Atrial FDG Avidity is Associated with Reduced Atrial Strain and Contractility Independent of Atrial Fibrillation and Cardiac Sarcoidosis

Aims Atrial myopathy encompasses structural, functional, electrical, and metabolic changes in the atrial myocardium. While remodeling such as left atrial (LA) dilation and reduced strain are well documented, metabolic alterations remain underexplored. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) provides a non-invasive tool to assess myocardial glucose metabolism. This study evaluates the relationship between atrial FDG avidity and LA remodeling in patients undergoing cardiac imaging for suspected cardiac sarcoidosis (CS). Methods We studied 120 patients who underwent both cardiac MRI and FDG-PET/CT at the University of Washington Medical Center. LA structural volume index (LAVi) and functional emptying fraction (LAEF), average long-axis strain, and phasic strain indices were derived from cine MRI using feature tracking. Atrial FDG avidity was quantified by SUVmax and atrial target-to-background ratio (aTBR) from PET/CT. Results LA average long axis strain was 37.1 ± 34.0%, LAEF 47.6 ± 16.1%, and LAVi 36.0 ± 23.0%. Atrial avidity was 2.4 ± 0.7 SUV. LA strain negatively and mildy correlated with both SUVmax (R= -0.44; P<0.001) and moderately with aTBR (R= -0.53; P<0.001), while LAVi positively and mildly correlated with both (R= 0.40 and R = 0.52, respectively; P < 0.001). These associations persisted after adjusting for age, gender, diabetes, CS, history of AF, HR, and pre-PET scan rhythm status. AF patients exhibited reduced LA strain and higher FDG avidity. Conclusion Increased atrial FDG avidity is independently associated with impaired strain and enlarged LA, highlighting a metabolic component of atrial myopathy that may precede clinical AF.