Emerging evidence demonstrates increased fluorine-18–fibroblast activation protein inhibitor (18F-FAPI) accumulation in the right ventricular (RV) and pulmonary arteries (PAs) of patients with pulmonary arterial hypertension (PAH). However, the data regarding the prognostic utility of this molecular imaging biomarker remain limited.

This study evaluated the prognostic value of 18F-FAPI uptake by positron emission tomography/computed tomography (PET/CT) in PAH patients.

Forty-six consecutive PAH patients underwent 18F-FAPI PET/CT between August 2022 and June 2024. The patients were stratified into the low-, intermediate- and high-risk groups using a 3-strata risk model. The primary endpoint was defined as clinical worsening events. 18F-FAPI uptake was quantified as target-to-background ratio (TBR) for both RV and PAs. The relationships between the PET/CT parameters and clinical worsening were determined using Cox regression and Kaplan-Meier analyses.

Over a median follow-up period of 17.0 months, 22 patients (47.8%) experienced clinical worsening events. The TBR in the RV and PAs progressively increased with higher risk strata (all P < 0.05). Significantly higher TBR in the RV and PAs were observed in clinical worsening vs non–clinical worsening patients (all P < 0.05). Multivariable Cox regression analysis identified the TBR of RV free wall (TBRRVFW) as an independent predictor of clinical worsening (HR: 1.699 [95% CI: 1.153-2.415]; P = 0.007). TBRRVFW predicted clinical worsening (area under the curve [AUC]: 0.75; 95% CI: 0.60-0.87), and AUC was further improved based on a combination of TBRRVFW, World Health Organization functional class, and RV fractional area change (0.83; 95% CI: 0.69-0.93). Kaplan-Meier curves indicated that patients with TBRRVFW > 2.1 had a poorer prognosis (log-rank P = 0.005).

18F-FAPI PET uptake in the RV free wall may be a noninvasive and promising prognostic indicator for PAH.