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Ann Thorac Surg 2000;70:888-889
© 2000 The Society of Thoracic Surgeons
Discussion
DR VALAVANUR A. SUBRAMANIAN (New York, NY): This is indeed an excellent paper presented by the group from Boston University Medical Center. We have been interested in looking at the differences in the biological and pharmacologic characteristics of radial artery grafts in various groups of patients. It is a preliminary study we recently presented at the Society of Vascular Biology Annual Meeting last year.
People who are diabetic, who have smoked within a week of off pump coronary artery bypass (OPCAB), and those who have been on daily aspirin (325 mg), had decreased prostacyclin synthesis, higher intimal thickening, and reduced nitric oxide synthesis in their radial artery grafts. My question is, have you looked at the incidence of diabetes between the two groups and also the incidence of smoking, as thse preoperative risk factors may have an influence on the effectiveness of the drug, and also the tendency to spasm may be higher in this group?
DR SHAPIRA: We have not looked at the incidence of vasospasm in different groups, although it is our impression that there are definitely more problems in patients who are actively smoking and not in patients who are diabetic. In patients who are actively smoking we continue the antispasmodic treatment for up to 1 year postoperatively, and we strongly encourage patients to cease smoking.
With regard to nitric oxide, we did look at nitric oxide synthesis in the radial artery and actually found it to be at least as high as the nitric oxide synthesis in the internal mammary artery. This gives hope that long-term patency of the radial artery graft would be equivalent to the internal mammary artery graft. Certainly smoking impairs nitric oxide synthesis and therefore, these patients are a high-risk group for graft occlusion. Some surgeons would consider this a contraindication to use the radial artery. We still use the radial artery in heavy smoking patients, but we treat them with nitroglycerin for a longer period of time.
DR BRIAN F. BUXTON (Heidelberg, Australia): Doctor Shapira, I enjoyed that paper very much. For those of us who were not very keen on the use of diltiazem because of its negative inotrope incidence, it certainly will come as some relief.
What I would like to ask you is to provide some detail about the preparation of the radial artery itself. As you know, nitroglycerin works through the nitric oxide cyclic GMP pathway, and you have indicated that the effect is significantly enhanced by the use of topical neuronine or papaverine. First, can you tell us how you prepared the graft, and second, do you think it is necessary to continue the nitrate therapy for up to 6 months when you would expect that the endothelial function would recover in 3 to 5 days or perhaps a week?
DR SHAPIRA: With regard to preparation of the radial artery, we are aware of the work by you and others showing improved flow when you use either nitroglycerin alone or in combination with verapamil to flush the conduit. We do not flush the radial artery at all. We just spray the graft with papavarine. We think we have good enough results without using those additional agents.
With respect to the duration of treatment, it is a good question. That is one of the limitations of the study. We did not examine this in the study. There are both angiographic and clinical data suggesting that radial artery increased reactivity exists up to 1 year. One year after the operation the reactivity is much less, particularly the response to serotonin and endothelin-1. This also has been shown in patients following coronary artery bypass grafting in vivo. Therefore, treatment for 3 to 4 days only would still be associated with increased risk of vasospasm and I think it is too short a period of time.
DR CEM H. ALHAN (Istanbul, Turkey): I enjoyed your presentation very much, Dr Shapira. I have a question. Diltiazem used during cardiopulmonary bypass has been reported to be a risk factor for the development of acute renal failure. Did you find any difference between the two groups with regard to renal failure?
DR SHAPIRA: We specifically looked at this phenomenom being aware of a paper published just recently looking at renal failure associated with diltiazem. In our study we did not notice any differences in renal function between the groups, and I think one of the reasons is because we tried to optimize hemodynamics. We switched from diltiazem to nitroglycerin in 5 patients who had low cardiac output or other hemodynamic compromise that might increase the risk of renal failure.
Related Article
Ann. Thorac. Surg. 2000 70: 883-888.
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