Evaluation of coronary bypass flow with color-Doppler and magnetic resonance imaging techniques: comparison with intraoperative flow measurements

Objectives. After coronary artery bypass surgery, patency and flow assessme nt is based on invasive methods such as angiography and intravascular ultra sound or flow wire techniques. The aim of the study was to compare intraope rative transit time flow measurements of coronary bypass grafts with early postoperative color-Doppler and MR-imaging assessment. Methods: In 22 patie nts (62 +/- 8.5 years) undergoing elective coronary bypass surgery the flow was measured in all internal mammary artery grafts (IMA) and saphenous vei n grafts using the transit time flow technique. Postoperatively (days 5-7) all patients had a color-Doppler IMA graft assessment followed by a MR angi ography and flow measurement (navigator echo phase contrast technique with and without contrast bolus application) to determine patency and graft flow . Results: Data are expressed as the mean +/- SD). (1) In all patients the left IMA graft to the left anterior descending coronary artery (LAD) could be identified and flow could be assessed with both color-Doppler and MRI. V enous grafts could only visualized by MRI. The use of an intravenous contra st bolus enhanced the visualization of coronary artery bypass grafts. (2) T he mean IMA to LAD flow was 33 +/- 17 ml/min intraoperatively by transit ti me and postoperatively 36 +/- 25 ml/min by MR respectively 66 +/- 54 ml/min by color-Doppler technique. (3) The systolic/diastolic flow ratio was 0.44 +/- 0.12 intraoperatively and 0.43 +/- 0.17 postoperatively by MR respecti vely 0.67 +/- 1.0 by color-Doppler. (4) A statistically significant correla tion could be demonstrated between intraoperative transit time and postoper ative MR flow measurements (r = 0.57; P < 0.04), whereas the correlations t o color-Doppler flow were poor. Postoperatively MR and color-Doppler showed a good correlation of systolic/diastolic flow ratio (r = 0.88; P < 0.008). Conclusions: The color-Doppler method during echocardiography and MR-imagi ng are useful non-invasive techniques to visualize postoperative IMA grafts for patency assessment. The quantification of IMA flow is still difficult with either technique, but MR flow measurements showed the best correlation to the intraoperatively measured transit time flow. The MR technique is th e most promising non-invasive method for postoperative evaluation of corona ry bypass grafts, since it allows visualization and reliable flow quantific ation. (C) 1999 Elsevier Science B.V. All rights reserved.