Background: Atrial inflammation and fibrotic remodelling underlie the pathophysiology of atrial cardiomyopathy (ACM), which is associated with development of atrial fibrillation (AF) and atrial flutter (AFL). 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) has been used to detect inflammatory processes. Recent studies have revealed an increased FDG-uptake in the atria of patients with AF, but also in patients with diagnosis of cardiac sarcoidosis. The current study assesses the impact of systemic inflammatory sarcoidosis on the degree of atrial inflammation (FDG-uptake) in patients with vs. without AF/AFL.

Purpose: To determine the degree of inflammation in atrial myocardium of patients with and without atrial arrhythmia (AF/AFL) in a population of patients with dedicated cardiac FDG-PET/CT.

Methods: We investigated fifty consecutive patients (64±9 years, 72% male) who underwent 18F-FDG PET/CT scan with dedicated cardiac specific preparation (heparin infusion, 12 hours fasting, and a high-fat low carbohydrate diet). We excluded patients diagnosed with ventricular cardiac sarcoidosis. 18F-FDG PET/CT scans were indicated in patients with systemic sarcoidosis in search for cardiac lesions or in patients without diagnosis of sarcoidosis but with arrhythmia in search for cardiac sarcoidosis. We measured the maximum standardized uptake value (SUVmax) in atrial myocardium and mean standardized uptake value (SUVmean) in blood pool and calculated the target-to-background ratio (TBR) of SUVmax in atrial myocardium to SUVmean in blood pool. All medical records, ECG data on arrhythmia type (AF or AFL) and diagnosis of systemic sarcoidosis (and absence of ventricular sarcoidosis) were used for the analysis. Systemic sarcoidosis was diagnosed based on the criteria established in 2006 by the Japanese Ministry of Health and Welfare. The collected data were sorted according to presence of arrhythmia and systemic sarcoidosis and TBR of each group were compared.

Results: AF or AFL was found in 17/50 (34%) patients. Systemic sarcoidosis was found in 21/50 (42%) patients. Significant difference of TBR was found between the group without AF/AFL (median: 1.18, 1st-3rd quartile: 1.14-1.24) and the group with AF/AFL (median: 1.29, 1st-3rd quartile: 1.20-1.35) (p = 0.005).
Within patients without systemic sarcoidosis, the difference in TBR did not reach statistical significance between the group without AF/AFL (median: 1.18, 1st-3rd quartile: 1.14-1.23) and the group with AF/AFL (median: 1.24, 1st-3rd quartile: 1.18-1.31) (p = 0.072). Within patients with systemic sarcoidosis, TBR was significantly higher in patients with AF/AFL (median: 1.33, 1st-3rd quartile: 1.30-1.92) than in patients without AF/AFL (median: 1.18, 1st-3rd quartile: 1.14-1.24) (p = 0.008).