INTERNAL THORACIC ARTERY GRAFT FUNCTION DURING EXERCISE ASSESSED BY TRANSTHORACIC DOPPLER ECHOGRAPHY

Background. Noninvasive quantitative assessment of internal thoracic a rtery (ITA) graft function at rest and during exercise is important in patients who have undergone coronary artery bypass grafting. Methods. Blood flow in the ITA graft was measured using transthoracic color Do ppler echography before and after operation in 50 patients who underwe nt coronary artery grafting using an ITA to the left anterior descendi ng artery. The patients were divided into three groups according to th e degree of coronary stenosis and previous anterior myocardial infarct ion: Group 1 included 12 patients with severe (90% or more) coronary s tenosis accompanied by anterior infarction. Group 2 included 26 patien ts with severe coronary stenosis without anterior infarction. Group 3 included 12 patients with moderate (75% or less) coronary stenosis wit hout anterior infarction. Transthoracic echographic images of the ITA were obtained through the first intercostal space using a 7.5-MHz prob e, and the diameter and cross-sectional area of the ITA were measured on B-mode imaging. Systolic, diastolic, and mean blood flow velocity a nd volume were measured by the Doppler method. Results. Internal thora cic artery diameter increased significantly from 2.2 mm to 2.4 mm afte r operation. The ITA flow patterns in both flow velocity and volume ch anged from systolic-dominant to diastolic-dominant after operation. Po stoperative ITA graft flow was 82 +/- 24 mL/min, 53 +/- 30 mL/min, and 31 +/- 15 mL/min (p < 0.01, group 1 versus 3; p < 0.05, group 1 versu s 2) and percent diastolic fraction of ITA flow was 72%, 68%, and 62% (not significant) in groups 1, 2, and 3, respectively. Compared with i ntraoperative ITA flow, which was measured using an ultrasound transit -time flowmeter, postoperative ITA graft flow was increased in group 1 but not changed in group 2 or 3. The ITA graft flow was measured befo re and after exercise in 19 patients and was compared with ITA flow in 10 normal control subjects. The ITA graft flow increased significantl y with exercise in all patients in the three groups. Percent diastolic fraction of ITA flow increased significantly with exercise in patient s with severe coronary stenosis (groups 1 and 2), but decreased signif icantly in patients with moderate stenosis (group 3). Conclusions. Cha nges in native coronary artery and ITA graft may be predicted by asses sing ITA flow pattern during exercise. Transthoracic color Doppler ech ography is a clinically useful noninvasive method of assessing ITA gra ft function at rest and during exercise.