Narrow complex tachycardia, CL 320msec, V:A = 1:1.
The earliest A is in distal CS (CS 1,2) = eccentric conduction.
The 2 most likely diagnoses are O-AVRT using left-sided accessory pathway and left atrial tachycardia.
Below are examples of left-sided accessory pathway.
Right-sided accessory pathway.
