Understanding how atrial fibrillation (AF) progresses from paroxysmal to persistent forms remains a major clinical challenge. A study published in JACC: Cardiovascular Imaging used 18F-labeled aluminum fluoride (AlF) fibroblast activation protein inhibitor (FAPI) positron emission tomography–magnetic resonance imaging (PET-MRI) to assess fibrosis across different AF stages.

The study included 78 patients with AF and 49 healthy volunteers who underwent FAPI-PET-MRI to quantify fibrosis in multiple atrial regions, including the posterior wall, septum, anterior wall, appendage, and roof. Participants were classified as having paroxysmal, persistent, or permanent AF. An additional cohort of 36 surgical patients provided image-guided atrial tissue samples for histologic correlation.

Fibrosis levels were significantly higher in persistent and permanent AF compared with paroxysmal AF and controls. The left atrial posterior wall exhibited the greatest fibrotic activity and achieved excellent discrimination between AF stages, with an area under the curve of 0.991 for distinguishing paroxysmal from persistent AF. Histologic analysis confirmed increased collagen deposition in regions with elevated FAPI uptake.

These findings indicate that posterior wall fibrosis may play a central role in AF progression. FAPI-PET-MRI could serve as a noninvasive tool for early detection of atrial remodeling and guide targeted interventions in AF management.