Effects of milrinone on blood flow of the Y-graft composed with the radial and the internal thoracic artery in patients with coronary artery disease §

Objective: Milrinone has been known to dilate the internal thoracic artery (ITA) and the radial artery (RA). The effect of milrinone, however, on each graft is unclear when the left ITA (LITA) and the RA form a Y-graft. This study evaluated the changes in blood flow of a composite Y-graft in response to milrinone. Methods: Thirty-two patients undergoing an isolated coronary artery bypass graft surgery were included in this study. AY-graft was created with an in situ LITA and free RA graft attached to the proximal side of the LITA. Graft flow was measured by opening the graft end for 30 s, and is expressed in 'ml/min'. Graft flow and hemodynamic data were recorded before and 10 min after intravenous milrinone (50 μg/kg) administration. Results: Milrinone significantly increased the RA graft flow, measured while the LITA graft end was clamped, and total Y-graft flow. Respective graft flows were not increased by milrinone when both clamps were released simultaneously, in spite of a significant decrease in the resistance of both grafts. The ratio of flows through the RA and the LITA grafts was not changed by milrinone. Conclusion: Milrinone significantly reduced RA and LITA resistances and increased the total Y-graft flow. Milrinone might dilate each individual arterial graft to a different degree. Milrinone did not, however, change the flow ratio through the RA to LITA grafts when they were measured simultaneously. Therefore, it would not significantly divert graft flow to one side in a composite Y-graft.