What do you recommend if I have a history of atrial fibrillation but this did not show up on the holter monitor. Any suggestions on an actual cause?

Event monitor. If you are continuing to have symptoms that you feel are possible atrial fibrillation, but you were unlucky enough to not have symptoms during a 24 hour ecg, you physician can order an event monitor. This is an ECG monitor that you can wear for 30 days, which will increase the likelihood of detecting an arrhythmia.