Electrocardiographic gated (99m)Tc-MIBI SPECT for functional assessment of patients after coronary artery bypass surgery: comparison of wall thickening and wall motion analysis

Abstract

Abnormal septal motion after coronary artery bypass graft surgery (CABG) is a common finding. This study was undertaken to investigate the change in various global and regional ventricular function parameters measured by gated myocardial perfusion SPECT after surgery and to determine which quantitative parameter of WT and WM is more appropriate for the evaluation of regional cardiac function, especially in the septum of patients with CABG.

Methods: Before and 3 to 5 wk after CABG (all patients underwent at least 1 bypass grafting to the left anterior descending coronary artery), 35 patients (28 men, 7 women) underwent gated SPECT using (99m)Tc-methoxyisobutylisonitrile. Quantitative global and regional ventricular functional analysis was performed using quantitative gated SPECT software.

Results: Global ejection fraction did not change (59.3% +/- 16.0% to 60.5% +/- 14.5%, P = 0.24). However, end-diastolic and end-systolic volumes lessened significantly after CABG (81.4 +/- 37.3 mL to 68.9 +/- 28.9 mL, P < 0.0001, and 38.1 +/- 33.1 mL to 30.4 +/- 23.0 mL, P < 0.005, respectively). As global function parameters, the changes in both total WM (r = 0.88) and WT (r = 0.86) correlated well with the change in ejection fraction after surgery. Segmental analysis showed a significant postoperative increase in relative tracer uptake in the anterior, anteroseptal, inferoseptal, and inferior walls and in the apex. Segmental wall motion (WM) deteriorated in the anteroseptal, inferoseptal, and mid anterior walls. On the other hand, anterolateral, inferolateral, and inferior WM increased. As a whole, these WM changes showed a reduction in septal motion associated with a concomitant increase in lateral motion after surgery. Segmental wall thickening, however, did not decrease in septal areas and did not increase in the lateral wall and correlated with percentage tracer uptake (r = 0.69) better than WM did (r = 0.30) after CABG.

Conclusion: In patients with CABG, postoperative WM analysis by gated SPECT underestimated septal motion and overestimated lateral motion because of exaggerated systolic anteromedial cardiac translation. Therefore, wall thickening analysis would be recommended for the evaluation of postoperative cardiac function.