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Eur J Cardiothorac Surg 1998;13:410-415
© 1998 Elsevier Science NL

Endothelium-dependent and endothelium-independent flow reserve in vascular regions supplied by the internal mammary artery before and after bypass grafting

^a Department of Interventional Cardiology, St. Georg Medical Center, Delitzscher Str. 141, 04129 Leipzig, Germany
^b Department of Cardiology and Department of Cardiothoracic Surgery, J.W. Goethe-University Medical Center, Frankfurt, Germany
^c Department of Cardiothoracic Surgery, University Medical Center, Freiburg, Germany

Received 1 September 1997; received in revised form 16 December 1997; accepted 6 January 1998.

Corresponding author. Tel.: +49 341 9092422; fax: +49 341 9092423.

Objective: 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.

Key Words: Endothelium • Coronary artery bypass graft • Coronary flow reserve • Microcirculation