Increased right atrial 18f-FDG uptake in persistent atrial fibrillation: insights across young vs. old age groups

Young-onset AF may have different metabolic profile and underlying pathophysiology of atrial fibrillation (AF) from old-onset AF requiring distinctive clinical progression and management. However, alterations in atrial metabolism in AF, especially stratified by age, is poorly understood. We aimed to explore potential age-related differences in atrial metabolic activity that may discriminate young- from old-onset AF from 18F-fluorodeoxyglucose (FDG) PET imaging.

From Oct 2021 to June 2024, The 18F-FDG PET imaging after myocardial suppression protocol was prospectively obtained from 40 young-onset AF (AF diagnosed < 50 year) and 40 old-onset AF (AF diagnosed ≥ 60 years). We compared visual and quantitative 18F-FDG uptake of right and left atria (RA/LA) wall and right and left appendages (RAA/LAA) between young- and old-onset AF. Visual 18F-FDG uptake was graded as no (0), mild (1), moderate (2), and marked (3). Quantitative uptake was measured as the target-to-background ratio (TBR), calculated by atrial maximum standardized uptake value (SUVmax)/blood pool SUVmean.

Of total, the mean age was 59.3±13.5 years (young-onset AF, 47.0±5.2 years; old-onset AF, 71.6±5.5 years) with median AF duration 3.6 (0.8-6.8) years. There were 41 paroxysmal and 39 persistent AF patients, with similar proportions in both young- and old-onset AF groups (p>0.05). Overall, TBR of RA/LA wall and RAA/LAA showed no significant variation across the age, except for the numerically higher value of RAA in old- (1.7±0.8) than young-onset AF (1.4±0.4), p=0.071. When stratified by the type of AF, findings reveal a significant increase in RA FDG uptake in persistent AF. The proportion of RA (either wall or appendage) visual uptake in persistent AF was higher than paroxysmal AF; 15/41 (36.6 %) vs. 31/39 (79.5%), p<0.001 for uptake ≥1 and 4/41 (9.8%) vs. 12/39 (30.8%), p=0.019 for uptake ≥2, in paroxysmal and persistent AF, respectively. The increased RA uptake in persistent AF was consistently observed across the age with adjusted odds ratio (OR) and 95% confidence interval (CI) as 7.54 (1.98-28.73), p=0.003. The clinical factor associated with bi-atrial uptake (either RA or LA with visual grade ≥1) was drinking status: adjusted OR (95% CI), 3.54 (1.07-11.64), p=0.038.

There was no age-specific atrial FDG uptake pattern in patients with AF. However, we found persistent AF presented higher RA FDG uptake than paroxysmal AF, consistently across the age, providing further insight to the increased atrial metabolic demand or inflammatory activity of RA which potentially contributes to the persistence of AF.