Extending Interoperable Emergency Department Data: Standards-Based Design and Evaluation in AKTIN

Interoperable datasets and infrastructures are technically and organizationally difficult to modify, making timely incorporation of newly emerging clinical concepts very difficult. Flexible yet standards-conformant mechanisms are needed to accommodate unforeseen documentation requirements without disrupting established infrastructures based on slowly evolving datasets. This work aims to enable controlled extensibility of the HL7 CDA and FHIR-based emergency department dataset within the AKTIN infrastructure through a "wildcard" mechanism for structured addition of new variables. We implemented two open CDA entry templates and integrated them into the existing AKTIN data-processing pipeline, combined with corresponding FHIR profiles to enable semantic alignment across standards. Evaluation with synthetic CDA documents demonstrated standards-conformant processing throughout validation, transformation, and storage in the AKTIN data warehouse. While FHIR has already defined extension options, the proposed wildcard mechanism provides a concept for controlled extensibility in CDA infrastructures. It preserves interoperability and provenance within defined datatype boundaries and establishes a foundation for future governance and real-world evaluation.