Antidromic Atrioventricular Reentry Tachycardia with Wolff Parkinson White Syndrome: A Rare Beast.

Orthodromic atrioventricular reentrant tachycardia (AVRT) is the second-most-common form of supraventricular tachycardia (SVT) and is inducible in approximately 55% of individuals with Wolff Parkinson White (WPW) syndrome. Antidromic AVRT, where the accessory atrioventricular connection is used as the antegrade limb and the atrioventricular node serves as the retrograde limb of the circuit, has been clinically documented in less than 5% of patients with WPW syndrome and may be induced in less than 10% of these WPW cases in the electrophysiology laboratory. Left lateral pathways are considered more frequent and septal locations are less common when associated with antidromic AVRT. We report a case of 21-year-old male with a history of WPW syndrome who had undergone a prior electrophysiology study in 2010 at an outlying facility, documenting an anteroseptal accessory pathway near the His bundle along with an unsuccessful attempt at radiofrequency ablation at that time. No supraventricular tachycardia was induced at that previous study. The surface electrocardiogram (ECG), at this time, was consistent with the anteroseptal WPW pattern. The patient now presented with a complaint of intermittent palpitations with no definitive trigger. He also described a recent syncopal episode while walking inside his home. His physical exam and all lab work were within normal limits for his age. He underwent a repeat electrophysiology (EP) study where the baseline PR interval was 62 milliseconds and the QRS duration was 172 milliseconds in a pre-excited pattern. There was found to be an antegrade-only conducting accessory pathway at the anteroseptal region near the His bundle. Antegrade AVRT was induced with a single ventricular extra stimulus while on 2 mcg/min isoproterenol. Cryoablation was performed in a position slightly posterior to the His bundle, which successfully resolved the accessory pathway conduction. First-degree atrioventricular (AV) block was noted in the sinus rhythm with a PR interval of 226 milliseconds post-cryoablation. There was no recurrence of accessory pathway conduction on follow-up ECG 24 hours post-cryoablation. Antidromic AVRT is a very rare finding in WPW syndrome during an EP study. Catheter ablation is the treatment of choice for patients who have symptomatic WPW syndrome. Catheter ablation can be especially challenging when the accessory pathway is in close proximity to the normal conduction pathways. The prognostic significance of inducible antidromic AVRT is controversial in asymptomatic patients and limited data indicate it may be a poor prognostic sign in children. In adults, the prognostic significance is not well-established. Cryoablation is an option for the ablation of accessory pathways that are close to the normal conduction pathways. "Cryomapping" is designed to have precise ablation and to reassure the absence of complications.