Septal glucose metabolism in patients with coronary artery disease and left bundle-branch block

Positron-emission tomography (PET) using 18F-deoxyglucose (FDG) is used for assessment of myocardial viability in regions with impaired resting perfusion and contractility. This report describes FDG-PET septal findings in six patients with complete left bundle-branch block (LBBB) and chronic coronary artery disease (CAD) compared to a reference population without LBBB.

All patients had documented left anterior descending artery stenosis and septal wall-motion abnormality. Attenuation-corrected PET scans were acquired after the administration of oral glucose load, and myocardial perfusion at rest was assessed using 99mTc-methoxyisobutylisonitrile (MIBI) single-photon emission computed tomography (SPECT). Myocardial FDG and MIBI uptake in 25 regions of interest were expressed as percentage uptake of the individual reference region, and average uptake values as well as the FDG/MIBI ratio were calculated for the entire septum and lateral wall.

Relative to septal MIBI uptake, septal FDG uptake was decreased in patients with LBBB and increased in patients with LBBB. The septal FDG/MIBI ratio was significantly lower in patients with LBBB than in those without LBBB (0.62 +/- 0.12 vs 1.24 +/- 0.24, respectively; P < 0.001) and did not exceed 0.8 in patients with LBBB. In patients without LBBB, the ratio constantly exceeded 0.8.

In patients with LBBB and CAD, septal reduction of FDG uptake may significantly exceed the reduction of septal perfusion as assessed by MIBI-SPECT. Decreased septal FDG uptake may be attributed in part to the conduction abnormality, resulting in limited value for this tool as an assessment of septal viability in this patient group.