Assessment of left atrial fibrosis by 18F-FDG PET/CT in persistent atrial fibrillation : comparison to electroanatomical mapping and cMR late gadolinium enhancement
Authors: Raoult T , Gerber B G , Roelants V R , Garnir Q G , Scavee C S , Varnavas V V , Wauters A W , Gruson D G , Nellessen E N , Hesse M H , Beauloye C B , Marchandise S M 
Published: November 2023

Abstract

A wide body of evidence suggests that left atrial (LA) interstitial fibrosis is a key contributor to persistent atrial fibrillation (peAF) and that its extent is predictive of the success of catheter ablation (CA) for this condition. Late gadolinium enhanced magnetic resonance imaging (LGE-cMR) has become increasingly popular for non-invasive detection and quantification of atrial fibrosis prior to CA. However, it is limited by a high rate of suboptimal scans and by large variability of quantification of fibrosis. We recently described the ability to obtain high quality 18- fluorodeoxyglucose (FDG) positron emission tomography (PET) of the atria after acipimox administration, and hypothesize that, similar to the left ventricle (LV), atrial metabolic activity could be a marker of cellular viability, indicating the absence of atrial fibrosis.
The objective of our study was to investigate the potential utility of 18FDG uptake in the LA as an indicator of atrial scar and a predictor of CA success in patients with peAF. To this end, we compared the LA 18FDG uptake to LA voltage mapping during electrophysiological studies (EP) and cMR-LGE as a reference standard.

Method
33 nondiabetic patients with nonvalvular peAF hospitalized for a first CA in our center prospectively underwent 18FDG-PET/CT, and LGE-CMR prior to EP and CA procedures. FDG-PET, LGE-cMR and electoanatomical maps were segmented and corregistrated in 3D surface models based on anatomical information from the contrast enhanced cMR angiograms. For 18FDG-PET/CT, maximum intensity projection of standardized uptake values (SUVs) along the surface was calculated and abnormal low metabolism was identified using a threshold of four standard deviations below the average SUV value of the atrial blood. Electrical scarring on EP voltage maps was defined as bipolar measurements of &lt; 0.3 mV in AF, while fibrosis by LGE-CMR was evaluated using several thresholds of 2-5 standard deviations above the average blood signal intensity and the average intensity of the enhancement around the mitral valve. All three parameters of scar were expressed in percentage of the total LA area.

Results
Atrial hypometabolism by FDG-PET correlated strongly with electrical scaring by low voltage area during EP study (p&lt;0.001, R² = 0.573). Atrial wall mean SUV standardized by LV uptake was also associated with low voltage, also the association's strength was mild (p =0.012, R²=0.22). There was good spatial corregistration of areas of low FDG metabolism with low voltage areas during EP study (Figure 2). By contrast there was no association between PET and LGE-cMR and association between atrial LGE by cMR and atrial voltage for all used thresholds.

Conclusion
Low 18FDG uptake by PET/CT showed a good correlation with atrial electrical scaring, while LGE-CMR did not. Our data suggest that atrial FDG PET could therefore be a valuable technique for non-invasive evaluation of atrial fibrosis prior to CA.Low metabolism versus low voltageMetabolic and voltage maps