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J Thorac Cardiovasc Surg 2005;130:1227-1228
© 2005 The American Association for Thoracic Surgery

Letters to the Editor

Reply to the Editor

Department of Cardiothoracic Surgery, John Radcliffe Hospital, Oxford, United Kingdom

We thank Dr Moran for his interest in our editorial concerning the use of radial arteries (RA) as coronary bypass conduits. ¹ His letter invites us to expand on two important points covered in our article:

1 The use of oral calcium channel antagonists as prophylaxis for delayed vasospasm

2 Use of RA conduits as grafts to coronary vessels with proximal stenoses in excess of 70% favours improved long term patency

Concerning the first point, we would agree that despite previous anecdotal recommendations there is no substantial evidence for the use of oral calcium channel antagonists to prevent delayed vasospasm of RA conduits. Certainly, Gaudino and associates ² randomized 120 patients receiving RA grafts to treatment with oral calcium channel antagonist therapy or not, and showed no difference in ischemic symptoms, scintigraphic evidence of ischemia, or RA angiographic patency at 5 years. This is consistent with the data published by Moran and coworkers. ³

Concerning the second point, Moran and colleagues elegantly demonstrated the improved patency of RA conduits when anastomosed to target vessels with high-grade (>70%) proximal stenoses. This finding was subsequently confirmed in a larger series with a longer interval to angiographic follow-up. ⁴

Graft patency is influenced not only by the biology and quality of the conduit but also by physical factors such as luminal blood pressure and runoff, which govern luminal blood flow. The concept of competitive flow suggests that graft flow is influenced by native coronary flow. Royse and colleagues ⁵ have reported that blood flow through composite arterial grafts (left internal thoracic artery–RA T-grafts) fell by 44% on reintroduction of native coronary flow. Shear stress resulting from flow activates endothelial nitric oxide synthase and results in the production of nitric oxide. ⁶ Intuitively, grafted conduits should fare better in conditions of poor native coronary flow typified by high grade coronary stenoses, as increased conduit blood flow will contribute to improved nitric oxide production.

References

1. Mussa S, Choudhary BP, Taggart DP. Radial artery conduits for coronary artery bypass grafting. current perspective. J Thorac Cardiovasc Surg. 2005;129:250-253.[Free Full Text]
   
2. Gaudino M, Glieca F, Luciani N, Alessandrini A, Possati G. Clinical and angiographic effects of chronic calcium channel blocker therapy continued beyond first postoperative year in patients with radial artery grafts. results of a prospective randomized investigation. Circulation. 2001;104(Suppl):I64-I67.[Medline]
   
3. Moran SV, Baeza R, Guarda E, Zalaquett R, Irarrazaval MJ, Marchant E, et al. Predictors of radial artery patency for coronary bypass operations. Ann Thorac Surg. 2001;72:1552-1556.[Abstract/Free Full Text]
   
4. Maniar HS, Sundt TM, Barner HB, Prasad SM, Peterson L, Absi T, et al. Effect of target stenosis and location on radial artery graft patency. J Thorac Cardiovasc Surg. 2002;123:45-52.[Abstract/Free Full Text]
   
5. Royse AG, Royse CF, Groves KL, Bus B, Yu G. Blood flow in composite arterial grafts and effect of native coronary flow. Ann Thorac Surg. 1999;68:1619-1622.[Abstract/Free Full Text]
   
6. Bevan JA, Kaley G, Rubanyi GM. Flow-dependent regulation of vascular function. New York: Oxford University Press; 1995.
   

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