A 95-year-old woman presents with palpitations. She has no relevant medical history and the present complaint is several days old. She is not using any medication. Physical examination reveals an irregular pulse and heartbeat (pulse deficit 20 beats/min) and no further abnormalities.

Her ECG is attached. What does the ECG suggest? *This case is from the Editorial team of Docplexus and is meant for educative purposes only. The answer is posted in the comment section below!