Adverse effects of circumflex coronary artery occlusion on blood flow to remote myocardium supplied by a stenosed left anterior descending coronary artery in anesthetized open-chest dogs

Left anterior descending coronary artery occlusion in open-chest dogs causes a decrease in endocardial blood flow to the remote posterior bed supplied by a stenosed left circumflex coronary artery. To determine if "remote" myocardial ischemia also occurred in the anterior bed after circumflex occlusion, myocardial blood flow (radiolabeled microspheres) and hemodynamics were measured before and after circumflex occlusion in the presence of a stenosed left anterior descending artery (gradient: 28 ± 2 mm Hg) in 10 open-chest dogs. Aortic pressure fell from 108 ± 3 to 100 ± 3 mm Hg (p = 0.02) and mean distal left anterior descending coronary artery pressure fell from 81 ± 4 to 69 ± 5 mm Hg (p = 0.02) after circumflex occlusion. Transmural flow to normal myocardium supplied by unstenosed and unoccluded coronary arteries increased from 0.69 ± 0.04 to 0.84 ± 0.04 ml/min/gm (p < 0.0001) after circumflex occlusion. Although epicardial flow to the remote anterior bed supplied by the stenosed left anterior descending coronary artery increased after left circumflex occlusion (0.61 ± 0.03 to 0.73 ± 0.04 ml/min/gm, p = 0.004), remote anterior bed endocardial flow did not increase, and the remote bed endocardial: epicardial blood flow ratio decreased from 0.98 ± 0.06 to 0.78 ± 0.10 (p < 0.05). Therefore, in this model, remote anterior bed ischemia, relative to the normal myocardial flow response, developed when the left circumflex coronary artery was occluded in the presence of the stenosed left anterior descending coronary artery.