I Have Atrail Fibulation Of 5 Month Duration Documented By

I have Atrail Fibulation of 5 month duration documented by many EKGs. My resting heart rate is 60-80 but irregular i.e. short and long R intervals. Recently I had a stress EKG and echocardiogram where the pulse rate rose to a maximum of 130 BPM (85% of my age adjusted maximum rate). The QRS complex is well formed with no incidence of PVCs. So I assume the AV node, transistion tissue, and bundle of His are active.

Question: How can I have exercise adapted pulse rate without pulsing from the Sinus Node?