Retrograde Flow in the Internal Mammary Artery

Thirty-two patients undergoing coronary artery bypass grafting were studied to evaluate retrograde flow in the internal mammary artery (IMA). The left IMA pedicle was prepared in routine fashion from the level of the first rib superiorly to just distal to the IMA bifurcation. Following cannulation for cardiopulmonary bypass but before institution of extracorporeal circulation, the IMA was divided 5 mm proximal to its bifurcation and allowed to bleed freely. The flow from each end was then measured by allowing the segment to bleed for 30 seconds. The mean antegrade flow was 73 ± 34 ml/min, and the retrograde flow was 25 ± 17.2 ml/min. The difference between the flows was significant ( p < 0.05). Based on these data we do not recommend the retrograde IMA technique as a primary form of revascularization of the myocardium. In selected circumstances it may be used if adequate retrograde flow is demonstrated before constructing the anastomosis.