CABG surgery comes results in AF for many people. So that is my best guess of what you have. It happens because of the scar tissue that formed as a result of the surgery. It can be mapped and ablated at an experienced center. So yes it can be cured. Just make sure the ablationist that you choose have done a lot of AF or more complex procedures.
Considering your age, it could be possible you're having some atrial fibrillation, a-fib. It's completely possible that when you're not experiencing this arrhythmia, a Holter test would indicate a normal heart. Your medication is comprised of aspirin, a statin, and an anticoagulant, so you might be marginally protected in the event it could be a-fib. The formation of clots is the primary concern. You should keep an eye on this.