Narrow QRS tachycardia with extreme rightward axis. What is the mechanism?

A 25  year old lady presented with palpitation to the emergency department. Her pulse rate was 210 beats per minute. She was hemodynamically stable with a blood pressure of 100/60 mm Hg. 12 lead surface electrocardiogram (ECG) was recorded during the presentation (Fig. 1) and rhythm strip (Fig. 2A) during administration of IV adenosine. What is the likely diagnosis?

Source: Journal of Electrocardiology - April 20, 2018 Category: Cardiology Authors: Krishna Kumar Mohanan Nair, Narayanan Namboodiri, Hiren Kevadiya, Ajitkumar Valaparambil Source Type: research