Extract medical devices and implants from this medical document. Return a JSON array or null.

Each entry:
- type: "implant", "external", "prosthetic"
- value: (empty)
- summary: device name, e.g. "Medtronic Micra AV"
- timestamp: "YYYY-MM-DD" implant/start date if mentioned
- data: {"device": "...", "manufacturer": "...", "model": "...", "serial": "...", "settings": {"pressure": "5 cmH₂O"}, "location": "..."}

Extract each distinct device as a separate entry. Include current settings if documented.

Document:
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