Pseudo-focal retrograde atrial activation due to undetected slow pathway potentials during atypical atrioventricular nodal reentrant tachycardia

Background The optimal ablation target for atypical atrioventricular nodal reentrant tachycardia (AVNRT) remains controversial: the anatomical slow pathway (SP) region or the site of retrograde earliest atrial activation (EAA). Purpose This study aimed to investigate the relationship between retrograde atrial activation patterns during atypical AVNRT and SP potentials using high-resolution mapping with multi-electrode catheters. Methods Thirteen atypical AVNRT cases (fast-slow, n=11; slow-slow, n=2) in 12 consecutive patients (mean age 72 years; 6 men) were evaluated. The diagnosis of AVNRT was based on fulfillment of established criteria. Electroanatomical maps were created during both sinus rhythm and atypical AVNRT. The cases were classified into two groups based on their retrograde atrial activation patterns during atypical AVNRT: pseudo-focal and focal. A pseudo-focal activation pattern was defined as the presence of multiple simultaneously activated sites within 10 ms of the onset of retrograde atrial activation. Results A pseudo-focal pattern was observed in 38% (5/13) of the cases. Clinical characteristics did not differ significantly between groups. SP potentials were identified at the posteroseptal tricuspid annulus (TA) during both sinus rhythm and AVNRT in all patients. The EAA site was located at the posteroseptal TA (n=9) and within the coronary sinus (n=4). The median distance between the SP site and the EAA site was significantly longer in the pseudo-focal group than in the focal group (11.0 vs 2.5 mm, p=0.02). The SP amplitude during AVNRT was significantly lower in the pseudo-focal group than in the focal group (0.05 vs 0.12 mV, p=0.02). In the pseudo-focal group, retrograde atrial potentials at the anatomical SP region were preceded by low-voltage SP potentials that the automated near-field signal annotation algorithm failed to detect. SP potential-guided ablation was performed in all cases, except for one pseudo-focal case who underwent EAA-guided ablation. This case exhibited two distinct breakthroughs within the coronary sinus, both of which required to be eliminated for successful ablation. Atypical AVNRT was successfully eliminated in all cases without complications. Conclusions The automated near-field signal annotation algorithm fails to detect low-voltage SP potentials in approximately 40% of atypical AVNRT cases, resulting in a pseudo-focal retrograde atrial activation pattern. In such cases, an EAA-guided strategy may require extensive ablation to eliminate multiple SP exits. Therefore, visual identification and manual annotation of low-voltage SP potentials at the posteroseptal TA are crucial for effective ablation in the era of automated signal detection.