Relationship between mechanical and metabolic dyssynchrony with left bundle branch block: Evaluation by 18-fluorodeoxyglucose positron emission tomography in patients with non-ischemic heart failure

Background: Ventricular dyssynchrony is a common finding in patients with heart failure (HF), especially in the presence of conduction delays. The loss of ventricular synchrony leads to progressive impairment of contractile function, which may be explained in part by segmental abnormalities of myocardial metabolism. However, the association of these metabolic disarrangements with parameters of ventricular dyssynchrony and electrocardiography (ECG) findings has not yet been studied. Methods: Our aim was to determine the correlation between the presence of left bundle branch block (LBBB) with left ventricular (LV) mechanical synchrony assessed by multiple-gated acquisition scan (MUGA) and with patterns of 18-fluorodeoxyglucose (¹⁸FDG) uptake in patients with non-ischemic heart failure. Twenty-two patients with non-ischemic cardiomyopathy, LV ejection fraction (LVEF) ≤45% and New York Heart Association (NYHA) Functional Class II or III symptoms under standard medical therapy were included, along with 10 healthy controls matched for age and gender. A 12-lead ECG was obtained to measure the length of the QRS. Mechanical LV synchrony was assessed by MUGA using phase analysis. All patients and controls underwent positron emission tomography with ¹⁸FDG to determine the distribution of myocardial glucose uptake. The standard deviation of peak ¹⁸FDG uptake was used as an index of metabolic heterogeneity. Student's t-test and Pearson's correlation were used for statistical analysis. Results: The mean age of the patients with HF was 54 ± 12 years and 72% were male. The length of the QRS was 129 ± 31 milliseconds and LBBB was present in 9 patients. Patients with HF had decreased LV ¹⁸FDG uptake compared with controls (7.56 ± 3.36 vs 11.63 ± 4.55 standard uptake value; p = 0.03). The length of the QRS interval correlated significantly with glucose uptake heterogeneity (r = 0.62; p = 0.002) and mechanical dyssynchrony (r = 0.63; p = 0.006). HF patients with LBBB showed marked glucose uptake heterogeneity compared with HF patients without LBBB (41.4 ± 10 vs 34.7 ± 4.9 ml/100 g/min, respectively; p = 0.01). Conclusions: Patients with non-ischemic heart failure exhibit a global decrease in myocardial glucose uptake. Within this group, subjects who also have LBBB exhibit a marked heterogeneity in segmental glucose uptake, which directly correlates with QRS duration.