INTRAOPERATIVE MONITORING OF IMA FLOW - WHAT DOES IT MEAN

Background. This study examines whether the measurement of internal th oracic artery (ITA) graft flow can determine the adequacy of the ITA-l eft anterior descending coronary artery (LAD) anastomosis. Methods. To study a wide range of clinical problems, we used a computer simulatio n of the cardiovascular system. The model included a time-varying elas tance model of the heart, a systemic circulation represented by a mult ielement nonlinear model of the aorta and its major branches, a nonlin ear model of the LAD circulation, and a model of the ITA bypass graft. Results. With a mild LAD stenosis, ITA graft flow was low and flow re versal occurred. As the percent stenosis increased, ITA flow and the p ercentage of ITA-to-total LAD now increased. The ITA graft helped to m aintain resting LAD blood flow. A partial obstruction (40%) at the ITA -LAD anastomosis reduced ITA graft flow at similar levels of LAD steno sis. However, overlap in flow values comparing a normal with a partial ly obstructed anastomosis occurred. Conclusions. Flow patterns in the ITA are highly dependent on the degree of stenosis of the LAD as well as the integrity of the anastomosis. The predictive power of ITA flow measurement increases with severe stenosis or total occlusion of the p roximal LAD and with high coronary blood flow demands. (C) 1997 by The Society of Thoracic Surgeons.