Do internal mammary artery side-branches have the potential for haemodynamically significant flow steal?

Objective: To evaluate the potential for flow steal of the internal mammary artery (IMA) side-branches at rest and in case of dilatation of their vasc ular bed (as probably occurs during physical exercise). Methods: Transthora cic echo-Doppler evaluation of IMA flow was performed preoperatively in 40 patients undergoing myocardial revascularization. IMA flow was measured at rest and in condition of peripheral vasodilatation (obtained using forced v entilation for 2 min, dypiridamole 0.84 mg/kg endovenous (e.v.), xantinole nicotinate 500 mg e.v., nifedipine 20 mg sublingual (s.l.)). Results: IMA m ean peak systolic velocity increased 23% after forced ventilation (from 67 to 83 cm/s), 6% after dypiridamole (from 75 to 80 cm/s), 30% after xantinol e infusion (from 62 to 81 cm/s) and 23% after nifedipine administration (fr om 60 to 74 cm/s). IMA flow increased 17.7% after forced ventilation (from 39.5 to 46.5 ml/min), 4.8% after dypiridamole (from 39.2 to 41.1 ml/min), 2 0.2% after xantinole infusion (from 41.4 to 49.8 ml/min) and 16.5% after ni fedipine administration (from 41.6 to 48.5 ml/min). Conclusions: The limite d functional flow reserve of the in situ IMA, even after pure muscular vaso dilatation, seems to minimize the possibility of significant flow steal fro m patent IMA graft collaterals. (C) 1999 Elsevier Science B.V. All rights r eserved.