Supraventricular tachycardia with double trouble

A 23-year-old healthy woman who was 10 weeks pregnant presented to the hospital with palpitations. Her presenting rhythm is shown in Figure 1A. The tachycardia terminated with administration of adenosine. Her baseline sinus rhythm electrocardiogram (ECG) is shown in Figure 1B. Metoprolol was initiated, but she had a recurrence of tachycardia. What is your interpretation of the ECGs? What are treatment options?