Pseudo Mobitz II AVB and intrahis block abolished by cardioneural ablation (CNA).

18y.oF without PMH, presented after 6m of presyncope and palpitation. Normal ECG. Repeated 24-hr Holter showed 40-200 episodes of AVB, day and night, many without significant PP or PR prolongation, with rates of 120bpm, and a PR of 130ms, compatible with Mobitz II 2’AVB. Few episodes had other characteristics. No clinical vagal triggers preceded the AVB. Normal cardiac imaging, genetic and blood tests and exercise test without AVB. Tilt-test didn’t evoke AVB nor clinical prodrome. EPS showed normal baseline conduction; HV=40ms with AV nodal level block during atrial pacing. Programed atrial extrastimulation showed intrahis block at 600:350ms. Ajmalin prolonged HV to 78ms, without AVB. Nevertheless, physiological intrahissian and infrahissin block due to the short S2 and RR intervals was considered. CNA targeting only the inferior paraseptal-GP was performed. Baseline WCL=550ms. Post-ablation WCL=330ms. Atropine 2mg verifyed near maximal vagal effect abolition on the AV node. No AVB on repeated Holters post-ablation. Holter at 3-month FU demonstrated a single dropped beat during night sleep. The disappearance of AVB post CNA proves vagally-mediated AVB.

In the case, Holter findings were suggestive of infranodal (intra-His) disease: QRS was narrow and AVB suggested 2’Mobitz II, as they occurred during sinus tachycardia, without change in PRor PP before and after the block, without vagal-triggers. However, ECG hints for AV nodal block were few AVB with slight PP slowing prior to AVB, and 1:1 conduction after AVB at shorter PP intervals. Infranodal block typically worsens during higher rates, thus PP shortening post-AVB is not expected to conduct with 1:1 AV relationship. However,in vagal AVB, conduction may improve during high rates and worsen during PP slowing which suggests simultaneous vagal effect on the sinus and AV nodes. Additionally, lack of AVB during exercise supports vagally-mediated block. The case is unique as the vagally-mediated AVB occurred during sinus tachycardia without sinus node slowing andultimately proved by abolition of AVB with CNA.