Atrioventricular nodal re-entrant tachycardia with QRS voltage and cycle length alternation and aberrant conduction due to two distinct antegrade slow pathways.

QRS voltage and cycle length alternation can be seen during supraventricular re-entrant tachycardias, especially in atrioventricular (AV) re-entrant tachycardia. We present a case of a 20-year-old man, in which AV nodal re-entrant tachycardia (AVNRT) shows alternation of QRS voltage and cycle length, as well as right bundle branch block aberration due to a re-entrant circuit using two distinct, beat-to-beat alternating slow AV nodal pathways antegradely and a single fast pathway retrogradely. Although more than one antegrade slow pathway exists, creation of a single lesion at the right posterior atrial septum using the conventional right-sided approach successfully eliminated AVNRT.