Two distinct fast/slow atrioventricular nodal reentrant tachycardias in patients with both left and right atrioventricular nodal inferior extensions. The role of right inferior slow pathway

During fast/slow atrioventricular nodal reentrant tachycardia (AVNRT), the retrograde slow pathway (SP) conduction propagates through atrioventricular (AV) nodal left or right inferior extensions (LIE or RIE). Objectives: This study aimed to assess two distinct fast/slow AVNRTs in a patient with bilateral inferior extensions. Methods: We present four cases of two distinct fast/slow AVNRTs. Results: The diagnosis of LIE or RIE was based on the sites of the earliest retrograde atrial activation during VA conduction by electroanatomical 3D-mapping, which was inside the coronary sinus (CS) or posterior tricuspid annulus (TA). Case 1 and case 2 had originally two fast/slow AVNRTs each with LIE and RIE, and case 1 showed an alternance of the retrograde SP between LIE and RIE during the tachycardia. Case 3 and case 4 had initially fast/slow AVNRT with LIE, and another fast/slow AVNRT with RIE emerged after the ablation of their LIE exit. Ablation targeting the exits of LIE or RIE successfully eliminated any tachycardias in all except for Case 1 in whom conventional SP ablation was performed additionally. Conclusions: In patients who have both LIE and RIE, distinct AVNRTs each using individual SP might occur.