narrow QRS complex tachycardia

Where is the origin of a narrow QRS complex tachycardia?

A narrow QRS complex always reflects excitation via the His-Purkinje system, since this is the only way to synchronously excitate the two ventricles in a short time (that is, in less than 120 ms). The origin of a tachycardia with a narrow QRS complex must therefore be upstream of the His-Purkinje system and thus lie within the atria.