An uncommon response to a His refractory premature ventricular complex during a short RP supraventricular tachycardia: What is the mechanism?

Abstract

A 33-year old woman presented with regular palpitations and documented a short RP narrow QRS complex tachycardia. A 12-lead surface electrocardiography during sinus rhythm showed no delta waves. At electrophysiological study, the retrograde conduction was decremental and concentric with the earliest activation site at the His bundle region. Para-Hisian pacing indicated retrograde conduction over the fast pathway of the atrioventricular (AV) node. No retrograde dual AV nodal physiology was observed, while programmed atrial extrastimuli exhibited an AH interval jump, demonstrating the presence of anterograde dual AV nodal pathways. No pre-excitation was inducible at any pacing site or atrial rate. After the AH interval jump, a narrow QRS tachycardia at a cycle length (CL) of 360 ms was reproducibly induced.A single late ventricular premature complex (VPC) applied from the right ventricular apex (RVA) during the tachycardia is shown in Figure 1. What is the mechanism of this tachycardia? DISCUSSIONThe differential diagnosis of a short RP supraventricular tachycardia with the earliest atrial activation in the His bundle region includes atrial tachycardia (AT) originating from near the AV node, orthodromic reciprocating tachycardia (ORT) using a septal accessory pathway, typical (slow-fast form) atrioventricular nodal reentrant tachycardia (AVNRT), junctional tachycardia (JT), and orthodromic nodofascicular (NF), or nodoventricular (NV) reentrant tachycardia (NFRT/NVRT). 1-6 The tachycardia with a short septal VA interval of <70 ms excludes ORT, although septal AT with a prolonged AV conduction is possible. 3 The His-refractory VPC stopped the tachycardia without changing the retrograde atrial activation sequence (RAAS) and AA interval, which excludes the diagnosis of AT and JT, leaving us the possibility of NFRT or AVNRT with bystander NF pathway. 4,7,8 Whereas a His-refractory VPC terminates the tachycardia without conducting to the atrium, it should not have any effect on the ongoing tachycardia during AVNRT. However, the presence of an NF or NV pathway connected to the nodal slow pathway may explain the paradoxical delay in His or termination of tachycardia by VPC maintaining the same RAAS (Figure 2). Although NF/NV connections are rare accessory pathways,their presence must be recognized because they can lead to diagnostic confusion, whether or not they participate in the tachycardia. 9-11 The para-Hisian pacing is generally not useful since an AV nodal response is not diagnostic of pure AV nodal conduction but can also be observed with a NF pathway. 12 The tachycardia induction with critical AH jump is also not discriminative evidence. Because the His bundle is not part of the AVNRT circuit, in theory it should be possible to dissociate the His-bundle potential from the tachycardia, 13 which favor AVNRT compared with NFRT. 14,15 Ho et al reported that the His-refractory VPC is the only maneuver to identify a concealed, bystander NFRT during atypical AVNRT. 12 It can terminate AVNRT in the presence of a concealed...

A narrow QRS complex during a left bundle branch block morphology wide QRS tachycardia: A clue for manifest or bystander involvement of nodofascicular pathway?

“…NF/NV pathways, depending on their level of takeoff relative to the area of physiologic delay, can be associated with either a short or normal PR interval; therefore they commonly present with minimal preexcitation 6 . While NF/NV pathways may participate as the retrograde limb of NCT, 7,8 antidromic/manifest NF/NV pathways can comprise the anterograde limb of WCT 1,6,9,10 or exist merely as bystanders 11 . As most of these pathways are right‐sided, the QRS morphology during an ART is typically an LBBB morphology 3,10 …”

Unusual response to His‐refractory atrial premature complex: What is the mechanism?

“…The tachycardia on the left in Figure 1 is without significant doubt AVNRT, an A on V tachycardia. This is not a challenge although technically could conceivably be a nodo‐fascicular NQT 11,12 . In AVNRT, an AES delivered when the His is refractory can conduct to the ventricle by the slow pathway 13‐17 .…”

Atrial pacing‐induced paroxysmal atrioventricular block: Concealed conduction or phase 3 block or intrahisian reentry?

“…At EP study, the programmed atrial extrastimuli exhibited a PAVB immediately after AH jump (Figure , Supplementary Video ) as a reproducible finding (Supplementary Video ). A short RP narrow QRS complex tachycardia with bystander nodo‐fascicular (NF) pathway was confirmed, and then the slow pathway ablation eliminated both tachycardia and the atrial pacing‐induced PAVB. The possible mechanisms of PAVB in current tracing could relate to concealed His extrasystoles rendering the AV node intermittently refractory or to concealed penetration of the AV node via the NF pathway .…”

“…[6][7][8] Phase 4 AV block occurs mostly in the diseased HPS, whereas phase 3 AV block is a normal physiological phenomenon (physiological or functional block) and can occur in the normal HPS after a conducted atrial premature depolarization or at the beginning of a supraventricular tachycardia. 2 bystander nodo-fascicular (NF) pathway was confirmed, 9,10 and then the slow pathway ablation eliminated both tachycardia and the atrial pacing-induced PAVB. The possible mechanisms of PAVB in current tracing could relate to concealed His extrasystoles rendering the AV node intermittently refractory or to concealed penetration of the AV node via the NF pathway.…”

“…However, the mechanism remains unsettled with phase 3 block ( voltage‐dependent or tachycardia‐dependent PAVB [TD‐PAVB] ), phase 4 block ( pause‐dependent or BD‐PAVB as associated with a phase‐4 enhanced automaticity ), and the CC all proposed . Indeed, we recently encountered a 33‐years‐old woman with regular palpitations and exercise induced‐dizziness and presented it at electrophysiology (EP) rounds section . At EP study, the programmed atrial extrastimuli exhibited a PAVB immediately after AH jump (Figure , Supplementary Video ) as a reproducible finding (Supplementary Video ).…”