56 years old male patient presenting with palpitation to emergency room. On examination: tachycardic, BP 96/70. What is the diagnosis? Rhythm strip shows wide and narrow QRS tachycardias alternating. It could either be a narrow QRS tachycardia with intermittent aberrant conduction or two simultaneous tachycardias. It is more likely one tachycardia since the rate and regularity is not changing.
