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Ann Thorac Surg 2001;71:147
© 2001 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Washington University School of Medicine, One Barnes-Jewish Hospital Plaza, Suite 3108 Queeny Tower, St. Louis, MO 63110, USA
e-mail: barnerh{at}msnotes.wustl.edu
Blood vessels react to increased flow by vasodilatation, a response to increased shear stress that is detected by the endothelial cells, which signal the smooth muscle to relax. When changes in flow persist, there is restructuring of the vessel wall, including both cellular and noncellular elements, with significant change in luminal cross-sectional area and relatively small or no change in wall thickness. The end result of this vascular remodeling is normalization of wall shear stress as detected by the endothelium. Conversely, when flow, and therefore shear, is reduced, remodeling occurs to achieve a reduction in luminal area that restores normal shear stress. In the internal thoracic artery (ITA), this has been recognized as a "string sign."
The authors have observed diameter change of the left ITA grafted to the left anterior descending coronary artery between an early and late catheterization (interval 4.5 ± 1.5 years). When coronary stenosis did not change there was no significant change in ITA diameter, but with progression of stenosis there was a significant increase in ITA diameter. These observations are consistent with the well-studied phenomenon of vascular remodeling to achieve normalization of shear stress.
The authors also observed that when the ITA was grafted distally on the coronary, its ultimate diameter was less than when it was grafted more proximally. In these instances the coronary artery was occluded proximally, the subserved myocardium healthy, and there was no apparent competitive flow with the ITA. They concluded from this that the ITA should therefore be grafted more proximally on the coronary so that "its growth" will be greater.
I agree with the authors observations but not this conclusion. I believe that the anastomosis should be placed to the healthiest coronary segment with a diameter of at least 1.5 mm, with the goal of achieving the best long-term patency. If the coronary is healthy, then a more proximal anastomosis is reasonable.
There is abundant evidence that healthy arteries dilate or narrow when flow dictates this response. Although the authors have tried to ascertain that the patients with proximal or distal ITA anastomosis had similar flow requirements, they did not measure conduit flow, and the vagaries of coronary flow, collateral flow, and competitive flow are well known. The ultimate size (diameter) of the ITA graft reflects these considerations, and smaller does not mean inferior but is a reflection of the flow demands. Should they increase or decrease, the ITA will respond physiologically.
Related Article
Ann. Thorac. Surg. 2001 71: 142-147.
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