Endothelium-Dependent and Endothelium-Independent Flow Reserve in Vascular Regions Supplied by the Internal Mammary Artery Before and after Bypass Grafting

Objective: It was the goal of this study to compare endothelium-dependent and endothelium-independent Bow 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 in 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 mu g i.c.) and endothelium-independent with nitroglycerin (NTG 0.3 mg i.c.) followed by papaverin (10mg i.c.) Flow indices were calculated from intraluminal Doppler blood Bow velocity measurements and the vascular ness-sectional area as determined by quantitative angiography. An index for vascular resistance was defined as the ratio of pressure gradient and resting or peak Bow. Results: After endothelium-dependent stimulation with acetylcholine 25 mu g (50 mu g), Bow 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 mu g(50 mu g) to 35 +/- 16.8% (23 +/- 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. (C) 1998 Elsevier Science B.V. All rights reserved.