ECG of the Month: Tachycardia

A 75-year-old male with a past medical history including type A aortic dissection with surgical repair and mechanical aortic valve replacement, paroxysmal atrial fibrillation, hypertension and hyperlipidemia presented to antiarrhythmic medications clinic for follow-up monitoring of Flecainide. The patient is asymptomatic. ECG 1 (below) is his baseline ECG.

Figure 1

ECG 2 (below) was taken in clinic at the time of the appointment.

Figure 2

Which option best explains the ECG findings in the ECG 2?

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