Implantable cardiac pacemakers are marked with a three-letter code (XYZ), in which each letter means:
- AX - paced chamber; Y - sensed chamber; Z - mode of pacing.
- BX - sensed chamber; Y - paced chamber; Z - mode of pacing.
- CX - mode of pacing; Y - sensed chamber; Z - paced chamber.
- DX - mode of pacing; Y - paced chamber; Z - sensed chamber.
- EX - paced chamber; Y - mode of pacing; Z - sensed chamber
