No abstract

As the next generation of implanted medical devices for cardiac rhythm management moves towards multi-nodal leadless systems that do without the limitations of transvenous leads, new security threats arise from the wireless communication between the systems' nodes. Key management and the key distribution problem used in traditional cryptographic methods are considered to be too computationally expensive for small implanted medical devices. Instead, inherent human biometrics could provide a reliable alternative. In this work, we tested the key generation process across different nodes of a mimicked dualchamber leadless cardiac pacemaker system and a subcutaneous implantable relay (S-relay). The proposed key generation process utilizes the randomness available from inter beat intervals (IBIs). A pre-clinical in-vivo experiment was performed in one dog in order to validate the concept by implanting conventional bipolar cardiac pacemaker leads in the right atrium, the right ventricle and the subcutaneous space. Based on the available randomness and entropy of recorded IBIs, 3-bits were extracted per IBI by approximating a sequence of intervals with a normal distribution. This allowed for the generation of a 128-bit key string across the nodes with an average bit mismatch rate of about 3%. Parity check methods were used to reconciliate the keys across the multiple nodes of a multi-nodal leadless pacemaker and subcutaneous device system. The findings are encouraging and demonstrate that IBIs can be used to generate secure keys for data encryption across different nodes of a leadless pacemaker system and S-relay.