EFFECT OF CHRONIC NATIVE FLOW COMPETITION ON INTERNAL THORACIC ARTERYGRAFTS

Residual competitive flow from the native coronary artery has been pro posed as a mechanism that reduces how in an internal thoracic artery g raft (ITA), resulting in narrowing and ultimately failure of the graft . Results from acute experiments have indicated that competitive now f rom a fully patent native artery did not abolish ITA graft flow. The p resent study was designed to examine the consequences of dynamic flow competition between the native vessel and the ITA graft in a chronic m odel. Fifteen mongrel dogs underwent coronary artery bypass grafting u sing the pedicled left ITA anastomosed to the normal, fully patent cir cumflex (CFX) coronary artery. The procedure was performed through a s terile thoracotomy, without systemic cardiopulmonary bypass, using a b rief local occlusion to construct the anastomosis. Intraoperatively, I TA flow was measured in situ on the chest wall, before the pedicle was mobilized. Internal thoracic artery graft and distal CFX how were mea sured after the anastomosis was completed, with and without brief occl usion of the proximal CFX. Angiography was performed 72 hours, 4 weeks , and 8 weeks later; graft patency and diameter were evaluated. After 8 weeks, open-chest direct now measurements comparable with the intrao perative assessment were obtained. Two grafts (13%) occluded early, th e technical result of poor anastomotic construction. In the 13 remaini ng animals, all grafts were widely patent at all time points. Internal thoracic artery now in situ averaged 10.9 +/- 7.8 mL/min (mean +/- st andard deviation), and was maintained after grafting (11.5 +/- 4.4 mL/ min; p = not significant). Internal thoracic artery graft flow represe nted 38.7% of total distal CFX now (11.5/29.7) acutely. Comparable flo ws were obtained after 8 weeks of chronic competitive flow (11.9/ 30.4 ; 39.1%; p = not significant). Even after 8 weeks, when the proximal C FX was occluded transiently, flow increased in the ITA graft to provid e 95% of the distal CFX requirements (30.4 +/- 7.8 mL/min with proxima l CFX open versus 28.9 +/- 11.6 mL/min with proximal CFX occluded). Th e results demonstrate that even after 2 months of maximal chronic flow competition from a fully patent native artery, ITA graft flow was mai ntained above in situ levels, and a recruitable now reserve from the I TA graft could be demonstrated when the native vessel was occluded. Th e data suggest that ITA. grafts are dynamic and may remain patent desp ite significant residual now in the native vessel.