Experimental supplemental vein grafting and hypoperfusion syndrome

An additional saphenous vein graft (SVG) sometimes is required to the same coronary system if acute internal thoracic artery (ITA) graft flow is inadequate. These experiments were conducted to determine the consequences produced by ITA-SVG dual grafting. Fourteen dogs each received two coronary grafts (without bypass, using local occlusion) to the proximal circumflex coronary artery, using the ITA and an SVG, and then the circumflex artery was ligated proximally. Simultaneous flow in both grafts was determined at rest and after pharmacologic (adenosine, phenylephrine) or physiologic (cardiac pacing) stimulation. Serial angiography was performed during the first 4 weeks after grafting to determine patency patterns of the ITAs and SVGs. In the resting heart, flow was 7.5 ± 1.6 mL/min (17.5%) in the ITA graft and 35.3 ± 5.2 mL/min (82.5%) in the SVG (mean ± standard deviation [% total distal perfusion]), and the combined flow was not significantly different from the original native flow. Intravenous adenosine (0.2 mg·kg−1·min−1) preferentially increased both the total ITA flow and its fractional contribution to total distal perfusion (18.4 ± 3.2 [31.1%]; p < 0.05 versus rest). Saphenous vein graft flow was not changed significantly (40.3 ± 6.0 mL/min), in part due to a modest decrease in arterial pressure. In contrast, intravenous phenylephrine (0.003 mg·kg−1·min−1) decreased both absolute ITA flow and its relative contribution to distal perfusion (6.1 ± 1.1 [10.9%]; p < 0.05 versus rest), despite an increased systemic perfusion pressure, which increased SVG flow significantly (50.1 ± 4.8 [89.1%]; p < 0.05 versus rest). Increasing ventricular rate by 25% from 120 to 150 beats/min increased both ITA and SVG flow significantly (ITA, 10.8 ± 2.5 mL/min; SVG, 42.6 ± 6.2 mL/min; both p < 0.05 versus rest) but did not change the flow balance between the grafts. Six animals were studied chronically, and serial angiography demonstrated the following results: all vein grafts retained patency throughout, but 2 ITA grafts were occluded within 7 days, 2 additional grafts were occluded within 2 weeks, and the remaining 2 grafts were occluded within 3 weeks after grafting. These data demonstrate that the ITA graft did not survive in this canine dual grafting model, and suggest that the necessary acute perfusion benefit of supplemental vein grafting for hypoperfusion syndrome may eliminate any long-term patency advantages of the ITA graft.