Left-Variant Form of Slow-Fast AVNRT Requiring Ablation Along the Mitral Annulus

Background: The reentry circuit of the slow-fast AV nodal reentrant tachycardia (AVNRT) has not been precisely delineated. Although conventional right-sided slow pathway ablation at the inferoseptal to midseptal tricuspid annulus (TA) or inside the coronary sinus (CS) is effective in most slow-fast AVNRT cases, rare cases of the left-variant form resistant to the conventional right-sided slow pathway ablation and requiring the left-sided ablation along the mitral annulus (MA) have been reported. Purpose: To evaluate the effects of the left-sided ablation along the MA in patients with the slow-fast AVNRT resistant to the conventional right-sided slow pathway ablation. Methods & Results: In 5 out of 250 cases with the slow-fast AVNRT who underwent the slow pathway ablation, extensive right-sided slow pathway ablation at the mid to inferoseptal TA, CS ostium or inside the CS (>10 applications) failed to eliminate tachycardia inducibility. In those 5 cases, the left-sided ablation along the inferoseptal to inferolateral MA with transseptal approach was performed during the sinus rhythm. In 2 cases, accelerated junctional rhythm was induced during the ablation along the MA and tachycardias were rendered non-inducible (upto one AV nodal echo beat). In other 2 cases, accelerated junctional rhythm was not induced during the ablation along the MA, but tachycardia became non-sustained (2-5 AV nodal echo beats). In the remaining one case, tachycardia still remained inducible even after extensive left-sided ablations. Conclusion: The left-variant forms of the slow-fast AVNRT were observed in 1.6% of all slow-fast AVNRT cases and the slow pathway ablation along the inferoseptal to inferolateral MA was effective for eliminating the tachycardia inducibility. The left-sided deviation of the reentrant circuit might explain the resistance to the right-sided slow pathway ablation and efficacy of the left-sided ablation along the MA in those cases.