Step-by-step sequence of what happens during the actual upgrade procedure (implantation day)?
1. Pre-procedure: Interrogate old LP. 2. Access: Insert sheath via femoral vein. 3. Implant new atrial and ventricular LPs. 4. Pair devices for bicameral pacing. 5. Deactivate old LP. 6. Confirm synchrony and separation by testing and fluoroscopy. 7. Post-procedure monitoring. This ensures smooth transition from unicameral to bicameral pacing.