Respiratory Sinus Arrhythmia (RSA) Pacing Post-CABG Surgery in Patients With HFrEF

The goal of this clinical trial is to test a new type of pacemaker in heart failure patients following a heart bypass operation. The new pacemaker restores respiratory sinus arrhythmia which is a natural pattern where the heart rate increases when the participants breathe in and slows down when participants breathe out. The main questions the trial aims to answer are: * Is the new type of pacemaker safe? * Does the new type of pacemaker improve how patients' hearts work (also known as cardiac output)? Participants will have a range of tests before their operation and during their recovery in hospital while participants have the new type of pacemaker in place, and will be monitored very closely. Participants will also receive a phone call 1 month after their surgery. Researchers will compare the new type of heart pacing against standard treatment to see if it is as safe, and if it is any better for patients.