Septal perfusion and wall thickening in patients with left bundle branch block assessed by technetium-99m-sestamibi gated tomography.

Abstract

Septal hypoperfusion is often observed in patients with complete left bundle branch block (LBBB) in myocardial perfusion imaging. Abnormal wall motion in the septal region may potentially cause artifactual perfusion abnormalities. To assess the effect of abnormal wall thickening on myocardial perfusion images, ECG-gated sestamibi SPECT was performed on 12 patients with LBBB and 10 normal subjects used as controls. After administration of 740 MBq 99mTc-sestamibi injection at rest, ECG-gated SPECT was obtained 60 min later with division of the cardiac cycle into eight frames. Septal hypoperfusion was noted in 10 patients on nongated images and 11 patients on end-systolic (ES) images, whereas only two patients showed abnormalities on end-diastolic (ED) images. The septal to lateral wall count ratio in the LBBB group was lower (0.72 +/- 0.09) than in the control group (0.84 +/- 0.09) (p < 0.01) at nongated images, while it was similar at ED images (0.84 +/- 0.11 versus 0.86 +/- 0.12; ns). In addition, the count increase from ED to ES during a cardiac cycle in the septal region was smaller compared with the lateral region in the LBBB patients (25% +/- 19% in the septal region, versus 48% +/- 14% in the lateral region; p < 0.01), indicating less wall thickening in the septal region. Smaller count increase due to reduced wall thickening in the septal region may mimic hypoperfusion in patients with LBBB. This artifact can be eliminated with ECG-gated 99mTc-sestamibi SPECT, particularly with ED images.