It was the goal of this study to compare endothelium-dependent and endothelium-independent flow reserve in vascular regions supplied by the left internal mammary artery before and after bypass graft surgery.Methods:
The native internal mammary artery in situ was investigated in 13 patients (age 61.8±8.0 years) with angiographically proven coronary artery disease. The internal mammary artery after bypass grafting was investigated in ten patients (age 60.8±7.3 years) 3.5±2.8 years after the operation. Flow reserve was evaluated endothelium-dependent with acetylcholine (ACh 25 and 50 μg i.c.) and endothelium-independent with nitroglycerin (NTG 0.3 mg i.c.) followed by papaverin (10 mg i.c.). Flow indices were calculated from intraluminal Doppler blood flow velocity measurements and the vascular cross-sectional area as determined by quantitative angiography. An index for vascular resistance was defined as the ratio of pressure gradient and resting or peak flow.Results:
After endothelium-dependent stimulation with acetylcholine 25 μg (50 μg), flow in the internal mammary increased by 352.3±152% (412±145%) before surgery, whereas it increased only by 213±134% (193±120%) after surgery (P<0.05). Endothelium independent stimulation with papaverin resulted in a flow increase of 391±234% before surgery vs. 315±135% after surgery (n.s.). The resistance index decreased after endothelium-dependent stimulation with acetylcholine 25 μg (50 μg) to 35±16.8% (28±8.9%) before surgery, whereas it decreased only to 59±26% (72±43%) after surgery (P<0.05). Endothelium independent stimulation with papaverin resulted in a decrease of the vascular resistance index to 31±14% before surgery vs. 32±14% after surgery (n.s.).Conclusion:
Vascular regions supplied by the internal mammary artery as a graft demonstrate a significantly reduced endothelium-dependent flow reserve but a preserved endothelium-independent flow reserve as compared to vascular regions supplied by the native internal mammary artery. The selective decrease in endothelium-dependent flow reserve may be due to microvascular changes in the myocardial region supplied by the internal mammary artery after bypass grafting.