressure distention. In our study, GV solution was superior to papaverine in preserving endothelial integrity. GV treatment also preserved ATP content of the saphenous vein wall. A glyceryl trinitrate-containing solution has theoretical advantages over other dilators in that it enhances nitric oxide concentration in the vessel wall, which has beneficial actions including reduced platelet and endothelial adhesiveness.
The study by Okon and colleagues is essentially a laboratory one. The next step would be to use their novel vasodilator combination in the operating room to test its efficacy under clinical conditions. The practicalities of using a particular technique in the operating room may sometimes prevent its adoption despite its demonstrated efficacy. This applies particularly in the case of combination vasodilator solutions, such as the solution recommended in the present study and also GV solution, because of the difficulties in making up combination solutions in the operating room. Ideally, these solutions would be available commercially in a pre-mixed form. We have recently shown that the dilator actions of glyceryl trinitrate and verapamil that have different mechanisms of action are additive but not synergistic in the dilatation of the saphenous vein [2].
The saphenous vein has acquired a bad reputation because of poor long-term patency, widely quoted as 50% at ten years, with 25% of the patent grafts showing marked atherosclerosis [3]. However, we are all familiar with angiograms of patients with widely patent, normal looking saphenous vein grafts 10 or even 20 years after coronary bypass surgery. Why do some veins last 20 years and others occlude after 2 to 3 years? As with other biological systems, the difference is probably explained by a combination of "nature" and "nurture". Veins that are of a varicose or torturous nature before harvesting might be expected to occlude sooner than structurally normal veins. However, I believe the main differences in patency are due to differences in the preparation technique ("nuture") for the vein. A good analogy for this is the story of the radial artery graft. When the radial artery was first used in the 1970's the patency was very low [4]. When the radial artery graft was revived in the 1990's by Acar the results were dramatically better [5]. What caused the difference? In the early days, the radial artery was harvested with a traumatic technique; severe spasm occurred and the artery was forcefully dilated with metal probes with resulting damage. Acar's preparation technique, now widely used, involves an atraumatic surgical technique and the use of intraoperative and postoperative vasodilators. This has produced much better results for radial arteries in the current era. This difference in patency, depending on the surgical technique of conduit preparation, is almost certainly operative in the case of the saphenous vein. Poor preparation technique equates with poor long-term patency.
In conclusion, there is a wealth of information in the literature now, on the effect of preparation technique on the integrity and long-term results of the saphenous vein [6] which is supported by the current study and may be summarized as follows. Uncontrolled high pressure distention causes structural and functional damage to the endothelium and the media of the saphenous vein. The use of a vasodilator solution during harvesting and preparation of the saphenous vein can reduce the need for high pressure distention, and result in a graft which is intact structurally and physiologically. An improved graft at implantation will almost certainly equate with improved long term patency [7]. After all, if you or I were having a saphenous vein graft, would we prefer one with 50% of its endothelium missing and an inability to respond to normal vasomotor mediators or one which was structurally and functionally normal at implantation?
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  M. R. Dashwood, K. Savage, A. Dooley, X. Shi-Wen, D. J. Abraham, and D. S.R. Souza Effect of Vein Graft Harvesting on Endothelial Nitric Oxide Synthase and Nitric Oxide Production Ann. Thorac. Surg., September 1, 2005; 80(3): 939 - 944. [Abstract] [Full Text] [PDF]
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