Evidence of Nitric Oxide Produced by the Internal Mammary Artery Graft in Venous Drainage of the Recipient Coronary Artery

The endothelium of the internal mammary artery produces nitric oxide in greater quantity than other vessels employed in revascularization of the ischemic myocardium. The aim of this study was to measure the concentration of stable metabolite (nitrite) of the endothelium-derived nitric oxide in the venous drainage (anterior interventricular vein) of the recipient coronary artery, which was the left anterior descending branch. The sampling was carried out before and after anastomosis completion. Nitrite levels in the anterior interventricular vein, before and after anastomosis completion, in the left internal mammary artery free flow, and in the subclavian vein were measured. Fluroscopy after 4-hydroxycoumarin nitrozation was utilized to measure nitrite content of blood samples in 50 consecutive, partly heparinized patients undergoing off-pump coronary bypass surgery. Nitrate content of all samples was removed by Cadmium pearls. One hundred and sixty-four samples taken from 41 patients were feasable to analyze. A significant increase of nitric oxide (nitrite) level was found in the anterior interventricular vein, when comparing concentrations measured before and after the anastomosis between the left internal mammary artery and the left anterior descending artery. Mean values in the anterior inteventricular vein before and after anastomosis completion were as follows: 44.8 μMol (SD 4.9) and 70.7 μMol (SD 8.1), respectively. The increased production of nitric oxide by the internal mammary arterial graft may provide a perpetual vasodilatory response and partially protect the distal coronary vessel from atherosclerosis.