Let me begin with a highly cited introductory technical paper on medical device security and privacy especially targeting implantable ones :- "Security and Privacy for Implantable Medical Devices" - IEEE Pervasive Computing Mobile and Ubiquitous Systems 2008. 

Brief Introduction: 

• Balance security-privacy-safety-utility with efficacy.
• General framework for evaluating security and privacy of wireless IMDs giving design goals for the same.
• Safety and utility goals: data access/accuracy, software update, configurability, resource efficient, multidevice coordination and device identification.
• Security and privacy goals: authorization, availability, device software and settings, data integrity, device knowledge/presence and sensitive information privacy.
• Tradeoffs: security versus emergency access-device resources-usability.
• Cryptographic and energy-centric methods for providing security and privacy at low cost without diminishing the efficacy of IMD functionality.