POSTERIOR (ATYPICAL) ATRIOVENTRICULAR JUNCTIONAL REENTRANT TACHYCARDIA

The aim of this study was to characterize a relatively rare type of at rioventricular (AV) junctional reentrant tachycardia (AVJRT). Posterio r AVJRT is a type of AV nodal tachycardia in which the site of earlies t atrial activation is posterior to the AV node near the coronary sinu s orifice. The mechanism of this tachycardia is not well understood. T he characteristics of posterior AVJRT (n = 15) were compared with thos e of anterior (''common'') AVJRT (n = 146) and supraventricular tachyc ardia using single posterior septal accessory pathways (n = 13). Durin g posterior AVJRT, the AH interval was longer than the retrograde cond uction time (His to earliest atrial activity) in 11 cases (73%), indic ating that these tachycardias were not fast slow types of AVJRT. The m ean ventriculoatrial (VA) interval in posterior AVJRT (93 +/- 41 ms) w as longer than in anterior AVJRT (11 +/- 20 ms; p <0.005), but was sim ilar to that in tachycardias using accessory pathways (106 +/- 16 ms; p = NS). The site of earliest atrial activation during posterior AVJRT was similar to that in tachycardias using accessory pathways. In all cases of accessory pathway-mediated tachycardia, atrial activation cou ld be advanced by ventricular extrastimuli delivered coincident with t he His deflection, but atrial activation was not advanced in any case of posterior AVJRT unless the extrastimulus was delivered >80 ms befor e the His deflection. Anterograde conduction was similar in the poster ior and anterior AVJRT groups. During ventricular pacing, the VA inter val was longer in patients with posterior AVJRT (287 +/- 113 ins) than in those with anterior AVJRC (199 +/- 48 ms; P <0.005) or accessory p athways (133 +/- 43 ms; p <0.005), and closely coupled ventricular ext rastimuli caused greater increases in the VA interval (172 +/- 114 vs 102 +/- 31 and 60 +/- 60 ms, respectively; both p <0.01). In 73% of ca ses, posterior AVJRT used a slow pathway for anterograde conduction an d a different ''slow'' pathway for retrograde conduction, and thus was not an antidromic form of ''common'' AV nodal reentry. The retrograde limb of the circuit did not have the characteristics of an accessory pathway.