I work for a medical device company that makes implantable cardiac devices. The majority of these devices have a feature that adjusts to accommodate higher heart rates during exercise. My company calls it rate response (different companies have other names for it). Ask your cardiologist if your device has this feature, it most likely does. You should have no trouble with exercise. There are many distance runners with pacemakers or ICDs who do marathons with no issues. I totally get the anxiety about working out when you have/had arrhythmia issues.

I also have a history of arrhythmias (exercise induced ventricular tachycardia). I had an ablation in 1991 (still investigational at that time) that was mostly successful. I've completed 17 marathons since 1991 without any issues. I had issues again in 2003 and had an implantable diagnostic monitor for a year and a half - I ran 2 marathons with the monitor. In fact, my cardiologist encouraged me to stay active but that was after extensive testing.