Beyond 70,000: Reassessing the Global Fontan Population Through Citation-Chain Analysis and Tiered Epidemiologic Estimation

Background Research funding, drug development, trial design, and health policy for the Fontan population all depend on reliable prevalence denominators. The most widely cited global estimate — "50,000 to 70,000" survivors worldwide — appears in the 2019 AHA Scientific Statement, clinical training resources, pharmaceutical filings, and grant applications, yet its methodological basis has never been publicly reported. This study traces the estimate's provenance and proposes a transparent, tiered framework to replace inherited figures while global registry data mature. Methods A citation chain analysis traced the estimate from the AHA Statement through all referenced sources to determine whether a peer-reviewed methodology exists, complemented by a PubMed search. All published country-specific Fontan population data were compiled into a three-tier framework stratifying countries by data availability and income. A disaggregated birth-incidence analysis across the nine cardiac diagnoses that can require Fontan palliation quantified uncertainty via Monte Carlo simulation (10,000 iterations, triangular distributions). Results The citation chain forms a closed loop. The AHA Statement [1] cites Schilling et al. [2], which reported 1,265 survivors in Australia/New Zealand and no global estimate; d'Udekem [3] attributed the figure to "some investigators"; StatPearls attributes it to d'Udekem personally. No node contains a derivation, and the PubMed search retrieved 12 results, none describing a study that produced the figure. Re-estimation from verified data suggests approximately 83,000–94,000 survivors in high-income countries and 105,000–176,000 globally — both conservative lower bounds. The birth-incidence analysis is reported as a two-tier estimate separating quantities the literature has conflated: anatomic incidence — infants born with Fontan-requiring anatomy — at ~ 0.52/1,000, about 73,000 per year (95% CI ~ 63,000–85,000); and, after applying published survival-to-completion rates, those expected to reach a completed Fontan — about 43,000 per year (95% CI ~ 37,000–51,000). Both tiers are fully sourced and reproducible from an open script. Conclusions The global Fontan population has been characterized using an inherited estimate with no published methodological basis, propagated through authoritative literature by citation-chain failure; the true population is almost certainly substantially larger. This paper proposes that the field replace reliance on static, unsourced figures with a transparent, tiered estimation framework — distinguishing Fontan survivors, Fontan-pathway candidate births, and the broader population requiring but not completing Fontan palliation — to provide the reliable denominators that research funding, registry architecture, and health policy require. It offers the tool that inherited figure never had, and stands not as a final answer but as a foundation others can test, refine, and build upon.