Description of the APOLLO Registry: Integrated Cardio-Renal Perfusion Assessment and Cardiometabolic Phenotyping Using Cardiac 82Rb-PET/CT

Background: Cardiovascular, kidney, and metabolic diseases are closely interconnected and may share common pathophysiological mechanisms, including microvascular dysfunction. Although cardiac 82Rb-PET/CT is routinely used for myocardial perfusion imaging, its potential for integrated cardio-renal perfusion assessment and cardiometabolic phenotyping remains underexplored. We recently developed a compartment modelling approach to quantify renal perfusion from routine cardiac 82Rb-PET/CT, enabling simultaneous assessment of cardio-renal perfusion. However, real-world imaging registries integrating these phenotypes with longitudinal clinical outcomes are lacking. Aim: To establish a real-world imaging registry that repurposes routine cardiac 82Rb-PET/CT by integrating PET-derived hemodynamic measures and CT-derived imaging biomarkers with detailed clinical, echocardiographic, laboratory, and clinical outcome data. Methods: The APOLLO registry is a single-centre retrospective registry of consecutive patients undergoing routine cardiac 82Rb-PET/CT at Alrijne Hospital (Leiderdorp, the Netherlands) between 2021-2023. Clinical, laboratory, medication, echocardiographic, and imaging data were collected to enable integrated cardio-renal perfusion assessment and cardiometabolic phenotyping. Inverse probability of selection weighting analysis was performed to account for renal coverage selection criteria. Cardiac perfusion was quantified using myocardial blood flow and myocardial flow reserve, while renal perfusion was derived using our previously developed compartment-model. Additional phenotyping included adiposity and frailty-related biomarkers, great vessel diameters, vascular calcification, diastolic dysfunction grading, H2FPEF score, Cardio-Kidney-Metabolic (CKM) staging, and longitudinal assessment of major adverse cardiovascular events. Conclusion: APOLLO registry extends routine cardiac 82Rb-PET/CT beyond myocardial perfusion imaging by integrating cardio-renal perfusion measurements with detailed cardiometabolic, clinical, and outcome phenotypes. This real-world registry provides a unique platform for future mechanistic and outcome-based research across the CKM disease spectrum.