Clinical and electrophysiological characteristics of idiopathic ventricular arrhythmias originating from the slow pathway region

Background: The slow pathway region (SPR) is commonly targeted during ablation of atrioventricular nodal reentrant tachycardia. However, its role in idiopathic ventricular arrhythmias (IVAs) remains unknown. Objective: The purpose of this study was to describe the electrocardiographic and electrophysiological characteristics of IVAs that were successfully ablated from the SPR. Methods: Medical records of consecutive patients undergoing ablation of IVAs in the para-Hisian region between 2010 and 2018 were reviewed to identify subjects whose ventricular arrhythmias were targeted from the SPR. Results: Among 63 patients with para-Hisian IVAs undergoing ablation, the SPR was targeted in 12 (20%; mean age 64 ± 7 years; 9 men). All patients presented with ventricular premature depolarizations manifesting left bundle branch block morphology with variable precordial transition (leads V₂–V₅) and a mean QRS duration of 131 ± 11 ms. In all cases, leads I and aVL had positive forces (R or Rs) and lead aVR had negative forces (QS or Qr). In the majority of cases, lead II had positive forces (R or Rs; n = 9 [75%]) and lead III had negative forces (rS or QS; n = 9 [75%]). Mean activation at the SPR was 31 ± 5 ms pre-QRS. All patients had initial ablation with radiofrequency, resulting in junctional rhythm in 9 (75%); 3 (25%) patients required additional cryoablation. Ablation was successful in 11 patients (92%). One patient required a permanent pacemaker for heart block but subsequently recovered intrinsic conduction. Conclusion: The SPR can be a source of IVAs, which can be safely and successfully ablated in most cases using radiofrequency energy. IVAs arising from this location manifest unique electrocardiographic features.