BACKGROUND: Differentiating between atypical atrioventricular node re-entrant tachycardia (aAVNRT) and orthodromic reciprocating tachycardia (ORT) utilizing a septal accessory pathway is a complex challenge. OBJECTIVE: We introduce the "local VA index," a straightforward method based on signals from the coronary sinus (CS) catheter, to distinguish between these arrhythmias during tachycardia and entrainment. The V-A interval on the CS catheter is measured during tachycardia and entrainment, at the site of earliest atrial activity. The difference between these two situations defines the "local VA index". Additionally, we propose a mechanism to clarify the limitations of historical pacing maneuvers, such as PPI-TCL and SA-VA, by examining nodal decrement and intraventricular conduction delay. METHODS: In a retrospective study involving 75 patients referred for supraventricular tachycardia (SVT) evaluation, 37 were diagnosed with AVRT with ORT, and 38 with AVNRT (27 typical, 11 atypical). RESULTS: In comparison to AVRT patients, AVNRT patients exhibited longer PPI-TCL (176±47ms vs. 113±42ms; p<0.01) and SA-VA (138±47ms vs. 64±28ms; p<0.01). The AVRT group had a mean local V-A index of -1 ± 13ms, while the AVNRT group had a significantly longer index of 91 ± 46ms (p<0.01). An optimal threshold for differentiation was a local VA index of 40ms. Importantly, there was no significant correlation between pacing cycle length and nodal decrement, as well as intraventricular delay related to pathway location. This interindividual variability might explain misleading interpretations of PPI-TCL and SA-VA. CONCLUSION: This novel approach is advantageous due to its simplicity and effectiveness, requiring only two diagnostic catheters. A local VA interval difference of less than 40ms provides a clear distinction for AVRT.< Leer menos