Electrophysiological and anatomical differences of the slow pathway between the fast-slow form and slow-slow form of atrioventricular nodal reentrant tachycardia.

Aims This study aimed to clarify whether electrophysiological and anatomical properties of the slow pathway (SP) could be different between the fast–slow form (F/S) and the slow–slow form (S/S) atrioventricular nodal reentrant tachycardia (AVNRT). Methods and results Nine patients with F/S and 15 patients with S/S of atypical AVNRT were studied. The patients with S/S were divided into two groups; those with the anterograde SP being eliminated (S/S aSP-E) or preserved (S/S aSP-P) during catheter ablation. HA (CS-His) was determined as the difference of the shortest HA interval between the His bundle region and the coronary sinus (CS) region. The ratio of the amplitudes of atrial and ventricular potential (A/V ratio) of the successful ablation site of the SP was also evaluated. Effective refractory period of the retrograde SP was shorter and HA intervals during both tachycardia and ventricular pacing were longer in F/S than in S/S. HA (CS-His) did not differ between F/S and S/S (−4.3 ± 20.2 vs.−4.4 ± 18.4 ms, NS). The A/V ratio was significantly greater in the S/S aSP-P group compared with the both groups of F/S and S/S aSP-E (0.83 ± 0.29 vs. 0.38 ± 0.09 and 0.26 ± 0.15 ms, P < 0.01). Conclusion Properties of the retrograde SP differ between F/S and S/S of AVNRT. Fast–slow form may utilize the same pathway for the retrograde conduction as the anterograde SP in S/S.