Blood flow and vasoactive drug effects in internal mammary and venous bypass grafts

Cardiac output and pressure-flow measurements were made in left internal mammary artery-to-left anterior descending coronary artery grafts and left subclavian artery-to-left circumflex coronary artery vein grafts after proximal coronary artery ligation. Similar measurements were also made in left internal mammary artery-to-left anterior descending coronary artery grafts and aortocoronary saphenous vein grafts in patients with coronary artery disease. Hemodynamic parameters and graft blood flows were measured during control baseline conditions and after pharmacological interventions using isoproterenol, phenylephrine, and epinephrine in random order. Blood flow through vein grafts and internal mammary artery grafts was similar under basal conditions and increased similarly with each of these vasoactive agents. Other hemodynamic parameters changed variably with the various pharmacological agents used. There was no close correlation between mammary artery or vein graft blood flow and arterial mean pressure and cardiac output over the wide range observed with the different drugs was associated with either an increase in perfusion pressure or a decrease in coronary vascular resistance. If the percentage increase in coronary blood flow above the basal control value in response to pharmacological stress is considered as a reflection of coronary vascular reserve, these studies suggest that coronary vascular reserve in patients with coronary artery disease is less than that of the normal dog heart.