Wide Complex Tachycardia

This is a 41-year-old female with a past medical history of cervical cancer, s/p hysterectomy bilateral salpingectomy, s/p radiation therapy and chemotherapy, and hyperlipidemia who was transferred to our hospital for symptomatic tachycardia evaluation. She has a history of intermittent palpitations and lightheadedness.

During an episode of her palpitations and lightheadedness, her cardiac monitor showed tachycardia with heart rate of approximately 200-280 beat per minute with systolic blood pressure in the 60's. The following electrocardiogram (ECG) #1 was obtained:

Figure 1: ECG #1

Figure 1

Then the rhythm changed into narrow QRS tachycardia as shown in ECG #2:

Figure 2: ECG #2

Figure 2

An intravenous push of adenosine 6 mg and 12 mg was unsuccessful necessitating direct current synchronized cardioversion with 200 joules to restore normal sinus rhythm.

She underwent an echocardiogram, which showed normal cardiac structure and left ventricular ejection fraction at 55-60%.

ECG #1 and #2 shows which of the following?

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