An experimental in vivo study of the canine internal mammary artery and its response to vasoactive drugs

The internal mammary artery is clearly the preferred conduit for most patients undergoing coronary artery bypass grafting. However, the hemodynamic responses of this graft to vasoactive agents immediately after bypass have not been documented. We have therefore studied blood flow in the canine internal mammary artery after anastomosis to the left anterior descending artery, and its response to epinephrine, metaraminol, isoproterenol, and calcium chloride. Blood flow in the internal mammary artery clearly paralleled changes in systolic blood pressure with perfusion pressure being of prime importance in maintaining flow in the internal mammary artery. No deleterious effect of systemic vasoconstricting agents was demonstrated. We suggest that the administration of these drugs is safe in patients with internal mammary artery grafts.