Comparative hemodynamic properties of vein and mammary artery in coronary bypass operations

To understand better the observed differences in bypass flows between vein and internal mammary artery (IMA) grafts, a technique was devised for anastomosing both vein and IMA to the same anterior descending coronary artery in 14 patients. In the stable postperfusion state, flows in the two bypass conduits were simultaneously recorded as well as pressure relationships in both grafts and the left ventricle. The supply/demand ratio for left ventricular performance was calculated with respect to the diastolic pressure-time index/tension-time index (DPTI/TTI) for each bypass independently and simultaneously and then compared. The DPTI/TTI ratio was nearly two times greater with the vein bypass than with the IMA. This difference was further confirmed by the flow studies, in which blood flow through the vein ranged 2 to 3 times higher than IMA flow to the same coronary bed. By present criteria the DPTI/TTI ratio for IMA grafts to the left ventricle was inadequate in the majority of patients studied, and atrial pacing markedly lowered the DPTI/TTI ratio of the IMA. The choice of vein or IMA as a bypass is a critical determinant of the resultant bypass-left ventricular DPTI/TTI ratio. Vein bypasses exhibited far superior hemodynamic capability in the resting state, and the effect of atrial pacing on the DPTI/TTI ratio in IMA-vein-left ventricle bypasses confirms this point.