Mediation occurred via triglycerides (up to 38.5% of ω-6/ω-3-AF association) and CRP (up to 10.7% of PhenoAgeAccel-HF association).<h4>Conclusion</h4>Higher PhenoAgeAccel and ω-6/ω-3 PFUA ratios were independently associated with higher risks of AF-HF transitions, with these associations partly explained by lipid and inflammatory pathways. The gene discussed is CRP; the disease is hydrops fetalis.