Postoperative flow characteristics of left internal thoracic artery grafts

Twenty patients whose left internal thoracic artery (LITA) was anastomosed to the left anterior descending artery (LAD) underwent postoperative coronary angiography and Doppler ultrasound velocimetry. During angiography, the diameter of the LITA conduit was measured at three points: proximal, mid, and distal. The degree of left anterior descending artery stenosis proximal to the anastomotic site was evaluated by densitometry. The LITA flow velocity pattern was obtained at the three points to calculate the total, systolic, and diastolic flow volume. There were significant differences in the total LITA flow among the three points (proximal, 36.0 +/- 17.2 mL/min; mid, 29.9 +/- 15.2 mL/min; distal, 27.2 +/- 14.0 mL/min; p < 0.001 between the proximal and the mid or distal portions). The degree of left anterior descending artery stenosis affected the distal LITA flow and diameter (r = 0.823 and 0.811, respectively). There were significant differences in the systolic LITA flow among the three points (proximal, 13.2 +/- 6.5 mL/min; mid, 8.1 +/- 4.7 mL/min; distal, 5.6 +/- 3.4 mL/min; p < 0.001 between the proximal and the mid or distal portions). However, there was no statistically significant difference in the diastolic LITA flow among the three points (proximal, 22.9 +/- 11.0 mL/min; mid, 21.7 +/- 10.8 mL/min; distal, 21.6 +/- 10.8 mL/min). We conclude that a lower degree of LAD stenosis significantly reduces the LITA flow, inducing the string phenomenon. Additionally, during the diastolic phase, the LITA graft transports the blood primarily to the coronary artery but not to the side branches. Therefore, the steal phenomenon might not apply in the setting of an LITA graft.