  Since the inception of the Bitcoin technology, its underlying data
structure--the blockchain--has garnered much attention due to properties such
as decentralization, transparency, and immutability. These properties make
blockchains suitable for apps that require disintermediation through trustless
exchange, consistent and incorruptible transaction records, and operational
models beyond cryptocurrency. In particular, blockchain and its smart contract
capabilities have the potential to address healthcare interoperability issues,
such as enabling effective interactions between users and medical applications,
delivering patient data securely to a variety of organizations and devices, and
improving the overall efficiency of medical practice workflow. Despite the
interest in using blockchain for healthcare interoperability, however, little
information is available on the concrete architectural styles and patterns for
applying blockchain to healthcare apps. This paper provides an initial step in
filling this gap by showing: (1) the features and implementation challenges in
healthcare interoperability, (2) an end-to-end case study of a blockchain-based
healthcare app we are developing, and (3) how applying foundational software
patterns can help address common interoperability challenges faced by
blockchain-based healthcare apps.
