Abstract 1541: Atypical Atrioventricular Nodal Reentrant Tachycardia with Anterior Retrograde Slow Pathway: Incidence, Electrophysiological Characteristics and Effect of Slow Pathway Ablation
BACKGROUND: Atypical AV nodal reentrant tachycardias (AVNRT) usually exhibit earliest retrograde atrial activation (ERAA) at the right posteroseptum (Rt-PS) or proximal coronary sinus (PCS). However, previous studies have shown that atypical AVNRT could rarely exhibit ERAA at the right anteroseptum (Rt-AS). The purpose of this study was to elucidate the incidence, characteristics and effect of slow pathway (SP) ablation in atypical AVNRT with an anterior retrograde SP.
METHODS: The electrophysiological and ablation data were reviewed in 360 AVNRTs induced in 340 consecutive patients. Atypical AVNRT was differentiated from typical form by a longer H-A interval during ventricular pacing at the tachycardia cycle length (TCL) (HAp: =/>70ms), and evidences for a lower common pathway (LCP), including second-degree AV block without tachycardia interruption, HAp longer than the HA interval during tachycardia (HAt). Atypical AVNRTs were classified into two types; the posterior type with ERAA at the Rt-PS or PCS; and anterior type with ERAA at the Rt-AS.
RESULTS: In a total of 360 AVNRTs, there were 300 typical (83%) and 60 atypical forms (17%). Among the 60 atypical forms, 51 (14%) were classified into the posterior type, while the remaining 9 (3%) were classified into the anterior type. The anterior type of atypical AVNRT (TCL: 322+/−37ms) exhibited ERAA at the Rt-AS during the tachycardia and ventricular pacing, shorter A-H interval (162+/−39ms), longer HAt (167+/−40 ms), longer HAp (184+/−53ms), and evidences for a LCP, including a second-degree AV block during the tachycardia (n=4) and HAt being shorter than the H-Ap (n=9). All posterior types of atypical AVNRT were rendered non-inducible after an ablation to the ERAA site. In anterior type, the conventional SP ablation at the Rt-PS did not eliminate any of the 9 tachycardias; however, ablations at the right midseptum eliminated 7 (78%) of the 9 anterior types of atypical AVNRT.
CONCLUSION: Atypical AVNRT with an anterior retrograde SP was observed in 3% of all AVNRTs. Conventional Rt-PS ablation was ineffective; and the midseptal ablation was modestly effective in this entity. The tachycardia circuit of the anterior type might be deviated to more anterior part of the Koch’s triangle than that of the posterior type.