Recently, studies using late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) to identify structural changes of atrial tissue have contributed significantly to understanding the pathophysiology and progression of atrial fibrillation (AF). Moreover, imaging of atrial fibrosis using MRI has evolved to be a tool to improve clinical outcome of AF ablation procedures by allowing a patient-specific individualized management approach. LGE-MRI has been shown to predict AF ablation outcome based on pre-procedural imaging to define the extent of atrial fibrosis. The results of the ongoing DECAAF II (Delayed-Enhancement MRI Determinant of Successful Radiofrequency Catheter Ablation of Atrial Fibrillation) trial might extend ablation strategies from pulmonary vein isolation alone to a substrate-based approach. Furthermore, an improved understanding of the underlying mechanisms of atrial structural remodeling is crucial in order to reduce the occurrence of AF-associated complications (e.g., ischemic stroke and heart failure). This review article provides current methodology of atrial fibrosis imaging using LGE-MRI and delineates actual clinical implications and future directions for this imaging approach.
Background
Fibroblast activation protein (FAP) as a specific marker of activated fibroblasts can be visualized by positron emission tomography (PET) using Ga-68-FAP inhibitors (FAPI). Gallium-68-labeled FAPI is increasingly used in the staging of various cancers. In addition, the first cases of theranostic approaches have been reported. In this work, we describe the phenomenon of myocardial FAPI uptake in patients who received a Ga-68 FAPI PET for tumor staging.
Method and results
Ga-68 FAPI PET examinations for cancer staging were retrospectively analyzed with respect to cardiac tracer uptake. Standardized uptake values (SUV) were correlated to clinical covariates in a univariate regression model.
From 09/2018 to 11/2019 N = 32 patients underwent FAPI PET at our institution. Six out of 32 patients (18.8%) demonstrated increased localized myocardial tracer accumulation, with remote FAPI uptake being significantly higher in patients with vs without localized focal myocardial uptake (SUVmax 2.2 ± .6 vs 1.5 ± .4, P < .05 and SUVmean 1.6 ± .4 vs 1.2 ± .3, P < .05, respectively). Univariate regression demonstrated a significant correlation of coronary artery disease (CAD), age and left ventricular ejection fraction (LVEF) with remote SUVmean uptake, the latter with a very strong correlation with remote uptake (R2 = .74, P < .01).
Conclusion
Our study indicates an association of CAD, age, and LVEF with FAPI uptake. Further studies are warranted to assess if fibroblast activation can be reliably measured and may be used for risk stratification regarding early detection or progression of CAD and left ventricular remodeling.
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