“Atrial fibrillation (AFib) is an irregular and often very rapid heart rhythm but it can also be a in slow rate for some. An irregular heart rhythm is called an arrhythmia and that is all AFIB patients who are diagnosed with it. AFib can lead to blood clots in the heart. The condition also increases the risk of stroke, heart failure and other heart-related complications.

During atrial fibrillation, the heart’s upper chambers — called the atria — beat chaotically and irregularly. They beat out of sync with the lower heart chambers, called the ventricles. For many people, AFib may have no symptoms. But AFib may cause a fast, pounding heartbeat, shortness of breath or light-headedness due to the rapid heart rate.

AFib can also be bradycardia (a slow heart beat rhythm).

You could have pauses  in that AFIB bradycardia that are called sick sinus syndrome or a longer pauses causing sinus arrest.  Each pt’s heart is unique on how it operates.”

MAYO CLINIC