Po-05-222 novel approaches for the diagnosis of concealed nodo-ventricular and his-ventricular pathways

Concealed nodo-ventricular (cNV) or His-ventricular (cHV) pathways are rare accessory pathway variants that represent important challenges for the clinician to separate from the more common supraventricular tachycardia arrhythmias. To describe novel observations to aid in diagnosing cNV or cHV pathways. We present a case series of seven patients with re-entrant arrhythmias involving cNV (5 cases) or cHV (2 cases) pathways. We focus on several laboratory observations: (1) differential ventricular overdrive pacing (VOD) from the right ventricular base vs. apex, (2) response to His refractory premature ventricular complexes (PVCs), (3) paradoxical atriohisian (AH) response in long RP tachycardia, and (4) the role of adenosine to aid in the diagnosis. (1) Three cases underwent differential basal vs. apical VOD during tachycardia. All demonstrated a shorter post-pacing interval minus tachycardia cycle length during basal pacing than apical pacing with one case exhibiting apical VOD results compatible with atrioventricular nodal reentrant tachycardia (AVNRT). In one case with a cHV pathway, basal VOD was useful for localizing the ventricular connection and guiding the ablation site. (2) In 3 cases, His refractory PVCs reset the tachycardia without conduction the atrium, which excluded atrioventricular reentry, atrial tachycardia, or AVNRT alone. One case had His refractory PVCs followed by subsequent constant AA and HH intervals and then tachycardia termination, suggesting a bystander cNV pathway involvement. (3) Two cNV pathway cases presented with long RP tachycardia had shorter AH intervals during tachycardia than those during sinus rhythm of >15ms, suggesting parallel activation of the atrium and the atrioventricular node. (4) Low-dose adenosine (3 and 6 mg) terminated the tachycardia with a retrograde block in 2 cases with cNV pathways, while high dose adenosine titrated up to 18 mg failed to convert in a case with a HV pathway. cNV and cHV pathways mediated tachyarrhythmias can present with variable clinical presentations. We emphasized (1) the role of differential VOD and the importance of the basal VOD for a proper diagnosis and pathway localization (Figure, Panel A), (2) the importance of His refractory PVCs that reset or terminate the tachycardia without conducting the atrium (Panel B), (3) the importance of paradoxical AH response in long RP tachycardia (Panel C), and the use of adenosine for possibly distinguishing cNV from cHV pathways (Panel D).