A 68-year-old man is comes to the physician for fatigue, lightheadedness and palpitations. He has a history of myocardial infarction and has been smoking 2 packs of cigarettes per day for 40 years. Pulse is 150/min and blood pressure is 100/60 mmHg. Cardiac examination shows a regular rate and rhythm and no murmur. Lungs are clear to auscultation. Electrocardiogram (ECG) shows a sawtooth atrial pattern which is positive in V1 and negative in II, III and AVF and a 2:1 atrial to ventricular rate ratio.

Which of the following is the most likely diagnosis?