ITA versus SVG: a comparison of instantaneous pressure and flow dynamics during competitive flow

OBJECTIVE: Competitive flow from patent native coronary vessels isimplicated in the failure of internal thoracic artery (ITA) grafts, but itis not thought to affect saphenous vein graft (SVG) patency. This studyexamines instantaneous pressure and flow dynamics in left ITA and SVGgrafts in competition with a patent left anterior descending (LAD) artery.METHODS: SVG (3.0-4.0 mm) and ITA (1.5-2.0 mm) to proximal LAD (2.5-3.0 mm)coronary bypass was performed in 10 mongrel dogs. Flow and pressure weremeasured in the occluded (No Competition) and opened (Competition) ITA, SVGand LAD. RESULTS: The ITA and SVG, when each was the sole inflow to theLAD, provided similar flow as the native LAD. During competitive flow,total LAD flow was preserved and flow in the ITA and SVG were reduced (8.20+/- 1.25 and 10.00 +/- 1.73 ml/min; P < 0.005). SVG diastolic flow wasreduced to 11.52 +/- 2.17 ml min (55.5%); P < 0.003. Flow in the SVGremained predominantly antegrade. In contrast, ITA diastolic flow wasreduced more drastically, to 5.37 +/- 1.25 ml/min (80.7%); P < 0.0001.When the ITA was the only inflow to the LAD, there was delay in the LADpressure wave. This delay disappears during competition due to the large,systolic retrograde flow up the ITA. CONCLUSION: The ITA, compared to theSVG, is a longer and narrower conduit with lower levels of flow duringcompetition. Due to a delay in the pressure wave, the ITA flow isretrograde during early systole. Low levels of flow, with a markedlydecreased diastolic phase, and the oscillating pattern in systole(retrograde/antegrade) may be poorly tolerated by the ITA endothelium andlead to graft deterioration.