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Is septal glucose metabolism altered in patients with left bundle branch block and ischemic cardiomyopathy?
Kerry Thompson1, George Saab, David Birnie
1Division of Cardiology, National Cardiac PET Centre, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
Insights
Left bundle branch block (LBBB) does not always reduce septal glucose metabolism in ischemic cardiomyopathy patients. Absence of reduced metabolism often indicates lateral wall perfusion defects, impacting heart failure therapies.
Area of Science:
- Cardiology
- Nuclear Medicine
- Medical Imaging
Background:
- Left bundle branch block (LBBB) is prevalent in heart failure (HF) and exacerbates left ventricular (LV) dysfunction.
- Abnormal septal motion in LBBB may affect septal metabolic demand, a factor not fully understood in ischemic cardiomyopathy (ICM).
Purpose of the Study:
- To investigate the impact of LBBB on myocardial glucose metabolism in the septum of patients with ICM and LV dysfunction.
- To assess perfusion-metabolism differences in the septum and lateral wall in patients with and without LBBB.
Main Methods:
- Positron Emission Tomography (PET) with (18)F-FDG and (82)Rb was used to measure glucose metabolism and perfusion in 53 patients (34 LBBB, 19 controls).
- Septal and lateral wall scar, mismatch (hibernating myocardium), and reverse-mismatch (R-MM) were quantified.
Main Results:
- Septal (18)F-FDG uptake was significantly lower in LBBB patients (64.0%) compared to controls (74.9%).
- Septal R-MM was higher in LBBB patients (19.1%) versus controls (4.7%).
- Over 30% of LBBB patients lacked septal R-MM, often correlating with lateral wall perfusion defects, suggesting altered septal metabolic demand.
Conclusions:
- LBBB is not consistently associated with reduced septal glucose metabolism relative to perfusion in ICM patients.
- The absence of septal R-MM in LBBB patients may indicate underlying lateral wall ischemia, influencing therapeutic strategies.
- Findings suggest potential implications for cardiac resynchronization therapy and warrant further investigation.
Unlabelled:
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 (
Results:
(18)F-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.
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