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Is Septal Glucose Metabolism Altered in Patients with Left Bundle Branch Block and Ischemic Cardiomyopathy?

¹ Division of Cardiology, National Cardiac PET Centre, University of Ottawa Heart Institute, Ottawa, Ontario, Canada; ² Department of Diagnostic Radiology, University of Western Ontario, London, Ontario, Canada; ³ Electrophysiology Group, Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada; ⁴ Division of Nuclear Medicine, University of Ottawa, Ottawa, Ontario, Canada; ⁵ Department of Medicine, Turku University Central Hospital and PET Centre, Turku, Finland; and ⁶ Henry Ford Hospital, Detroit, Michigan

Correspondence: For correspondence or reprints contact: Rob S.B. Beanlands, MD, Cardiac Imaging, National Cardiac PET Centre, University of Ottawa Heart Institute, 40 Ruskin St., Ottawa, Ontario, Canada K1Y 4W7. E-mail: rbeanlands{at}ottawaheart.ca

Left bundle branch block (LBBB) is common in patients with heart failure (HF) and contributes to left ventricular (LV) dysfunction. The abnormal septal motion may alter septal metabolic demand but this has not been well characterized in patients with ischemic cardiomyopathy (ICM) and LV dysfunction. The aim of this study was to determine the effect of LBBB on septal metabolism in patients with ICM, LV dysfunction, and LBBB. Methods: Fifty-three patients with LV dysfunction and ICM were identified: 34 with LBBB, 19 with normal QRS (100, control patients). PET using ¹⁸F-FDG and ⁸²Rb was used to measure myocardial glucose metabolism and perfusion, respectively. Perfusion-metabolism differences were determined. Scar scores (matched decreases in ¹⁸F-FDG and ⁸²Rb), mismatch scores (hibernating myocardium with decreased ⁸²Rb relative to ¹⁸F-FDG), and reverse-mismatch (R-MM) scores (reduced ¹⁸F-FDG relative to ⁸²Rb) were assessed in the septum and lateral wall. Results: ¹⁸F-FDG uptake in the septum was reduced in patients with LBBB (64.0% ± 15.4%) compared with control patients (74.9% ± 14.3%; P < 0.05). Mean septal R-MM was greater in patients with LBBB (19.1% ± 15.3%) versus control patients (4.7% ± 10.6%; P < 0.05). However, 32% (11/34) of patients with LBBB did not demonstrate septal R-MM, 91% (10/11) of whom demonstrated lateral wall perfusion defects. Of the 68% (23/34) of patients with LBBB and septal R-MM, 52% (12/23) demonstrated lateral wall perfusion defects (P < 0.05). There was a significant difference in the percentage of the lateral wall with scar between those with septal R-MM (9.3% ± 10.5%) and those without (19.9% ± 14.3%; P < 0.05). Conclusion: Previously, LBBB was believed to be characterized by reduced glucose metabolism relative to perfusion in the septum; however, this is not always the case in ICM. LBBB is not associated with septal R-MM in >30% of this patient population. Absence of this finding was often associated with lateral wall perfusion defects, suggesting an alteration in the metabolic demand on the septum. This may have implications for HF therapies such as resynchronization and requires further study.

Key Words: PET • left bundle branch block • ischemic heart disease

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