Initiation of an atrioventricular nodal reentry tachycardia
Initiation of an atrioventricular nodal reentry tachycardia
Initiation of an atrioventricular nodal reentry tachycardia

There is an abnormal P wave (P′) and atrioventricular nodal delay (long P′R interval) before onset of the tachycardia.