P2.032: Unmasking of Manifest Preexcitation Following Successful Ablation of a Concealed Accessory Pathway: A Clinical Paradox

Introduction: Orthodromic atrioventricular reentrant tachycardia (AVRT) is a common form of supraventricular tachycardia (SVT) in children. It can be mediated by a concealed accessory pathway (AP) that conducts only retrograde. While catheter ablation remains curative for supraventricular tachycardia (SVT) mediated via such pathways, the emergence of manifest preexcitation post-ablation of a concealed retrograde conducting concealed pathway is rarely reported in the literature.

Case Description: An 18-year-old female underwent an electrophysiology study (EP) for documented episodes of SVT. Baseline Electrocardiogram (ECG) showed no evidence of preexcitation (Figure 1A). Electrophysiologic (EP) study revealed a Orthodromic AVRT via a concealed left posterior-lateral accessory pathway with eccentric ventriculoatrial (VA) conduction. Irrigated radiofrequency ablation via transseptal approach with subsequent VA and Atrioventricular (AV) block was confirmed using adenosine (Figure 1B) with no inducible arrhythmias or evidence of antegrade conduction. Unexpectedly, post-procedure the patient demonstrated new ventricular preexcitation with a pattern consistent with a left lateral accessory pathway (Figure 2). Ambulatory Holter monitoring showed intermittent preexcitation, predominantly at lower sinus rates ( < 80 bpm) with no recurrence of SVT. The patient continues to be asymptomatic and has had no recurrence of SVT. Our patient has elected not to pursue ablation of their accessory pathway at this point in time.

Discussion: This case illustrates a rare and paradoxical phenomenon of emergence of manifest preexcitation following ablation of a concealed pathway. The new preexcitation pattern noted for the first time following successful ablation of orthodromic AVRT via a concealed pathway, raises the possibility of unmasking of antegrade conduction in a previously dormant pathway or recruitment of an adjacent pathway not identified during initial EP mapping. This case underscores the complexity of concealed accessory pathways and their potential to develop manifest anterograde conduction following ablation. While the patient remains asymptomatic with no recurrence of SVT, careful long-term follow-up is crucial to assess the risk of arrhythmia recurrence and the need for further intervention. This case highlights the importance of thorough post-ablation evaluation and continuous monitoring in patients with accessory pathways.

Conclusion: The emergence of ventricular pre-excitation post-procedure, despite prior absence, suggests the possibility of unmasked or residual conduction pathways. While the patient remains asymptomatic with no recurrence of SVT, careful long-term follow-up is crucial to assess the risk of arrhythmia recurrence and the need for further intervention. Recognition of this phenomenon is essential for appropriate post-ablation evaluation and follow up.