Differentiation of Slow‐Slow Form of AVNRT from AVRT through a Posteroseptal Accessory Pathway by Retrograde P‐Wave Amplitude

BACKGROUND: This study aimed to clarify whether retrograde P-wave amplitude during tachycardia can be used to differentiate slow-slow form of atrioventricular nodal reentrant tachycardia (S/S-AVNRT) from atrioventricular reentrant tachycardia through a posteroseptal accessory pathway (PS-AVRT). METHODS: Sixteen patients with S/S-AVNRT and 14 patients with PS-AVRT constituted the study group. Electrocardiographic and electrophysiological parameters were compared between both the groups. HA(CS-His), which indicates the location of the earliest atrial activation site during tachycardia, was calculated as the difference of the shortest HA interval in the His bundle region and the coronary sinus region. RESULTS: Negative deflection of the retrograde P wave during tachycardia was significantly greater in S/S-AVNRT than in PS-AVRT in the inferior leads (lead aVF, -0.22 ± 0.04 mV vs -0.10 ± 0.07 mV; P < 0.001). Among the electrocardiographic parameters, retrograde P-wave amplitude in lead aVF had the highest diagnostic accuracy (area under the curve 0.975, sensitivity 93%, and specificity 88% for a cutoff value of -0.16 mV). HA(CS-His) was negatively greater in S/S-AVNRT than in PS-AVRT (-24 ± 13 ms vs -3 ± 18 ms; P = 0.001), and was significantly correlated with the retrograde P-wave amplitude in lead aVF (P = 0.004). CONCLUSION: Deeper negative deflection of the retrograde P wave in the inferior lead can help differentiate S/S-AVNRT from PS-AVRT.