Last Entrainment Response: A Novel Technique for Localizing Slow Pathway During Atrioventricular Nodal Re-entrant Tachycardia.

BACKGROUND

The method for identifying the atrial entrance to the slow pathway (E-SP) during slow-fast atrioventricular nodal re-entrant tachycardia (AVNRT) remains unclear.

OBJECTIVES

This study examined whether the E-SP could be identified by analyzing the last entrainment response (LER) of AVNRT.

METHODS

The LER was analyzed at 6 intra-atrial sites-His bundle site (HB); 3 equidistantly divided sites from the HB to the coronary sinus ostium (CSOS) (sites S, M, and I); inferior-CSOS; and posteroinferior-CSOS-after manifest entrainment of AVNRT in 40 patients. We hypothesized that E-SP would be captured antidromically during entrainment and that its post-pacing interval (PPI) to the last entrained beat would equal the tachycardia cycle length (TCL).

RESULTS

In group A (n = 27), the area from HB to site I was captured orthodromically, and inferior- and posteroinferior-CSOS were captured antidromically. PPIs from HB to site I were shorter than TCL (P < 0.0001), PPI at inferior-CSOS did not differ from TCL (389.3 ± 51.9 vs 389.2 ± 51.8 milliseconds; P = 0.3265), PPI at posteroinferior-CSOS was longer than TCL (P < 0.0001). In group B (n = 13), the area from HB to site M was captured orthodromically, and that from site I to posteroinferior-CSOS was captured antidromically. PPIs from HB to site M were shorter than TCL (P < 0.001), PPI at site I did not differ from TCL (354.7 ± 36.5 vs 354.8 ± 36.6 milliseconds; P = 0.3370), and PPIs at inferior- and posteroinferior-CSOS were longer than TCL (P < 0.001). These findings indicated that the E-SP was located at inferior-CSOS in group A and site I in group B. Successful slow pathway ablation sites matched these sites.

CONCLUSIONS

Analysis of the LER accurately identified the E-SP in AVNRT.