The physiologic conditions required to initiate the first reentrant beat or to sustain the reentrant process prevent tachycardia in most persons. An increase in ectopy and physiologic changes may allow development of the tachycardia with increasing age. Fast-slow tachycardias use the fast pathway antegrade and the slow pathway retrograde. Slow-slow tachycardias appear to require the presence of two slow pathways. The anatomic substrate is similar to the slow-slow form.
True syncope is unusual.
Its absence does not exclude the diagnosis. The resulting contraction of the atrium on a closed atrioventricular valve accounts for the characteristic neck pounding as well as the typical absence of P waves, which are buried within the QRS complex. Vagal maneuvers, such as carotid sinus massage, the Valsalva maneuver, or both, may terminate tachycardia. The patient should be asked to lie on his or her back and relax as much as possible. Adenosine is the first drug of choice.