Abnormal Motion of the Interventricular Septum after Coronary Artery Bypass Graft Surgery: Comprehensive Evaluation with MR Imaging

Objective: To define the mechanism associated with abnormal septal motion (ASM) after coronary artery bypass graft surgery (CABG) using comprehensive MR imaging techniques. Materials and Methods: Eighteen patients (mean age, $58{\pm}12$ years; 15 males) were studied with comprehensive MR imaging using rest/stress perfusion, rest cine, and delayed enhancement (DE)-MR techniques before and after CABG. Myocardial tagging was also performed following CABG. Septal wall motion was compared in the ASM and non-ASM groups. Preoperative and postoperative results with regard to septal wall motion in the ASM group were also compared. We then analyzed circumferential strain after CABG in both the septal and lateral walls in the ASM group. Results: All patients had normal septal wall motion and perfusion without evidence of non-viable myocardium prior to surgery. Postoperatively, ASM at rest and/or stress state was documented in 10 patients (56%). However, all of these had normal rest/stress perfusion and DE findings at the septum. Septal wall motion after CABG in the ASM group was significantly lower than that in the non- ASM group ($2.1{\pm}5.3$ mm vs. $14.9{\pm}4.7$ mm in the non-ASM group; p < 0.001). In the ASM group, the degree of septal wall motion showed a significant decrease after CABG (preoperative vs. postoperative = $15.8{\pm}4.5$ mm vs. $2.1{\pm}5.3$ mm; p = 0.007). In the ASM group after CABG, circumferential shortening of the septum was even larger than that of the lateral wall $-20.89{\pm}5.41$ vs. $-15.41{\pm}3.7$, p < 0.05) Conclusion: Abnormal septal motion might not be caused by ischemic insult. We suggest that ASM might occur due to an increase in anterior cardiac mobility after incision of the pericardium.