FAPI Imaging Predicts Adverse Cardiac Events in Chronic Total Occlusion

Chronic total occlusion (CTO) of coronary arteries represents one of the most complex and challenging subsets of coronary artery disease and is associated with increased cardiovascular risk. While percutaneous coronary intervention (PCI) for CTO lesions has evolved substantially due to advances in imaging, devices, and operator experience, long-term prognostic evaluation remains suboptimal. In particular, no imaging biomarker currently allows non-invasive prediction of major adverse cardiovascular events (MACE) following CTO PCI.

Fibroblast activation plays a central role in myocardial fibrosis and atherosclerotic plaque instability, both of which contribute to adverse cardiovascular outcomes.

The fibroblast activation protein inhibitor (FAPI), labeled with radionuclides for PET/CT imaging, has recently emerged as a promising tool for quantifying fibrotic activity both in the myocardium and within coronary plaques. Preliminary data from the original FACT study showed that FAPI imaging may predict ventricular remodeling 6 months post-PCI. However, its long-term prognostic value and its role in detecting plaque vulnerability have not been fully evaluated in prospective studies.

The FACT-2 study is a prospective observational cohort study designed to evaluate whether FAPI PET/CT imaging can predict 1-year MACE in patients with CTO undergoing PCI. All enrolled patients will undergo baseline 18F-FAPI PET/CT scans prior to PCI and will be followed for 12 months post-intervention. The study aims to establish a FAPI-based risk stratification model, integrating FAPI uptake parameters with plaque morphology (via OCT and histopathology), serological fibrosis markers, and patient-reported quality of life scores.

The primary endpoint of the study is the incidence of MACE, defined as a composite of cardiac death, myocardial infarction, stroke, and urgent revascularization within one year of PCI. Secondary endpoints include all-cause mortality, repeat PCI events (including in-stent restenosis, target lesion/vessel revascularization, and de novo lesion intervention), and quality of life changes assessed by the Seattle Angina Questionnaire (SAQ).

In this study, FAPI uptake will be quantified by multiple parameters including total uptake volume (FAPI%), standardized uptake values (SUVmax, SUVmean), and target-to-background ratio (TBR). These parameters will be analyzed for correlation with clinical outcomes and histopathological features of plaque vulnerability (e.g., positive remodeling, microcalcification, lipid-rich necrotic core). The goal is to determine whether FAPI PET/CT can serve as a novel imaging biomarker for both myocardial and systemic fibrotic activity and stratify future cardiovascular risk.

By addressing the current evidence gaps in CTO prognosis and risk stratification, the FACT-2 study aims to provide scientific and clinical justification for incorporating molecular imaging into routine management of complex coronary artery disease. This study will also contribute to a more personalized treatment paradigm, bridging the gap between anatomical repair and biologically targeted intervention in cardiovascular medicine.

Inclusion criteria

• Age ≥18 years.
• Confirmed diagnosis of ≥1 untreated chronic total occlusion (CTO):Defined as complete occlusion of a major coronary artery or relevant collateral (reference vessel diameter ≥2.5 mm or confirmed by two independent interventional cardiologists), with TIMI flow grade 0 in the distal segment and duration ≥3 months.Preoperatively confirmed by coronary angiography or coronary computed tomography angiography (CTCA).
• Willingness to undergo FAPI-PET imaging and receive PCI under imaging guidance.
• Ability to provide written informed consent.

Exclusion criteria

• Contraindications to antiplatelet therapy: Allergy or intolerance to aspirin, clopidogrel, or ticagrelor.
• Severe liver dysfunction: Liver function parameters exceeding 3× the upper limit of normal.
• Severe chronic kidney disease: Estimated glomerular filtration rate (eGFR) <30 mL/min/1.73 m².
• Life expectancy <1 year due to non-cardiovascular comorbidities.
• Pregnancy or women of childbearing potential (unless surgically sterile or using contraception).