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Ann Thorac Surg 2001;72:2012
© 2001 The Society of Thoracic Surgeons
a Department 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
Limitations of the T-graft configuration are complexity and the potential for technical error, conduit spasm, and adequacy of flow. The authors have addressed the last concern by dobutamine stress echocardiography six months postoperatively in 40 patients having bilateral internal thoracic artery (ITA) T grafts directed to the left, but not the right, coronary circulation. In no instance was there evidence of inadequate T graft flow manifest by wall motion abnormality but in 8 patients an ischemic response was observed in the territory of the right coronary (due to inadequate conduit flow in two). Wendler and colleagues [1] measured T graft flow reserve using adenosine vasodilation and the doppler guide-wire one week and six months postoperatively. They found no change in baseline flow but a significant increase in flow reserve at six months. In this report both ITA and radial artery T grafts were studied and there were no flow differences between the two types of T grafts in which all coronary arteries (not just the left) were grafted.
Improved flow reserve at six months likely represents conduit remodeling (although impaired coronary vasoreactivity early postoperatively may also be a factor) which may occur in any artery where there is an increase or decrease in chronic flow beyond what is usual. Flow creates shear stress at the endothelial surface which is sensed, transduced and translated into vasodilation or passive vasoconstriction acutely and if the change in flow is chronic there is associated vascular remodeling to maintain shear stress in a physiologic range. The time course of vascular remodeling has not been precisely defined but appears to be relatively complete by six months in man.
An often overlooked fact regarding the flow capacity of the T graft is the gradual diminution in diameter of the ITA over its length so that the distal internal diameter is commonly 2.0 mm, but at the level of the T-anastomosis it is 0.5 to 1.0 mm greater. This equates to a lumenal cross sectional area of 4.90 mm2 or 7.06 mm2 versus 3.14 mm2 which is the prime determinant of resistance and, therefore, flow in the Poiseuille equation. Thus, the proximal ITA has greater flow capacity than the distal segment which we tend to accept as usual ITA flow.
These two reports provide supportive evidence for T grafting from the standpoint of flow capacity.
References
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