Association between atrial FDG uptake and atrial fibrillation in patients with PET/CT performed under strict ketogenic dietary preparation

Introduction: Atrial inflammation seen as increased FDG uptake on PET/CT has been reported to be associated with atrial fibrillation (AF). However, results are largely from case reports and a few studies conducted in oncology patients with PET/CT performed without strict dietary preparation, which may overestimate atrial FDG activity due to physiological myocardial uptake.To overcome this potential bias, we reviewed all FDG PET/CT scans performed with strict ketogenic dietary preparation in the past 8 years for evaluation of cardiac sarcoidosis, and then compared atrial FDG uptake in patients with and without AF.

Methods: A total of 195 scans were included after excluding 35 scans (35/230=15.7%) with incomplete suppression of physilogic myocardial FDG uptake due to insufficient dietary preparation. Analysis was performed as scan based (195 scans) and patient based (164 pts, M=104, age 56.7±10.8; F=60, age 57.2±10.3), respectively. It was pre-determined during the study design that when performing patient based analysis, if a patient had more than 1 scan, only the most recent one would be included. AF cases (persistent or paroxysmal) were documented by chart review (ECG, or physician’s notes) within ± 6 months of the PET/CT. Positive atrial FDG uptake was defined as activity higher than the mediastinal blood pool by visual evaluation. Uptake pattern (focal or diffuse) and SUVmax in the atrium were then recorded. Atrial FDG uptake (positive rate, mean SUVmax) was compared in patients with and without AF. Two investigators performed the chart review blinded to the image findings, while another two measured the PET/CT scans blinded to the clinical diagnosis. Any discrepancy of AF diagnosis and image measurement was resolved by a third investigator. It was also pre-determined that if both left and right atriums showed FDG uptake, only the right atrium would be counted and included in the analysis. Data were input in Excel and analyzed using SAS with assist from a biostatistician.

Results: With scan based analysis, positive atrial FDG uptake was seen in 8.7% of the scans (17/195) in this patient population with PET/CT performed under strict dietary preparation. Increased atrial FDG uptake was seen in 0 (0/5=0%) with persistent AF, 5 (5/35=14.3%) with paroxysmal AF, and 12 (12/155=7.7%) with non AF, respectively, without statistical difference (Chi-square, Fisher’s exact test, P=0.42). There was also no difference when only paroxysmal AF and non AF groups were compared (190 scans after excluding the 5 scans of persistent AF) (P=0.32). There was no difference of the mean atrial SUVmax between the paroxysmal (6.8±3.2) and non AF (5.7±1.9) groups (Wilcoxon test, P=0.68) either. To evaluate whether active cardiac sarcoidosis could be a potential confounder for atrial FDG uptake, analysis was conducted in cases without active cardiac sarcoidosis, and again there was no difference of the positive atrial uptake rate between the paroxysmal AF (3/27=11.1%) and non AF (7/109=6.4%) groups (P=0.42). Similarly, when data were stratified by the cardiac sarcoidosis, there was no difference of the distribution of this variable between the atrial uptake positive and negative groups (P=0.26). Logistic regression analysis showed no association of cardiac sarcoidosis (P=0.40), extra-cardiac sarcoidosis (P=0.25), or LVEF (P=0.06) with atrial FDG uptake, respectively. These results do not suggest these variables as the confounders for atrial FDG uptake. Further, patient based analysis (n=167) showed the same findings as the scan based (data not shown).

Conclusions: In a patient population with FDG PET/CT scans performed under strict ketogenic dietary preparation, there was no difference of positive atrial FDG uptake rate between the AF and non AF groups. The finding is in contrast to the previous reports which were conducted in PET/CT scans without dietary preparation. Further work with more cases is needed to clarify the relationship between atrail FDG uptake (representing inflammation) and AF.