Magnetic resonance imaging to evaluate patency of aortocoronary bypass grafts

R I Rubinstein, A D Askenase, D Thickman, M S Feldman, J B Agarwal, R H Helfant
1987 Circulation  
To assess the efficacy of magnetic resonance (MR) imaging in evaluating graft patency after coronary bypass surgery, 20 patients who had prior surgery (average 5.5 years, range 1.5 to 14) and recent cardiac catheterization because of chest pain were studied. No patient had surgical intervention or change in symptoms in the time interval between catheterization and MR imaging. These 20 patients had a total of 47 grafts, defined as proximal anastomoses: 20 to the left anterior descending or
more » ... al artery (LAD), 13 to the left circumflex artery marginal branches (LCX), and 14 to the right coronary artery or posterior descending artery (RCA). The patients underwent cardiac and respiratory gated MR scans in a 0.5 tesla magnet with an echo time of 22 msec and two repetitions in a 128 x 256 matrix. In-plane resolution was 2.7 mm. Every patient had a scan in the transaxial plane and some underwent scanning in the sagittal and coronal planes as well. A graft was considered patent by MR when a signal-free lumen was visualized in an anatomic position consistent with that of a bypass graft, had a lumen larger than the native vessels, was seen on more than one slice, and was seen at a level higher than that of the native vessels. If a known graft was not seen it was considered occluded. The scans were interpreted by consensus of two physicians aware of the operative but not the cardiac catheterization data. Twenty-six of 29 patent grafts and 13 of 18 occluded grafts were correctly classified (sensitivity 90%, specificity 72%). Eighteen of 20 (90%) LAD grafts, 11 of 14 (79%) RCA grafts, and 11 of 13 (85%) LCX grafts were correctly classified. When the results from three patients with technically poor studies because of poor cardiac gating were excluded, the overall sensitivity and specificity were 92% and 85%, respectively. This study demonstrates the high sensitivity and moderate specificity of MR for evaluating the patency of coronary artery bypass 786 onance (MR) scan of the chest. Since that time other authors have described the visualization of bypass grafts with MR imaging.2 4 These preliminary studies demonstrated that MR imaging of patients with a history of coronary bypass surgery was safe and artifacts from implanted metals did not interfere with the interpretation of results. Bypass grafts have also been imaged by cine computed tomography,5 6 but this technique requires the injection of radiographic contrast dye and the use of ionizing radiation, which is not needed for graft visualization with MR imaging. With MR imaging vascular structures are well seen with the use of the spin-echo technique. With this type of pulse sequence, rapid flow in the large arteries of the chest appears signal free because excited spins move out of the imaging plane, and slow flowing blood or occluded vessels will not.7' 8 Currently available MR imaging systems have an inplane resolution on the order of 2 mm. We reasoned that MR imaging should be able to routinely detect bypass grafts in cardiac gated scans because of its sensitivity CIRCULATION by guest on
doi:10.1161/01.cir.76.4.786 pmid:3498558 fatcat:n6ad33q5t5ce3fxofk4kpssfku