A case of arrhythmia

50-year old male patient came to our hospital complaining of palpitations. He had steted that the onset was about 45 minutes ago and was relater to a fall from a ladder. The patient showed no dyspnea or chest pain. He was not on any medications. There was no signs of distress. His BP was 100/60 and heart rate was 140 bpm and irrregularly irregular. 12-lead ECG was done and here it is:
Click on it to enlarge







What do you thin is the diagnosis and what should we do?


Update: see the tracing after cardioversion below